Photoluminescence of GaN Grown by Molecular Beam Epitaxy on Freestanding GaN Template

Abstract

AbstractWe studied photoluminescence (PL) of GaN layers grown by molecular beam epitaxy on freestanding high-quality GaN templates. The layers with thickness of ∼ 1 νm were grown under Ga-rich conditions using radio-frequency plasma as a nitrogen source. The PL spectra from both the epilayer and the substrate contain a plethora of very sharp peaks related to excitonic transitions. Through the analysis of the excitonic part of the spectra, we have identified two shallow donors with the binding energies of 28.8 and 32.6 meV, attributed to SiGa and ON, respectively. The PL spectra involved also emissions due to shallow donor-acceptor pair transitions with the main peak at 3.26 eV and a broad band peaking at ∼2.5 - 2.6 eV (green band). The green bands in the GaN substrate and GaN overgrown layer have different energy positions invoking the suggestion that they must have their genesis in different defect centers.