Freestanding AlN single crystals enabled by self-organization of 2H-SiC pyramids on 4H-SiC substrates

A sublimation-recondensation process is presented for high quality AlN (0001) crystals at a high growth rate by employing 4H-SiC substrates with a predeposited epilayer. It is based on the coalescence of well oriented AlN microrods, which evolve from the apex of 2H-SiC pyramids grown out of hexagonal pits formed by thermal etching of the substrate during a temperature ramp up. This process yields stress-free 120-mu m-thick AlN single crystals with a dislocation density as low as 2x10(6) cm(-2).