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We have studied the local structure of hydrogenated amorphous silicon-carbon alloy films, a-${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{C}}_{\mathit{x}}$:H, by measuring the extended x-ray-absorption fine structure at the Si K edge. We find that first-coordination-shell average bond lengths are 2.35 A\r{} for Si-Si and 1.86 A\r{} for Si-C and are constant with concentration to within \ifmmode\pm\else\textpm\fi{}0.015 A\r{}. By comparing the composition of the first coordination shell around Si with the average concentration, we show that the alloy tends to be chemically ordered, in that heteroatomic bonds are preferred.

We present a study of the heterojunctions formed when Ge is deposited onto a variety of atomically clean Si-based amorphous substrates. With the use of synchrotron-radiation photoemission spectroscopy we are able to measure the valence-band discontinuities and also probe the local order at the interface. We find that linear theories of band discontinuities are valid to an accuracy of 0.2 eV for these materials. © 1988 The American Physical Society.