Porous GaN subjected to heat treatment under in situ MOCVD chamber annealing at 850C for 3 minutes has shown significant annihilation of threading dislocations and improvement of its optical quality. Similar phenomenon was not observed for the 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 might cause them to bend horizontally and annihilate each other. Dark-field cross-section transmission electron microscopic images confirms the annihilation of threading dislocations within the porous/air-gap region. This dislocation density reduction caused 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