Probing room temperature indirect and minimum direct band gaps of h-BN

Abstract

Hexagonal boron nitride (h-BN) has attracted considerable interest as an ultrawide bandgap (UWBG) semiconductor. Experimental studies focused on the detailed near band-edge structure of h-BN at room temperature are still lacking. We report a direct experimental measurement of the near band-edge structure performed on h-BN quasi-bulk wafers via photocurrent excitation spectroscopy (PES). PES resolved the band-to-band transitions near M- and K-points in the Brillion zone (BZ), from which the room temperature indirect band gap of ${E}_{g}^{MK}$ ∼6.02 eV, minimum direct bandgap at M-point of ${E}_{g}^{M}=6.36\,{\rm{eV}}$ and next lowest direct energy bandgap at K-point of ${E}_{g}^{K}=6.56\,{\rm{eV}},$ have been simultaneously determined for the first time experimentally. The measured energy differences between K- and M-points in the conduction band minimum (CBM) and valence band maximum (VBM) are Δ ${E}_{C}^{MK}=0.54\,{\rm{eV}}$ and Δ ${E}_{V}^{MK}$ = 0.34 eV, respectively, in good agreement with the calculation results. Significantly differing from its III-nitride wurtzite counterparts, in which only electrons and holes in the conduction and valence band extremes at the Γ-point are predominantly involved in the optical and transport processes, the results highlighted that charge carriers associated with both M- and K-valleys control to the optical excitation, recombination and charge transport processes in h-BN.

Keywords

• ultrawide bandgap semiconductors
• h-BN
• band-edge structure
• HVPE growth
• quasi-bulk crystals of h-BN