PbxSn1−xTe layers by rf multicathode sputtering

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Abstract
High‐quality epitaxial PbxSn1−xTe films have been obtained for the first time on Ge substrates. The films have been deposited employing a rf multicathode sputtering system capable of simultaneous and sequential sputtering at different rates from three different targets. Heteroepitaxial films of PbxSn1−xTe at substrate temperatures lower than the ones needed in conventional evaporation techniques have been obtained using NaCl and BaF2 substrates. Using the cosputtering technique, it has been possible to obtain n ‐type and p ‐type PbxSn1−xTe layers by controlling the quantity of excess metal, or tellurium, respectively. Electrical properties close to the best reported single‐crystal values have been measured. Middle‐infrared detector arrays have been made using PbxSn1−xTe films deposited on silicon and germanium substrates since such substrates can easily incorporate the electronic readout elements for a completely integrated thermal imaging system. Peak detectivity values up to 2.4×108 cm Hz1/2/W have been measured in photoconductive epitaxial thin films. Polycrystalline films deposited on SiO2‐covered Ge and Si substrates have shown exceptionally high responsivity values (480 V/W). Peak detectivities, D*λ (8.5 μ, 800,1), higher than 109 cm Hz1/2/W have been obtained with a 2π‐sr field of view at an operating temperatue of 77°K. Measurements of noise, responsivity, and detectivity of linear detector arrays are reported.

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