New technique for sublimation growth of AlN single crystals

Single crystalline platelets of aluminum nitride (AIN) were successfully grown by a new technique. It consists of (1) depositing an AIN buffer layer on a SiC substrate by metal organic chemical vapor deposition (MOCVD) below 1100°C, (2) forming an (AIN)_x(SiC)_1-x alloy film on the AIN film by condensing vapors sublimated at a temperature of 1800°C from a source mixture of AIN-SiC powders, followed by (3) condensing vapors sublimated from a pure AIN source (at 1800°C). The necessity of the first two steps for the successful AIN sublimation growth on SiC substrate was illustrated by the initial nucleation studies of alloys on SiC substrates with and without MOCVD AIN buffer layers: an AIN MOCVD buffer layer leads to continuous, single grain growth mode; The (AIN)_x(SiC)_1-x alloy film reduces the crack density because its thermal expansion coefficient is intermediate between SiC and AIN. X-ray diffraction (XRD) and Raman spectroscopy studies indicated the high quality of the AIN single crystal.