Fermi Level Stabilization and Surface States at the Interfaces of Si(111) Surfaces and Insulating Layers

Abstract

Temperatvre dependence of the surface potential (total bending of bands) in Si(111) surfaces (n- and p-type bulk) deposited with a silicon dioxide and a silicon nitride was obtained by measuring the saturation value of surface photovoltage, in the range between 150 and 600°K. Substantially similar results were obtained for both the surfaces. Bands always bend upward in n- and downward in p-type Si. In Si crystals with relatively high impurity concentrations, the bending of bands was founds to decrease linearly with elevating temperature and in Si with relatively low impurity concentrations, the bending of bands also decreases linearly with temperature but levels off, tending to the flat bands. These results are well explained by assuming that there is a surface state band of a hyperbolic cosine from having a neutral point around the gap center and the Fermi level at the Si surfaces in nearly stabilized in a wide range of temperature. Total number of surface states estimated from the above distribution is larger than 2×10¹¹ cm⁻².