Experimental evidence of electron capture and emission from trap levels in Cz silicon

Up to now the existence of trap levels - defect levels in the forbidden band gap which temporary trap minority charge carriers - in Cz silicon was controversially discussed. We directly monitor the transient dynamics of the free electron density in the conduction band by the means of a time correlated single photon counting of photoluminescence. A variation of the experimental conditions reveals both a decrease of the electron density on a timescale of microseconds, which is not governed by recombination and an apparent generation of electrons on a scale of up to multiple seconds. We discuss that the transient dynamics may be excellently described by trap levels, providing strong evidence for their existence.