Growth and probing the band-to-impurity transitions in oxygen-doped h-BN

Intentionally oxygen-doped hexagonal boron nitride (h-BN) thick epilayers have been produced using hydride vapor phase epitaxy (HVPE). Oxygen doping significantly enhanced the crystalline quality of h-BN, likely due to the reduced nitrogen vacancies by substitutional oxygen donors. By eliminating carbon impurity emission lines through HVPE growth, the origin of the commonly observed, yet poorly understood, emission lines in the 5.3–5.5 eV spectral region in h-BN can be definitively attributed to the recombination between electrons bound to substitutional oxygen donors on nitrogen sites (ON) and free holes in the valence band, along with phonon replicas involving K-point phonons via a strong hole–phonon interaction, a result of its indirect energy bandgap nature. Unlike the generally “dark” band-to-band and excitonic transitions in perfect h-BN, the zero-phonon line of the oxygen donor-related band-to-impurity transition prominently contributes to the emission intensity due to the deep-level nature of oxygen donors. This study resolves the long-standing question of the physical origin of the 5.3 eV emission line in h-BN, providing a more comprehensive understanding of common impurities/defects in h-BN, which is vital for monitoring and continuously improving the material quality and purity of h-BN, paving the way for future applications of this emerging ultrawide bandgap (UWBG) semiconductor.