Combined photoacoustic and photoconductive spectroscopic investigation of nonradiative recombination and electronic transport phenomena in crystallinen-type CdS. II. Theory

Abstract

A theoretical model of the coupled photoconductive (PC) and microphone gas-coupled photoacoustic (PA) signal generation is presented. The model includes numerical solutions to the following: (i) the carrier transport equations leading to PC signal generation in the presence of two different types of recombination centers, (ii) the Poisson equation relating the difference between electron and hole densities to the internal electric field, and (iii) the heat diffusion equation, relating the carrier population density to the heat generation rate and ultimately to the PA signal generation. Spectroscopic simulations with the CdS absorption spectrum as input data essentially show agreement between theory and experiment in the band-gap and sub-band-gap spectral regions. Parameter variation reveals that PA and PC experimental data (preceding paper) can be predicted if, and only if, a wavelength-dependent nonradiative quantum efficiency is assumed with a substantial increase at photon energies below the band gap, coupled with signal contributions at higher photon energies due to band-to-band intrinsic transitions.