Thermal Chemical Vapor Deposition of Epitaxial Rhombohedral Boron Nitride from Trimethylboron and Ammonia

Epitaxial rhombohedral boron nitride films were deposited on α-Al2O3(001) substrates by chemical vapor deposition, using trimethylboron, ammonia, and with a low concentration of silane in the growth flux. The depositions were performed at temperatures from 1200 to 1485 °C, pressures from 30 to 90 mbar and N/B ratios from 321 to 1286. The most favorable conditions for epitaxy were: a temperature of 1400 °C, N/B around 964, and pressures below 40 mbar. Analysis by thin film X-ray diffraction showed that most deposited films were polytype-pure epitaxial r-BN with an out-of-plane epitaxial relationship of r-BN[001]∥ w-AlN[001]∥ α-Al2O3[001] and with two in-plane relationships of r-BN[110]∥ w-AlN[110]∥ α-Al2O3[100] and r-BN[110]∥ w-AlN[110]∥ α-Al2O3[1̅00] due to twinning.