Blar i NTNU Open på forfatter "Weman, Helge"
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Graphene-Based Transparent Conducting Substrates for GaN/AlGaN Nanocolumn Flip-Chip Ultraviolet Light-Emitting Diodes
Liudi Mulyo, Andreas; Mukherjee, Anjan; Høiaas, Ida Marie; Ahtapodov, Lyubomir; Nilsen, Tron Arne; Toftevaag, Håvard Hem; Vullum, Per Erik; Kishino, Katsumi; Weman, Helge; Fimland, Bjørn-Ove (Journal article; Peer reviewed, 2021)Flip-chip ultraviolet light-emitting diodes based on self-assembled GaN/AlGaN nanocolumns have been fabricated, exploiting single-layer graphene not only as a growth substrate but also as a transparent conducting electrode. ... -
Growth study of self-assembled GaN nanocolumns on silica glass by plasma assisted molecular beam epitaxy
Liudi Mulyo, Andreas; Konno, Yuta; Nilsen, Julie Stene; Van Helvoort, Antonius; Fimland, Bjørn-Ove; Weman, Helge; Kishino, Katsumi (Journal article; Peer reviewed, 2017)We demonstrate GaN nanocolumn growth on fused silica glass by plasma-assisted molecular beam epitaxy. The effect of the substrate temperature, Ga flux and N2 flow rate on the structural and optical properties are studied. ... -
III-V Semiconductor Nanowire/Graphene Hybrid Structures: for Applications in Solar Cells and Ultraviolet Light-Emitting Diodes
Mukherjee, Anjan (Doctoral theses at NTNU;2022:211, Doctoral thesis, 2022)Recent development on high-crystalline and almost defect-free one-dimensional nanowire (NW) structures of III-V semiconductors through various epitaxial growth techniques leads to the possibility of producing a new generation ... -
Inducing a direct-to-pseudodirect bandgap transition in wurtzite GaAs nanowires with uniaxial stress
Signorello, G.; Lörtscher, E; Khomyakov, P.A.; Karg, S.; Dasa Lakshmi Narayana, Dheeraj; Gotsmann, B.; Weman, Helge; Riel, H. (Journal article; Peer reviewed, 2014)Many efficient light-emitting devices and photodetectors are based on semiconductors with, respectively, a direct or indirect bandgap configuration. The less known pseudodirect bandgap configuration can be found in wurtzite ... -
The influence of AlN buffer layer on the growth of self-assembled GaN nanocolumns on graphene
Liudi Mulyo, Andreas; Rajpalke, Mohana; Vullum, Per Erik; Weman, Helge; Kishino, Katsumi; Fimland, Bjørn-Ove (Peer reviewed; Journal article, 2020)GaN nanocolumns were synthesized on single-layer graphene via radio-frequency plasma-assisted molecular beam epitaxy, using a thin migration-enhanced epitaxy (MEE) AlN buffer layer as nucleation sites. Due to the weak ... -
Micro-Photoluminescence Spectroscopy of Au-assisted MBE Grown AlGaAs Nanowires with Axial GaAs Inserts
Wahl, Markus Solberg (Master thesis, 2012)AlGaAs nanowires (NWs) with axial GaAs inserts, grown with molecular beam epitaxy will be investigated with micro-photoluminescence spectroscopy, including CW and pulsed excitation at cryogenic and ambient temperatures. -
Micro-photoluminescence spectroscopy of self-catalyzed zincblende GaAs nanowires grown by molecular beam epitaxy
Mjåland, Terje Sund (Master thesis, 2012)In this thesis, single zincblende GaAs nanowires grown by molecular beam epitaxy using the self-catalyzed approach were studied with m-photoluminescence spectroscopy in order to assess the optical quality of self-catalyzed ... -
Optical and Electrical studies of GaAs Nanowire arrays on Si substrates
Wolden, Eivind Halmøy (Master thesis, 2015)Syv ulike prøver bestående av GaAs/AlGaAs grodd ved den selvkatalyserte teknikken har blitt analysert ved bruk av elektron mikroskopi og fotoluminsense spectroskopi. Målet var å optimalisere veksten ved å finne en fri ... -
Optical Characterization of GaAs Nanowires Using Specular Mueller Matrix Ellipsometry
Storås, Christian Alexander (Master thesis, 2015)The purpose of this thesis is to preform ellipsometric measurements to investigate the possibility of in situ characterization of nanowire growth. This will give an advantage for scientist in the future when growing nanowires ... -
Optical Properties of III-V Semiconductor Nanowire Structures
Ahtapodov, Lyubomir Aleksandrov (Doctoral theses at NTNU;2017:241, Doctoral thesis, 2017)The present thesis deals with the characterisation of the optical properties of GaAsbased III-V semiconductor nanowires (NW) and with the exploration of the potential of such NWs for applications in light emitting devices. ... -
Optical Studies of Single Semiconductor Nanowires by Micro-Photoluminescence Spectroscopy
Karlberg, Thomas Andre (Master thesis, 2010)Over the recent years semiconductor nanowires have gained much attention for their potential to either improve existing technology or create novel devices. This potential has been realized in devices such as semiconductor ... -
Origin of Leakage Currents and Nanowire-to-Nanowire Inhomogeneity in Radial p-i-n Junction GaAs Nanowire Array Solar Cells on Si
Mukherjee, Anjan; Ren, Dingding; Mosberg, Aleksander Buseth; Vullum, Per Erik; Van Helvoort, Antonius; Fimland, Bjørn Ove Myking; Weman, Helge (Journal article; Peer reviewed, 2023)To realize the promising potential of radial junction nanowire (NW) array-based solar cells, it is crucial to get physical insight into how the overall photoconversion efficiency (PCE) is impacted by the hole mask properties, ... -
Photoluminescence study of as-grown self-catalyzed GaAs/AlGaAs core-shell nanowires
Slåttnes, Patrick Rene Tollefsen (Master thesis, 2012)A macro-photoluminescence study of self-catalyzed nanowires, using a specializedsetup for this purpose, has been performed. Several samples were even comparedto single nanowire micro-photoluminescence measurements, on the ... -
Pulsed Laser Deposition of ZnO Nanostructures for Hybrid Inorganic/Organic Solar Cells
Skåre, Daniel Gundersen (Master thesis, 2009)Au catalyst ZnO nanostructures have been grown on the a- and c-plane sapphire substrate by PLD. Influence of substrate lattice orientation, substrate surface and different substrate annealing temperature have been characterized ... -
Raman spectroscopy of ZnO thin films and nanorods deposited by Pulsed Laser Deposition (PLD) on Sapphire
Thomassen, Marius Vetaas (Master thesis, 2010)ZnO is a promising material for optoelectronic applications. ZnO thin films and nanostructures are under active investigation for such applications as solid state lasers, light emitting diodes and photovoltaic devices as ... -
Selective area growth of AlGaN nanopyramid arrays on graphene by metal-organic vapor phase epitaxy
Munshi, A Mazid; Kim, Dong-Chul; Heimdal, Carl Philip J; Heilmann, Martin; Christiansen, Silke; Vullum, Per Erik; Van Helvoort, Antonius; Weman, Helge (Journal article; Peer reviewed, 2018)Wide-bandgap group III-nitride semiconductors are of special interest for applications in ultraviolet light emitting diodes, photodetectors, and lasers. However, epitaxial growth of high-quality III-nitride semiconductors ... -
Semiconductor-graphene hybrid structures and optoelectronic devices
Høiaas, Ida Marie (Doctoral theses at NTNU;2020:258, Doctoral thesis, 2020)In order to utilise the intriguing properties discovered in nanomaterials during the last decades, structures and devices that do exactly that have to be developed. Graphene, the carbon wondermaterial discovered in 2004, ... -
Single-Mode Near-Infrared Lasing in a GaAsSb-Based Nanowire Superlattice at Room Temperature
Ren, Dingding; Ahtapodov, Lyubomir; Nilsen, Julie Stene; Yang, Jianfeng; Gustafsson, Anders; Huh, Junghwan; Conibeer, G; Van Helvoort, Antonius; Fimland, Bjørn-Ove; Weman, Helge (Journal article; Peer reviewed, 2018)Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibilities for a variety of applications including nanophotonic circuits, optical sensing, and ... -
Vertical GaN nanocolumns grown on graphene intermediated with a thin AlN buffer layer
Liudi Mulyo, Andreas; Rajpalke, Mohana Krishnappa; Kuroe, Haruhiko; Vullum, Per-Erik; Weman, Helge; Fimland, Bjørn-Ove; Kishino, Katsumi (Journal article; Peer reviewed, 2018)We report on the self-assembled growth of high-density and vertically-oriented n-doped GaN nanocolumns on graphene by radio-frequency plasma-assisted molecular beam epitaxy. Graphene was transferred to silica glass, which ... -
Zinc Oxide Nanolaser: Photoluminescence spectroscopy and optical pumping of zinc oxide nanowires
Heitmann, Filip August (Master thesis, 2012)This Master's thesis is a continuation of the specialization project I did during the spring of 2011. The goal of said project was to set up a system for UV-photoluminescence experiments in the Nanophotonics laboratory at ...