Band discontinuities at beta -FeSiSUB2/SUB/Si heterojunctions as deduced from their photoelectric and electrical properties

摘要

Experimental photoresponses and electrical characteristics of metal/ beta -FeSi2/Si structures are presented. Three kinds of samples are compared: two with a thin epitaxial silicide layer (180 AA), prepared by two different methods, and one with a thick polycrystalline silicide layer (2500 AA). The rectifying behaviour and the photoelectric response of the three kinds of samples are different. In the thin samples these properties are governed by those of the beta -FeSi2/Si interface, whereas for thick samples bulk mechanisms dominate. Analysis of the photocurrent in one kind of thin sample shows that two contributions exist. Their intensities follow similar temperature behaviours but the two transition thresholds do not. These considerations allow assignment of the initial and final states of the transitions, and the upper threshold is shown to correspond to an internal photoemission effect at the beta -FeSi2/Si interface. The conduction band offset is deduced from the difference between the two thresholds. The valence band discontinuity is less than 50 meV between 360 K and 260 K, whereas it changes sign when the temperature decreases below 260 K, the two bandgaps becoming nested within each other. These properties are also discussed for the other kinds of sample and related to the mechanisms which are responsible for the electrical characteristics.