Space-Charge Formation in Small PbS Particles

Abstract

A theoretical model is discussed for the effect of oxygen on the electrical properties of PbS thin films. The films are assumed to be composed of very small n-type microcrystals, on the surface of which oxygen is adsorbed. The adsorbed atoms are singly ionized by electrons from the interior of the microcrystals. The appropriate Poisson-Boltzmann equation is solved for particles of radius 5×10—8 m and 5√10×10—8 m, and for donor concentrations of 1023 m—3 and 1024 m—3. The potential distribution is given as a function of the surface acceptor concentration required for the conservation of charge. Models for the electron and hole conductivities are given, and the results of calculations based on these models are compared with experiment. This theory is contrasted with the earlier bulk diffusion theory of the effect of oxygen. The free energy of adsorption is roughly calculated. Implications of this theory are discussed—on the general character of conduction in PbS films, on the temperature coefficient of conduction, and on the nature of photoconduction.