Growth of wurtzite GaP in InP/GaP core-shell nanowires by selective-area MOVPE

A GaP nanowire is promising from the viewpoint of device applications because when its crystal phase is changed from zinc blende (ZB) to wurtzite (WZ), its band gap changes from indirect to direct. GaP in the WZ phase is theoretically and experimentally shown to have the possibility of "green" emission. Here we report on the growth of WZ GaP in InP/GaP core-shell nanowires by selective-area metal-organic vapor-phase epitaxy (SA-MOVPE). WZ InP nanowires were used as a template for transferring the WZ structure to GaP. Transmission electron microscopy revealed that WZ GaP was grown on the sidewalls of the InP core in the lateral <-2 1 1 > direction and that ZB GaP was grown on the top of the le core in the axial < 1 1 1 > A direction. A growth model for the different crystal structures of the GaP shell is proposed from the viewpoint of the growth direction. The WZ structure is "transferred" from the InP core to the GaP shell only when GaP grows in the direction perpendicular to the WZ stacking direction of the InP core. This so-called "crystal structure transfer" can also be applied to p- and n-doped GaP and is therefore promising for fabricating WZ-GaP-basecl light-emitting diodes. (C) 2014 Elsevier B.V. All rights reserved.