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This book focuses on novel bismuth-containing alloys and nanostructures, covering a wide range of materials from semiconductors, topological insulators, silica optical fibers and to multiferroic materials. It provides a timely overview of bismuth alloys and nanostructures, from material synthesis and physical properties to device applications and also includes the latest research findings. Bismuth is considered to be a sustainable and environmentally friendly element, and has received increasing attention in a variety of innovative research areas in recent years. The book is intended as a reference resource and textbook for graduate students and researchers working in these fields.

### Chapter 1. Electronic Properties of Dilute Bismides

Abstract
In this chapter, electronic properties of dilute bismide III-V semiconductors are reviewed briefly. Theoretical and computational methods are collected and discussed extensively. Empirical models, including tight-binding (TB) model, band anti-crossing (BAC), valance band anti-crossing (VBAC), and k·p model, have been widely applied in calculations of electronic properties of dilute bismide III-V materials. First-principle methods have also been used to investigate many kinds of Bi-containing compounds, such as models of bulk, surface, and nanostructure. Several combined methods are also reviewed.
Pengfei Lu, Dan Liang, Xiaoning Guan, Qian Wang, Huiyan Zhao, Liyuan Wu

### Chapter 2. Molecular Beam Epitaxy Growth and Properties of GaAsBi and AlAsBi

Abstract
GaAsBi alloys have been extensively studied in recent years, and the highest Bi concentration yet reached has been 22 %. Many photoelectric devices using this material have been produced, such as quantum well lasers, LEDs, solar cells, etc. The Bi incorporated into AlAs is expected to change the bandgap from indirect to direct. There are only a few theoretical reports on AlAsBi, however, experimental research results are seldom reported. In this chapter, we review the molecular beam epitaxy of GaAsBi and analyze the growth mechanism. Besides, we present the synthesis of AlAsBi by molecular beam epitaxy. The growth temperature, As/Ga flux ratio, Bi flux and the growth rate all have great influence on the Bi incorporation. Bismuth atoms play a surfactant role under As-rich conditions and an anti-surfactant role under Ga-rich conditions. Droplets tend to be formed on the surface of GaAsBi alloys due to the atomic size mismatch between Bi atoms and As atoms. The high-angle annular dark-field mode of scanning transmission electron microscopy images confirm Bi atoms cluster exsiting in GaAsBi films. Furthermore, we show the optical properties of GaAsBi and discuss the localized states induced by Bi. The photoluminescence wavelength of GaAsBi redshifts with increasing Bi concentration. The bandgap of GaAsBi is insensitive to temperature, which is important for developing un-cooled lasers. We discuss the influence of Bi incorporation on the electric and transport properties of GaAsBi. The types of dominant point defects induced by Bi incorporation are analyzed. The measurement results of the electron effective mass demonstrate that Bi incorporation not only changes the valence band but also has non-negligible influence on the conduction band in GaAsBi. For AlAsBi, we review the theoretical simulations and present the molecular beam epitaxy growth without substrate rotaion to investigate the influence of As/Al flux raio and the Bi flux on Bi incorporation.
Li Yue, Xiaolei Zhang, Weiwen Ou, Zhenghao Shen, Shumin Wang

### Chapter 3. MOVPE Growth and Device Applications of Ternary and Quaternary Dilute Bismide Alloys on GaAs Substrates

Abstract
III/V semiconductors containing bismuth (Bi) show some interesting properties for high efficient optoelectronic applications in the near- and mid-IR region. However, the alloys are highly metastable due to the large covalent radius of the Bi atom compared to the other group V atoms, which are replaced in the cubic zinc-blende lattice. Hence, carefully adjusted growth conditions at low growth temperatures are required in order to incorporate a significant amount of Bi into the host lattice. In this book chapter, we review our current understanding of the growth of dilute Bi-containing III/V semiconductor alloys on GaAs substrates, the factors, which limit the Bi incorporation, as well as the application of the material in electrically pumped LASER diodes. Bi fractions of up to 4.2% Bi and 7% Bi can be achieved using metal-organic vapor phase epitaxy (MOVPE) as growth technique using pulsed as well as continuous flow conditions, respectively. The influence of different growth conditions, i.e., the growth temperature and partial pressures of the used precursors are investigated and the results are discussed in detail. Exceeding a critical Bi concentration, accumulation of metal droplets on the surfaces is found which hampers high-quality growth of subsequent layers, which is however necessary for devices. This limitation in the Bi incorporation makes quaternary alloys, like GayIn1−yAs1−xBix structures on GaAs substrates interesting for optoelectronic applications. Optimization of the material quality resulted in the demonstration of electrically pumped GaAs1−xBix laser diodes with up to 4.1% Bi operating at room temperature. As there is this current upper limit of 7% Bi incorporation using MOVPE growth, we discuss factors, which might influence and limit the Bi incorporation in the host material. The use of alternative Bi precursors is investigated with regard to the impact of different carbon (C)-containing radicals on the surface. The impact of strain on the Bi incorporation is discussed by adding nitrogen or phosphorus and hence tensilely prestraining the layer. Finally, we also investigate the influence of trimethylindium (TMIn) on the Bi incorporation in GayIn1−yAs1−xBix and compare its growth to the one of GaAs1−xBix.
Thilo Hepp, Lukas Nattermann, Kerstin Volz

### Chapter 4. Strategic Molecular Beam Epitaxial Growth of GaAs/GaAsBi Heterostructures and Nanostructures

Abstract
In this chapter, we go over epitaxial growth of bismide thin films, multiple quantum wells, and nanostructures (nanowires) using molecular beam epitaxy (MBE) and their surface morphology, structural, and optical properties are investigated along with device applications. We describe how the Bi content in GaAs1−xBix epilayers grown on (100), (411)A, and (411)B GaAs substrates can be controlled by the growth conditions. Nonstandard growth conditions such as two-substrate-temperature technique (TST) are required for GaAs1−xBix because of the strong tendency of Bi atom segregation under usual growth conditions. We have reported a GaAs0.96Bi0.04/GaAs multiple quantum well LED grown by TST technique with a room temperature photoluminescence and electroluminescence at 1.23 μm emission wavelength. The TST procedure proves as a very efficient method to reduce Bi segregation and thus improves the quality of the GaAsBi layer at GaAs interfaces.
Pallavi Kisan Patil, Satoshi Shimomura, Fumitaro Ishikawa, Esperanza Luna, Masahiro Yoshimoto

### Chapter 5. Phosphorus and Nitrogen Containing Dilute Bismides

Abstract
Phosphorus and nitrogen containing dilute bismides differ from arsenic and antimony containing bismides in that the anions have large differences in atomic size and electronegativity, offering rich potentials for strain as well as bandgap engineering. In this chapter, we show theoretical modeling, epitaxy and characterizations of III-PBi and III-NBi and their quaternary alloys.
Shumin Wang, Tingting Jin, Shuyan Zhao, Dan Liang, Pengfei Lu

### Chapter 6. GaSbBi Alloys and Heterostructures: Fabrication and Properties

Abstract
Dilute bismuth (Bi) III-V alloys have recently attracted great attention, due to their properties of bandgap reduction and spin–orbit splitting. The incorporation of Bi into antimonide-based III-V semiconductors is very attractive for the development of new optoelectronic devices working in the mid-infrared range (2–5 µm). However, due to its large size, Bi does not readily incorporate into III-V alloys and the epitaxy of III-V dilute bismides is thus very challenging. This chapter presents the most recent developments in the epitaxy and characterization of GaSbBi alloys and heterostructures.
O. Delorme, L. Cerutti, R. Kudrawiec, Esperanza Luna, J. Kopaczek, M. Gladysiewicz, A. Trampert, E. Tournié, J.-B. Rodriguez

### Chapter 7. Dilute Bismuthides on InP Substrates: From Materials to Devices

Abstract
Dilute bismuthides, achieved by incorporating a small amount of bismuth (Bi) into conventional III–V semiconductors, have drawn extensive attention as a class of novel material for various promising applications ranging from optoelectronics to thermoelectrics due to their interesting properties such as band gap reduction, strong spin–orbit coupling, relatively weak temperature sensitivity, etc. This chapter focuses on the study of dilute bismuthides on InP substrates: InGaBiAs and InPBi. MBE growth conditions, material morphology and properties (especially electrical and optical properties), and the related potential applications will be discussed, as will the band gap narrowing and the band anticrossing (BAC) model.
Jing Zhang, Yuejing Wang, Joshua M. O. Zide

### Chapter 8. Bismuth-Related Nanostructures

Abstract
Bismuth can modify surface reconstruction of III-V semiconductors and affect their growth conditions. Bismuth incorporation into III-Vs strongly changes their electronic properties. We present an overview of how the above Bi-related effects influence structural and optical properties of III-V nanostructures.
Lijuan Wang, Hao Liang, Zhenghao Shen, Shumin Wang

### Chapter 9. Surface Mediated Growth of Dilute Bismides

Abstract
It has been well established that growing semiconductor films in the presence of a surfactant significantly influences the surface morphology and the compositional homogeneity in the bulk [1]. There is a great deal of evidence in the literature that suggests that this is particularly true in Bi-containing films. Kawano and co-workers [2] first showed that pre-depositing Bi on Si(001) did not result in its incorporation into the subsequent Ge film. Furthermore, Bi suppressed the formation of 3D islanding despite the lattice mismatch. The classic model for surface segregation in III-V compound semiconductor films is thermodynamic in nature, where there is an energetic driving force for the segregating species to reside at the surface as a surfactant [3]. Since that initial report of the smoothing effect of Bi on surface morphology, similar results have been reported for other materials systems including GaAs [4] and GaAsN [5] thin films, InGaAs/GaAs heterostructures, [6] and InAs/InGaAs(001) nanocomposites. [7] Pre-deposition of Bi was also observed to impact ordering in GaAsSb [8] and InGaP [9] and the incorporation of Sb in InAsSb [10]. Furthermore, the presence of Bi has been shown to change the crystal phase of GaAs nanowires, [11] and the sizes of InAs/GaAs quantum dots increase when a Bi surfactant is used [12]. All of these phenomena point to the fact that Bi strongly alters the growing surface of a semiconductor film. This chapter describes the atomic-scale surface reconstructions present during the growth of Bi-containing films, and the factors that contribute to the incorporation of Bi. A major part of this work also considers the mechanisms that compete with Bi incorporation, including the formation of droplets, and their ramifications on the uniformity of the films.
Joanna M. Millunchick, C. R. Tait

### Chapter 10. Structural Properties of Bi Containing InP Films Explored by Cross-Sectional Scanning

Abstract
The structural properties of highly mismatched III-V semiconductors with small amounts of Bi are still not well understood at the atomic level. In this chapter, the potential of cross-sectional scanning tunneling microscopy (X-STM) to address these questions is reviewed. Special attention is paid to the X-STM contrast of isovalent impurities in the III-V system, which is discussed on the basis of theoretical STM images of the (110) surface using density functional theory (DFT) calculations. By comparing high-resolution X-STM images with complementary DFT calculations, Bi atoms down to the third monolayer below the InP (110) surface are identified. With this information, the Short-range ordering of Bi is studied, which reveals a strong tendency toward Bi pairing and clustering. In addition, the occurrence of Bi surface segregation at the interfaces of an InP/InP$$_{1-x}$$Bi$$_{x}$$/InP quantum well with a Bi concentration of $$2.4~\%$$ is discussed.
C. M. Krammel, P. M. Koenraad, M. Roy, P. A. Maksym, Shumin Wang

### Chapter 11. Optical Properties of Dilute Bismides

Abstract
Dilute bismides have attracted great attention due to their promising optoelectronic applications, of which the optical properties are a major theme experimental studies. In this chapter, recent progress in the optical spectroscopic study of several representative III-V group dilute bismides is overviewed, with a focus on the photoluminescence (PL) and photoreflectance (PR) results especially by improved spectroscopic methods. Typical data from dilute bismides by other spectroscopic techniques of, e.g., Raman scattering, absorption and refractive index, are also briefly reviewed.
Xiren Chen, Bing Yan, Jun Shao

### Chapter 12. The Physics of Bismide-Based Lasers

Abstract
In this chapter, we briefly review existing approaches for near- and mid-infrared lasers and show why III-V bismides are attractive as an alternative approach to conventional semiconductor material systems. We discuss a range of possibilities for practical applications for bismuth-containing semiconductor lasers that benefit from the  additional flexible and effective control of energy bands and for the suppression of Auger recombination and inter-valence band absorption; the main processes limiting the performance of existing commercial lasers and responsible for significant energy usage. We discuss progress towards the final goal of temperature insensitive laser diodes and present a comprehensive set of data on the characterisation of GaAsBi lasers including optical gain and absorption characteristics and an assessment of the dominant carrier recombination processes in current state-of-the-art devices. We review the potential of GaAsBiN and InGaAsBi material systems for near- and mid-infrared photonic devices on GaAs and InP platforms, respectively, as well initial results on mid-infrared GaSbBi lasers grown on GaSb substrates.
Igor P. Marko, Stephen J. Sweeney

### Chapter 13. Dilute Bismide Photodetectors

Abstract
Dilute bismide III-V semiconductors have many unique properties and have been extensively investigated in recent decades. As the development of material research has progressed, some promising dilute bismide devices have been explored. Incorporation of a small amount of Bi in III-V host materials results in a large band-gap narrowing, which makes dilute bismides potential candidates in long-wavelength photodetectors. In this chapter, we review recent progress on GaAsBi, InAsBi, InSbBi, and InGaAsBi photodetectors, as well as GaAsBi and InGaAsBi THz photoconductive detectors. Some preliminary demonstrations and detector properties have been reported on these dilute bismide photodetectors, while the material quality still needs to be improved and the specific detector properties of dilute bismides still need more understanding.
Yi Gu, Robert D. Richards, John P. R. David, Yonggang Zhang

### Chapter 14. Epitaxial Growth of Bi2X3 Topological Insulators

Abstract
Tetradymite-type Bi2X3 (X = Se, Te, Sb) systems have been used as the best thermoelectric materials for decades. Recently, such V-VI compound materials have attracted immense interests because they are identified as topological insulators with salient features associated with the unique topological surface states. In this chapter, we review the use of molecular beam epitaxy technique to achieve single-crystalline Bi2X3 thin films with atomically smooth surface and extremely low-defect density. In particular, we will explore the unique van der Waals epitaxy growth mechanism, providing detailed discussions on the choice of key growth procedures and parameters during the MBE growth. Furthermore, we will introduce advanced growth techniques such as functional doping and structural engineering so that the functionalities can be further multiplied. Finally, we will give an outlook on Bi2X3-based materials system for exploring new physics and device applications.
Xufeng Kou, Kang L. Wang

### Chapter 15. Quantum Spin Hall States in 2D Bismuth-Based Materials

Abstract
Berrys phase, an inherent constituent of the electronic wave functions, has revolutionarily enriched our understanding of the fundamental states of matter and has triggered the discovery of many interesting phenomena in condensed matter physics, such as quantum charge/spin pumping, polarization, topological insulating phase, etc. Among them, the discovery of the two-dimensional (2D) quantum spin Hall (QSH) states protected by time-reversal symmetry (TRS) boosts the wide interest in the study of topological materials in the past decade. These include the 2D quantum anomalous Hall states (QAH), three-dimensional topological insulators (TIs), Dirac semimetals (SM), and topological nodal-line SMs as well as Weyl SMs. This article by no means can cover everything of this rapidly developing field, we rather focus on the bismuth-based honeycomb materials hosting large-gap QSH/QAH states, which promise applications for room-temperature spintronic. We will explain their topological mechanisms in terms of Berrys phase and topological invariant. After introducing a concrete material example which has been successfully grown in experiment, e.g., Bi/SiC(0001), various theoretical proposals on atom substitution and functionalization based on bismuth honeycomb lattice will then be discussed, from which a general designing principle for achieving large topological gaps can be summarized. This article hopes to stimulate more experimental activities toward the examination of large-gap QSH/QAH theoretical proposals and the potential applications in spintronic devices.
Gang Li, Shumin Wang

### Chapter 16. Dilute Bismuth Optical Fibers

Abstract
Dilute bismuth optical fiber is potentially useful for fiber amplifiers and lasers with its good luminescence properties. In this chapter, we reviewed the structures and luminescence properties of different valence states’ Bi active center in dilute bismuth optical fiber. The structure of the chapter is given as follows. In Sect. 16.1, the background of dilute bismuth optical fiber is presented. In Sect. 16.2, the bismuth active centers based on first-principle calculations are reviewed. In Sect. 16.3, interactions of bismuth with intrinsic defects are presented. This chapter is intended for better understanding of the luminescence mechanism of Bi active center and for better preparation of dilute bismuth optical fiber.
Pengfei Lu, Baonan Jia, Shihao Sun, Xiang Li, Binbin Yan, Gang-Ding Peng