High resolution X-ray diffraction and X-ray topography study of GaN on sapphire

High resolution X-ray diffraction and X-ray topography study of GaN thin films, grown on sapphire (11.0) substrate by reduced pressure metalorganic vapor phase epitaxy (MOVPE) under various conditions, were performed. The strained lattice parameters, stress, misorientation and dislocation density of GaN films were estimated. The experimental stress compares well with the theoretical stress obtained from the difference in the thermal expansion coefficient between the film and substrate. The dislocation density was found to be highest in the thinner GaN film. It was also higher in the film without any buffer layer. For the same carrier concentration, the mobility of one of the film was lower than the other which could be due to the presence of higher dislocation density. Slip lines associated with dislocations, stacking faults, cellular structure of dislocations and double positioning boundaries were found in the X-ray topography from the GaN films.