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 sapphire substrate was developed. By heat treatment at 1450 ℃ in a gas flow containing H2 and NH3, many voids could be formed at the interface between a thin (100 nm) AlN layer grown at 1065 ℃ 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 surface, a dislocation density of 1.1× 109 cm-2, and an optical transparency for wavelengths above 208.1 nm.

Single‐crystal layers of AlN have been grown on sapphire substrates between 1000 and 1100 °C by vapor‐phase reaction of aluminum chlorides with ammonia. The purity, color, crystallinity, growth morphology, and electrical resistivity of the epitaxial layers have been investigated. Infrared specular reflection measurements showed the presence of an appreciable strain at the AlN‐sapphire epitaxy interface. Optical absorption data strongly suggest the AlN is a direct band‐gap material with a value of about 6.2 eV at room temperature.


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