Investigation of void formation mechanism beneath thin AlN layers grown on foreign substrates

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Thin AlN layers were grown on sapphire and SiC substrates with various orientations at 1065℃by hydride vapor phase epitaxy. Then, heat-treatment of the substrates was performed in NH_3 added H_2 flow up to 1450℃. It was found that hydrogen diffuses through the thin AlN layer to the interface via dislocations and reacts with the substrate, which yields voids beneath the thin AlN layer. Self-separation of thick AlN layers, subsequently grown at 1450℃after the void formation, occurred during post-growth cooling when segment ratio of voids at interface was about 50%