Crystallographic Symmetry of Surface State Density in Thermally Oxidized Silicon

The detailed dependence of surface state density on crystallographic orientation was determined by measuring the ac metal-oxide-semiconductor conductance on the surface of a thermally oxidized single-crystal silicon hemisphere. It was found that the 〈111〉 poles are located at maxima, the 〈100〉 poles at minima, and the 〈110〉 poles at saddle points in the surface state density distribution. The symmetry of the surface state density distribution is generally similar to that of the ``fixed'' interface charge density, but differences are noted in the vicinity of the 〈100〉 directions.