High-frequency conductivity of disordered semiconductors in the region of the transition from the linear to quadratic frequency dependence

Features of the high-frequency conductivity of disordered semiconductors related to hopping electron transport over the impurity band are discussed. The frequency dependence of the real part of the low-temperature phononless conductivity in the region of the transition (crossover) from the linear to quadratic frequency dependence of the conductivity is calculated in the pair approximation. It is shown that the crossover in the terahertz-frequency range is related to the transition of the conductivity from the variable-range to fixed-range hopping regime with increasing frequency.