Band-edge transitions in hexagonal boron nitride epilayers

Abstract

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 10 K is about 500 times stronger than that of high quality AlN 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⇀emi⊥c⇀⁠) is about 1.7 times stronger than the component along the c-axis (⁠E⇀emi‖c⇀⁠). This is in contrast to AlN, in which the band-edge emission is known to be polarized along the c-axis, (⁠E⇀emi‖c⇀⁠). Time-resolved PL measurements revealed a decay lifetime of around 4.3 ns at 10 K 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.