Bandgap and exciton binding energies of hexagonal boron nitride probed by photocurrent excitation spectroscopy

Photocurrent excitation spectroscopy has been employed to probe the band structure and basic parameters of hexagonal boron nitride (h-BN) epilayers synthesized by metal-organic chemical vapor deposition. Bias dependent photocurrent excitation spectra clearly resolved the band-to-band, free exciton, and impurity bound exciton transitions. The energy bandgap (E_g), binding energy of free exciton (E_x), and binding energy of impurity bound exciton (E_bx) in h-BN have been directly obtained from the photocurrent spectral peak positions and comparison with the related photoluminescence emission peaks. The direct observation of the band-to-band transition suggests that h-BN is a semiconductor with a direct energy bandgap of E_g = 6.42 eV at room temperature. These results provide a more coherent picture regarding the fundamental parameters of this important emerging ultra-wide bandgap semiconductor.