Freestanding Highly Crystalline Single Crystal AlN Substrates Grown by a Novel Closed Sublimation Method

We fabricated thick freestanding AlN films by a novel close-spaced sublimation method. The spacing between a sintered AlN polycrystal and a SiC substrate is 1 mm. A Ta ring was used to control the spacing between the AlN polycrystal and the SiC substrate. In addition, a special AlN adhesive was also used to fill in the gap between the AlN polycrystal, the Ta ring, and the SiC substrate. By a combination of these techniques, an AlN growth rate as high as 600 µm/h was achieved. A freestanding AlN layer was obtained by the sublimation of the SiC substrate during the AlN growth.