BAND DISCONTINUITIES AT BETA-FESI2 SI HETEROJUNCTIONS AS DEDUCED FROMTHEIR PHOTOELECTRIC AND ELECTRICAL-PROPERTIES/

Experimental photoresponses and electrical characteristics of metal/be ta-FeSi2/Si structures are presented. Three kinds of samples are compa red: two with a thin epitaxial silicide layer (180 angstrom), prepared by two different methods, and one with a thick polycrystalline silici de layer (2500 angstrom). The rectifying behaviour and the photoelectr ic response of the three kinds of samples are different. In the thin s amples these properties are governed by those of the beta-FeSi2/Si int erface, whereas for thick samples bulk mechanisms dominate. Analysis o f the photocurrent in one kind of thin sample shows that two contribut ions exist. Their intensities follow similar temperature behaviours bu t the two transition thresholds do not. These considerations allow ass ignment of the initial and final states of the transitions, and the up per threshold is shown to correspond to an internal photoemission effe ct at the beta-FeSi2/Si interface. The conduction band offset is deduc ed from the difference between the two thresholds. The valence band di scontinuity is less than 50 meV between 360 K and 260 K, whereas it ch anges sign when the temperature decreases below 260 K, the two bandgap s becoming nested within each other. These properties are also discuss ed for the other kinds of sample and related to the mechanisms which a re responsible for the electrical characteristics.