Influence of growth parameters on the optical properties of selective area grown GaN nanorods by plasma-assisted molecular beam epitaxy

We demonstrate the selective area growth (SAG) of GaN nanorods (NRs) on patterned Ti/Si(1 1 1) substrate by plasma-assisted molecular beam epitaxy. Nanoholes pattern on Si(1 1 1) substrate were fabricated by a colloidal lithography technique and then GaN NRs were grown by varying the growth parameters, namely growth temperature, N-2 plasma power and Ga flux. Under similar experimental conditions, GaN NRs grown on patterned Ti/Si(1 1 1) substrate showed improved size homogeneity and optical properties compared to GaN NRs grown on non-patterned Si(1 1 1) substrate. Photoluminescence spectra of SAG GaN NRs exhibited emission peaks corresponding to neutral donor bound excitons (D degrees X), donor-acceptor pair (DAP) and yellow luminescence (YL) bands at 3.477 eV, 3.280 eV and 2.245 eV respectively. Unlike D degrees X, both DAP and YL bands showed strong dependence on growth conditions. Results demonstrate that V-Ga-involved defects act as deep acceptors and are responsible for the observed defect emissions in GaN NRs. (C) 2014 Elsevier B.V. All rights reserved.