Carrier localization in basal-plane stacking faults in Si-doped nonpolar a-plane (1120) GaN epilayers containing different defect densities

We investigated carrier localization in basal-plane stacking faults (BPSF) in Si-doped nonpolar a-plane GaN (a-GaN) epilayers containing various BPSF densities. Different SiN_x interlayers were used to control the BPSF density in the a-GaN films. Significantly reduced BPSF densities were realized by the insertion of thick SiN_x and multi-SiN_x/GaN interlayers. BPSF-related emissions in low-temperature photoluminescence (PL) spectra showed the smallest full width at half maximum (25 meV), as well as predominant near-band-edge emission peaks for samples with multi-SiN_x/GaN interlayers. The role of BPSFs as carrier/exciton localization centers was confirmed from the S-shaped temperature dependence of the BPSF peak energies. Moreover, carrier localization energies, extracted from the S-shaped curve fitted to Varshni's formula, were determined not to be solely dependent on BPSF density. It is suggested that localization energy can be influenced by other factors such as donors in the vicinity of a BPSF or polarization-induced electric fields. Carrier localization energies within BPSFs were in good agreement with the low-temperature activation energies from Arrhenius plots of integrated PL intensity. Stronger carrier localization within BPSFs can be realized when a-GaN epilayers contain multi-SiN_x/GaN interlayers.