Defects in free-standing gallium nitride were examined. Electron beam induced current mapping evidence a low density of dislocations in the first microns from the upper Ga-terminated surface; correspondingly, deep levels detected by junction spectroscopy exhibited point-like characteristics. Spectral photoconductivity measurements in the poorly dislocated region show the characteristic red, yellow, green, and blue bands, which shifted toward higher energies with decreasing temperatures according to Varshni's law. Spectral photoconductivity measurements carried out in depth evidenced, instead, the quenching of the defect-related yellow band and the prevalence of the green band when temperature increased. This behavior suggested a dislocation-assisted connection between the yellow and green bands, in agreement with theoretical models on their common origin involving complexes VGa-ON.

Defect Characterization in GaN - Possible Influence of Dislocations in the Yellow-Band Features. L.Polenta, A.Castaldini, A.Cavallini: Journal of Applied Physics, 2007, 102[6], 063702