Growth and Properties of Hg1−xCdxTe Epitaxial Layers

Abstract

The epitaxial growth of Hg1−xCdxTe has been investigated by means of a technique in which the source and substrate are close spaced, and both under isothermal conditions and with a temperature gradient between the source and substrate. The effect of excess mercury pressure in the ampoule on the growth rate and the compositional profile within the isothermally grown epitaxial layers has been investigated in detail. A simple isothermal process is described for making epitaxial layers having a controlled surface alloy composition. The presence of a temperature gradient between the source and the substrate significantly enhances the deposition rate and results in a linear relation between the layer thickness and deposition time. The electrical and optical properties of the isothermally grown epitaxial layers are discussed along with the results of photoconductivity measurements on layers having surface composition of x=0.20 and x=0.25.

Isothermal vapour-phase epitaxy of mercury-cadmium telluride (Hg,Cd)Te

“…Equation 14 is strictly valid for the case when the source and the substrate are at the same temperature; therefore we shall consider the situation when the source is at a higher temperature than the substrate. Neglecting the thermal diffusion process in gas phase, which is proportional to the temperature gradient, allows a good agreement with the experi- (10) mental results of Tufte and Stelzer [35] to be obtained. Suppose that the mercury partial pressure (11) corresponds to the equilibrium value of the mercury partial pressure.…”

“…According to the literature data accessible to the author [27][28][29][30][31][32][33][34][35][36][37], the work that led to the development of the ISOVPE originated in France at the National Center of Scientific Research (CNRS). In 1963, H. Rodot and J. Henoc [27] and F. Bailly et al [28] published the first results of their investigations of the interdiffusion of cadmium and mercury when single-crystal slabs of HgTe and CdTe are brought into contact.…”

“…The comprehensiveness of the paper by Tufte and Stelzer [35] make it an important work on the early development of ISOVPE. These two authors described in detail all the procedures of the synthesis and the preparation of the HgTe or the Hgl_xCdxTe source and the CdTe substrate.…”

“…The ampoule was evacuated to 10-6 torr before it was sealed. Then the ampoule was suspended in a vertical [34,35] ISOVPE on alternative substrates [36,37]. Ambient temperature HgCdTe detectors fabricated by ISOVPE.…”

“…It was especially interesting to compare our theory to the experimental data of Tufte and Stelzer [35], regarding the deposition of epitaxial layers for the case of different temperatures of source and substrate. For the mentioned data, we performed the calculation with the following parameters: Ts = 620 °C, a sourceto-substrate spacing of 10 ram, T1 = 600°C, source composition xs = 0.2, Pn~ ~ 2 bar.…”