Band-edge transitions in hexagonal boron nitride epilayers

Hexagonal boron nitride (hBN) epilayers have been synthesized on sapphire substrates by metal-organic chemical vapor deposition (MOCVD). These MOCVD grown epilayers exhibit highly efficient band-edge photoluminescence (PL) emission lines centered at around 5.5 eV. The results represent a remarkable improvement over the optical qualities of hBN films synthesized by different methods in the past. It was observed that the emission of hBN at 10K is about 500 times stronger than that of high quality AIN epilayers. Polarization-resolved PL spectroscopy revealed that hBN epilayers are predominantly a surface emission material, in which the band-edge emission with electric field perpendicular to the c-axis ((E) over right arrow (emi) perpendicular to (c) over right arrow) is about 1.7 times stronger than the component along the c-axis ((E) over right arrow (emi) parallel to (c) over right arrow). This is in contrast to AIN, in which the band-edge emission is known to be polarized along the c-axis, ((E) over right arrow emi parallel to (c) over right arrow). Time-resolved PL measurements revealed a decay lifetime of around 4.3 ns at 10K for the dominant band-edge transition line. The present result together with the ability of p-type doping of hBN represents a major step towards the realization of hBN based practical devices. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742194]