Growth of Low Defect Density Gallium Nitride (GaN) Films on Novel Tantalum Carbide (TaC) Substrates for Improved Device Performance
ARMY RESEARCH LAB ADELPHI MD SENSORS AND ELECTRON DEVICES DIRECTORATE
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To potentially improve device performance, we attempted to grow gallium nitride GaN films with better crystalline quality fewer mismatch dislocations using a tantalum carbide TaC substrate, which is more closely lattice matched to GaN than currently used substrates. We created the TaC substrate, using pulse laser deposition PLD of TaC onto 0001 SiC substrates at tilde 1000 deg C, and grew GaN films, using metal organic chemical vapor deposition MOCVD. Using x-ray diffraction, we determined the TaC films grown on-axis were higher quality than the off-axis films, but the latter could be improved to a comparable quality by annealing at 1200-1600 deg C for 30 min. We also deposited GaN films onto the TaC after it had been nitrided with NH3 for 3 min at 1100 deg C and used aluminum nitride AlN as a low temperature nucleation layer. Using these methods, the crystalline quality of the GaN films was higher - the grains were tilde 10 times larger than those typically seen in films grown on SiC or sapphire, and they contained more than an order of magnitude fewer dislocations compared to a typical value of 4 x 10exp 9 sq cm. However, the grains lacked the required 0001 texture, producing a very rough surface.
- Inorganic Chemistry
- Laminates and Composite Materials
- Nuclear Physics and Elementary Particle Physics