Understanding radiative emissions in the vicinity of selected-area regrown GaN diodes*

Selected-area growth (SAG) is a promising approach to achieve vertical p-n diodes for high power devices. However, leakage currents at vertical and lateral junctions often limit diode performance. Here we examine correlations between interfacial impurities and cathodoluminescence (CL) emission in SAG GaN trenches with and without Mg-doping. In all spectra, a 3.40 eV peak due to near band edge emission is observed. Most spectra also include a beam-energy dependent peak at 2.25 eV, termed yellow luminescence (YL). Since all interaction volumes include UID-GaN, YL is associated with V_Ga or its complexes with Si or C. For p-GaN trenches, emissions at 2.85 and 3.25 eV are observed near the trench edge and center, respectively. Interestingly, atom probe tomography reveals increased [O] at trench edges and secondary-ion mass spectroscopy reveals increased [Si] at planar regrowth interfaces.  Thus,  we attribute the 2.85 and 3.25 eV emissions to O-Mg donor-acceptor pair (DAP) and Si-Mg shallow-donor-acceptor pair (SDAP) emissions. These assignments are confirmed by a lack of DAP and SDAP emissions in spectra from UID-GaN trenches. We discuss the relationship between [Mg], the intensity of CL emission, and its implications for diode performance.