Research and development of cadmium zinc telluride substrates for mercury cadmium telluride epitaxial films

摘要

Cadmium zinc telluride (Cd_(1-y)Zn_yTe) single crystals are important material for infrared detectors fabricating process and radiation detectors. Cd_(1-y)Zn_yTe crystal wafers are widely used as substrate to grow epitaxial layers of mercury cadmium telluride (Hg_(1-y)Cd_xTe) that is an important process for infrared detectors with high resolution. Especially, Cd_(1-y)Zn_yTe with small concentrations (y=0.03～0.04) is favored for this purpose since the lattice constant of Cd_(1-y)Zn_yTe (y=0.03?0.04) is close to that of Hg_(0.8)Cd_(0.2)Te, which has a bandgap corresponding to 10 micron. These applications impose certain requirements on the Cd_(1-y)Zn_yTe crystals. Impurity concentrations should be low, especially for Cu, which can readily diffuse into the epitaxial layer and alter its electrical properties. Dislocation etch pits density should be low, typically no more than 1X10~5 cm~(-2). Infrared transmission should be high, usually greater than 60%, from 2.5 to 20 μm. Precipitates, visible as dark spots in infrared transmission microscopy, should be no larger than 10 μm in diameter, and their density no higher than 0.5 X 10~5～1 X 10~5 cm~(-2). This paper reports results on how these requirements can be met by our research and development works in Kunming Institute of Physics mainly through controlling the cadmium partial pressure in the quartz ampoule.