Self-Separation of a Thick AlN Layer from a Sapphire Substrate via Interfacial Voids Formed by the Decomposition of Sapphire

A technique for separating a thick AlN layer grown by hydride vapor phase epitaxy (HVPE) on a (0001) sapphire substrate was developed. By heat treatment at 1450 °C in a gas flow containing H 2 and NH 3 , many voids could be formed at the interface between a thin (100 nm) AlN layer grown at 1065 °C and the sapphire substrate due to the preferential decomposition of sapphire. During the cooling process after the subsequent growth of a thick (85 µm) AlN layer, the thick AlN layer separated from the sapphire substrate with the aid of the interfacial voids. The freestanding AlN substrate thus obtained had a smooth (0001) surface, a dislocation density of 1.1 × 10 9 cm -2 , and an optical transparency for wavelengths above 208.1 nm.