Growth of low defect density gallium nitride (GaN) films on novel tantalum carbide (TaC) substrates for improved device performance

Original publisher: Adelphi, MD : Army Research Laboratory, [2009] OCLC Number: (OCoLC)422549730 Subject: Gallium nitride. Excerpt: ... ( a ) ( b ) ( d ) ( c ) Figure 3. SEM micrographs of TaC films ( a ) as-deposited at 800 ° C, ( b ) deposited at 800 ° C and annealed at 1200 ° C, ( c ) deposited at 800 ° C and annealed at 1600 ° C, and ( d ) deposited 1000 ° C and annealed at 1600 ° C. The SEM micrographs in figure 4 for a TaC film deposited on an on-axis substrate at 1000 ° C show that the film that looks relatively smooth at low magnification ( figure 3a ) has a distinct grain structure at higher magnification and the grains have a diameter of ~ 200 nm ( figure 4a ). Also, as shown in figure 4b, there were a few regions with ~ 200 nm diameter micropores, but there were very few of them showing that the coverage was very good. The as-deposited and annealed films looked qualitatively the same, but the grain structure was more distinct in the annealed films, suggesting that recrystallization occurs during the anneal. Also, the morphology of films grown off-axis was similar to those grown on-axis. 7