Theoretical study of carrier confinement in a-Si–SiC quantum wells

We present a systematic theoretical analysis of carrier confinement in amorphous semiconductor quantum wells. Our study is based on a fourfold-coordinated continuous random-network model for the amorphous state. A semiempirical tight-binding approach and the recursion method are used to calculate the average electronic density of states of clusters consisting of typically 57 600 atoms. For narrow wells we find that the average local density of states near the well center exhibits these features both at the valence- and conduction-band edge. Comparison with calculations for the bulk and corresponding crystalline quantum wells allows the interpretation that quantum confinement effects due to the presence of barrier materials are responsible for these features in the density of states. For quantum well width below about 20 Å the onset of a gap formation which separates strongly localized states from extended conduction-band states is observed.