Abstract
Abstract We report on a surface related study of the cathodoluminescence (CL) properties of high purity epitaxial GaAs. The nature of the surface has been modified by chemical passivation with (NH4)2S and by low-voltage electron beam charging. We have investigated low temperature excitonic behaviour and compared the CL response with photoluminescence (PL). CL exhibits a greater sensitivity and diversity in behaviour to surface treatment and excitation than does PL. The sulphidation treatment is found to increase the dark surface electric field (0.1 eV shift in the Fermi level toward the valence band) and decrease the surface recombination velocity. Exciton-polariton notches correlate with the presence of surface oxide and level of crystal excitation. We discuss the possible role of microscopic roughness (scattering derived from spatial fluctuations in the dielectric constant) in this anomalous behaviour. Differences observed in exciton injection-level behaviour also point to a fundamental distinction betw...
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