  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.
