Growth of Single Crystals and Fabrication of GaN and AlN Wafers

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, oatherina and maintainina the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this gathering and maintaining the data needed, and completing and reviewing collection of information, including suggestions for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget Paperwork Reduction Project (0704-0188), Washington, DC 20503, REPORT TYPE AND DATES COVERED 1. AGENCY USE ONLY (Leave blank)2. REPORT DATE July, 2000Semiannual: 1/1/00 -6/30/00 TITLE AND SUBTITLE Growth of Single Crystals and Fabrication of GaN and A1N Wafers AUTHOR(S)Z. Sitar, R. F. Davis PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)North Carolina State University Hillsborough Street Raleigh, NC 27695 GaN and A1N single crystals were grown from the vapor phase by evaporation of gallium or aluminum metals under an ammonia or nitrogen flow in a high temperature reactor. A growth rate of 500 |im/hr in the c direction was achieved for GaN while the growth rates for A1N were as high as a few millimeters per hour. The crystal size reached 3 mm for GaN and up to 15 mm for A1N. For both materials, the crystal aspect ratio (c/a) could be controlled by temperature and partial pressure of reactants. The resulting crystals were transparent and of excellent crystalline quality, as confirmed by x-ray diffraction, Raman scattering, and transmission electron microscopy studies. Photoluminescence studies on GaN conducted at 77 K showed a sharp emission peak centered at 359 nm. Time dependent photoluminescence measurements revealed optical metastability in bulk GaN. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS(ES)Sponsoring SUBJECT TERMSGaN, A1N, bulk crystal growth, growth from vapor phase, photoluminescence, optical absorption, Raman, SIMS. growth runs were performed using Al metal and nitrogen gas, and yielded high-quality A1N crystals of up to 1 cm size. A complete study of the relevant growth parameters is currently in progress; initial results on the influence of temperature on crystal size, morphology and quality will be reported below. EquipmentThe growth reactor consists of a vacuum chamber containing a 2.25" diameter reaction tube made of hot-pressed BN. The reaction tube is heated by a cylindrical, resistive graphite heater (6.5" long) capable of heating the reaction zone up to 2400°C (-12 kW electrical power). The heater assembly is encapsulated in a hot-pressed BN cylinder (wall thickness 0.25"). Porous graphite heat insulation separates the heater assembly from the water-cooled walls of the vacuum chamber. A schematic cross-section of the reactor is shown in Fig A set of mass-flow controllers allows accurate contr...