Power broadening and nonlinear FIR magneto-photoconductivity in n-GaAs

Abstract

The saturation of the photoconductivity due to 1s-2p+ shallow donor transitions in n-GaAs has been investigated using a high power cw-FIR-laser. Magnetic field strengths were chosen in such a way that 2p+ energy levels were either below or above the N=0 conduction band Landau level. In the former case 1s-p+ transitions are found to be inhomogeneously broadened with a saturation intensity as low as 0.84 mW/cm2, giving an effective lifetime of the 2p+ state of 1.5 mgrs. Above the band edge the integrated photoconductivity does not saturate though the intensity-normalized peak photosignal decreases and the linewidth increases with raising intensity. This strange behaviour is tentatively attributed to optical excitations of 2p+ electrons to higher lying electron Landau states.