Defect reduction processes in heteroepitaxial non-polar a-plane GaN films

The growth of nonpolar a-plane GaN on r-plane sapphire by metalorganic vapor-phase epitaxy has been investigated using a low-temperature nucleation layer (LT-NL) and using direct growth without a LT-NL. The dislocation densities in a-plane GaN films can be reduced significantly from (6.2±0.3)×1010 cm−2 to (2.1±0.3)×109 cm−2 using direct growth. The dislocation densities can also be reduced from (6.2±0.3)×1010 cm−2 to (2.1±0.3)×109 cm−2 by introducing a SiNx interlayer into the film grown with a LT-NL. However, introducing a similar SiNx interlayer into the film grown without a LT-NL produces no further dislocation reduction. Both the SiNx interlayers and the growth without a LT-NL reduce the dislocation density through the formation of islands, which promote dislocation bending and annihilation.

► Dislocation densities in a-plane GaN are reduced by SiNx IL and/or direct growth.
► Reduction is achieved by the TD bending during island growth in both techs.
► Bent dislocations terminate at the void, annihilate one another or ‘bunch’ together.