Effects of sapphire nitridation and growth temperature on the epitaxial   growth of hexagonal boron nitride on sapphire
  This paper reports on the epitaxial growth of hexagonal boron nitride (hBN) films on sapphire substrates in a cold wall chemical vapor deposition (CVD) system where different sapphire nitridation and hBN growth temperatures were employed. A thin and amorphous nitridated layer was formed at a low temperature (850 C), which enabled subsequent epitaxial hBN growth at 1350 C. The influences of the sapphire nitridation temperature and the growth temperature on the film quality were analyzed by X-ray diffraction (XRD) measurements. Higher than optimum nitridation and growth temperatures improve the crystalline quality of the nitridated layer, but does not favor the epitaxial growth of hBN. hBN films grown at the optimum conditions exhibit the c-lattice constant of 6.66 {\AA} from the XRD {\theta}-2{\theta} scan, and the characteristic in plane stretching vibration at 1370.5/cm from Raman spectroscopy. X-ray photoelectron spectroscopy analysis confirmed the formation of stoichiometric hBN films with excellent uniformity. 
Kawser Ahmed, Rajendra Dahal, Adam Weltz, James J.-Q. Lu, Yaron Danon,   and Ishwara B. Bhat
cond-mat.mtrl-sci