Observation of persistent photoconductivity and modified permittivity in bulk gallium arsenide and gallium phosphide samples at cryogenic temperatures

The whispering gallery modes have been used to characterize the effect of the light on gallium arsenide and gallium phosphide placed in darkness at 50K at frequencies respectively equal to 18.94GHz and 11.54GHz. The experiment shows a change in the polarization state of the semiconductor, which is consistent with a free electron-hole creation/recombination process. The permittivity and the loss tangent of the semiconductor are modified by shifting of the free electrons from the valence band to the conduction band.