Line width of inter-subband absorption in inversion layers

The broadening of the inter-subband absorption is calculated in space-charge layers on a Si surface. Scatterers are assumed to be dominated by charged ions at the Si-SiO2 interface. Among two different contributions to the broadening, the intra-subband process shows a drastic dependence on the strength of the depletion field, while dependence is smaller for the inter-subband process. The results explain recent experiments in accumulation layers on the Si (100) surface where extra Na+ ions are intentionally introduced at the interface. (author)