Effects of AlN nucleation layers on the growth of AlN films using high temperature hydride vapor phase epitaxy

AlN layers were grown on c-plane sapphire substrates with AlN nucleation layers (NLs) using high temperature hydride vapor phase epitaxy (HT-HVPE). Insertion of low temperature NLs, as those typically used in MOVPE process, prior to the high temperature AlN (HT-AlN) layers has been investigated. The NLs surface morphology was studied by atomic force microscopy (AFM) and NLs thickness was measured by X-ray reflectivity. Increasing nucleation layer deposition temperature from 650 to 850 degrees C has been found to promote the growth of c-oriented epitaxial HT-AlN layers instead of polycrystalline layers. The growth of polycrystalline layers has been related to the formation of dis-oriented crystallites. The density of such disoriented crystallites has been found to decrease while increasing NLs deposition temperature. The HT-AlN layers have been characterized by X-ray diffraction theta - 2 theta scan and (0 0 0 2) rocking curve measurement, Raman and photoluminescence spectroscopies, AFM and field emission scanning electron microscopy. Increasing the growth temperature of HT-AlN layers from 1200 to 1400 degrees C using a NL grown at 850 degrees C improves the structural quality as well as the surface morphology. As a matter of fact, full-width at half-maximum (FWHM) of 0 0 0 2 reflections was improved from 1900 to 864 arcsec for 1200 degrees C and 1400 degrees C, respectively. Related RMS roughness also found to decrease from 10 to 5.6 nm. (C) 2012 Elsevier B. V. All rights reserved.