Springer Handbook of Crystal Growth

A brief overview of crystal growth techniques and crystal analysis and characterization methods is presented here. This is a prelude to the details in subsequent chapters on fundamentals of growth phenomena, details of growth processes, types of defects, mechanisms of defect formation and distribution, and modeling and characterization tools that are being employed to study as-grown crystals and bring about process improvements for better-quality and large-size crystals.

This chapter deals with the thermodynamics and kinetics of nucleation on surfaces, which is essential to the growth of single crystals and thin epitaxial films. The starting point is the equilibrium of an

infinitely

large crystal and a crystal with a finite size with their ambient phase. When the system deviates from equilibrium density fluctuations or aggregates acquire the tendency to unlimited growth beyond some critical size – the nucleus of the new phase. The Gibbs free energy change of formation of the nuclei is calculated within the framework of the macroscopic thermodynamics and in terms of dangling bonds in the case of small clusters. In the case of nucleation from vapor the nuclei consist as a rule of very small number of atoms. That is why the rate of nucleation is also considered in the limit of high supersaturations. The effect of defect sites and overlapping of nucleation exclusion zones with reduced supersaturation formed around the growing nuclei is accounted for in determining the saturation nucleus density. The latter scales with the ratio of the surface diffusion coefficient and the atom arrival rate. The scaling exponent is a function of the critical nucleus size and depends on the process which controls the frequency of attachment of atoms to the critical nuclei to produce stable clusters, either the surface diffusion or the incorporation of atoms to the critical nuclei. The nucleation on top of two-dimensional (2-D) islands is considered as a reason for roughening in homoepitaxial growth. The mechanism of formation of three-dimensional (3-D) islands in heteroepitaxial growth is also addressed. The effect of surface-active species on the rate of nucleation is

nucleation

at surface

explored.

Growth from solutions is widely used both in research laboratories and in many industrial fields. The control of crystal habit is a key point in solution growth as crystals may exhibit very different shapes according to the experimental conditions. In this chapter a concise review is given on this topic. First, the equilibrium shape is rather deeply developed due to its primary importance to understand crystal morphology, then the growth shape is treated and the main factors affecting the crystal habit are briefly illustrated and discussed. A rich literature completes the chapter.

This

generation

of defects

propagation of defects

chapter presents a review of the typical growth defects of crystals fully grown on (planar) habit faces, i.e., of crystals grown in all kinds of solutions, in supercooled melt (mainly low-melting organics) and in the vapor phase. To a smaller extent growth on rounded faces from the melt is also considered when this seems appropriate to bring out analogies or discuss results in a more general context. The origins and typical configurations of defects developing

during

growth and

after

growth are illustrated by a series of selected x-ray diffraction topographs (Lang technique) and, in a few cases, by optical photographs.

After an overview (Sect.

4.1

) the review starts with the formation of inclusions (Sect.

4.2

), which are the main origin of other growth defects such as dislocations and twins. Three kinds of inclusions are treated: foreign particles, liquid inclusions (of nutrient solution), and solute precipitates. Particular attention is directed to the regeneration of seed crystals into a fully facetted shape (

capping

), and inclusion formation due to improper hydrodynamics in the solution, especially for potassium dihydrogen phosphate (KDP).

Section

4.3

deals briefly with striations (treated in more detail in Chap. 6 of this Handbook) and more comprehensively with the different kinds of crystal regions grown on different growth faces: growth sectors, vicinal sectors, and facet sectors. These regions are usually differently perfect and possess more or less different physical properties, and the boundaries between them are frequently faulted internal surfaces of the crystal. Two subsections treat the optical anomalies of growth and vicinal sectors and the determination of the relative growth rates of neighboring growth faces from the orientation of their common sector boundary.

In Sect.

4.4

distinction is made between dislocations connected to and propagating with the growth interface (

growth dislocations

), and dislocations generated

behind

the growth front by plastic glide due to stress relaxation. The main sources of both types of dislocations are inclusions. In crystals grown on planar faces, growth dislocations are usually straight-lined and follow (frequently noncrystallographic) preferred directions depending on the Burgers vector, the growth direction, and the elastic constants of the crystal. These directions are explained by a minimum of the dislocation line energy per growth length, or equivalently by zero force exerted by the growth surface on the dislocation. Calculations based on anisotropic linear elasticity of a continuum confirm this approach. The influence of the discrete lattice structure and core energy on dislocation directions is discussed. Further subsections deal with Burgers vector determination by preferred directions, postgrowth movement of grown-in dislocations, generation of postgrowth dislocations, and the growth-promoting effect of edge dislocations.

Section

4.5

presents

twinning

, the main characteristics of twins and their boundaries, their generation by nucleation and by inclusions, their propagation with the growth front, and their growth-promoting effect. Postgrowth formation of twins by phase transitions and ferroelastic (mechanical) switching is briefly outlined. Finally, Sect.

4.6

compares the perfection of crystals (KDP and ammonium dihydrogen phosphate (ADP)) slowly and rapidly grown from solutions. It shows that the optical and structural quality of rapidly grown crystals is not inferior to that of slowly grown crystals, if particular precautions and growth conditions are met.

Based on detailed investigations on morphology (evolution and variation in external forms), surface microtopography of crystal faces (spirals and etch figures), internal morphology (growth sectors, growth banding and associated impurity partitioning) and perfection (dislocations and other lattice defects) in single crystals, we can deduce how and by what mechanism the crystal grew and experienced fluctuation in growth parameters through its growth and post-growth history under unconstrained condition. The information is useful not only in finding appropriate way to growing highly perfect and homogeneous single crystals, but also in deciphering letters sent from the depth of the Earth and the Space. It is also useful in discriminating synthetic from natural gemstones. In this chapter, available methods to obtain molecular information are briefly summarized, and actual examples to demonstrate the importance of this type of investigations are selected from both natural minerals (diamond, quartz, hematite, corundum, beryl, phlogopite) and synthetic crystals (SiC, diamond, corundum, beryl).

This chapter gives an overview of the important defect types and their origins during bulk crystal growth from the melt. The main thermodynamic and kinetic principles are considered as driving forces of defect generation and incorporation, respectively. Results of modeling and practical in situ control are presented. Strong emphasis is given to semiconductor crystal growth since it is from this class of materials that most has been first learned, the resulting knowledge then having been applied to other classes of material.

The treatment starts with zero-dimensional defect types, i.e., native and extrinsic point defects. Their generation and incorporation mechanisms are discussed. Micro- and macrosegregation phenomena – striations and the effect of constitutional supercooling – are added. The control of dopants by using the nonconservative growth principle is considered. One-dimensional structural disturbances – dislocations and their patterning – are discussed next. The role of high-temperature dislocation dynamics for collective interactions, such as cell structuring and bunching, is shown. In a further section second-phase precipitation and inclusion trapping are discussed. The importance of in situ stoichiometry control is underlined. Finally two special defect types are treated – faceting and twinning. First the interplay between facets and inhomogeneous dopant incorporation, then main factors of twinning including melt structure are outlined.

The application of steady magnetic fields during crystal growth of indium phosphide is described, and the effect of the magnetic fields on crystal properties is analyzed. The use of magnetic fields is one of many engineering controls that can improve homogeneity and crystal quality. This method is especially relevant to InP because of the high pressure requirement for crystal growth. Under high pressure, fluid flows in the melt and in the gas environment can become uncontrolled and turbulent, with negative effects on crystal quality and reproducibility. If properly configured, a steady magnetic field can reduce random oscillatory motion in the melt and reduce the likelihood of defect formation during growth. This chapter presents the history and development of magnetic-field-assisted growth of InP and an analysis of the effects of applied fields on crystal

indium (In)

phosphide (InP)

defect

control

applying steady magnetic field

magnetic liquid encapsulated Czochralski growth (MLEC)

magnetic liquid encapsulated Kyropoulos growth (MLEK)

quality.

This chapter reviews growth and characterization of Czochralski silicon single crystals for semiconductor and solar cell applications. Magnetic-field-applied Czochralski growth systems and unidirectional solidification systems are the focus for large-scale integrated (LSI) circuits and solar applications, for which control of melt flow is a key issue to realize high-quality crystals.

Czochralski crystal growth is one of the major methods of crystal growth from melt for bulk single crystals for commercial and technological applications. Most crystals, such as semiconductors and oxides, are grown from melt using this technique due to the much faster growth rates achievable. A detailed description of the process can only be given for specific materials; there is no universal crystal pulling system available commercially. The details of the basic principle and the design of automatic diameter control Czochralski crystal growth system elements are given in this chapter so as to enable any researcher to design and fabricate his/her own system. This chapter is devoted to the growth of bulk oxide photorefractive materials such as lithium niobate and sillenite crystals including the development in these materials during the last decade. A number of problems (and possible solutions) encountered by the authors during growth in their respective laboratories over the last two decades are discussed.

Section

9.2

provides the introduction to crystals and crystal growth mechanism and various methods of growing photorefractive crystals. Section

9.3

discusses in detail the Czochralski method of crystal growth, including selection of appropriate components for setting up a crystal growth system such as the heating system design, and raising, lowering, and rotation mechanisms. Section

9.4

discusses the growth and properties of lithium niobate crystals. A brief introduction to other photorefractive crystals is given in Sect.

9.5

. The details of the growth and properties of sillenite crystals are given in Sect.

9.6

. Section

9.7

summarizes the present state of these two important crystals in terms of growth and applications.

Ternary

bulk

crystal growth of ternary III–V semiconductor

semiconductor substrates with variable bandgaps and lattice constants are key enablers for next-generation advanced electronic, optoelectronic, and photovoltaic devices. This chapter presents a comprehensive review of the crystal growth challenges and methods to grow large-diameter, compositionally homogeneous, bulk ternary III–V semiconductors based on As, P, and Sb compounds such as GaInSb, GaInAs, InAsP, AlGaSb, etc. The Bridgman and gradient freezing techniques are the most successfully used methods for growing ternary crystals with a wide range of alloy compositions. Control of heat and mass transport during the growth of ternary compounds is crucial for achieving high-quality crystals. Melt mixing and melt replenishment methods are discussed. The scale-up issues for commercial viability of ternary substrates is also outlined.

Materials for the generation and detection of 7–12 μm wavelength radiation continue to be of considerable interest for many applications such as night vision, medical imaging, sensitive pollution gas monitoring, etc. For such applications HgCdTe has been the main material of choice in the past. However, HgCdTe lacks stability and uniformity over a large area, and only works under cryogenic conditions. Because of these problems, antimony-based III–V materials have been considered as alternatives. Consequently, there has been a tremendous growth in research activity on InSb-based systems. In fact, InSb-based compounds have proved to be interesting materials for both basic and applied research. This chapter presents a comprehensive account of research carried out so far. It explores the materials aspects of indium antimonide (InSb), indium bismuth antimonide (InBi

x

Sb

1

–x

), indium arsenic antimonide (InAs

x

Sb

1

–x

), and indium bismuth arsenic antimonide (InBi

x

As

y

Sb

1

–x–y

) in terms of crystal growth in bulk and epitaxial forms and interesting device feasibility. The limiting single-phase composition of InAs

x

Sb

1

–x

and InBi

x

Sb

1

–x

using near-equilibrium technique has been also addressed. An overview of the structural, transport, optical, and device-related properties is presented. Some of the current areas of research and development have been critically reviewed and their significance for both understanding the basic physics as well as device applications are discussed. These include the role of defects and impurity on structural, optical, and electrical properties of the materials.

Single crystals of various congruently and incongruently melting oxides have been recently grown by the

floating zone (FZ)

floating zone (FZ) and

traveling solvent floating zone (TSFZ)

traveling solvent floating zone (TSFZ) techniques. For the incongruently melting materials, the use of solvent with an experimentally determined composition allows the establishment of the

practical

steady state much faster, leading to better, more stable growth. Growth conditions for different oxides are compared. Important problems in crystal characterization and assessment of micro- and macrodefects are briefly presented.

The laser-heated pedestal

laser

heated pedestal growth (LHPG)

growth (LHPG) technique, when compared with conventional growth methods, presents many advantages, such as high pulling rates, a crucible-free process, and growth of high and low melting

melting point (mp)

point materials. These special features make the LHPG technique a powerful material research tool. We describe the background history, theoretical fundamentals, and how the features of LHPG affect the

oxide

growth of oxide fibers. We also present a list of materials processed by laser heating in recent decades, such as LiNbO

3

, Sr–Ba–Nb–O, Bi

12

TiO

20

, Sr

2

RuO

4

, Bi–Sr–Ca–Cu–O, ZrO

2

:Y

2

O

3

, LaAlO

3

, and also the eutectic fibers of Al

2

O

3

:GdAlO

3

, Al

2

O

3

:Y

2

O

3

, and ZrO

2

:Al

2

O

3

.

This

refractory

material

skull melting (SM)

oxide

crystal

chapter discusses methods of growing refractory oxide single crystals and synthesis of refractory glasses by skull melting technique in a cold crucible. It shows the advantages of radiofrequency (RF) heating of dielectric materials in a cold crucible and points out some specific problems regarding the process of growing crystals by directional crystallization from the melt and by pulling on a seed from the melt. The distinctive features of the method of directional crystallization from the melt are

zirconia

discussed in detail on the example of technology of materials based on zirconia, i.e., cubic single crystals and partly stabilized single crystals. It is shown that the size and quality of crystals are functions of the process conditions, such as thermal conditions under crystallization, growth rate, and chemical composition. We provide an overview of research on the structure, phase composition, and physicochemical properties of crystals based on zirconia. The optical, mechanical, and electric properties of these crystals make them suitable for a number of technical and industrial applications in optics, electronics, materials processing, and medicine. In this chapter, we also consider some

oxide

glass

problems regarding the synthesis of refractory glasses by skull melting technique. The physicochemical and optical properties of glasses are given and their practical applications in technology are discussed. We note that one of the better developed and most promising applications of skull melting technique is the immobilization of liquid and solid waste (also radioactive waste) into solid-state materials by vitrification.

Following

laser

host fluoride

oxide

the discovery of the first laser action based on ruby, hundreds of additional doped crystals have been shown to lase. Among those, many crystals, such as Ti:Al

2

O

3

, Nd:Y

3

Al

5

O

12

, Nd:YVO

4

, Yb:Y

3

Al

5

O

12

, Yb:Ca

5

(PO

4

)

3

F, and Cr:LiCAF have come to practical application, and are being widely used in scientific research, manufacturing and communication industries, military applications, and other fields of modern engineering. These crystals are mainly oxides and fluorides, which are grown from melt. This chapter reviews the major results obtained during recent years in the growth of various crystalline oxides and fluorides for laser operation, with emphasis on crystals doped with the additional ions Ti

3+

, Nd

3+

, and Yb

3+

. On the other hand, special attention is paid to discuss the elimination of growth defects in these crystals. Limited by the length of this chapter, for each crystal, only outstanding defects are considered herein.

Crystals of specified shape and size (shaped crystals) with controlled

shaped

crystal growth (SCG)

defect and impurity structure have to be grown for the successful development of modern engineering. Since the 1950s many hundreds of papers and patents concerned with shaped growth have been published. In this chapter, we do not try to enumerate the successful applications of shaped growth to different materials but rather to carry out a fundamental physical and mathematical analysis of shaping as well as the peculiarities of shaped crystal structures. Four main techniques, based on which the lateral surface can be shaped without contact with the container walls, are analyzed: the Czochralski technique (CZT),

dynamic stability of crystallization (DSC)

stability analysis (SA)

Czochralski technique (CZT)

Verneuil

technique (VT)

floating zone (FZ)

technique of pulling from shaper (TPS)

the Verneuil technique (VT), the floating zone technique (FZT), and technique of pulling from shaper (TPS). Modifications of these techniques are analyzed as well. In all these techniques the shape of the melt meniscus is controlled by surface tension forces, i.e., capillary forces, and here they are classified as capillary shaping techniques (CST). We look for conditions under which the crystal growth process in each CST is dynamically stable. Only in this case are all perturbations attenuated and a crystal of constant cross section

capillary

shaping technique (CST)

grown

without any special regulation

. The dynamic stability theory of the crystal growth process for all CST is developed on the basis of Lyapunovʼs dynamic stability theory. Lyapunovʼs equations for the crystal growth processes follow from fundamental laws. The results of the theory allow the choice of stable regimes for crystal growth by all CST as well as special designs of shapers in TPS. SCG experiments by CZT, VT, and FZT are discussed but the main consideration is given to TPS. Shapers not only allow crystal of very complicated cross section to be grown but provide a special distribution of impurities. A history of TPS is provided later in the chapter, because it can only be described after explanation of the fundamental principles of shaping. Some shaped crystals, especially sapphire and silicon, have specified structures. The crystal growth of these materials, and some metals, including crystal growth in space, is discussed.

The growth of crystals has been of interest to physicists and engineers for a long time because of their unique properties. Single crystals are utilized in such diverse applications as pharmaceuticals, computers, infrared detectors, frequency measurements, piezoelectric devices, a variety of high-technology devices, and sensors. Solution crystal growth is one of the important techniques for the growth of a variety of crystals when the material decomposes at the melting point and a suitable solvent is available to make a saturated solution at a desired temperature. In this chapter an attempt is made to provide some fundamentals of growing crystals from solution, including improved designs of various crystallizers.

Since the same solution crystal growth techniques could not be used in microgravity, authors had proposed a new cooled sting technique to grow crystals in space. Authorsʼ experiences of conducting two Space Shuttle experiments relating to solution crystal growth are also detailed in this work. The complexity of these solution growth experiments to grow crystals in space are discussed. These were some of the earliest experiments performed in space, and various lessons learnt are described.

A brief discussion of protein crystal growth, which also shares the basic principles of the solution growth technique, is given along with some flight hardware information for such growth in microgravity.

In this chapter, the importance of the hydrothermal technique for growth of polyscale crystals is discussed with reference to its efficiency in synthesizing

hydrothermal growth

polyscale crystal

high-quality crystals of various sizes for modern technological applications. The historical development of the hydrothermal technique is briefly discussed, to show its evolution over time. Also some of the important types of apparatus used in routine hydrothermal research, including the continuous production of nanosize crystals, are discussed. The latest trends in the hydrothermal growth of crystals, such as thermodynamic modeling and understanding of the solution chemistry, are elucidated with appropriate examples. The growth of some selected bulk, fine, and nanosized crystals of current technological significance, such as quartz, aluminum and gallium berlinites, calcite, gemstones, rare-earth vanadates, electroceramic titanates, and carbon polymorphs, is discussed in detail. Future trends in the hydrothermal technique, required to meet the challenges of fast-growing demand for materials in various technological fields, are described. At the end of this chapter, an Appendix

18.A

containing a more or less complete list of the characteristic families of crystals synthesized by the hydrothermal technique is given with the solvent and pressure–temperature (PT) conditions used in their synthesis.

Crystals are the unacknowledged pillars of modern technology owing to their ever-increasing applications in various technologies such as electronics, microelectronics, magnetics, optics, nonlinear optics, photonics, optoelectronics, magnetoelectronics, biomedicine, biophotonics, biotechnology, nanotechnology, etc. Accordingly the size and quality of crystals control their application potential, as the properties also vary greatly with size, i.e., from bulk crystals to nanocrystals, due to the quantization effect. Hence, a new terminology (

polyscale crystals

) has become more appropriate in recent years for contributions like this devoted to the hydrothermal growth of crystals of different compositions and sizes. When the hydrothermal technique was initiated in the mid 19th century, the focus was essentially on mineral synthesis, also in the form of bulk single crystals. During World War II the importance of the hydrothermal technique was realized with the tremendous success in the growth of larger-size quartz crystals, and the focus shifted to the design of different types of autoclaves which could hold fluids under high-pressure and high-temperature conditions over a longer period. A greater variety of crystals hitherto unknown or without natural counterparts was synthesized during the 1960s and 1970s. Although there was a slight decline in the popularity of the hydrothermal technique during the 1980s, it has now picked up as one of the best methods to grow not only bulk crystals, but also fine and nanocrystals with desired shape, size, and properties. Hence, there has been a sudden surge in activities related to hydrothermal research in the last decade, because of the high-quality crystals of different sizes that can be grown well under hydrothermal conditions. This is further supported by the overwhelming success in the field of thermodynamic modeling and solution chemistry under hydrothermal conditions, which have drastically reduced the PT conditions required for crystal growth.

Zinc oxide (ZnO)

zinc

oxide (ZnO)

and gallium nitride (GaN)

GaN

are wide-bandgap semiconductors with a wide array of applications in optoelectronic and electronics. The lack of low-cost, low-defect ZnO and GaN substrates has slowed development and hampered performance of devices based on these two materials. Their anisotropic crystal structure allows the polar solvents, water and ammonia, to dissolve and crystallize ZnO and GaN at high pressure. Applying the techniques used for hydrothermal production of industrial single-crystal quartz to ZnO and GaN opens a pathway for the inexpensive growth of relatively larger crystals that can be processed into semiconductor wafers. This chapter will focus on the specifics of the hydrothermal growth of ZnO and the ammonothermal growth of GaN, emphasizing requirements for industrial scale growth of large crystals. Phase stability and solubility of hydrothermal ZnO and ammonothermal GaN is covered. Modeling of thermal and fluid flow gradients is discussed and simulations of thermal and temperature profiles in research-grade pressure systems are shown. Growth kinetics for ZnO and GaN respectively are reviewed with special interest in the effects of crystalline anisotropy on thermodynamics and kinetics. Finally, the incorporation of dopants and impurities in ZnO and GaN and how their incorporation modifies electrical and optical properties are discussed.

In

RbTiOPO

4

(RTP)

stoichiometry

stoichiometry

potassium

domain structure

domain structure

ferroelectric

crystal

KTP-type

nonlinear optical (NLO)

crystal

recent years the growth technologies of only a few inorganic oxide crystals, such as

BaB

2

O

4

(BBO)

BBO (BaB

2

O

4

),

LiB

3

O

5

(LBO)

LBO (LiB

3

O

5

), and the

KTiOPO

4

(KTP)

KTP (KTiOPO

4

) group of isomorphic compounds, have matured to a degree allowing their extensive integration into commercial laser systems in the form of

nonlinear optical (NLO)

nonlinear optical (NLO) and

electrooptic (EO)

electrooptic (EO) devices. The KTP-type crystals are ferroelectrics at room temperature. They are also well known for their large birefringence, high NLO and EO coefficients, wide acceptance angles, thermally stable phase-matching properties, and relatively high damage threshold. These properties make them especially useful for high-power wavelength-conversion applications, such as the

second-harmonic generation (SHG)

second-harmonic generation (SHG) and

optical

parametric oscillation (OPO)

optical parametric oscillations (OPO), as well as for electrooptic phase modulation and Q-switching. Lately, a great deal of effort has been put into the development of

periodically poled KTP (PPKTP)

periodically poled KTP (PPKTP) devices based

quasi-phase-matched (QPM)

on quasi-phase-matched (QPM) wavelength conversion. However, both birefringent and QPM properties of KTP crystals depend on their structural characteristics, such as morphology, chemical composition, point defect distribution (stoichiometric and impurities), and particularly the ferroelectric domain structure, which are closely related to the specific crystal growth parameters. Current research includes studies of nonstoichiometry and distribution of point defects, e.g., vacancies and impurities, as well as the basic mechanisms underlying ferroelectric domain formation during KTP crystal growth and cool-down. By controlling the stoichiometry and achieving single-domain growth of bulk crystals it is also possible to create as-grown

gray track

top-seeded solution growth (TSSG)

periodic domain structures useful for nonlinear QPM applications.

high-temperature

solution growth

Growth methods based on high-temperature solutions, traditionally also known as

flux

growth

flux growth methods, and especially the top-seeded solution growth (TSSG)

top-seeded solution growth (TSSG)

and liquid-phase epitaxy (LPE)

liquid phase

epitaxy (LPE)

methods, are some of the most popular methods by which to grow single crystals. These methods have to be used when the grown materials melt incongruently, melt at very high temperatures, or suffer from polymorphic transitions below the crystallization temperature. In this chapter we review the main advances produced in these crystal growth techniques during recent years, both in bulk and epitaxial films, and for two families of oxide materials, specifically those commonly used for solid-state lasers and nonlinear optical crystals. We intend to focus on the application to the real problems related to crystal growth in solutions with different viscosities, while revisiting some of the main strategies developed to overcome these problems to enable growth of bulk single crystals and single-crystalline films with good optical quality.

Crystals of potassium dihydrogen phosphate (KDP, KH

2

PO

4

)

potassium dihydrogen phosphate, KH

2

PO

4

(KDP)

and its deuterated analogs

K(D

x

H

1−

x

)

2

PO

4

(DKDP)

(DKDP, K(D

x

H

1

–x

)

2

PO

4

) have been studied for their interesting electrical and optical properties, structural phase transitions, and ease of crystallization. They are the only nonlinear crystals currently applied in

inertial confinement fusion (ICF)

inertial confinement fusion (ICF), which has made them a hot topic of research for decades. To yield enough large crystals exceeding 50 cm in all three dimensions, the point-seed technique was recently developed. This method can grow crystals one order of magnitude faster than conventional methods. Recent developments in both the techniques and science of growth phenomena and defect formation under various conditions are described in this chapter, which also reviews significant advances in understanding of the fundamentals of KDP crystal growth, other growth methods to yield large high-quality crystals, growth defects and optical performance, and evaluations of crystal quality.

Silicon carbide is a semiconductor that is highly suitable for various high-temperature and high-power electronic technologies due to its large energy bandgap, thermal conductivity, and breakdown voltage, among other outstanding properties. Large-area high-quality single-crystal wafers are the chief requirement to realize the potential of silicon carbide for these applications. Over the past 20 years, considerable advances have been made in silicon carbide single-crystal growth technology through understanding of growth mechanisms and defect nucleation. Wafer sizes have been greatly improved from wafer diameters of a few millimeters to 100 mm, with overall dislocation densities steadily reducing over the years. Device-killing micropipe defects have almost been eliminated, and the reduction in defect densities has facilitated enhanced understanding of various defect configurations in bulk and homoepitaxial layers. Silicon carbide electronics is expected to continue to grow and steadily replace silicon, particularly for applications under extreme conditions, as higher-quality, lower-priced large wafers become readily available.

Despite considerable research in thin-film growth of wide-bandgap

group III nitride

wide-bandgap semiconductor

group III nitride semiconductors, substrate technology remains a critical issue for the improvement of nitride devices. With applications ranging from high-power electronics to optoelectronics, an increasing number of nitride semiconductor devices are becoming commercially available. Currently, many of these devices are being grown heteroepitaxially on nonnative substrates, leading to a high defect density in the active layers, which limits device performance and lifetime. Aluminum nitride (AlN)

aluminum nitride (AlN)

is considered a highly desirable candidate as a native substrate material for III-nitride epitaxy, especially for AlGaN devices with high Al concentrations. AlN crystals have been grown by a variety of methods. High-temperature growth of AlN bulk crystals by

physical vapor transport (PVT)

physical vapor transport (PVT) has emerged as the most promising growth technique to date for production of large, high-quality single crystals. This chapter reviews recent growth and characterization results of AlN bulk crystals grown by PVT and discusses several issues that remain to be addressed for continued development of this technology.

Organic

organic semiconductor

single-crystal

semiconductor crystal growth presents a very different set of challenges than their inorganic counterparts. Although single crystals of organic semiconductors can be grown by the same techniques used for inorganic semiconductors, the weak intermolecular bonds, low melting temperatures, and high vapor pressures and solvent solubilities require specific modifications to crystal growth techniques of these materials. Bulk crystals of only a handful of different materials have been grown from the melt. The Czochralski, Bridgman, and general melt growth techniques are hampered by the high vapor pressure, which causes fast evaporation of the material during the growth process. However, the significant vapor pressure of organic semiconductors makes gas-phase growth methods suitable for most of them. In general, multistep synthesis of organic molecules produces impure materials which need extensive purification. Small crystals, mostly for structure determinations, have been grown from organic solvents. Zone melting has been used for a few materials, but many organic molecules decompose before reaching the melting temperature. The crystal growth of volatile molecules in a stream of flowing gas is therefore a widely used method that combines purification and crystal growth. Although gas-phase grown crystals tend to be small in size, they have high structural quality and superior purity and are therefore preferred for physical property measurements.

III-nitrides

growth of

III-nitrides with halide vapor-phase epitaxy (HVPE)

can be grown by employing several different techniques,

molecular-beam epitaxy (MBE)

such as molecular-beam epitaxy (MBE),

metalorganic vapor-phase epitaxy (MOVPE)

metalorganic vapor-phase epitaxy (MOVPE),

halide vapor-phase epitaxy (HVPE)

halide vapor-phase epitaxy (HVPE), high-pressure solution growth, and sputtering. Each of these are suited for a particular application; the specific property of HVPE is a much larger growth rate, which makes this technique the natural choice for growth of very thick layers that can be used as high-quality native substrates for subsequent growth of device structures using other techniques. Such substrates will be needed for certain devices with high current density or high voltage load, where the high defect density caused by growth on foreign substrates (heteroepitaxy) cannot be tolerated. The HVPE technology is still under development, and below we present the present situation with emphasis on GaN. The thermodynamic limitations of HVPE growth are discussed first, including the high-temperature chemistry in both the source zone and growth zone of a growth reactor. Examples of the design of growth systems are given; in particular, issues such as flow patterns, parasitic growth, and growth rates are discussed. Methods to reduce the defect density for growth on foreign substrates are discussed, as well as various lift-off techniques to prepare free-standing GaN wafers. Common characterization techniques are mentioned, and important physical properties of high-quality GaN wafers are given. The ongoing developments of HVPE growth for AlN and InN are also briefly summarized.

Growth

semiconductor

single crystal

vapor phase (VP)

of single crystals from the vapor phase is considered to be an important method to obtain stoichiometric crystalline materials from inexpensive and readily available raw materials. Elements or compounds which are relatively volatile can be grown from vapor phase. Most II–VI, I–III–VI

2

, and III–N compounds are high-melting-point materials which may be grown as single crystals by careful use of vapor phase. The

chemical vapor transport (CVT)

chemical vapor transport (CVT) method has been widely used as an advantageous method to grow single crystals of different compounds at temperatures lower than their melting points. This method is quite useful for the growth of II–VI and I–III–VI

2

compounds, which generally have high melting point and large dissociation pressure at the melting point. In addition, they undergo solid-state phase transition during cooling or heating processes, which makes the growth of these compounds by some other methods, such as from the melt, difficult. In addition, the low growth temperature involved reduces defects produced by thermal strain, pollution from the crucible, and the cost of the growth equipment. II–VI compound semiconductors cover a very broad range of electronic and optical properties due to the large range of their energy gaps. These materials in the form of bulk single crystals or thin films are used in light emitters, detectors, linear and nonlinear optical devices, semiconductor electronics, and other devices. The development of growth technology for II–VI compound semiconductors from the vapor phase with the necessary theoretical background is important. I–III–VI

2

chalcopyrite compounds are of technological interest since they show promise for application in areas of visible and infrared light-emitting diodes, infrared detectors, optical parametric oscillators, upconverters, far-infrared generation, and solar energy conversion.

The

silicon carbide (SiC)

chemical vapor deposition (CVD)

properties of silicon carbide materials are first reviewed, with special emphasis on properties related to power device applications. Epitaxial growth methods for SiC are then discussed with emphasis on recent results for epitaxial growth by the hot-wall chemical vapor deposition method. The growth mechanism for maintaining the polytype, namely

step-controlled epitaxy

, is discussed. Also described is the selective epitaxial growth carried out on SiC at the authorʼs laboratory, including some unpublished work.

The chapter presents a review of the growth of single-crystal bulk

liquid phase

electroepitaxy of semiconductors

semiconductor

semiconductors by liquid-phase electroepitaxy (LPEE). Following a

liquid phase

electroepitaxy (LPEE)

short introduction, early modeling and theoretical studies on LPEE are briefly introduced. Recent experimental results on LPEE growth of GaAs/GaInAs single crystals under a static applied magnetic field are discussed in detail. The results of three-dimensional numerical simulations carried out for LPEE growth of GaAs under various electric and magnetic field levels are presented. The effect of magnetic field nonuniformities is numerically examined. Crystal growth experiments show that the application of a static magnetic field in LPEE growth of GaAs increases the growth rate very significantly. A continuum model to predict such high growth rates is also presented. The introduction of a new electric mobility in the model, i.e., the

electromagnetic

mobility, allows accurate predictions of both the growth rate and the growth interface shape. Space limitation required the citation of a limited number of references related to LPEE [

29.1

,

2

,

3

,

4

,

5

,

6

,

7

,

8

,

9

,

10

,

11

,

12

,

13

,

14

,

15

,

16

,

17

,

18

,

19

,

20

,

21

,

22

,

23

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24

,

25

,

26

,

27

,

28

,

29

,

30

,

31

,

32

,

33

,

34

,

35

,

36

,

37

,

38

,

39

,

40

,

41

,

42

,

43

,

44

,

45

,

46

,

47

,

48

,

49

,

50

,

51

,

52

,

53

,

54

,

55

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56

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57

,

58

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59

,

60

,

61

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62

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63

,

64

,

65

,

66

,

67

,

68

,

69

,

70

,

71

,

72

,

73

]. For details of many aspects of the LPEE growth process and its historical developments, the reader is referred to these references and also others cited therein.

The state of the art and recent developments of lateral overgrowth of compound semiconductors are

epitaxial lateral overgrowth (ELO)

of semiconductors

epitaxial lateral overgrowth (ELO)

reviewed. First we focus on the mechanism of epitaxial lateral overgrowth (ELO) from the liquid phase, highlighting the phenomena that are crucial for growing high-quality layers with large aspect ratio. Epitaxy from the liquid phase has been chosen since the equilibrium growth techniques such as liquid-phase epitaxy (LPE) are the most suitable for lateral overgrowth. We then present numerous examples for which the defect filtration in the ELO procedure is very efficient and leads to significant progress in the development of high-performance semiconductor devices made of lattice-mismatched structures. Structural perfection of seams that appear when layers grown from neighboring seeds merge is also discussed. Next, we concentrate on strain commonly found in various ELO structures and arising due to the interaction of ELO layers with the mask. Its origin, and possible ways of its control, are presented. Then we show that the thermal strain in lattice-mismatched ELO structures can be relaxed by additional tilting of ELO wings while still preserving their high quality. Finally, recent progresses in the lateral overgrowth of semiconductors, including new mask materials and liquid-phase electroepitaxial growth on substrates coated by electrically conductive masks, are presented. New versions of the ELO technique from solution and from the vapor (growth from ridges and pendeo-epitaxy) are described and compared with standard ELO. A wide range of semiconductors, including III–V compounds grown from solution and vapor-grown GaN, are used to illustrate phenomena discussed. Very often, the similar behavior of various ELO structures reveals that the phenomena presented are not related to a specific group of compounds or their growth techniques, but have a much more general nature.

The performance of many electronic and optoelectronic devices critically depends on the structural quality and homogeneity of the base material, which is often an epitaxial film grown by either

vapor phase (VP)

epitaxy (VPE)

liquid phase

epitaxy (LPE)

vapor-phase epitaxy (VPE) or liquid-phase epitaxy (LPE).

This chapter presents the state of the art in LPE growth of selected advanced materials:

1.

High-temperature superconductors

2.

Calcium gallium germanates (langasite-type materials)

3.

III–V wide-bandgap nitrides.

It is not the aim, herein, to present LPE growth of more

traditional

III–V semiconductors (Si, Ge, GaAs, GaP, InP, GaP) and garnets, which have already been described extensively in the literature since about 1960. Instead, some of the most relevant literature references are given in the historical overview, which also provides a very good insight into the potential of LPE growth of newer materials. Despite the fact that LPE growth has gained less attention over the past decades, mainly due to the development of VPE growth techniques, there is a silver lining which clearly indicates that the highest-quality epitaxial films, for most efficient electronic and optoelectronic devices, will ultimately be achieved from liquid-assisted or LPE-grown films.

Epitaxial HgCdTe

HgCdTe

grown by molecular-beam epitaxy (MBE)

molecular-beam epitaxy (MBE)

is the material of choice for advanced infrared (IR) detection and imaging devices. Its bandgap is easily tunable over the entire IR range with only very small changes in lattice constant, offering the possibility of multilayer device structures and thus an unlimited choice of device designs, and it yields devices with quantum efficiencies as high as 0.99. Despite a number of unresolved challenges in achieving its ultimate promise for industrial application, the great achievements in the MBE growth of HgCdTe are made evident by its routine use in the industrial manufacture of focal-plane arrays (FPAs).

focal-plane array (FPA)

MBE growth can be continuously monitored in situ by reflection high-energy electron diffraction, spectroscopic ellipsometry (SE), and other characterization tools, providing instantaneous feedback on the influence of growth conditions on film structure. This allows the growth of a large range of unique structures such as superlattices (SLs), quantum well devices, lasers, and advanced design devices such as multicolor and high-operating-temperature IR sensors and focal-plane arrays. This chapter considers the theory and practice of MBE growth of HgCdTe and HgTe/CdTe superlattices and the use of HgCdTe in IR devices, emphasizing such incompletely resolved issues as the choice and preparation of substrates, dislocation reduction, p-doping, and the uses of SE.

The theory of MBE growth is summarized briefly in Sect.

32.2

, followed by a lengthy discussion of substrate-related issues in Sect.

32.3

, including a summary of the relative merits and demerits of different substrate materials. The growth hardware is discussed very briefly in Sect.

32.4

, followed by a discussion of the in situ characterization tools used for monitoring and control of the growth in Sect.

32.5

and of the growth procedure for HgCdTe in Sect.

32.6

. A discussion of the doping of HgCdTe, including the serious issues still surrounding p-type doping, is given in Sect.

32.7

. The properties achievable in MBE-grown HgCdTe are summarized in Sect.

32.8

, with emphasis on the types of defects common in MBE-grown material, their effects on device performance, and possible methods to reduce the present defect densities. The use of MBE-grown HgTe/CdTe SLs for IR absorbers in lieu of HgCdTe alloy material is considered in Sect.

32.9

. Finally, a brief discussion of the devices enabled by the MBE growth of HgCdTe and of their fabrication is given in Sects.

32.10

and

32.11

, and a brief concluding summary of the chapter is given in Sect.

32.12

.

Metalorganic vapor-phase epitaxy offers the ability for controlled layer deposition down to the monolayer range. Versatile application in a wide range of materials and its upscaling ability has established this growth technique in industrial mass production, particularly in the field of semiconductor devices. A topic of current research is the extension of the well-developed GaAs-based technology to the near-infrared spectral range for optoelectronic applications. The complementary approaches of either employing dilute nitrides quantum wells or quantum dots have recently achieved significant advances in the field of laser diodes. This chapter introduces the basics of metalorganic vapor-phase epitaxy and illustrates current issues in the growth of InGaAsN/GaAs quantum wells and InAs/GaAs quantum dots. Section

33.1

gives a brief introduction to the growth technique, exemplified by the classical GaAs epitaxy. Sections

33.2

and

33.3

address two current topics of GaAs-related MOVPE, which are intensely studied for, e.g., datacom laser applications: Epitaxy of dilute nitrides and InGaAs quantum dots.

The Si/Ge

SiGe heterostructure

system provides a lot of varieties of materials growth due to the lattice mismatch between Si and Ge. From the point of view of device applications, both pseudomorphic growth and strain-relaxed growth are important. Not only the layer growth but also dot formation is now attracting much attention from both the scientific community and for device applications. Comprehensive studies on the growth mechanisms have resulted in the development of novel formation techniques of SiGe heterostructures and enable us to implement strain effects in Si devices. It is obvious that the device applications largely depend on the material growth, particularly control of surface reaction and formation of dislocations and surface roughness that strongly affect device performances. Here we review the fabrication technology of SiGe heterostructures aiming at growth of high-quality materials. The relaxation of strain of SiGe buffer layers grown on Si substrates is discussed in detail, since many devices are formed on the strain-relaxed buffer layers that are sometimes called

virtual substrates

. Carbon incorporation and dot formation that are now studied to extend the possibilities of SiGe are discussed in this chapter too.

Surface bombardment by energetic particles strongly affects thin-film

plasma

energetics

pulsed laser deposition (PLD)

pulsed electron deposition (PED)

interface

processing

surface

modification

plasma

processing

growth and allows surface processing under non-thermal-equilibrium conditions. Deposition techniques enabling energy control can effectively manipulate the microstructure of the film and tune the resulting mechanical, electrical, and optical properties. At the high power densities used for depositing stoichiometric films in the

pulsed laser deposition (PLD)

case of pulsed ablation techniques such as pulsed laser deposition (PLD) and pulsed

pulsed electron deposition (PED)

electron deposition (PED), the initial energetics of the material flux are typically on the order of 100 eV, much higher than the optimal values (≤10  eV) required for high-quality film growth. To overcome this problem and to facilitate particle energy transformation from the original as-ablated value to the optimal value for film growth, one needs to carefully select the ablation conditions, conditions for material flux propagation through a process gas, and location of the growth surface (substrate) within this flux. In this chapter, we discuss the evolution of the material particles energetics during the flux generation and propagation in PLD and PED, and identify critical control parameters that enable optimum thin-film growth. As an example, growth optimization of epitaxial GaN films is provided.

PED is complementary to PLD and exhibits an important ability to ablate materials that are transparent to laser wavelengths typically used in PLD. Some examples include wide-bandgap materials such as SiO

2

, Al

2

O

3

, and MgO. Both PLD and PED can be integrated within a single deposition module. PLD–PED systems enable in situ deposition of a wide range of materials required for exploring the next generation of complex structures that incorporate metals, complex dielectrics, ferroelectrics, semiconductors, and glasses.

During melt growth of bulk crystals, convection in the melt plays

growth of

bulk crystals

convection

a critical role in the quality of the grown crystal. Convection in the melt can be induced by buoyancy force, rotation, surface tension gradients, etc., and these usually coexist and interact with one another. The dominant convection mode is also different for different growth configurations and operation conditions. Due to the complexity of the hydrodynamics, the control of melt convection is nontrivial and requires a better understanding of the melt flow structures. Finding a proper growth condition for optimum melt flow is difficult and the operation window is often narrow. Therefore, to control the convection effectively, external forces, such as magnetic fields and accelerated rotation, are used in practice. In this chapter, we will first discuss the convections and their effects on the interface morphology and segregation for some melt growth configurations. The control of the flows by external forces will also be discussed through some experimental and simulation results.

Good understanding of transport phenomena in vapor deposition systems is critical to fast and effective crystal growth system design. Transport phenomena are complicated and are related to operating conditions, such as temperature, velocity, pressure, and species concentration, and geometrical conditions, such as reactor geometry and source–substrate distance. Due to the limited in situ experimental monitoring, design and optimization of growth is mainly performed through semi-empirical and trial-and-error methods. Such an approach is only able to achieve improvement in the deposition sequence and cannot fulfill the increasingly stringent specifications required in industry. Numerical simulation has become a powerful alternative, as it is fast and easy to obtain critical information for the design and optimization of the growth system. The key challenge in vapor deposition modeling lies in developing an accurate simulation model of gas-phase and surface reactions, since very limited kinetic information is available in the literature. In this chapter, GaN thin-film growth by iodine vapor-phase epitaxy (IVPE)

iodine

vapor-phase epitaxy (IVPE)

is used as an example to present important steps for system design and optimization by the numerical modeling approach. The advanced deposition model will be presented for multicomponent fluid flow, homogeneous gas-phase reaction inside the reactor, heterogeneous surface reaction on the substrate surface, heat transfer, and species transport. Thermodynamic and kinetic analysis will be presented for gas-phase and surface reactions, together with a proposal for the reaction mechanism based on experiments. The prediction of deposition rates is presented. Finally, the surface evolution of film growth from vapor is analyzed for the case in which surface diffusion determines crystal grain size and morphology. Key control parameters for film instability are identified for quality improvement.

The

continuum-scale quantitative defect dynamics in growing Czochralski silicon crystal

vast majority of modern microelectronic devices are built on monocrystalline silicon substrates produced from crystals grown by the

Czochralski (CZ)

floating zone (FZ)

Czochralski (CZ) and float-zone (FZ) processes. Silicon crystals inherently contain various crystallographic imperfections known as microdefects that often affect the yield and performance of many devices. Hence, quantitative understanding and control of the formation and distribution of microdefects in silicon crystals play a central role in determining the quality of silicon substrates. These microdefects are primarily aggregates of intrinsic point defects of silicon (vacancies and self-interstitials) and oxygen (silicon dioxide). The distribution of microdefects in a CZ crystal is determined by the complex dynamics, influenced by various reactions involving the intrinsic point defects and oxygen, and their transport. The distribution of these microdefects can also be strongly influenced and controlled by the addition of impurities such as nitrogen to the crystal. In this chapter, significant developments in the field of defect dynamics in growing CZ and FZ crystals are reviewed. The breakthrough discovery of the

initial point defect incorporation

in the vicinity of the melt–crystal interface, made in the early 1980s, allows a simplified quantification of CZ and FZ defect dynamics. Deeper insight into the formation and growth of microdefects was provided in the last decade by various treatments of the aggregation of oxygen and the intrinsic point defects of silicon. In particular, rigorous quantification of the aggregation of intrinsic point defects using the classical nucleation theory, a recently developed lumped model that captures the microdefect distribution by representing the actual population of microdefects by an equivalent population of identical microdefects, and another rigorous treatment involving the Fokker–Planck equations are discussed in detail. The industrially significant dynamics of growing CZ crystals free of large microdefects is also reviewed. Under the conditions of large microdefect-free growth, a moderate vacancy supersaturation develops in the vicinity of the lateral surface of a growing crystal, leading to the formation of oxygen clusters and small voids, at lower temperatures. The vacancy incorporation near the lateral surface of a crystal, or the

lateral incorporation of vacancies

, is driven by the interplay among the Frenkel reaction, the diffusion of the intrinsic point defects, and their convection.

A review of CZ defect dynamics with a particular focus on the growth of large microdefect-free crystals is presented and discussed.

A major

dislocation

generation

melt

based compound

crystal growth

issue in the growth of semiconductor crystals is the presence of line defects or dislocations. Dislocations are a major impediment to the usage of III–V and other compound semiconductor crystals in electronic, optical, and other applications. This chapter reviews the origins of dislocations in melt-based growth processes and models for stress-driven dislocation multiplication. These models are presented from the point of view of dislocations as the agents of plastic deformation required to relieve the thermal stresses generated in the crystal during melt-based growth processes. Consequently they take the form of viscoplastic constitutive equations for the deformation of the crystal taking into account the microdynamical details of dislocations such as dislocation velocities and interactions. The various aspects of these models are dealt in detail, and finally some representative numerical results are presented for the liquid encapsulated Czochralski (LEC) growth of InP crystals.

In this chapter several mathematical models describing processes which take place in the Bridgman–Stockbarger (BS) and edge-defined film-fed growth (EFG) systems are presented. Predictions are made

Bridgman–Stockbarger (BS)

edge-defined film fed growth (EFG)

concerning the impurity repartition in the crystal in the framework of each of the models. First, a short description of the real processes which are modeled is given, along with the equations, boundary conditions, and initial values defining the mathematical model. After that, numerical results obtained by computations in the framework of the model are provided, making a comparison between the computed results and those obtained in other models, and with the experimental data.

X-ray scattering analysis and instrumentation has been evolving rapidly to meet the demands arising from the growth of sophisticated device structures. X-ray scattering is very sensitive to composition, thickness and defects in layered structures of typical present-day electronic device dimensions. Considerable information can be obtained from simple profiles, including an estimate of layer thickness and composition (by measuring peak separations) and a measure of the sample quality (from the peak broadening). The full simulation of the profiles takes this a stage further to interpret very complex structures and obtain more reliable parameter estimates. By obtaining two-dimensional scattering data the information becomes more extensive, including layer strain relaxation and defect analysis, quantum dot composition and shape. Generally the data is averaged over a few mm, however reducing the beam size can break this averaging to reveal inhomogeneities, isolating small regions and in some circumstances isolate individual quantum dots for analysis. This article gives an overview of the status, differentiating those methods that are easily accessible and those that require a collaborative approach because they are still being established.

X-ray topography is the general term for a family of x-ray diffraction imaging techniques capable of providing information on the nature and distribution of structural defects such as dislocations, inclusions/precipitates, stacking faults, growth sector boundaries, twins, and low-angle grain boundaries in single-crystal materials. From the first x-ray diffraction image, recorded by Berg in 1931, to the double-crystal technique developed by Bond and Andrus in 1952 and the transmission technique developed by Lang in 1958 through to present-day synchrotron-radiation-based techniques, x-ray topography has evolved into a powerful, nondestructive method for the rapid characterization of large single crystals of a wide range of chemical compositions and physical properties, such as semiconductors, oxides, metals, and organic materials. Different defects are readily identified through interpretation of contrast using well-established kinematical and dynamical theories of x-ray diffraction. This method is capable of imaging extended defects in the entire volume of the crystal and in some cases in wafers with devices fabricated on them. It is well established as an indispensable tool for the development of growth techniques for highly perfect crystals (for, e.g., Czochralski growth of silicon) for semiconductor and electronic applications. The capability of in situ characterization during crystal growth, heat treatment, stress application, device operation, etc. to study the generation, interaction, and propagation of defects makes it a versatile technique to study many materials processes.

In the present chapter we first briefly consider mechanisms for the etching of semiconductors

etching of semiconductors

(Sect.

43.1

) and relate these principles to methods for controlling surface morphology and revealing defects (Sect.

43.2

). Section

43.3

describes in some detail defect-sensitive etching methods. Results are presented for the classical (orthodox) method used for revealing dislocations in Sect.

43.3.1

. More recently developed open-circuit (photo)etching approaches, sensitive to both crystallographic and electrically active inhomogeneities in semiconductors, are reviewed in Sect.

43.3.2

. In particular, attention will focus on newly introduced etchants and etching procedures for wide-bandgap semiconductors.

Since

transmission

electron microscopy (TEM)

the first observation of dislocations published in 1956, transmission electron microscopy (TEM) has become an indispensable technique for materials research. TEM not only provides very high spatial resolution for the characterization of microstructure and microchemistry but also elucidating the mechanisms controlling materials properties. The results of TEM analyses can also shed light on possible ways for improving the crystal quality. With the recent development of the electron exit wave reconstruction technique, the resolution of TEM has exceeded the typical Scherzer point resolution of ≈0.18  nm and observation of dislocation cores with an accuracy of 10 pm has been achieved. Most TEM studies are carried out in a static status; however, dynamic studies using in situ heating, in situ stressing, and even in situ growth can be conducted to study the development, interaction, and multiplication of defects.

Electron paramagnetic resonance

point defect

characterization

(EPR) spectroscopy identifies, counts, and monitors

electron paramagnetic resonance (EPR)

point defects in a wide variety of materials. Unfortunately, this powerful tool has faded from the literature in recent years. The present trend away from fundamental studies and towards technological challenges, and the need for fast diagnostic tools for use during and after materials growth has weakened the popularity of magnetic resonance tools. While admittedly the use of EPR in industrial laboratories for routine materials characterization is limited, EPR spectroscopy can be, and has been, successfully used to provide reams of information directly relevant to technologically significant materials.

The interpretation of EPR spectra involves an understanding of basic quantum mechanics and a reasonable investment of time. Once a defect is identified, however, the spectra may be used as a fingerprint that can be used in additional studies addressing the chemical kinetics, charge transport, and electronic energies of the defect and surrounding lattice. Numerous examples are provided in this chapter. In addition, the fundamental information extracted from EPR analysis should not be forgotten. Perhaps knowing the distribution of spin states about the core of a defect will not expedite the production of material X for use as device Y, but it may provide the seed of knowledge with which to build the 21st centuryʼs technological revolution. We must remember that the basic understanding of semiconductors developed in the middle of the last century spawned the solid-state transistor, which unquestionably produced the computer revolution in the latter half of the 20th century.

This chapter will acquaint the reader with the fundamental methods used to interpret EPR data and summarize many different experiments which illustrate the applicability of the technique to important materials issues.

Positron annihilation spectroscopy is an experimental technique that

defect

characterization

semiconductor

positron

annihilation spectroscopy

allows the selective detection of vacancy defects in semiconductors, providing a means to both identify and quantify them. This chapter gives an introduction to the principles of the positron annihilation techniques and then discusses the physics of some interesting observations on vacancy defects related to growth and doping of semiconductors. Illustrative examples are selected from studies performed in silicon, III-nitrides, and ZnO.

A short overview of positron annihilation spectroscopy is given in Sect.

46.1

. The identification of vacancies and their charge states is described in Sect.

46.2

; this section also discusses how ion-type acceptors can be detected due to the positronsʼ shallow Rydberg states around negative ions. The role of vacancies in the electrical deactivation of dopants is discussed in Sect.

46.3

, and investigations of the effects of growth conditions on the formation of vacancy defects are reviewed in Sect.

46.4

. Section

46.5

gives a brief summary.

Nowadays, advances in genomics as well as in proteomics have produced thousands of new biological macromolecules for study in structural biology, biomedicine research, and drug design projects.

Novel and classical methods of protein crystallization as well as modern techniques for two-dimensional (2-D) and three-dimensional (3-D) characterization of different biomolecules are reviewed in this chapter. Production of high-quality single crystals will be analyzed in detail from classical approaches to modern, high-throughput crystal growth methods for x-ray diffraction, as will new strategies for reducing the amount of raw materials used, accelerating the work, and increasing success rates. It will be pointed out that this work on crystallization as well as characterization is multidisciplinary. These scientific efforts are also interrelated and require close collaboration between biochemists, biophysicists, microbiologists, and molecular biologists, as well as physicists and engineers to develop new strategies and equipment for structural purposes. Finally, some of the problems faced and plans for solving them by using x-ray diffraction, neutron diffraction, and electron microscopy will be revised.

Among the various crystallization techniques, crystallization in gels has found wide applications in the fields of biomineralization and macromolecular crystallization in addition to crystallizing materials having nonlinear optical, ferroelectric, ferromagnetic, and other properties. Furthermore, by using this method it is possible to grow single crystals with very high perfection that are difficult to grow by other techniques. The gel method of crystallization provides an ideal technique to study crystal deposition diseases, which could lead to better understanding of their etiology. This chapter focuses on crystallization in gels of compounds that are responsible for crystal deposition diseases. The introduction is followed by a description of the various gels used, the mechanism of gelling, and the fascinating phenomenon of Liesegang ring formation, along with various gel growth techniques. The importance and scope of study on crystal deposition diseases and the need for crystal growth experiments using gel media are stressed. The various crystal deposition diseases, viz. (1) urolithiasis, (2) gout or arthritis, (3) cholelithiasis and atherosclerosis, and (4) pancreatitis and details regarding the constituents of the crystal deposits responsible for the pathological mineralization are discussed. Brief accounts of the theories of the formation of urinary stones and gallstones and the role of trace elements in urinary stone formation are also given. The crystallization in gels of (1) the urinary stone constituents, viz. calcium oxalate, calcium phosphates, uric acid, cystine, etc., (2) the constituents of the gallstones, viz. cholesterol, calcium carbonate, etc., (3) the major constituent of the pancreatic calculi, viz., calcium carbonate, and (4) cholic acid, a steroidal hormone are presented. The effect of various organic and inorganic ions, trace elements, and extracts from cereals, herbs, and fruits on the crystallization of major urinary stone and gallstone constituents are described. In addition, tables of gel-grown organic and inorganic crystals are provided.

In situ

crystal growth

and ion exchange in titanium silicates

experiments, whether carried out in-house or at synchrotron sources, can provide valuable information on the nucleation and subsequent growth of crystals and on the mechanism of growth as well as mechanisms of phase changes and ion-exchange phenomena. This chapter describes the types of x-ray detectors, in situ cells, and detectors used in such studies. The procedures are illustrated by a study of the preparation of a tunnel-structured sodium titanium silicate, the partially niobium framework phase, and the mechanism of ion exchange as revealed by time-resolved x-ray data.

Scintillation materials are

scintillation material

employed to detect x-ray and

γ

-ray photons or accelerated particles. Wide-bandgap semiconductor or insulator materials with a high degree of structural perfection are suitable for this purpose. They must accomplish fast and efficient transformation of incoming high-energy photon/particles to a number of electron–hole pairs collected in the conduction and valence bands, respectively, and their radiative recombination at suitable luminescence centers in the material. Generated ultraviolet (UV) or visible light can then be detected at high sensitivity by conventional solid-state semiconductor- or photomultiplier-based photodetectors, which are an indispensable part of scintillation detectors.

An insight into this field will be provided for a wider scientific audience and at the same time we will point out some current hot topics. After reviewing the historical issues and fundamental physical processes of the x(

γ

)-to-visible light transformation occurring in scintillators, practically important material parameters, characteristics, and related measurement principles will be summarized. An overview of selected modern single-crystal and optical ceramic materials will be given. Particular attention will be paid to the relation between the manufacturing technology used and the occurrence of material defects and imperfections. The study and understanding of related trapping states in the forbidden gap and their role in the energy transfer and storage processes in the material will be shown to be of paramount importance for material optimization. Correlated experiments of time-resolved luminescence spectroscopy, wavelength-resolved thermally stimulated luminescence, and electron paramagnetic resonance offer a powerful tool for this purpose. Future prospects and directions for activity in the field will be briefly mentioned as well.

The

silicon (Si)

solar cell

solar cell

phenomenal growth of the silicon photovoltaic industry over the past decade is based on many years of technological development in silicon materials, crystal growth, solar cell device structures, and the accompanying characterization techniques that support the materials and device advances. This chapter chronicles those developments and serves as an up-to-date guide to silicon photovoltaic technology. Following an introduction to the technology in Sect.

51.1

, an in-depth discussion of the current approaches to silicon material crystal growth methods for generating solar cell substrates is presented in Sect.

51.2

. Section

51.3

reviews the current manufacturing techniques for solar cell devices and also presents the latest advances in device structures that achieve higher efficiency. Finally, a perspective on the technology and what might be expected in the future is summarized in Sect.

51.4

.

Wafer manufacturing (or wafer production) refers to a series of modern manufacturing processes of

wiresaw

wafer manufacturing

wafer manufacturing

and slicing using wiresaw

producing single-crystalline or poly-crystalline wafers from crystal ingot (or boule) of different sizes and materials. The majority of wafers are single-crystalline silicon wafers used in microelectronics fabrication although there is increasing importance in slicing poly-crystalline photovoltaic (PV) silicon wafers as well as wafers of different materials such as aluminum oxide, lithium niobate, quartz, sapphire, III–V and II–VI compounds, and others. Slicing is the first major post crystal growth manufacturing process toward wafer production. The modern wiresaw has emerged as the technology for slicing various types of wafers, especially for large silicon wafers, gradually replacing the ID saw which has been the technology for wafer slicing in the last 30 years of the 20th century. Modern slurry wiresaw has been deployed to slice wafers from small to large diameters with varying wafer thickness characterized by minimum kerf loss and high surface quality. The needs for slicing large crystal ingots (300 mm in diameter or larger) effectively with minimum kerf losses and high surface quality have made it indispensable to employ the modern slurry wiresaw as the preferred tool for slicing. In this chapter, advances in technology and research on the modern slurry wiresaw manufacturing machines and technology are reviewed. Fundamental research in modeling and control of modern wiresaw manufacturing process are required in order to understand the cutting mechanism and to make it relevant for improving industrial processes. To this end, investigation and research have been conducted for the modeling, characterization, metrology, and control of the modern wiresaw manufacturing processes to meet the stringent precision requirements of the semiconductor industry. Research results in mathematical modeling, numerical simulation, experiments, and composition of slurry versus wafer quality are presented. Summary and further reading are also provided.