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Nitride Semiconductors for Ultraviolet Detection.
Semiannual technical rept. for 1 Jul 94-31 Dec 94,
NORTH CAROLINA STATE UNIV AT RALEIGH
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Monocrystalline, undoped, high resistivity GaN thin films have been grown on 6H-SiC0001 wafers via organometallic vapor phase epitaxy OMVPE employing a high-temperature monocrystalline AlN buffer layer using a cold-wall, vertical pancake-style reactor with triethylgallium TEG, triethylaluminum TEA and ammonia. The surface morphologies of films deposited on both vicinal and on-axis, Si- and C-polar planes of SiC0001 are described. Controlled n-type Si-doping in GaN has been achieved with carrier concentrations from 10exp 17 to 10exp 20 cu cm. SEM and TEM of the latter films revealed high microstructural quality Photoluminescence PL of the undoped GaN revealed a sharp donor-bound exciton peak at 357.2 nm with a FWHM of 4 meV. The defect peaks in these samples were very weak. The Si-doped GaN exhibited a strong PL emission at 358 nm due to donor-to-valence band transitions. Mg-doped GaN emitted strong blue light with a peak wavelength of 426 nm. Cathodoluminescence measurements of AlxGa1-xN were also successful, with strong emission at the band-edge. An ammonia cracker cell, has also been designed and installed in the gas source MBE to replace the ECR plasma source to minimize film damage and to enhance film quality and growth rate. Low resistivity Al, Cu3Ge, and TiN ohmic contacts have been achieved on Si-doped, n-type GaN. Au and a AuMgAu layered structure exhibited ohmic behavior on p-GaN when annealed at high temperature or in the as-deposited condition, respectively. As-deposited Pt formed ohmic contacts to MgGaN. Microstructural characterization of the Aln-GaN and Aup-GaN contact systems revealed that interfacial reactions occurred during annealing and markedly affected contact performance.
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