The boron precursors, in their respective processes, are added through a separate quartz liner along with H2 to avoid the formation of intermediate adducts prematurely. A pyrometer (Heitronics KT81R, calibrated by a silicon melt test) is used to monitor the growth temperature. The process pressure is maintained using a throttle valve. As observed from prior experience, the addition of silane (SiH4) has proved useful to promote better crystallinity in the films grown by this process hence added while growing using both precursors. Optimized processes parameters are selected from previous studies on TEB and TMB. For all processes, the base pressure is kept below 2 x 10 -2 mbar. Carrier gas flow is maintained at 5000 sccm H2. The growth temperature for the process based on TMB was 1400°C and BN is grown of sp 2 -BN 60 min with a process pressure of 50 mbar, while the process based on TEB growth was done at 1500°C and BN is grown for typically 240 min with a process pressure of 70 mbar. The NH3/TMB ratio was kept at 966. Silane (SiH4, 99.999 % purity, 2000 ppm diluted in 99.9996 % H2) was supplied with a flow corresponding to 16.5 sccm 2 minutes prior to BN deposition. The NH3/TEB ratio was kept at 642. SiH4 (99.999 % purity, 2000 ppm diluted in 99.9996 % H2) was supplied with a flow corresponding to 13 sccm 2 minutes prior to film deposition.