Light Intensity Exponents as Sensitive Tools for the Detection of Impurities in a-Si:H

Abstract

We have shown recently that the temperature dependence of the phototransport properties can yield information regarding the state distribution in the forbidden gap of semiconductors. Of these properties the light intensity exponents of both, the majority carriers, γ e , and the minority carriers, γ h, were found to be very sensitive to the details of this distribution. In particular, noting that sub ½ values of the exponents are very unusual we have studied their origin in some a-Si:H materials. Finding experimentally such sub ½ values of γ h and running computer simulations of the recombination processes in a-Si:H led us to the conclusion that these low values are due to acceptor-like centers which have a relatively high capture coefficient for the holes. We attribute these centers to the unintentional oxygen doping in a-Si:H. We will show that the oxygen presence, usually ignored in the discussions of the phototransport properties of a-Si:H, appears to be, in many cases, the dominant factor in the properties of "intrinsic" a-Si:H.