Determination of the optical band-gap energy of cubic and hexagonal boron nitride using luminescence excitation spectroscopy

Abstract

Using synchrotron-based luminescence excitation spectroscopy in the energy range 4-20 eV at 8 K, the indirect-X optical band-gap transition in cubic boron nitride is determined as 6.36 ± 0.03 eV, and the quasi-direct band-gap energy of hexagonal boron nitride is determined as 5.96 ± 0.04 eV. The composition and structure of the materials are self-consistently established by optically detected x-ray absorption spectroscopy, and both x-ray diffraction and Raman measurements on the same samples give independent confirmation of their chemical and structural purity: together, the results are therefore considered as providing definitive measurements of the optical band-gap energies of the two materials.

Tetrahedral amorphous boron nitride: A hard material

“…Here by calculating total and partial electron density of states (given in Figure ), we reveal the electronic structure of tetrahedral amorphous BN and compare it with that of c‐BN. The forbidden energy band gap of c‐BN is projected to be ~4.85 eV that is, as expected, smaller than the experimental data of about 6.0‐6.4 eV due to the limitation of DFT‐GGA calculations. For the noncrystalline network, the estimated forbidden band gap is ~2.0 eV.…”

Resonant x-ray emission of hexagonal boron nitride

“…Including the approximate GW band-gap correction from the ordered cell gives 5.9(2) eV which compares well with a recent measurement which estimated the single-particle band gap to be 6.08 eV [3], albeit with significant uncertainties in our calculation. Previous optical measurements estimated single-particle gaps of 5.96 eV and 5.971 eV [50, 51]. However, photo-current measurements point to a larger 6.42 eV gap [4], and are consistent with valence BSE calculations that suggested an excitonic binding of 0.7 eV [52], significantly stronger than the values determined in the aforementioned optical measurements.…”

Theory of Oxygen-Boron Vacancy Defect in Cubic Boron Nitride: A DiamondNV−Isoelectronic Center

“…Figure 2 compares the electronic structures of an NV − and an O N −V B center calculated using the HSE06 functional with a 216-atom supercell. The calculated band gap is about 6.0 eV for c-BN within the HSE06 functional, this compares well with the recently measured value of 6.4 eV [22] for the minimum gap of c-BN. Similar to the NV − center in diamond, the O N −V B center also introduces optically active defect states, i.e., occupied a 1 and unoccupied e minority-spin states (shown in blue in the figure), deep inside the band gap, thereby enabling optical probe and/or control of the defect states.…”