Research Related to the Development, Fabrication and Characterization of UV Detectors and Cold Cathode Devices
Annual technical rept. 1 Jan-31 Dec 98
NORTH CAROLINA STATE UNIV AT RALEIGH DEPT OF MATERIALS SCIENCE AND ENGINEERING
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Pendeo-epitaxial growth of GaN films has been investigated as a function of growth temperature on etched, elongated GaN seed columns grown on AlN6H-SiC 0001 substrates via metalorganic vapor phase epitaxy MOVPE. Silicon nitride mask layers atop the GaN seed columns forced growth from the sidewalls of the columns. Higher growth temperatures resulted in improved coalescence due to greater lateral-to-vertical growth ratios. Thin films of AlN and GaN were also deposited via conventional approaches on alpha6H-SiC0001 wafers using H2 and N2 diluents. A computational fluid dynamic model of the deposition process was used to analyze the film growth conditions for both diluents. Low temperature 12 K photoluminescence of the GaN films grown in N2 had peak intensities and full widths at half maximum of 7 meV which were equal to or better than those films grown in H2. Cross-sectional and plan view transmission electron microscopy of GaN films grown in both diluents showed similar microstructures with a typical dislocation density of 10exp 9cm2. Hall measurements of n-type Si doped GaN grown in N2 revealed Hall mobilities equivalent to those films grown in H2. Acceptor-type behavior of Mg-doped GaN grown in N2 was repeatedly obtained without post-growth annealing. Secondary ion mass spectrometry revealed equivalent levels of H in Mg-doped GaN films grown in both diluents. The electrical properties of NiAu contacts on p-type, Mg-doped GaN films have been characterized using current-voltage measurements. Prior to the metallization, films with net ionized impurity concentrations of approximately 7x10exp 17cm3 and 2x10exp 17cm3 were heated to 990 deg C and 800 deg C, respectively, and subsequently exposed to a 300 W atomic nitrogen plasma for 10 minutes. The contacts treated at 990 deg C yielded the lowest specific contact resistivity, which was 50 - 7 omega.cm2.
- Ultraviolet Detection and Detectors
- Solid State Physics