Recent advances in nonsilica fifiber technology have prompted the development of suitable materials for devices operating beyond 1.55 m m. The III–V ternaries and quaternaries （AlGaIn）（AsSb）lattice matched to GaSb seem to be the obvious choice and have turned out to be promising candidates for high speed electronic and long wavelength photonic devices. Consequently, there has been tremendous upthrust in research activities of GaSb-based systems. As a matter of fact, this compound has proved to be an interesting material for both basic and applied research. At present, GaSb technology is in its infancy and considerable research has to be carried out before it can be employed for large scale device fabrication. This article presents an up to date comprehensive account of research carried out hitherto. It explores in detail the material aspects of GaSb starting from crystal growth in bulk and epitaxial form, post growth material processing to device feasibility. An overview of the lattice, electronic, transport, optical and device related properties is presented. Some of the current areas of research and development have been critically reviewed and their signifificance for both understanding the basic physics as well as for device applications are addressed. These include the role of defects and impurities on the structural, optical and electrical properties of the material, various techniques employed for surface and bulk defect passivation and their effect on the device characteristics, development of novel device structures, etc. Several avenues where further work is required in order to upgrade this III–V compound for optoelectronic devices are listed. It is concluded that the present day knowledge in this material system is suffificient to understand the basic properties and what should be more vigorously pursued is their implementation for device fabrication.
Historically, the research and development of various III–V compound semiconductors is associated with the wavelength of the optical fifiber loss minima.1 The shift in the fifiber loss minima towards higher wavelengths from 0.8 mm over the past 2 decades has shifted the material of interest from time to time.1 Even though the present day optical communication systems are tuned to 1.55 mm, the next generation systems may have to be operated well above this wavelength. This is because recent developments in the optical fifiber research have shown potentiality for certain classes of nonsilica fifibers for optical communication applications whose loss minima fall in the 2–4 m m range.2 For example, the heavy metal flfluoride glasses are speculated to have minimum attenuation at 2.55 mm with a loss, one to two orders of magnitude lower than the present day silica fifibers. This is also important since, at longer wavelengths, loss due to Rayleigh scattering is signifificantly reduced. Consequently, there has been an upthrust in research activities in new material systems for sources and detectors operating in the 2–4 mm regime. Among compound III–V semiconductors, gallium antimonide ( GaSb） is particularly interesting as a substrate material because its lattice parameter matches solid solutions of various ternary and quaternary III–V compounds whose band gaps cover a wide spectral range from ; 0.3 to 1.58 eV,3 i.e., 0.8–4.3 mm, as depicted in Fig. 1. Also, detection of longer wavelengths, 8–14 mm, is possible with intersubband absorption in antimonide based superlattices.4 These have stimulated a lot of interest in GaSb for basic research as well as device fabrication. Some of the important material properties of GaSb are listed in Table I.
From device point of view, GaSb based structures have shown potentiality for applications in laser diodes with low threshold voltage,6,7 photodetectors with high quantum effificiency,8 high frequency devices,9,10 superlattices with tailored optical and transport characteristics,11 booster cells in tandem solar cell arrangements for improved effificiency of photovoltaic cells and high effificiency thermophotovoltaic （TPV）cells.12 Interestingly, the spin-orbit splitting of the valence band is almost equal to the energy band gap in GaSb leading to high hole ionization coeffificients. This results in signifificant improvement in the signal-to-noise ratio at l . 1.3 m m in GaAlSb avalanche photodetectors grown on GaSb.8 GaSb is also predicted to have a lattice limited electron mobility greater than GaAs making it of potential interest in the fabrication of microwave devices. InGaSb has been proposed as an ideal material for transferred-electron devices by Hilsum and Rees10 with a low threshold yield and a large velocity peak-to-valley ratio, using a Monte Carlo simulation based on the three-level model.
Fig1
On the basis of electrical resistivity measurements, Minomura and Drickamer40 observed that GaSb undergoes a phase transition around 80–100 kbar at room temperature. The transition was presumed to be structural in nature, although melting could not be discounted. A study of the effect of pressure on the melting point of GaSb by Jayaraman, Klement, and Kennedy41 in the range 0–65 kbar indicates that the melting temperature decreases by 5 °C per kbar to a triple point near 56.5 kbar and 385 °C. The melting temperature of the high pressure form of GaSb increases 3.4 °C per kbar. The triple point observed by these workers verififies the speculation made by Minomura and Drickamer that the observed transition was solid–solid, but is not in good agreement quantitatively. Later Jamieson42 verifified that the room temperature transition was indeed solid-solid and that the high pressure form is tetragonal Sn type (metallic) with a5 5.348 Å and c5 2.937 Å. The transition pressure of 90 kbar observed by Jamieson tends to confifirm the pressure transition observed by Minomura and Drickamer. Ozolins et al.43 produced GaSb with excess amounts of the constituent elements and concluded that the lattice parameter is not a function of melt composition. Hence the compound has a very narrow homogeneity range.
The thermophysical properties of molten GaSb at the melting point are listed in Table II.44 These properties indicate that the growth of low dislocation density crystals is not very diffificult.39 Bulk GaSb crystals have been mainly grown by Czochralski technique ( CZ). There are a few reports on Bridgman （ BG) technique, travelling heater method (THM）, vertical gradient freeze （VGF）technique and liquid phase electro-epitaxy (LPEE) . A brief account of crystal growth using these techniques is given below.
