Nucleation mechanism of GaN nanowires grown on (111) Si by molecular beamepitaxy

Abstract

We have performed a real-time in situ x-ray scattering study of the nucleation of GaNnanowires grown by plasma-assisted molecular beam epitaxy on AlN(0001)/Si(111). Theintensity variation of the GaN diffraction peak as a function of time was found to exhibitthree different regimes: (i) the deposition of a wetting layer, which is followed by (ii) asupralinear regime assigned to nucleation of almost fully relaxed GaN nanowires, eventuallyleading to (iii) a steady-state growth regime. Based on scanning electron microscopy andelectron microscopy analysis, it is proposed that the granular character of the thin AlNbuffer layer may account for the easy plastic relaxation of GaN, establishing thatthree-dimensional islanding and plastic strain relaxation of GaN are two necessaryconditions for nanowire growth.