Electrical measurements have been carried out on epitaxial FeSi2 layers on silicon substrates, the silicide thickness being either 180 or 350 Å. A direct gap of 0.85 eV was measured by optical absorption. Current-voltage characteristics of mesa-structures Cr/Fe/FeSi2/Si show a p-type semiconductor behavior. Capacitance-voltage and capacitance-temperature data at different frequencies indicate a large response of deep levels or interface states. Admittance spectroscopy yields the activation energy and capture cross section of two levels. Finally an energy-band diagram is proposed.
Semiconducting βFeSi2 has been successfully grown on a Si (111) substrate. It has been proven that under ultrahigh vacuum conditions, the solid phase epitaxy temperature can be lowered to ∼800 K, where only the βFeSi2 phase is stabilized. The disilicide formation was monitored in situ by various surface-sensitive techniques such as low-energy electron diffraction, Auger electron spectroscopy, and ultraviolet photoelectron spectroscopy. The epitaxial relationships were ascertained by transmission electron diffraction and microscopy including high-resolution cross-sectional image. The results show the epitaxy of βFeSi2 (110) and (101) planes parallel to the Si (111) plane. The disilicide-silicon heterojunction displays an atomically abrupt interface.
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