Band structure and transport properties of semiconducting rhenium silicide thin films grown epitaxially on silicon

Abstract

Summary form only given, as follows. Transport properties of semiconducting rhenium silicide thin films have been measured, in directions both parallel and perpendicular to the silicon substrate. Optical properties are also reassessed. This silicide, which shows a commensurable fit with the (111) surface of silicon, has been epitaxially grown on such substrates by reactive deposition at 650/spl deg/C of the simultaneous flux of rhenium and silicon atoms coming from two sublimation cells. Post-anneals at 750/spl deg/C and 850/spl deg/C in hydrogen partial pressure have been done. From Hall effect measurements, the semiconducting silicide appears as p-type in the first case and n-type in the second case, with a lower concentration of residual doping. But in any case, the intrinsic regime is almost reached near room temperature, in agreement with the band gap deduced from optical absorption measurements. The band gap is also found as the difference between the two transition thresholds observed in the internal photoemission response, evaluated from the photocurrent induced by illumination in the silicide-silicon heterojunction. Band discontinuities with silicon are also deduced. Conductivity and Hall effect measurements on high resistivity silicon substrates show that the electron mobility is at least 200 cm2/Vs at ambient temperature and in excess of 1000 cm/sup 2//Vs at the liquid nitrogen temperature. These facts indicate that the rhenium silicide thin film quality has been dramatically improved by the aforementioned thermal treatment and may be used in photodetector devices in the infrared range up to wavelengths near 5 /spl mu/m with the inherent advantage of its compatibility with silicon technology.