Influence of light excitation on mesoscopic electrical non-uniformities inundoped n-type high-resistivity LEC GaAs

Point contact current measurements with high spatial resolution were perfor med on undoped high-resistivity (up to semi-insulating) LEC GaAs samples un der IR light excitation. Mesoscopic electrical non-uniformities, existing i n the samples and strongly related to the cellular structure of dislocation s, show different reactions to the light excitation depending on the dark c arrier concentration of the samples. Especially, in samples with a Hall mob ility strongly reduced by such non-uniformities the amplitude of the fluctu ations of the point contact current, respectively of the resistivity betwee n cell walls and cell centres, is clearly reduced by light excitation. This homogenization is connected with an enhancement of the photo Hall mobility in these samples compared to the dark Hall mobility.