Mg and Si dopant incorporation and segregation in GaN

Abstract

The surface segregation of Mg and Si dopant species and theiratomic incorporation sites in GaN films grown by metal-organicvapour phase epitaxy (MOVPE) on sapphire (0001) substrateshave been analysed by X-ray photoemission spectro-micro-scopy and X-ray standing waves (XSW). As revealed byspectro-microscopy, both Mg and Si tend to segregate to thesurface. In case of Mg, an enhanced surface dopant concen-tration is found even after sputter-removal of several tens ofnanometres, which confirms a segregation mechanism pro-posed earlier [S. Figge et al., Appl. Phys. Lett.81, 4748 (2002)].Si doping has been found to result in the formation of facettedgrooves in the GaN films. The surface silicon concentration atthe facets is determined to be about 2.5 times higher ascompared to the planar (0001) surface by micro-spectroscopy.XSW results show that with increasing Mg dopant concen-tration, non-substitutional lattice sites are progressivelyoccupied. The results can quantitatively be explained by Mgatoms incorporated in an anti-bixbyite-like structure and isrelated to inversion domain boundaries. For Si doping, noevidence is found for the occupation of non-substitutional sites.However, a decrease in crystal quality is observed withincreasing Si concentration