Optical and electrical properties of electroless- deposited Pb_1-xHg_xS films

Abstract

Studies of the optical properties of electroless-deposited Pb_1-xHg_xS alloy films of α' and β' structures have shown that both are direct optical gap semiconductors. Whereas the optical gap of the α' alloy increases linearly with increasing x, a linear decrease is observed for the β' alloy. As-deposited films of Pb_1-xHg_xS of both structures are p-type extrinsic semiconductors with a carrier concentration of about 10¹⁷ cm^-3 and exhibit large (not less than about 0.5 mV ° C^-1) thermoelectric power. The conductivity is characterized by high temperature and low temperature activation energies (not less than about 0.07 eV above 250 K and not less than about 0.04 eV below 150 K) which increase with increase in the concentration of mercury in the α' alloy films. In contrast, the high temperature activation energy of the β' alloy films decreases slightly with x. Electrical conduction, both in the dark and under IR illumination, in these alloy films is explained on the basis of a model which considers the films to be made of conducting grains separated by high resistivity intergranular layers. The low temperature activation energy is the result of thermally assisted tunnelling through the intergrain barriers, whereas conduction at high temperatures takes place mainly by thermal excitations over the barriers.