Thin (00•1) films (1.25 to 2.25μm-thick), grown onto (11•0) sapphire substrates by metal-organic chemical vapor phase deposition with various numbers of AlN interlayers, were characterized by using triple-crystal diffractometry and synchrotron white-beam X-ray topography. The full-width at half-maximum of the X-ray rocking curves from symmetrical and asymmetrical reflections was used to estimate the dislocation density in the films. It was found that the edge dislocation density decreased from 1.63 x 1010 to 1.23 x 1010/cm2, and the screw dislocation density decreased from 2.0 x 108 to 1.1 x

108/cm2, when one AlN interlayer was inserted between the high-temperature GaN layer. The dislocation density decreased further with increasing number of interlayers. On the other hand, the compressive stress in the GaN film increased from -0.29 to -0.86GPa. The compressive stress further increased as the number of interlayers increased, but no cracking of the GaN film was observed. This was attributed to better adhesion between the film and the substrate, due to the interlayers. Synchrotron white beam X-ray topography in transmission, from a GaN(00•1)/Al2O3(11•0) sample, confirmed the orientation of the GaN and indicated that it was a single crystal with a high dislocation density. Synchrotron white beam X-ray topography from the Al2O3 substrate revealed a cellular dislocation structure.

Reduction of Dislocation Density in GaN Films on Sapphire using AIN Interlayers. J.Chaudhuri, J.T.George, D.D.Kolske, A.E.Wickenden, R.L.Henry, Z.Rek: Journal of Materials Science, 2002, 37[7], 1449-53