Liquid phase epitaxy (LPE) of GaN on c- and r-faces of AlN substrates

The direct growth of GaN by liquid phase epitaxy (LPE) on different AlN substrate orientations is demonstrated for the first time. The objective of this work was to study the seeding behaviour and morphology of GaN grown on different crystallographic orientations of the AlN substrate. Furthermore the incorporation of solvents and impurities in the epitaxial GaN was analysed. The surface treatment of the AlN-substrates before epitaxial growth turned out to be a challenging process, due to the fact, that polishing of the substrates is not yet developed in sufficient quality. Therefore, the aspect of surface treatment is addressed in brief. It was found that the growth of completely closed layers of GaN on Al-polar c-facets appears to be quite difficult compared to the formation of closed layers on N-polar c- and on r-facets. The growth of a closed GaN layer on single crystalline r-plane AIN substrates using the LPE technique could also be demonstrated. Characterisation by cathodoluminscence spectroscopy indicates that aluminium is incorporated with different content depending on the orientation.