Bandgap in Al1-xScxN

Aluminum scandium nitride (Al1-xScxN) layers deposited by reactive magnetron co-sputtering on sapphire 0001 substrates at 850 degrees C are epitaxial single-crystals for x <= 0.20. Their in-plane lattice constant increases linearly (3.111 + 0.744x angstrom) while the out-of-plane constant remains at 4.989 + 0.005 angstrom. 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. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795784]