Phase transition induced vertical alignment of ultrathin gallium phosphide nanowire arrays on silicon by chemical beam epitaxy

Abstract

We demonstrate high-density heteroepitaxial growth of sub-10 nm diameter gallium phosphide (GaP) nanowire (NW) arrays on silicon (Si), using chemical beam epitaxy (CBE). The vertical alignment of GaP NW arrays is facilitated by an initial phase transition from zinc blende (ZB) to wurtzite (WZ), which is determined based on the observations of a phase transition during the early heteroepitaxial growth for the wires with diameters below 10 nm and the crystallographic structure of the Au–Ga catalyst tip. We propose a new ledge-flow mechanism with a nucleus consisting of three atomic planes (C-B-A stacking) that enables the tilted growth directions of the ZB phase. With photoluminescence (PL), a band-to-band recombination occurs with an energy similar to the indirect band gap of bulk ZB GaP with a short lifetime. The band structure of bulk ZB and WZ GaP was calculated using different approaches.