Electron capture at the two acceptor levels of a zinc center in silicon

Abstract

Electron-capture rates in zero electric field at both zinc acceptor levels have been directly and accurately measured by the transient-capacitance techniques for the first time. The data elucidate two major outstanding questions in recombination physics: (1) It has been suspected for two decades that the carrier capture rates associated with many centers with multiple charge states were due to a local Auger mechanism. We show that this postulate can be experimentally tested by the double-pulse method, and in the case of Zn in Si the Auger effect plays a negligible role. (2) While several workers have stressed that the electronic barrier may be more important than the vibronic barrier in determining the temperature dependence of carrier-capture rates at repulsive centers below room temperature, the charge effect was usually ignored in the literature. We show that in the case of Zn in Si, tunneling through the screened Coulomb barrier controls the temperature dependence below 200 K and above which tunneling through the vibronic barrier becomes important. Overall, the effect of the electronic barrier below room temperature is predominant and it gives a temperature-dependent capture rate that can be easily mistaken as the occurrence of a multiphonon-emission mechanism. Failure to recognize the charge effect may result in fitting of trap parameters inconsistent with physical reality.