Growth of bulk AlN crystals by vaporization of aluminum in a nitrogen atmosphere

AlN single crystals were grown by vaporization of aluminum in a nitrogen atmosphere. The growth temperature was found to critically influence the crystal morphology, while nitrogen pressure and flow rate had no considerable influence on the growth process. Crystals were grown under quasi-stagnant conditions (nitrogen flow of 100 seem) at a reactor pressure of 500 Torr. At relatively low temperatures (1800-1900degreesC), AlN needles were grown at rates up to 10 mm/h along the e-axis. Twinned platelets were observed in a temperature range of 1900-2100degreesC. At temperatures above 2100degreesC, AlN c-plates (up to 50mm(2)) were grown by spontaneous nucleation within 2h. Extraordinarily large growth rates of 5 mm/h in the c-plane and 0.2 mm/h along the c-axis were observed. SEM pictures revealed step-flow growth on the c-plane surfaces. Raman spectroscopy indicated a drastic improvement in the crystal quality with growth temperature. (C) 2002 Elsevier Science B.V. All rights reserved.