Controlled MOVPE growth of sp2-bonded BAlN alloys: Influence of precursor injection schemes on crystal structure and optical properties

Hexagonal boron nitride (hBN) is a promising wide-bandgap layered semiconductor for deep ultraviolet (DUV) optoelectronics, yet the lack of efficient bandgap engineering strategies has hindered its implementation in quantum well structures. In this work, we report the controlled growth of sp 2 -bonded boron aluminum nitride (hB 1-x Al x N) alloys on sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) and present a systematic investigation of how precursors injection schemes influence alloy formation. Two distinct growth protocols: continuous flow growth (CFG) and flow modulation epitaxy (FME) were systematically compared to reveal their impact on crystal structure, morphology, aluminum incorporation, and optical response. CFG invariably led to the formation of misoriented, porous flakes, whereas FME enabled continuous layered growth with preserved crystallinity. By varying the precursor pulsing sequence in FME, we achieved an Al incorporation up to x =0.66% and observed pronounced differences in strain distribution, defect density, and absorption characteristics. The results revealed that simultaneous pulsing of TEB and TMAl, rather than their separation, enables more efficient aluminum incorporation while preserving the sp²-bonded layered structure, as confirmed by Fourier-transform infrared spectroscopy. Absorption measurements further showed that even low Al contents modify excitonic transitions near the band edge and influence the polytype of the material. Altogether, these results highlight a new pathway for compositional tuning in layered nitrides through precise control of co-injected precursors, demonstrating the crucial role of injection protocols in governing both structural integrity and optical performance of hB 1-x Al x N in the DUV spectral range. • Controlled MOVPE enables sp 2 -bonded BAlN growth on sapphire substrates • Flow modulation epitaxy improves layer continuity and crystallinity • Precursor injection sequence governs Al incorporation, optical, structural properties • Aluminum alters excitonic absorption in BAlN • Study provides guidelines for bandgap tuning in layered nitride alloys