ELECTRICAL-PROPERTIES OF AMORPHOUS-SILICON FILMS WITH DIFFERENT THICKNESSES IN METAL INSULATOR/SEMICONDUCTOR STRUCTURES/

The density of states (DOS) of hydrogenated amorphous silicon (a-Si:H) is an important issue in the study of the physics of amorphous semico nductors. In many earlier reports concerning the analysis of the field -effect conductance metal/insulator/ a-Si:H structures, namely, thin-f ilm transistors (TFTs), the potential at the semiconductor surface apa rt from the gate insulator/a-Si:H interface, i.e., the rear interface, was assumed to be zero. However, in principle, as the thickness of th e semiconductor film is smaller than the theoretically expected width of the space charge region, this assumption no longer holds. Hence, it is necessary to reconsider the band-bending phenomena of the a-Si:H a ctive layers. It was found that the DOS, which was extracted previousl y from the field-effect conductance of the TFTs based on the assumptio n of the zero-potential rear interface, was appropriate only for the t hick a-Si:H films. As for the thin semiconductor films, the accurate D OS can be obtained by fitting the calculated field-effect conductance, with a surmised possible DOS, to the experimentally measured data via the method developed.