Properties of insulator-semiconductor interfaces in amorphous silicon solar cell structures

Properties of amorphous silicon surfaces passivated by anodic and plasma CVD dielectrics are investigated, using MIS structures. Detailed MIS C-V and isothermal capacitance spectroscopy (ICTS) measurements were made. In order to analyze the observed extremely complicated behavior, theoretical MIS C-V curves are calculated on the basis of a rigorous admittance analysis. Contrary to the usual assumption that interface states do not play a major role in a-Si surfaces as compared with the bulk gap states, it is shown for the first time that the electrical characteristics of interfaces are controlled predominantly by the interface states and not by the bulk gap states. Interface states have the tendency to pin the surface Fermi level at 0.4 eV from the conduction band edge.