Transport and Recombination Properties of Lead Tin Telluride Alloys

摘要

Doping effects and photoconductivity were studied for single crystal films of lead tin telluride (Pb(0.8)Sn(0.2)Te) grown by vapor phase epitaxy. Growth of films was carried out by an evaporation condensation process in which the alloy was evaporated from a polycrystalline source and the vapor was condensed on a barium fluoride substrate. Interesting doping effects were obtained with indium which produces a deep level in the gap with unusual properties. Extensive galvanomagnetic measurements suggest that indium enters as a self-compensating impurity and pins the Fermi level near midgap, in contrast to other Group III elements such as gallium and thallium which dope the material n-type and p-type, respectively. An investigation of the kinetics of photoconductivity revealed that around the 'device temperature' of 77 K, the recombination of excess carriers is thermally activated, but becomes approximately temperature independent below 50 K. These results and the magnitude of the photoconductive life-time lead to the surprising conclusion that contrary to prevailing opinion, Auger recombination is not the dominant recombination mechanism for samples with carrier concentration in the 1-10/10 to the 16th power cc range. (Author)