Crystal defects and optical properties of GaN grown with different techniques: stacking fault related luminescence

Low temperature spectrally resolved CL and TEM investigations have been carried out on GaN epilayers grown on (0001) oriented Al2O3 and alpha(6H)-SiC (0001)(Si) substrates with different techniques. CL studies revealed an additional emission line at 3.425 eV whose intensity ratio with respect to the near emission band transition depended on the electron beam energy. This line, independently of the growth conditions, has been found to be present only in samples with a very high density of planar defects and has been ascribed to excitons bound to stacking faults.