Morphology of InSb and GaSb Single Crystals with the Face Effect

Abstract

The face effect has been described [1-11] for InSb and GaSb single crystals grown by Czochralski's method under conditions that facilitate maximum development of the channel in the billet [7, 8]. The initial material was zone-purified indium antimonide (n ~ 3-5. 10 14 cm-3), together with gallium and antimony of semiconductor grade. The dopes were tellurium (donor) and zinc, cadmium, and germanium (acceptors), which were added to the melt either in elemental form or as appropriate alloys. The seed crystals were oriented on (111) by standard x-ray methods to 1-2°. The crystals were grown as a rule in the B[In] direction. The usual methods were employed to measure the Hall effect of the specific resistance; the thermoelec-tric emf was measured with a semiautomatic system at 300 and 80-85°K by a method previously described [8, 11]. The crystal was cut along the (111) growth axis parallel to the {211} and {110} planes, and also perpendicular to the (111) axis on the A(111) and B(l11) planes in order to examine the structure. Figure 1 shows InSb and GaSb crystals with the face effect; under certain conditions, one can obtain crystals (Fig. 1a) whose volume is almost completely formed as a result of growth on the {111} face, which is important, because the material in the channel region may be more uniform than that outside it [7]. Figure 2 shows a longitudinal section of the upper part of the crystal, which shows the onset of channel formation; it is clear that the channel arose at the upper part of the hemisphere and subsequently increased in diameter on account of change in the curvature of the crystallization front. Table 1 gives the parameters of the crystals; the InSb and GaSb crystals were examined by chemical etching, which showed that the channel can be detected in these crystals when they are doped either with tellurium or tellurium together with any of the above acceptor materials, the tellurium concentration playing the decisive part. The face effect is not revealed by chemical etching for crystals doped with acceptors (Fig. 3). The effect is best seen in InSb crystals of nand p types with tellurium concentrations between 8. 10 17 and 8. 10 18 cm-3 , while in GaSb specimens of n and p types it is best seen in the range from 8. 10 17 to 3. 10 18 cm-3 • We determined for these crystals the value of R, which characterizes the face effect, and the values are given in Table 1; the largest R occur for InSb crystals doped with Te and Cd. The R for Te in InSb is appreciably reduced at high Te concentrations, which is confirmed by chemical etching and measurement of the thermo-emf. The R for Te and InSb and GaSb grown in the (Ill) polar directions is somewhat larger for B[ili] directions than it is for A[111] ones. 161 N. N. Sheftal' et al. (eds.), РОСТ КРИСТАЛЛОВ/Rost Kristallov/Growth of Crystals