ION CHANNELING STUDIES OF GAN LAYERS ON C-ORIENTED SAPPHIRE

The successful growth of epitaxial GaN films by metal organic vapor ph ase epitaxy (MOVPE) or gas source molecular beam epitaxy (GSMBE) has o pened up new applications in short wavelength photonic devices for dis plays and optical data storage systems. The large lattice mismatch of 14% between GaN and sapphire, usually used as the substrate, and the d ifferent thermal expansion coefficients generally lead to high densiti es of structural defects. In this paper we investigate the defect stru cture of MOVPE- and GSMBE-grown GaN layers on sapphire by Rutherford b ackscattering and ion channeling measurements. In addition to axial c- axis channeling, which reveals chi<INF>min</INF> values as low as 1.2% , channeling measurements along the (2 <INF></INF> (1) over bar (1) ov er bar 0) and (1 (1) over bar 0 0) crystal planes were performed in or der to improve the sensitivity to dechanneling by crystalline defects. Angular scans around the c-axis indicate clearly the hexagonal symmet ry of the GaN lattice. Dechanneling results were compared to observati ons of defects by transmission electron microscopy (TEM). This compari son suggests that the cross-section of dechanneling by edge dislocatio ns is about a factor of 4 larger than the dechanneling cross-section o f screw dislocations. (C) 1998 Elsevier Science B.V.