Impact of GaN buffer growth conditions on photoluminescence and X-ray diffraction characteristics of MOVPE grown bulk GaN

Properties of metalorganic vapor phase epitaxy (MOVPE) grown GaN bulk layers with varying GaN buffer growth conditions are characterized by low-temperature (6K) photoluminescence (LT-PL) and X-ray diffraction (XRD). Full width at half-maximum (FWHM) of the near-bandedge emission of undoped layers is between 4.9 and 10 meV, exhibiting no distinct dependence on buffer growth conditions. PL as well as photoreflectance measurements allowed the identification of neutral-donor bound exciton (D₀X) emission at ~3.48 eV, and free A and B exciton emission lines at ~6 and ~15 meV higher energies, respectively. UV/yellow luminescence integrated intensity ratio and XRD FWHM show clear dependence on buffer growth conditions. Decreasing buffer thickness results in increasing PL intensity ratio and decreasing XRD FWHM. For thicker buffers, increasing the temperature ramping time between buffer and bulk growth also improves optical layer quality. Si-doped GaN was grown with carrier concentrations between 9×10¹⁷ cm^-3 and 2×10¹⁹ cm^-3. The PL peak position decreases with increasing carrier concentration and its FWHM increases due to donor banding effects