The connection between carrier lifetime and doping density in nondegenerate semiconductors

Abstract

It is assumed that there exists a temperature Tf at which dominant recombination centers in the form of electrically neutral, mechanical defects (e.g., vacancies) are frozen into a semiconductor matrix. For this process we assume an Arrhenius-type law with an activation energy. From this assumption there follows by standard semiconductor statistics the doping dependencies of (a) the defect concentration and (b) the minority carrier lifetimes. The analysis can in principle be applied to any defect in any semiconductor which satisfies the above assumptions, provided the cross sections and related data are known. For the case of silicon we have deduced a set of parameters to fit the optimal experimental lifetimes. Assuming the unknown defects to have two charge states, neutral and negative, it is inferred that the levels lie near midgap and have recombination coefficients of order 10−9 cm3 s−1.