Defect-selective etching of bulk AlN single crystals in molten KOH/NaOH eutectic alloy

摘要

The effectiveness and reliability of estimating the dislocation density in GaN thin films and bulk crystals by defect selective etching in eutectic KOH/NaOH have already been successfully demonstrated. In this communication, we report the results of applying this technique to bulk AlN crystals. Etching produced hexagonal pits on the Al-polar (0001) plane, while hexagonal hillocks formed on the nitrogen face. According to synchrotron white beam X-ray topography (SWBXT) calibration, we believed that the etching pits at Al polarity form primarily at dislocations. The optimized etching temperature for Al-polarity is in the range of 350-380℃, which is typically 50-100℃ higher than that for nitrogen polarity, indicating higher stability of Al-polarity. For Al-polarity AlN single crystals grown on Si-face 6H-SiC (0001) substrates, the dislocation density is about 10~7 cm~(-2) and for self-seeded crystals, the dislocation densities for Al-polarity and the hillock densities for N-polarity are both on the order of 10~3 cm~(-2). As far as the dislocation density is concerned, self-seeded crystals have a better quality than crystals grown on Si-face 6H-SiC (0001) substrates.