Selected energy epitaxial deposition and low energy electron microscopy of AlN, GaN and SiC thin films. Quarterly report, 1 April--30 June 1998
Epitaxial AlN films were grown on as-received and hydrogen etched 6H-SiC(0001) substrates using an ammonia supersonic seeded beam. The films on the latter substrates exhibited a higher degree of order. Cross-sectional electron microscopy revealed sharper SiC-AlN interfaces with extended flat terraces. The few stacking mismatch boundaries originated from the 1.5 nm steps corresponding to the 6H stacking sequence. In situ LEEM/LEED studies were conducted on GaN homoepitaxial growth on MOCVD GaN substrates by plasma-assisted gas-source MBE. After 6 hours of growth at 660 C, LEEM images showed a GaN layer with a hexagonal parquet structure and a large number of dark spots on the surface. Ex situ AFM studies revealed that the former was a result of spiral growth and the latter were due to surface pits of hexagonal shape. In situ cleaning of MOCVD-grown GaN/AlN/6H-SiC substrates using NH{sub 3}-seeded supersonic molecular beams was investigated. Complete oxygen removal was achieved by heating in vacuum at 730 C. Surface carbon concentrations of {minus}3%, as evidenced by XPS, were achieved by heating at 730 C under a hyperthermal NH{sub 3} flux. Modifications have been made to the SEE system to provide a cleaner vacuum ambient and are detailed in this report A new substrate holder was fabricated that uses Mo clips and a polished Mo block to ensure good thermal contact without Ag paste. Outgassing of the colloidal Ag paste is believed to be one source of carbon contamination at high temperatures. The design of the N plasma source and testing chamber is also reported.
- Research Organization:
- North Carolina State Univ., Raleigh, NC (United States)
- OSTI ID:
- 676180
- Report Number(s):
- AD-A-353949/XAB; CNN: Contract NOOO14-95-1-0122; TRN: 83280073
- Resource Relation:
- Other Information: PBD: Jun 1998
- Country of Publication:
- United States
- Language:
- English
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