Elasticity moduli of Cd x Hg1–x Te solid solutions

Abstract

Results of investigations into the temperature dependences (4.2-300 K) of the low-frequency ultrasound velocity in CdxHg1-xTe single crystals are presented. The elastic moduli and the Debye temperatures are calculated for different solid solution compositions. Based on the data obtained, possible stresses are estimated on the heteroboundary of the materials with a number of substrates. In 2009, 50 years passed since synthesis of the CdxHg1-xTe solid solution. During this time, several ten thousand works devoted to the study of methods of synthesis of the material and its properties and to the development of different instruments on its basis have been published, numerous conferences and seminars have been held, and recognized monographs have been written. Nevertheless, a number of gaps still exist even in the materials science devoted to this solid solution. Among them are the elasticity moduli of this solid solution. Except (1, 2) devoted to two CdxHg1-xTe compositions, we do not aware of any other direct measurements of its elastic properties. This situation is also typical for other solid solutions of А 2 В 6 compounds. In our opinion, this is explained by two circumstances. First, the complexity of the corresponding investigations should be mentioned. To study the elastic properties of semiconductor materials by the conventional acoustic methods, sufficiently large oriented single crystals with homogeneous composition are required. The accuracy of measurements of the ultrasound velocity on a level of 10 -4 −10 -5 is conventionally reached for samples whose thickness and transverse dimensions are of the order of a centimeter. It is difficult to grow such crystals of solid solutions, and inhomogeneity of their composition is inevitable irrespective of the growth method. Second, when the necessity arises to use elasticity moduli of solid solutions, estimates representing linear extrapolation of the corresponding moduli for binary compounds forming the solid solution are often used. This can give significant errors. In the present work, results of investigations into the velocity of ultrasound wave propagation are given that allow the elasticity moduli to be calculated for a number of CdxHg1-xTe solid-solution compositions. The examined single crystals were grown by the method of vertical directed crystallization from the solid phase, which allowed samples with homogeneous composition to be synthesized with controllable levels of residual native defects. To decrease the level of defects, the crystals were doped by indium to a level of 10 14 cm -3 that had no effect on the electrophysical parameters of the material. Crystals used for measurements were shaped as discs or plane-parallel plates with sizes from 1 to 1.5 cm and thickness of about 0.1 cm. The normals to the plane sample surfaces and hence the directions of ultrasound propagation coincided with one of the (100), (110), and (111) crystallographic directions. Misorientation with respect to the indicated directions did not exceed 2°. To obtain plane-parallel surfaces, the central regions of preliminary oriented grinded and etched large (about 3 cm in diameter) plates were used. Plates with the above-indicated dimensions are optimal for excitation in them of ultrasound waves by the method of direct conversion of electromagnetic and acoustic waves in a constant magnetic field (3). To increase the efficiency of electromagnetic-acoustic conversion in the semiconductor material, aluminum layers with thickness of