Photoconductivity of semi-insulating gallium arsenide in the presence of a magnetic field

Abstract

The effect of a magnetic field on the photoconductivity of GaAs has been investigated at 300 °K and 90 °K. The field deflects the photocarriers towards the surface or the volume of the sample, resulting in a decrease or an increase of the photocurrent. The effect is attributed to lifetime inhomogeneities across the sample thickness and has been studied as a function of temperature, surface treatment of the sample, and wavelength of excitation. The results can be expressed as the ratio R = i_p⁺/i_p⁻, where i_p⁺ and i_p⁻ are the photocurrents when the carriers are deflected away or towards the sample surface respectively. For a sample mechanically polished, R = 10 at 300 °K and R = 40 at 90 °K while for a chemically polished sample R = 3.5 at 300 °K and R = 10 at 90 °K for B = 2.2 Wb/m², V = 400 V, and λ _excitation = 7500 Å. Independent measurements of the carrier mobilities and of their surface and bulk lifetimes have been performed to allow a direct comparison between experimental results and theoretical predictions based on a simple model.