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.

I. Introduction

The whispering gallery mode (WGM) method has been used to make the most accurate measurements of the complex permittivity of extremely low-loss dielectric materials, both ceramic and crystalline. The method has been employed for very precise measurements of the permittivity and the dielectric losses of both isotropic and uniaxial anisotropic materials. [1]–[3] The WGM technique has also been used to characterize the complex permittivity of semiconductors, including bulk gallium arsenide (GaAs) and gallium phosphide (GaP) [4], at microwave frequencies from cryogenic temperatures to room temperature. In the paper, we present the measurement of a change of the permittivity [5] and the quality factor [6] resulting from polarization changes in the semiconductors GaAs and GaP under white light at cryogenic temperature.