Porous GaN subjected to heat treatment under in situ MOCVD chamber annealing at 850C for 3 minutes exhibited significant annihilation of threading dislocations and improvement in its optical quality. A similar phenomenon was not observed for porous GaN samples annealed at lower temperatures. The annealing was done in a mixed of N2 and NH3 ambient, which resulted in air-gap formation. Encounter of threading dislocations with the air-gap could cause them to bend horizontally and annihilate each other. Dark-field cross-section transmission electron microscopy image confirms the annihilation of threading dislocations within the porous/air-gap region. This dislocation density reduction causes a significant enhancement of the optical quality as shown by doubled Raman intensity of E2 phonon peak after the annealing as compared to the as-fabricated porous GaN. Because the fabricated porous GaN samples were already relaxed, no further strain relaxation was observed after annealing. Such a template was suitable for use in high quality GaN growth.

Annihilation of Threading Dislocations in Strain Relaxed Nano-Porous GaN Template for High Quality GaN Growth. H.Hartono, C.B.Soh, S.J.Chua, E.A.Fitzgerald: Physica Status Solidi C, 2007, 4[7], 2572-5