Bandgap in Al1−xScxN

Abstract

Aluminum scandium nitride (Al_1−xSc_xN) layers deposited by reactive magnetron co-sputtering on sapphire 0001 substrates at 850 °C are epitaxial single-crystals for x ≤ 0.20. Their in-plane lattice constant increases linearly (3.111 + 0.744x Å) while the out-of-plane constant remains at 4.989 ± 0.005 Å. Optical absorption indicates a band gap of 6.15–9.32x eV and a linearly increasing density of defect states within the gap. The average bond angle decreases linearly with x, suggesting a trend towards the metastable hexagonal-ScN structure. However, an anomalous decrease at x = 0.20 indicates a structural instability which ultimately leads to phase separated rock-salt ScN grains for x > 0.4.