Growth of Low Defect Density Gallium Nitride (GaN) Films on Novel Tantalum Carbide (TaC) Substrates for Improved Device Performance

Report No. ARL-TR-4818
Authors: M. A. Derenge, K. A. Jones, K. W. Kirchner, T. S. Zheleva, and R. D. Vispute
Date/Pages: May 2009; 34 pages
Abstract: 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 ~1000 ¿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 ¿C for 30 min. We also deposited GaN films onto the TaC after it had been nitrided with NH3 for 3 min at 1100 ¿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 ~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 109 cm-2. However, the grains lacked the required (0001) texture, producing a very rough surface.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2009