Sublimation growth of 2 inch diameter bulk AlN crystals

摘要

The technology of sublimation growth of 15 mm diameter bulk single AlN crystals is scaled to grow similar 2-inch diameter crystals. The best results are currently achieved with the two-stage technique including 1) seeding and initial growth of 2-3 mm thick single-crystal AlN layers on 2-inch diameter 6H-SiC wafers in pre-carbonized Ta crucibles in graphite equipment and 2) growth of bulk AlN crystals on the above AlN layers in tungsten crucibles and equipment. Therninitial AlN layers prove of good crystallographic quality but may contain up to 6 at.% of Si impurities. The eventual bulk AlN crystals consist of about 40 mm diameter round single-crystal core and polycrystalline rim. No impurities in concentration higher than 0.01 at.% are found in the bulk crystals. The bulk AlN crystal may be separated from the initial AlN layer to use the latter repeatedly for growth of a new crystal. Such "secondary" crystals were found to be semi-insulating.