We modify the model of nonradiative carrier recombination on threading dislocation cores [Z. Z. Bandić, P. M. Bridger, E. C. Piquette, and T. C. McGill, Solid-State Electron. 44, 221 (2000)] to estimate quantitatively the light emission efficiency in GaN as a function of the dislocation density and nonequilibrium carrier concentration. The model predictions are in good agreement with available data on the minority carrier diffusion length in GaN. The dislocation density must be reduced, at least, down to ∼107 cm−2 in order to provide a light emission efficiency close to unity. The n-type background doping is found to be favorable for the further efficiency improvement.

GaN(0001) thick layers were grown on c-plane sapphire substrates by molecular-beam epitaxy using ${\mathrm{NH}}_{\mathrm{3}}.$ The evaporation of such GaN layers in vacuum was studied as a function of substrate temperature. In situ laser reflectivity was used to quantitatively measure the decomposition rate of the GaN(0001) plane. It is nearly zero below 750 °C, increases rapidly above 800 °C, and reaches 1 μm/h at 850 °C. An activation energy of 3.6 eV is deduced for the thermal decomposition of GaN in vacuum. The evaporation rate as a function of the incident ${\mathrm{NH}}_{\mathrm{3}}$ flux was also investigated for different substrate temperatures. A kinetic model is applied for the interpretation of the experimental results.