STRUCTURAL-PROPERTIES OF GAN FILMS GROWN ON SAPPHIRE BY MOLECULAR-BEAM EPITAXY

The structural characteristics of GaN films grown on sapphire substrat es by molecular beam epitaxy have been investigated using high-resolut ion synchrotron x-ray diffraction and electron microscopy. We find rem arkable correspondence between the in-plane structural order (coherenc e length and mosaic spread) and the electrical and optical properties. Contrary to common belief, our observations show unequivocally that t he out-of-plane structural features, which are considerably better dev eloped than the in-plane counterparts, cannot be used for determining the material quality with respect to their optical and electrical acti vity. In particular, the (001) mosaic spread is not a good indicator o f film quality. (C) 1996 American Institute of Physics.