C. B. Soh

Reduction of threading dislocation density in GaN grown on strain relaxed nanoporous GaN template

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.

Dislocation annihilation in regrown GaN on nanoporous GaN template with optimization of buffer layer growth

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 Quality GaN Grown from a Nanoporous 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 (high) 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.

Auger recombination as the dominant recombination process in indium nitride at low temperatures during steady-state photoluminescence

Auger recombination in InN films grown by metal-organic chemical vapor deposition was studied by steady-state photoluminescence at different laser excitation powers and sample temperatures. It was dominant over radiative recombination and Shockley-Read-Hall recombination at low temperatures, contributing to the sub-linear relationship between the integrated photoluminescence intensity and laser excitation power. Auger recombination rates increased gradually with temperature with an activation energy of 10–17u2009meV, in good agreement with values from transient photoluminescence reported in literature. As the Auger recombination rates were independent of material quality, they may form an upper limit to the luminous efficiency of InN.

Annihilation of Threading Dislocations in Regrown GaN on Electrochemically Etched Nanoporous GaN Template with Optimization of Buffer Layer Growth

Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nano-scale pores of size 20-50 nm in the underlying grains. Electrochemical etching at The effect of GaN buffer layer grown at various temperatures from 650°C to 1015°C on these as-fabricated nano-pores templates are 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. The PL spectrum for the regrowth GaN on nanoporous GaN template also shows an enhancement of PL intensity for GaN peak compared to as-grown GaN template, which is indicative of its higher crystal quality. This makes it as a suitable template for subsequent device fabrication.