Properties of exactly compensated semiconductors under excitonicmodulation of the charge of deep impurities

Abstract

Properties of exactly compensated semiconductors have been studied underexciton-stimulated modulation of the charge on deep impurities. Theelectron and hole lifetimes are shown to depend on deep impurityconcentration in a nonmonotonic manner.Their maximum values are determined by the exciton concentration and the probability of excitonmodulation of trap charges.The results obtained are interpreted in view of the fact that, in a exactly compensatedsemiconductor,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 mobilityon trap concentrations are also nonmonotonic.The exciton density and the probability of exciton modulation of the charge of deep traps areestimated for CdTe crystals at T = 300 K and shallow donorconcentration of 1017 cm-3.At high exciton densities, the rate of exciton-stimulated emission of trapped carriers becomescomparable with the rate of their capture, which decreases withincreasing deep centre concentration.As a result, the lifetimes become higher.The exciton-stimulated modulation of deep trap occupancy through charge exchange dominates over thatassociated with energy exchange.