Alloying hBN with aluminum influences absorption and electronic properties

The versatile range of applications for two-dimensional (2D) materials has encouraged scientists to engineer their properties. This is often accomplished by stacking atomically thin layered materials into complex van der Waals heterostructures. A less popular but technologically promising approach is alloying 2D materials. In this work, we demonstrate a first step towards tuning the intrinsic electronic properties of hexagonal boron nitride (hBN). We present a series of aluminum alloyed hexagonal boron nitride (hBAlN) samples grown by metal organic vapor phase epitaxy on 2-inch sapphire substrates with varying aluminum concentration. Importantly, the obtained samples revealed a sp²-bonded crystal structure and modifications in interband optical transitions. Optical absorption experiments disclosed two prominent peaks in the excitonic spectral range with absorption coefficients ~ 10⁶ cm^- 1. Their peak energies align closely with the energies of indirect and direct bandgap transitions in hBN. The presence of two absorption peaks can be attributed to mixing of electronic states in the K and M conduction band valleys, resulting in a substantial increase in the absorption coefficient for indirect transitions. The observed effects offer insights into hBN-based two-dimensional alloys, highlighting the potential for developing 2D material-based quantum well structures capable of operating in the challenging deep UV spectral range.