Growth of gallium nitride (GaN) on strain relaxed nanoporous GaN template by metal-organic chemical vapor deposition has produced GaN layer with 60% reduction in threading dislocation density (TDD). The porous GaN was annealed at 850°C for 3min in a mixed of nitrogen and ammonia ambient, which annihilated most TDs within the porous region via air-gap formation coupled with surface edge step pinning of dislocations. Enhancement of optical quality was indicated by doubled Raman intensity of E2 phonon peak of annealed porous as compared to as-fabricated porous GaN. Besides, a redshift of 0.7cm−1 in E2 phonon peak of porous GaN with respect to as-grown GaN corresponds to a relaxation of compressive stress by 0.17±0.05GPa. Further overgrowth of GaN on annealed porous GaN template gives high quality GaN with reduction in TDD.

Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nanoscale pores of size 20–50nm in the underlying grains. The effect of GaN buffer layer grown at various temperatures from 650to1015°C on these as-fabricated nanopores templates is investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850°C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however, not observed for the samples grown with other temperature buffer layers. Micro-Raman measurements show significant strain relaxation and improvement in the crystal quality of the overgrown GaN layer on nanoporous GaN template as compared to overgrown on conventional GaN template.

High density porous GaN has been fabricated by UV-enhanced electrochemical etching on Si-doped GaN layer grown by metallorganic chemical vapor deposition. A redshift from 0.7 to 567.7 cm −1 in the E 2 ͑high͒ phonon peak of GaN was observed in this porous GaN with respect to as-grown GaN. As the phonon peak of a stress-free GaN is observed at 567.5 cm −1 , it means that the fabricated porous GaN is almost stress free. GaN overgrown on this porous template showed nearly doubled photoluminescence intensity as compared to that overgrown on as-grown GaN, with average surface roughness which differs only by 0.04 nm for the same thickness. This method is simple and inexpensive even for large area porous GaN fabrication and is useful for template of GaN and its alloys growth.