锑化铟和锑化镓晶体的生长和表征

Abstract.

Indium antimonide and gallium antimonide were synthesized from the respective component elements using an indigenously fabricated synthesis unit. Bulk crystals of indium antimonide and gallium antimonide were grown using both the vertical and horizontal Bridgman techniques. Effect of ampoule shapes  and diameters on the crystallinity and homogeneity was studied. The grown crystals were characterized using X-ray analysis, EDAX, chemical etching, Hall effect and conductivity measurements. In the case of gallium  antimonide, effect of dopants (Te and In) on transport and photoluminescence properties was investigated.

Introduction 

Among the III–V binary semiconductors, indium antimonide (InSb) has attracted considerable attention over the last several years. Many of its interesting properties are directly associated with its very low effective electron  mass and high mobilities. Consequently, it is an important  candidate in high speed applications in transistors and other devices (van Welzenis and Ridley 1984; Egan et al 1994). It has the smallest bandgap among other III–V  binaries, measuring 0× 17 eV at 300 K that corresponds to IR wavelength (6× 2 µm) and the material is therefore useful as an infrared detector and filter.

New materials like InTlSb (van Schilfgaarde et al 1993) have also opened up  further possibility of their utilization in long wavelength IR region. However, the use of InSb in such devices requires a large diameter single crystal having homogeneous impurity distribution and low dislocation density to ensure optimum performance with high yield and good reliability. Similarly, from the device point of view, gallium antimonide (GaSb) based structures have shown potentiality for applications in laser diodes with low threshold, photodetectors, super lattices with tailored optical and transport characteristics (Nagao et al 1981; Munekata et al 1986; Santos et al 1988; Xie et al 1991). In fact, GaSb is found to be a useful substrate material because its lattice parameter matches with the solid solutions of various ternary and quaternary III–V compounds covering bandgaps over a wide spectral range from ~ 0× 3  (InGaAsSb) to 1× 58 eV (AlGaSb), i.e. 0× 8–4× 3 µm (Milnes  and Polyakov 1993). Consequently, GaSb based binary and ternary alloys have turned out to be important candidates for applications in longer wavelength lasers and photodetectors for fibre optic communication (Capasso et al 1980). These have stimulated a lot of interest in GaSb for basic research as well as device fabrication (Segawa et al 1976; Motosugi and Kagawa 1980; Hildebrand et al 1981). Although GaSb crystals are widely grown by Czochralski method (Moravec 1993), there are a few reports on the growth of GaSb using other  melt techniques, viz. vertical gradient freeze technique (Jamieson 1963), travelling heater method (Benz and Muller 1979; Muller and Neumann 1983), Bridgman technique (Harsy et al 1981; Roy and Basu 1990), etc.

A large number of growth techniques have been employed in the past for preparing a variety of Sb-based  compounds. However, the dopant striations, twinning, grain boundaries and other phenomena which degrade the  wafer quality are reported throughout the literature (e.g. Antonov et al 1983; Buzynin et al 1988; Brezina and Fousek 1989; Hayakawa et al 1990; Helmer et al 1995; Kozhemyakin 1995), the causes of which are not accounted for in sufficient details. Particularly, Bridgman technique is beset with the problems related to polycrystallinity and structural defects induced by the crucible walls. The incorporation of stress in the lattice due to differential thermal expansion of the crucible and the growing ingot is deleterious to device performance. The structural quality, crystallinity, impurity distribution etc in  crystals grown by directional solidification are generally controlled by temperature gradients and growth ambients around the growing crystal. This seems to be very challenging and arduous, particularly in the growth of such compound semiconductors.

In this paper we present some of our results concerning  the synthesis and crystal growth of indium antimonide and  gallium antimonide compounds from their respective component elements. To carry out the synthesis of InSb and GaSb, a suitable mixing furnace was designed and fabricated. It was then integrated into a home-made  synthesis unit. The growth experiments were carried out using both vertical and horizontal Bridgman techniques. In particular, for horizontal Bridgman growth experiments, a suitable high temperature growth furnace was also designed and then integrated into an indigenously built growth unit. However, vertical Bridgman growth experiments were carried out using a commercial BCG (UK) crystal growth apparatus. In addition to the development and modification of synthesis and growth units to  suit the material preparation of indium antimonide and gallium antimonide, some of the results on preliminary characterization on these crystals are also presented here.

Experimental 

Materials synthesis Most of the techniques that have been developed for preparing pure single crystals of germanium or silicon can also be applied to the III–V compounds. But in the preparation of these compounds there are often difficulties  which arise from the presence of two elements. Indium antimonide and gallium antimonide were synthesized starting from their respective high purity elements taken in appropriate quantities for which a synthesizing unit was  developed with a mixing furnace. The mixing furnace is a  horizontal cylindrical furnace with a 45 mm ID, 50 mm  long muffle wound with nichrome wire. The furnace can be powered to 250 watts to reach temperatures as high as ~ 850ºC to give 8 cm long isothermal region. The furnace  temperature is controlled through a Heatcon India ‘on/off’  controller having an accuracy of ±1ºC. A stainless steel tube of 25 mm ID, 28 mm OD and 64 cm long coaxial to the furnace muffle is supported by bearings on both sides.  The quartz ampoule filled with the starting elements is placed horizontally inside this tube. The steel tube has the  capability of periodic rotation both in clockwise and anti-clockwise directions at a rate of 9 rotations per minute facilitating proper mixing of the molten elements to form the compound.