The Spectrum of the Photoconductive and Photomagnetic Effects in Semiconductors

Abstract

The spectral distribution of the photoconductive (PC) and photomagnetoelectric (PM) effects in a semiconductor depend on the diffusion length, the surface recombination rates and the distribution of light intensity through the crystal. Results of a theoretical analysis of these effects for a parallel sided slab are presented and applied to experimental data on germanium. It is shown that the shape of the PM spectrum depends only on the diffusion length and the absorption constant, provided the surface recombination rates are the same at both back and front surfaces, whereas the PC spectral shape also depends on the surface recombination rates. The experimental data consist of measurements of the PC, PM and absorption spectra on single crystals of germanium at a number of temperatures from 20 °K to 300 °K. These data are analysed to find the diffusion length and surface recombination velocities and their dependence on temperature. The PC and PM spectra are also used to extrapolate the absorption spectrum to high absorption levels and to verify the Authors’ earlier observations that the absorption constant at low absorption levels is well represented by the sum of two quadratic functions of energy, indicating indirect transitions associated with phonon emission and absorption.