Dislocation reduction in gallium nitride films using scandium nitride interlayers

We describe a method of reducing threading dislocation densities in 0001-oriented GaN from (5.0 +/- 0.5)x10(9) cm(-2) to (3.1 +/- 0.4)x10(7) cm(-2) (for coalesced films) or to below 5x10(6) cm(-2) (for partially coalesced films) in a single step, without lithography. Lattice-matched, dislocation-blocking scandium nitride interlayers are deposited on a 500 nm GaN-on-sapphire template. Dislocation-free GaN islands grown on the ScN interlayer nucleate both on the interlayer and on tiny areas of the GaN template exposed through openings in the interlayer. However, some dislocations are generated above the interlayer during subsequent island coalescence.