A theoretical study of defects in amorphous group-V semiconductors

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Abstract
Clusters of about 55 atoms have been built to model possible bonding coordination defects (BCDs) in the amorphous group-V semiconductors (P, As, Sb). A tight-binding Hamiltonian is used to examine trends in the position and localisation of defect states due to the BCDs. Whereas similar studies have in the past included only nearest-neighbour interactions, the authors now explicitly consider longer-range effects. These are found to be crucial in determining the properties of certain of the defect states, especially these associated with overcoordinated atoms. They find that dangling bond states more closer to mid-gap as one goes down the group and that states due to the overcoordinated atom lie near mid-gap in all three elements. Both these results can be understood by chemical arguments and because they are in good agreement with experiment for As can be applied with confidence to amorphous P.