Directional Freezing Technique Research Articles

Electrical properties of GaSb-InSb alloys

Reasonably homogeneous, polycrystalline, solid ingots of GaSb-InSb alloys have been produced by slow directional freezing techniques, and have been used to investigate the variation of electrical properties as a function of composition. Values of extrapolated thermal energy gap E 0, electron mobility, and mobility ratio have been determined for some 25 specimens covering the complete composition range. Estimates have been made of the variation of effective mass values and, by comparison with optical energy gap values, of the energy gap temperature coefficient β. From the variation of mobility with temperature, values of mobility temperature exponent x have been obtained. At the InSb-rich end of the composition range, the results indicate a smooth variation of the various parameters with composition, without any appreciable change in the band structure from that of InSb. The results at the GaSb-rich end of the range are complicated, firstly by the presence in GaSb of two conduction bands of only small energy separation, and secondly by an effect which extends over a considerable range of composition and is thought probably to be due to ordering in the alloys. As a result, correlation of the optical and electrical results is difficult in this range of composition.

Optical Energy Gap Variation in the GaSb-InSb System

The production of specimens of alloys in the GaSb-InSb system suitable for electrical and optical work is first discussed. X-ray data are given to show the variation in composition and the degree of homogeneity of specimen sections cut from long rod ingots produced by very slow directional freezing techniques. The results of measurements of infra-red transmission on such specimens are presented together with a graph of the variation of wavelength for onset of transmission, interpreted as optical energy gap, as a function of composition. The form of this graph is briefly discussed.