Environments of ion-implanted dopants in amorphous silicon at various stages of annealing

https://doi.org/10.1016/0168-583X(93)90717-KGet rights and content

Abstract

Glancing angle X-ray absorption fine structure (XAFS) spectroscopy has been used to record the varying environments of Ga and As impurities ion-implanted in amorphous silicon (a-Si) - both glow discharge (gd) deposited and amorphised by ion beam damage (ii). Apart from small differences in coordination number and Debye-Waller factor due to the presence of hydrogen in gd material the environments for the same impurity in the two forms of a-Si are almost indistinguishable. The electronic activity of gd a-Si is therefore directly attributable to the lower density of intrinsic defects compared to ii a-Si. The coordination numbers of impurities in as-implanted material are found to differ from those of a-Si at various stages of anneal. Ga, for instance, falls from 3.8 (room temperature) to 3 (400°C) demonstrating a substantial change in the balance between tetrahedral and naturally bonded sites. Coordination numbers of both Ga and As increase for annealing at 700°C and the onset of crystallisation is identified in the appearance of outer shells of atoms in the impurity environments. Crystallisation, however, is only partial (≈25%) at this temperature even though thermal epitaxial regrowth of the majority of the Si matrix is complete. Clearly recrystallisation of a-Si is inhibited in the vicinity of naturally bonded dopant sites.

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