Photoinduced Microwave Permittivity of Semiconductors: Exciton Mechanism

Significant differences observed in the behavior of photoinduced permittivity ε of semiconductors in the gigahertz (GHz) and terahertz (THz) ranges are explained within the framework of the exciton mechanism by the different position of these ranges relative to the frequencies of exciton interlevel transitions. The measurements in the GHz range of the photoinduced changes of quantities Imε( P λ ) and Reε( P λ ) of CdS, CdSe and Si samples in a waveguide resonator ( f = 4.7 GHz) and transmittance T of Si samples in free space ( f = 8–36 GHz ) under fiber-optic irradiation ( P λ = 0–370 mW and λ = 0.97 µm) that exhibit non-Drude response prove the theoretical conclusions: an increase in Reε GHz ( P λ ) with increasing P λ and an increase in transmittance T with decreasing frequency f at fixed power P λ .