Thermal chemical vapor deposition of epitaxial rhombohedral boron nitride from trimethylboron and ammonia

Epitaxial rhombohedral boron nitride (r-BN) films were deposited on alpha-Al2O3(001) substrates by chemical vapor deposition, using trimethylboron, ammonia, and a low concentration of silane in the growth flux. The depositions were performed at temperatures from 1200 to 1485 degrees 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 degrees 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] parallel to w-AlN[001] parallel to alpha-Al2O3[001] and with two in-plane relationships of r-BN[110] parallel to w-AlN[110] parallel to alpha-Al2O3[100] and r-BN[110] parallel to w-AlN[110] parallel to alpha-Al2O3[(1) over bar 00] due to twinning. Published by the AVS.