Properties of exactly compensated semiconductors under excitonic modulation of the charge of deep impurities

Properties of exactly compensated semiconductors have been studied under exciton-stimulated modulation of the charge on deep impurities. The electron and hole lifetimes are shown to depend on deep impurity concentration in a nonmonotonic manner. Their maximum values are determined by the exciton concentration and the probability of exciton modulation of trap charges. The results obtained are interpreted in view of the fact that, in a exactly compensated semiconductor, the equilibrium concentration of majority carriers decreases sharply, by several orders of magnitude. Simultaneously, the resistivity grows abruptly. The dependences of the Hall coefficient and Hall mobility on trap concentrations are also nonmonotonic. The exciton density and the probability of exciton modulation of the charge of deep traps are estimated for CdTe crystals at T = 300 K and shallow donor concentration of 10¹⁷ cm^-3. At high exciton densities, the rate of exciton-stimulated emission of trapped carriers becomes comparable with the rate of their capture, which decreases with increasing deep centre concentration. As a result, the lifetimes become higher. The exciton-stimulated modulation of deep trap occupancy through charge exchange dominates over that associated with energy exchange.