Bulk crystal growth and infared absorption studies of gallium indium antimonide

The III-V compound semiconductor GaxIn 1-xSb is a promising candidate for infrared applications in the wavelength range of 1.8--7.2 mum. However the development of GaInSb based technologies has been slow due to the lack of device grade substrate material and inadequate understanding of the infrared as well as electronic properties. In this research, both these topics have been investigated and significant progress has been made in the technological area of ternary crystal growth and fundamental understanding of the infrared transmission properties (and its relationship to electronic properties) of the antimonide based III-V compounds.; Growth of compositionally homogenous ternary alloys is a technological challenge due to different segregation properties of the constituent atoms. Segregation changes the alloy composition along the growth axis during normal melt freezing. Growth of axially uniform composition crystals is possible by maintaining a constant melt composition (by adding the depleting component) and a constant melt-solid interface temperature throughout the crystal growth process. A periodic solute feeding mechanism has been developed in conjunction with vertical Bridgman technique that ensures precise composition control during growth. Growth of various compositions of the GaxIn 1-xSb alloy system exhibiting no micro-cracks or inclusions and possessing excellent below bandgap optical transmission characteristics has been demonstrated. The major parameters affecting growth have been identified and the best possible combination has been established. This method could be used to generate both seeds of varying compositions as well as uniform composition crystals.; The high quality substrates grown by our periodic solute feeding method has enabled us to perform extensive studies of the below bandgap optical absorption characteristics of GaxIn1- xSb alloy system for the first time. Various hole and electron absorption mechanisms such as due to free carriers, intra- and inter-band transitions give rise to significant changes in the absorption characteristics as a function of wavelength and alloy composition. We have been able to establish fitting parameters for undoped and doped GaSb and GaxIn 1-xSb, which resulted in excellent agreement between experimental transmission data and theoretical expressions for absorption processes. Based on these established fitting parameters, we can easily predict alloy compositions and doping levels (and thereby growth conditions) necessary for any specific absorption characteristics such as high optical transparency.; The results of this research work could be easily extended to the studies of other technologically important alloy systems such as GaInAs, GaInP, InAsP, HgCdTe, CdZnTe, etc.