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Accession Number:
ADA331740
Title:
Defects and Impurities in 4H- and 6H-SiC Homoepitaxial Layers: Identification, Origin, Effect on Properties of Ohmic Contacts and Insulating Layers and Reduction
Descriptive Note:
Quarterly technical rept. 1 Jul-30 Sep 97
Corporate Author:
NORTH CAROLINA STATE UNIV AT RALEIGH DEPT OF MATERIALS SCIENCE AND ENGINEERING
Report Date:
1997-09-01
Pagination or Media Count:
40.0
Abstract:
Aluminum nitride AlN thin films with very smooth surfaces have been grown by gas-source molecular beam epitaxy on 4H- and 6H-SiC substrates. Streaked reflection high energy electron diffraction patterns and reconstructions of the AlN surfaces indicated smooth films. Atomic force microscopy AFM and transmission electron microscopy TEM showed root mean square values less than or equal 1 nm and very flat surfaces, respectively. X-ray diffraction showed the films to be highly c-axis oriented and single phase. Major impurities in the AlN films were oxygen and carbon, as revealed by secondary ion mass spectrometry. A correlation has been found between the types and the distributions of the dominant defects, namely, micropipes and screw dislocations using optical microscopy, scanning electron microscopy, AFM, synchrotron white beam x-ray topography, and electron beam induced current EBIC studies. A ridge-type structure of the core of the micropipes, related to the growth front flow direction was observed with AFM. Triangular micro inclusions associated with the cubic 3C-SiC polytype beta-SiC were detected. EBIC studies revealed various types of electrically active defect regions, related to the beta-SiC phase and randomly distributed within the wafers and across different Shottky diodes. X-ray photoelectron spectroscopy, Auger electron spectroscopy AES, low energy electron diffraction LEED, and temperature programmed desorption TPD revealed that exposure of 6H-SiC to atomic hydrogen selectively removes Si from the surface and converts the 3x3 surface to a 1x1 surface. Additional etching of this surface was indicated by the reduction in the Si LVVC KLL ratio in AES from 1.3 to 0.4 following exposure of 3x3 surfaces to a remote rf H plasma.
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
