Figure 1 SEM and TEM images and elemental maps. (a) SEM image of the NPs prepared using UV metal-assisted electroless etching technique and (b) TEM image of NPs. (c) Overlaid elemental maps of Ga, N, and O in red, green, and blue, respectively, acquired
by EFTEM. In order to understand the difference in Blebbistatin solubility dmso the emission mechanism of as-grown GaN epitaxy and the as-fabricated NPs, we studied the normalized μPL spectra at 77 K. Figure 2a shows disparate emission characteristics of GaN in both GaN epitaxy and NPs. In the as-grown GaN epitaxy, we clearly observe the existence of one relatively sharp peak at the UV region, 3.479 eV (approximately 356 nm) with a full width at half maximum (FWHM) of 13 meV, which is attributed to the donor-bound exciton peak (D 0 X) [3]. The small hump at 3.484 eV is assigned to the free-excitonic peak (FX). We attribute the small
PL peak I ox at 3.4 eV mainly to oxygen impurities that originated from Al2O3, i.e., the oxygen impurity-related donor-to-valence band transitions as reported by Chung and Gershenzon [12] and Fischer et al. [13]. The donor-acceptor pair (DAP) peak at 3.308 eV has its longitudinal optical (LO) phonon peak at lower photon energy. Figure 2 Emission spectra of GaN epitaxy and GaN NPs, peak PL photon energy and FWHM dependence. (a) Normalized 77 K μPL emission spectra of as-grown 30-μm GaN epitaxy and GaN NP cluster with semi-log scale. (b) Normalized room temperature μPL emission spectra of as-grown GaN (dashed line) and GaN NP (solid line) cluster excited selleck chemical with increasing laser power (0.08, 0.8, 2, 4, and 8 kW/cm2). (c) The peak PL photon energy (black squares) and the FWHM (blue triangles) dependence over the excitation power. The μPL spectrum of the GaN NPs presents approximately 110-meV red shift that could be
attributed to the relaxation of the compressive strain [5], but foremost, we observe a relatively strong/prominent increase of the DAP and I ox peak intensities. In the SDHB n-type GaN DAP transitions, these acceptor-like sites have been reported by a number of authors to originate from Ga vacancies (V Ga) [14, 15]. The GaN NPs underwent chemical etching, thus resulting in an increase of oxygen and vacancy sites at the surface due to the competition between the formation and dissolution of Ga x O y (Figure 1c). This explains the increase in the emission intensity of DAP peaks. The power-dependent PL measurement was performed on the NPs. Figure 2b shows a typical room temperature μPL emission spectrum of the as-grown GaN excited at 0.08 kW/cm2 together with the excitation power-dependent μPL emission spectrum of the GaN NPs. Compared to the 77 K PL, we observe in the room temperature PL of the as-grown sample a quenching of D 0 X peak while the FX emission became https://www.selleckchem.com/products/MGCD0103(Mocetinostat).html dominant at 3.42 eV (approximately 362 nm). The broadening in the lower photon energy due to the oxygen impurity is still observable whereas the DAP peak disappeared. Most importantly, room temperature PL of GaN NPs excited at 0.