Influence of N/Ga-flux ratio on optical properties and surface morphology of GaN grown on sapphire(0001) by MBE

We studied the correlation between the low-temperature optical properties a nd the surface morphology of molecular beam epitaxy (MBE) grown GaN on sapp hire(0001). The samples were grown under Ga-rich conditions, with the Ga-fl ux as a parameter, and with all other growth parameters constant. High-reso lution scanning electron microscopy (SEM) provided a measure of the surface morphology, while the optical properties were characterised by low-tempera ture photoluminescence. These spectra were dominated by the exciton bound t o neutral donor transition, at 3.472-3.474 eV, indicating fairly strain rel axed layers. This peak width is increased when the surface morphology impro ved. Our results also showed a clear correlation between the optical proper ties and the purity of the nitrogen source, as improved oxygen purification improved the photoluminescence linewidth from 41 to 20 meV. (C) 2000 Elsev ier Science B.V. All rights reserved.