Seeded PVT Growth of Aluminum Nitride on Silicon Carbide

Seeded bulk crystal growth of AlN was conducted by physical vapor transport (PVT) using AlN powder as a starting material. SiC substrates with different crystallographic orientation were used as seeds. Materials compatibility was investigated; temperatures higher than 2000DGC lead to decomposition of the SiC seed and to degradation of the tungsten heaters. Hexagonal hillocks grow on c-plane SiC seeds leading to growth instabilities and layer quality deterioration, whereas for growth on a-plane seeds millimeter-sized a-oriented areas were obtained showing a smooth morphology typical for step-flow growth mode. A comparison of the natural growth habits of freely nucleated SiC platelets and prismatic elongated AlN can explain this behavior. The best crystal quality was obtained by employing slightly off-oriented a-plane SiC wafers at growth temperatures below 2000DGC, but growth rate and surface diffusion necessary for step-flow growth remain insufficient.