Methods for determining deep defect concentration from dependence of excess carrier density and lifetime on illumination intensity
Two methods are proposed for determining the deep defect concentration from dependences of excess majority carrier concentration and carrier lifetime on, respectively, illumination intensity and injection level. The methods are based on saturation of the excess majority carrier density with increasing illumination intensity and on an abrupt decrease in the lifetime of majority carriers with their increasing excess concentration, which takes place as a result of filling of the defect level by minority carriers. In contrast to the well known injection-level spectroscopy, both the methods make it possible to determine the density of a defect without knowing any of its parameters, such as energy level or recombination coefficient of electrons and holes. These methods are applied to boron-doped single-crystal silicon with radiation-induced deep defects of the phosphorus-vacancy, oxygen-vacancy and carbon-oxygen complex types. It is shown that with these methods it is possible to determine the density of only those deep defects which control free carrier density and lifetime and give rise to a significant difference between the excess concentrations and lifetimes of electrons and holes. The analysis is based on the assumption that (i) the density of deep defects is independent of the illumination intensity, (ii) processes of generation-recombination via deep defects are described within the Shockley-Read-Hall recombination theory and (iii) recombination via other defects, band-to-band recombination, Auger recombination, etc, are negligible.