Electrical properties of pure CdS

Abstract

Electrical measurements on single-crystal CdS are used to evaluate the various material parameters of vapor-grown material. Hall measurement data is used to obtain a computer fit to a single donor level partially compensated model for the purpose of determining the donor density, acceptor density, and activation energy. Hall mobility data is fitted to a scattering model which includes lattice, neutral impurity, and ionized impurity scattering. The donor level in the low density doping limit is found to be approximately 32 meV below the conduction band. Over a temperature range of 100 k–300 K lattice scattering is predominate and the mobility variations have little impact on the electrical properties; the major variations are due to ionized donor variations and the band-gap variations with donor densities. At low temperatures, impurity densities and the type of impurity scattering have a significant impact on the mobility. Pure CdS displays a very high mobility, i.e., μ>10 000 cm2/V sec at low temperatures in the absence of ionized vacancy scattering. The absence of ionized vacancy scattering at low temperatures is found to be the result of vacancy pairing which results in a neutral scattering center. Low mobilities at low temperatures are found to result from a relatively high density of netural impurity scattering centers.