Significant Carrier Extraction Enhancement at the Interface of an InN/p-GaN Heterojunction under Reverse Bias Voltage

In this paper, a superior-quality InN/p-GaN interface grown using pulsed metalorganic vapor-phase epitaxy (MOVPE) is demonstrated. The InN/p-GaN heterojunction interface based on high-quality InN (electron concentration 5.19 × 1018 cm−3 and mobility 980 cm2/(V s)) showed good rectifying behavior. The heterojunction depletion region width was estimated to be 22.8 nm and showed the ability for charge carrier extraction without external electrical field (unbiased). Under reverse bias, the external quantum efficiency (EQE) in the blue spectral region (300⁻550 nm) can be enhanced significantly and exceeds unity. Avalanche and carrier multiplication phenomena were used to interpret the exclusive photoelectric features of the InN/p-GaN heterojunction behavior

Krūvininkų dynamikos InGaN tyrimas liuminescencijos su erdvine skyra metodais

The thesis is aimed at gaining new knowledge on carrier localization and recombination in InGaN epilayers and structures by using photoluminescence spectroscopy with sub-micrometer spatial resolution. Optical characterization is combined with the structural analysis to provide a deeper insight into peculiarities of InGaN luminescence. Studies of InGaN epitaxial layers showed the relaxed layers to contain nanocolumn-like structures that additionally contribute to inhomogeneous photoluminescence distribution in InGaN layers. The feasibility of suppressing the defect-related emission in InGaN epilayers by laser annealing is demonstrated. The influence of unintentional annealing at elevated temperatures during fabrication of InGaN structures is revealed. A novel interpretation for negative correlation between photoluminescence intensity and band peak wavelength in high-indium-content InGaN multiple quantum wells is suggested. The enhancement of emission efficiency in InGaN quantum wells due to coupling of the optical dipole with localized surface plasmons in silver nanoparticles is investigated and the influence of potential fluctuations on the coupling with localized surface plasmons is revealed

Study of carrier dynamics in InGaN using spatially-resolved photoluminescence techniques

The thesis is aimed at gaining new knowledge on carrier localization and recombination in InGaN epilayers and structures by using photoluminescence spectroscopy with sub-micrometer spatial resolution. Optical characterization is combined with the structural analysis to provide a deeper insight into peculiarities of InGaN luminescence. Studies of InGaN epitaxial layers showed the relaxed layers to contain nanocolumn-like structures that additionally contribute to inhomogeneous photoluminescence distribution in InGaN layers. The feasibility of suppressing the defect-related emission in InGaN epilayers by laser annealing is demonstrated. The influence of unintentional annealing at elevated temperatures during fabrication of InGaN structures is revealed. A novel interpretation for negative correlation between photoluminescence intensity and band peak wavelength in high-indium-content InGaN multiple quantum wells is suggested. The enhancement of emission efficiency in InGaN quantum wells due to coupling of the optical dipole with localized surface plasmons in silver nanoparticles is investigated and the influence of potential fluctuations on the coupling with localized surface plasmons is revealed

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. A deposition temperature of ~375 °C is determined as optimal. The granularity, which is observed for the InN epilayers deposited on multilayer graphene, is shown to be eliminated, and the emission intensity is further enhanced by the introduction of an aluminum nitride (AlN) buffer layer between graphene and InN

Suppression of Defect-Related Luminescence in Laserannealed InGaN Epilayers

An In 0.21Ga 0.79N epilayer has been studied by using spatially-resolved photoluminescence spectroscopy and Auger electron spectroscopy. The photoluminescence intensity is shown to be distributed highly inhomogeneously, while the epilayer also exhibits strong defect-related emission. It is shown that laser annealing at high enough power densities causes redistribution of indium atoms and results in suppression of the defect-related emission. ? 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Influence of Laser Annealing on Defect-Related Luminescence of InGaN Epilayers

InGaN epilayers exhibiting strongdefect-related sub-band gap emission,which is undesirable in epilayers and quantum well structures designed for light-emitting diodes and laser diodes,have been studied by confocal photoluminescence spectroscopy,Auger electron spectroscopy,and atomic force microscopy. Inhomogeneous spatial distribution of band-edge luminescence intensity and compara- tively homogenous distribution of defect-related emission are demonstrated.It is shown that laser annealing at power densities causing the increase of the temperature at the epilayer surface high enough for indium atoms to move to the surface results in suppression of the defect-related emission