High-temperature thermal annealing of nonpolar (1 0 1¯ 0) AlN layers sputtered on (1 0 1¯ 0) sapphire

Thermal annealing at high temperatures of nonpolar (1 0 1¯ 0) m-plane AlN layers directly sputtered on m-plane sapphire was investigated. The crystallinity of the layers increased with increasing annealing temperature. The full-width at half maximum of the symmetric (1 0 1¯ 0) X-ray rocking curves along [0 0 0 1]/[1 1 2¯0]AlN decreased from about 3.5/2.0° to 0.24/0.19°. The density of basal stacking faults of the annealed layers was found to decrease from ∼1 × 105 to ∼5 × 103 cm−1. The annealed layers had a larger optical bandgap energy than the as-sputtered layers due to their better crystallinity and structural order.