Stress-induced anisotropy in the electrical properties of Si/Al2O3

Abstract

The effect of stress on the electrical properties for a number of orientations of Si/Al2O3 has been theoretically determined. The stress model developed and employed is based upon the differential in thermal expansion between Si film and an Al2O3 substrate. The anisotropy in substrate thermal expansion coefficients and in Si film stresses is rigorously included and treated within the framework of a thin-film thick-substrate approach. The phenomenological piezoresistance formalism is used to determine the effect of stress on resistivity which is then in turn related to the carrier mobility. Mobility calculations were performed for the common Si orientations— (001), (111), and (221) —and for a number or orientations not yet grown and investigated experimentally. For n-type Si the mobility is either reduced or enhanced depending upon mode of epitaxy and orientation. For p-type Si the mobility is always enhanced and for some orientations by a significant factor. The theoretical results obtained indicate that the thermal stress effect on mobility has a strong orientation dependence and that, compared with the commonly employed (001) Si/Al2O3 orientation, substantially larger mobilities could be obtained with other Si/Al2O3 orientations.