Phase transition and bandgap engineering in B_1-xAl_xN alloys: DFT calculations and experiments

BAlN is a promising ultrawide bandgap semiconductor, but systematic studies of its bandgap are scarce. Here, bandgap engineering of BAlN containing the phase transition factor (from hexagonal to wurtzite structures) has been investigated by DFT calculations and verified experimentally. The calculated bandgap bowing parameter of hexagonal BAlN (h-BAlN) is 2.29 eV, while the bandgap bowing parameters of wurtzite BAlN (w-BAlN) are −4.09 eV and 2.48 eV in the B-rich and Al-rich regions, respectively. Meanwhile, calculations indicate that BAlN preferentially forms w-BAlN at Al composition above 18.7%. So, the bandgap variation of BAlN is divided into three regions based on Al composition: h-BAlN (0–18.7%), B-rich w-BAlN (18.7%–50%), Al-rich w-BAlN (50%–1), and each has its own trend. Experimentally, h-BAlN and w-BAlN films were prepared by magnetron co-sputtering technique and the phase transition was observed in X-ray diffraction (XRD) patterns. h-BAlN shows a typical triangular morphology and the Raman and XRD peaks are located at 1371 cm⁻¹ and 44.3°, tending to (1 0 1) h-BN. w-BAlN has a “needle-felt” surface with Raman and XRD peaks at 656 cm⁻¹ and 35.9°, tending to (0 0 2) w-AlN. The experimental bandgap variation of BAlN shows a “W” shape, which can be well explained by the calculation results.