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 fi lms, grown on sapphire (11.0) substrate by reduced pressure metalorganic va por phase epitaxy (MOVPE) under various conditions, were performed. The str ained lattice parameters, stress, misorientation and dislocation density of GaN films were estimated. The experimental stress compares well with the t heoretical stress obtained from the difference in the thermal expansion coe fficient 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 witho ut any buffer layer. For the same carrier concentration, the mobility of on e of the film was lower than the other which could be due to the presence o f higher dislocation density. Slip lines associated with dislocations, stac king faults, cellular structure of dislocations and double positioning boun daries were found in the X-ray topography from the GaN films. (C) 1999 Else vier Science S.A. All rights reserved.