Advanced Semiconducting Materials and Devices

In this preliminary chapter discussing the fundamentals of semiconductor, the electrical and electronic materials are classified. Importance of semiconducting materials and their scope are elaborated. Conductors, semiconductors and dielectrics are differentiated from each other on the basis of energy bandgap. Different types of semiconducting materials, their merits and characteristics are listed. Various elemental form, compound and alloyed semiconductors are described. Basic semiconducting devices along with their working principles are briefed. Latest developments in the field of semiconducting materials have been included; the main among them are emerging and futuristic spintronic materials, ferromagnetic semiconductors, emerging wide bandgap semiconductors, left-handed materials, photocatalytic semiconductors, integrated circuit purpose semiconductors etc. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

In this chapter, the basic concepts of Materials Science are presented that will help to understand the lattice structure of semiconductors. Monocrystalline and polycrystalline solids, Bravais crystals system; different unit cells along with their geometry and examples are elaborated. Fundamentals and illustrations of Miller indices are presented for the understanding of the planes, family of planes, directions and family of directions through the unit cells. Atomic bonding: bonding forces, types and nature of bonds in semiconductors are presented. Covalent bonds, bond length, bond angle and percentage ionic character in compound semiconductors are explained. Diamond cubic structure of Silicon and Germanium, and zincblende and wurtzite lattice structures are given. Different types of crystal imperfections with emphasis on point imperfections are suggested. Details of Bohr atomic model, electron energy, spectral of hydrogen, modern concept of atom, quantum states etc. are discussed which will be useful for understanding the topics given in later chapters. Important applications and brief descriptions of some semiconductor devices are discussed. Details of Narrow bandgap and wide bandgap semiconductors along with their properties and applications are presented. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Role of valence electrons and free electrons in carrier transport through semiconductors is presented. Various electrons theories such as Free election theory, Energy band theory, and Brillouim zone theory are described. Mechanism of conduction by free electrons is elaborated. Fermi energy level, intrinsic and extrinsic semiconductors, energy diagrams of n-type and p-type semiconductors are given. Direct and indirect energy band semiconductors and effect of alloying on them are discussed. Concepts of effective mass, density of state, temperature dependence of carrier concentrations are developed. Drift of carriers under electric and magnetic fields, collision time, effects of temperature on mobility of carriers, effects of doping on mobility are explained. Degenerate semiconductors and effect of heavy doping are incorporated. The phenomenon of Hall Effect and its significance; Hall voltage, Hall angle, Hall coefficient etc. are described. Relation between Density of states and Fermi energy, momentum space, Fermi sphere, Fermi radius, Fermi velocity, Fermi momentum, Fermi temperature etc. are derived. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Most semiconductor devices operate by creation of charge carriers which are in excess of the charge carriers available at thermal equilibrium. Conduction in semiconductors are dominated by these excess carriers. Therefore, in this chapter optical absorption and its mechanism, absorption coefficient and factors affecting it, are explained. Luminescence, phosphorescence, electro-luminescence, mechanism of excitation and recombination are discussed. Carrier lifetime and its derivation, indirect recombination, steady state carrier generation and quasi-Fermi levels are described. Photoconductivity and photoconductive devices, photoconductive cell, photo-multiplier tube, and factors affecting the selection of semiconductors for photo-conducting purpose are explained. Concepts of diffusion of carriers, analysis of drift and diffusion carriers, Einstein relation, continuity equation for diffusion and recombination are presented. Equations have been derived for diffusion and diffusion length. Solution has been provided for charge transport and impurity distribution by error function method and Gaussian distribution method. Long diode and short diode are also discussed. Quantum efficiency, trapping centre, dark resistance of photoconductor, and derivation of junction-voltage etc. are briefed through solved solutions. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

P-N junction is an important control element for the performance of semiconductor devices. Devices such as amplifiers, rectifiers, linear and digital ICs etc. employ one or more P-N junctions for their working. Therefore, for a good understanding of all these, the P-N junction diode: their applications and working at equilibrium conditions are presented. In this chapter, relations have been established between contact potential and doping concentrations, for Fermi level at equilibrium, for the width of depletion region and penetration depth. Biased junctions: their working when not connected to a battery, forward-biased and reverse biased p-n junctions and their voltage-current characteristics are described. Poisson’s equation, junction breakdown mechanisms, Zener and avalanche breakdown, and junction capacitance are discussed. Rectifying diodes, half-wave rectifiers, Zener diode for electric meter protection and as peak clipper are given. The breakdown diode; specifications of p-n junction diode, their physical structures and terminal identifications are also elaborated. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

In this chapter, different types of specific purpose diodes viz. crystal diode, thermal diode, constant current diode, PIN diode, Schottky diode, gold-doped diode, super barrier diode, varicap diode, Esaki diode, laser diode, TVS diode and snap-off diode etc. are introduced besides many others. Their symbolic representation, diode model, ideal diode and real diode are also presented. Different conditions of working of p-n junctions and transient conditions are included. Time dependent variation in space charge, and solution for stored charge is mathematically elaborated. Switching diodes, narrow base diode, reverse recovery transient, and method to improve the switching speed are discussed. P-N junction capacitance, derivation of its expression; Graded junctions, linearly graded, abrupt and hyperabrupt junctions and their doping profile are given. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

In the recent past, the development of microwave devices having low noise, high frequency, greater bandwidth, lesser switching time etc. has yielded devices with improved performance. These devices have been used in drying machines for textile, food and papers industries etc., for biomedical applications, for electronic warfare etc. In this regard, several microwave devices have been developed. Therefore in this chapter, the majority carrier diodes for use at microwave frequencies are included. Tunnel diode: its response under zero-bias, reverse-bias, forward-bias and increased forward-bias conditions, its response beyond negative resistance region and characteristics are presented. Transitive devices, transit time effects, and requirements of a good transit time device are discussed. The backward diode, its characteristics and applications are given. Metal-semiconductor junctions, Schottky diodes: its operating mechanism, characteristics, limitations and applications are explained. Ohmic contacts, heterojunctions: their unique behaviour, band discontinuities and band bending, and potential well in it are described. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Microwave diodes are used to provide amplification, oscillation and other functions at microwave frequencies. They have a large bandwidth, therefore more information can be transmitted in microwave frequency range. It is the current trend to use microwaves more and more in long distance communication such as telephony, TV network, space communication, radars, microwave ovens etc. Therefore in this chapter, the Varactor diode; its construction, characteristics, performance and applications are presented, different types of semiconductor photodiodes are classified, and the IMPATT diode, TRAPATT diode and BARITT diode are elaborated along with their operation, performance and applications. The construction, operational characteristics and applications of p-n photodiodes, p-i-n photodiode, avalanche photodiode, and mid-infrared photodiodes are described. The transferred electron mechanism, valleys in conduction band and dependence of electron velocity on electric field are discussed. The Gunn diode: its fabricational materials, dielectric relaxation time etc. are given. The Dovett diode is also discussed. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Optoelectronics refers to the studies of optics and electronics. Optoelectronic devices involve the interaction of photons of semiconductors. These devices find important applications such as sensors, couplers, isolaters and emitters. In this chapter, the Optoelectronic semiconductor devices are enumerated. Optical properties and characteristics of illuminated junction, are elaborated. Solar cell: its construction, working, factors affecting its efficiency, fabrication and materials, advantages and limitations, and applications are narrated. Further, different types of photodetectors are classified, requirements of a good photodetector and methods to achieve fast responsing speed are discussed. Working, construction and choice of materials are given for p-i-n photodetector, silicon heteroface photodetector and photoconductive detector. Light emitting diode: its construction and working, advantages, applications, specifications, and suitable materials for them are described. Semiconductor lasers: their working, merits, characteristics and properties, applications, and suitable materials for them are elaborated. The lasers diodes, light dependent resistor, differences between homo-junction laser and heterojunction laser, and spontaneous emission and stimulated emission are explained. Importance of optoelectronic pair and population inversion are briefly presented. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

In this chapter, the transistors have been grouped into two major categories viz. Bipolar junction transistors (BJTs) and Field effect transistors (FETs). They have been further classified into p-n-p and n-p-n types; MESFET, MISFET, MODFET, MOSFET, n-channel, p-channel types etc. The details of BJTs such as their construction, fundamentals of operation, meaning and symbols of n-p-n and p-n-p are given. Forward and reverse biasing, transistor currents, circuit configurations and their characteristics are described. Comparison between CB, CE and CC configurations is presented. Amplification with different configurations of BJTs, their characteristics and uses, and phase reversal are discussed. Specifications of transistors and their terminal identifications are given. Meanings of cascade amplifier, Debye screening length, and Kirk effect are explained. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Detailed classification of different types of transistors is presented. The field-effect transistors (FETs) are exhaustively sub-classified into MESFET, MISFET, MODFET, MOSFET, IGFET, DE-MOSFET, E-only MOSFET, n-channel and p-channel types. The advantageous features of FETs over BJTs and applications of FETs are given. MISFETs: their construction, basic types and performance are discussed. MESFET: its construction, operation and characteristics are explained. MOSFETs: their basic types, construction, operation and short-channel effects are elaborated. IGFET and HEMT, n-channel and p-channel FET are described. The charge coupled devices: its operation and salient uses are explained. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Many industrial applications require control of power such as in variable speed drives, light-intensity controllers, temperature regulators etc. They are controlled by Power devices such as four-layer devices, semiconductor controlled rectifiers (SCRs) etc. In this regard, a P-N-P-N diode has been explained stating its conduction mechanism, two-transistor analogy, triggering mechanisms etc. SCRs are also explained showing their various shapes and sizes, biasing, operation and triggering. Applications of SCR, half-wave and full-wave power control, and silicon controlled switch are also explained. Bilateral devices such as Diac and Triac are presented along with their working, characteristics and applications. Insulated gate bipolar transistor (IGBT), its characteristics and advantages are also elaborated. Meaning of uni-junction transistor (UJT) and gate controlled switch (GCS) are also briefed. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

This chapter presents a brief outline of the technology associated with semiconductor processing. The production of highly pure electronic-grade silicon from raw feedstock is presented. Different techniques of semiconductor crystal growth are given. Czochralski (CZ) method and Bridgman method are explained. Zone refining process is also described. Semiconductor fabrication technology, and thin film micro-electronic circuit fabrication are presented. Preparation of wafers, epitaxy, masking, photolithography, interconnection by metalizing are discussed. Methods of ion-implantation, molecular beam epitaxy (MBE), sputtering and etching are explained. Semiconductor p–n junction (diode) formed by different methods, are described. Stepwise procedure for the formation of a semiconductor p–n junction, and transistor manufacturing processes (of grown junction, alloy formation, diffusion) are briefly narrated. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Semiconducting materials are used in widely varying fields for specific applications. Therefore, they are special purpose semiconductors. Such semiconductors are described in this chapter, for example; three-dimensional semiconductor solar cell, optical semiconductor, thermoelectric semiconductors, integrated circuit purpose semiconductors. The photocatalytic semiconductors which are used to make the environment free of pollution, are also discussed. Transparent oxide semiconductors and semiconductor based spintronic devices are also explained. Spin-charge converter, spin injection materials, plasmonic solar cells, and photonic semiconductors are also elaborated. Plasmonic and photovoltaic kinds of semiconductors are introduced. Applications of plasmonic (photovoltaic) solar cells, photonic processor, photonic crystals, and superlattices are given. Future of photonics is also incorporated. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

The present era is of nanotechnology and nano-materials. Therefore, a large number of investigations are being carried out in nano-structured semiconductors also. Consequently, the newer nano-based semiconducting materials and devices are being researched. Many recent developments in this field are included briefly in this chapter by incorporating the published research papers. The main emerging nano-semiconducting materials and devices included here are: semiconductor nanowires, nano crystals, nanogap devices, nanoparticle- based organic photovoltaic devices, nanoscale semiconductor, artificial electronic skin, semiconductor nanomembranes, nano-structured tin-dioxide materials, nano-structures based solar energy applications, metal-semiconductor hybrid nanostructures, inorganic semiconductor nanostructures etc.

Advancement in the knowledge of science and technology and newer developments has always shown the path of research. The present researches in the field of semiconducting materials and devices are numerous. To get the readers acquainted with those researches, the emerging trends in their investigations and developments are presented in this chapter. Consequently, the leading developments included here are: semiconductor disk lasers, bandgap engineering and gain mirror technology, optically pumped semiconductor lasers, polymer fullerene solar cells, polymer semiconductor crystals, plastic solar cells, skin-inspired electronic devices, dye-sensitized solar cells from photoanodes, Piezoelectric oxide semiconductor FET, oxide semiconductor thin-film semiconductors, SiC power devices etc.