Epitaxial Lateral Overgrowth of GaN on a Laser-Patterned Graphene Mask.

Epitaxial lateral overgrowth (ELO) of GaN epilayers on a sapphire substrate was studied by using a laser-patterned graphene interlayer. Monolayer graphene was transferred onto the sapphire substrate using a wet transfer technique, and its quality was confirmed by Raman spectroscopy. The graphene layer was ablated using a femtosecond laser, which produced well-defined patterns without damaging the underlying sapphire substrate.

MOVPE Growth of GaN via Graphene Layers on GaN/Sapphire Templates.

The remote epitaxy of GaN epilayers on GaN/sapphire templates was studied by using different graphene interlayer types. Monolayer, bilayer, double-stack of monolayer, and triple-stack of monolayer graphenes were transferred onto GaN/sapphire templates using a wet transfer technique. The quality of the graphene interlayers was examined by Raman spectroscopy.

Development of Quaternary InAlGaN Barrier Layer for High Electron Mobility Transistor Structures.

A quaternary lattice matched InAlGaN barrier layer with am indium content of 16.5 ± 0.2% and thickness of 9 nm was developed for high electron mobility transistor structures using the metalorganic chemical-vapor deposition method.

Enhancement of InN Luminescence by Introduction of Graphene Interlayer.

Indium nitride (InN) luminescence is substantially enhanced by the introduction of a multilayer graphene interlayer, mitigating the lattice mismatch between the InN epilayer and the Gallium nitride (GaN) template on a sapphire substrate via weak van der Waals interaction between graphene and nitride layers. The InN epilayers are deposited by radio-frequency plasma-assisted molecular beam epitaxy (MBE), and are characterized by spatially-resolved photoluminescence spectroscopy using confocal microscopy. A small blue shift of the emission band from the band gap evidences a low density of equilibrium carriers, and a high quality of InN on multilayer graphene.

Direct Auger recombination and density-dependent hole diffusion in InN.

Indium nitride has a good potential for infrared optoelectronics, yet it suffers from fast nonradiative recombination, the true origin of which has not been established with certainty. The diffusion length of free carriers at high densities is not well investigated either. Here, we study carrier recombination and diffusion using the light-induced transient grating technique in InN epilayers grown by pulsed MOCVD on c-plane sapphire.

Influence of carrier localization on high-carrier-density effects in AlGaN quantum wells.

The influence of carrier localization on photoluminescence efficiency droop and stimulated emission is studied in AlGaN multiple quantum wells with different strength of carrier localization. We observe that carrier delocalization at low temperatures predominantly enhances the nonradiative recombination and causes the droop, while the main effect of the delocalization at elevated temperatures is enhancement of PL efficiency due to increasing contribution of bimolecular recombination of free carriers. When the carrier thermal energy exceeds the dispersion of the potential fluctuations causing the carrier localization, the droop is caused by stimulated carrier recombination.

Photoluminescence efficiency droop and stimulated recombination in GaN epilayers.

The photoluminescence droop effect, i.e., the decrease in emission efficiency with increasing excitation intensity, is observed and studied in GaN epilayers with different carrier lifetimes.