Amorphous boron phosphide: An ab initio investigation

Abstract

We generate a structural model of amorphous boron phosphide (BP) by quenching the melt via ab initio molecular dynamics calculations and compare it structurally and electrically with the crystal. We find that both phases of BP have a significantly different short-range order. Namely, the amorphous network presents strong chemical disorder and structural defects. P-atoms form only undercoordinated defects while B atoms present both undercoordinated and overcoordinated defects. The mean coordination number of B and P atoms is 4.17 and 3.69, correspondingly. Some of overcoordinated B atoms with chemical disorder yield the formation of pentagonal-pyramid-like motifs and a cage-like B10 cluster in the amorphous network. About 13 % volume expansion is observed by amorphization, probably due to the low-coordinated structural defects. The amorphous configuration is semiconductor as in the crystal but has a smaller energy band gap.