Molecular Beam Epitaxial Growth and Device Characterization of AlGaN Nanowire Ultraviolet-B Light-Emitting Diodes (original) (raw)
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Effects of optical absorption in deep ultraviolet nanowire light-emitting diodes
Please cite this article in press as: M. Djavid, et al., Effects of optical absorption in deep ultraviolet nanowire light-emitting diodes, Photon Nanostruct: Fundam Appl (2017), https://doi. a b s t r a c t We report our study on the effect of optical absorption in nanowire ultraviolet light-emitting diodes (LEDs) using three-dimensional finite difference time domain simulation. Utilizing nanowire structures can avoid the emission of guided modes inside LED structure and redirect the trapped light into radiated modes. The optical loss due to material absorption can be decreased by reducing light propagation path inside the LED structure, and consequently enhance the light extraction efficiency (LEE). Nanowire form factors including size, and density play important roles on the LEE of ultraviolet (UV) nanowire LEDs. In this paper, the nanowire spacing and diameter are considered in simulation to reach maximum LEE. Our results show an unprecedentedly high LEE of ∼34% can be achieved for deep UV emission at 240 nm. Moreover, UV nanowire LEDs with random structure can exhibit LEE of ∼19% which is comparable or higher than that of high efficiency UV thin-film LEDs. Published by Elsevier B.V.
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We report on the demonstration of a new type of axial nanowire LED heterostructures, with the use of self-organized InGaN/AlGaN dot-in-a-wire core-shell nanowire arrays. The large bandgap AlGaN shell is spontaneously formed on the sidewall of the nanowire during the growth of AlGaN barrier of the quantum dot active region. As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns. The luminescence emission is also enhanced by orders of magnitude. Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL. The device displays strong white-light emission, with a color rendering index of ~95. An output power of >5 mW is measured for a 1 mm × 1 mm device, which is mo...
This paper reviews the device physics and technology of optoelectronic devices based on semiconductors of the GaN family, operating in the spectral regions from deep UV to Terahertz. Such devices include LEDs, lasers, detectors, electroabsorption modulators and devices based on intersubband transitions in AlGaN quantum wells (QWs). After a brief history of the development of the field, we describe how the unique crystal structure, chemical bonding, and resulting spontaneous and piezoelectric polarizations in heterostructures affect the design, fabrication and performance of devices based on these materials. The heteroepitaxial growth and the formation and role of extended defects are addressed. The role of the chemical bonding in the formation of metallic contacts to this class of materials is also addressed. A detailed discussion is then presented on potential origins of the high performance of blue LEDs and poorer performance of green LEDs (green gap), as well as of the efficiency reduction of both blue and green LEDs at high injection current (efficiency droop). The relatively poor performance of deep-UV LEDs based on AlGaN alloys and methods to address the materials issues responsible are similarly addressed. Other devices whose state-of-the-art performance and materials-related issues are reviewed include violet-blue lasers, 'visible blind' and 'solar blind' detectors based on photoconductive and photovoltaic designs, and electroabsorption modulators based on bulk GaN or GaN/AlGaN QWs. Finally, we describe the basic physics of intersubband transitions in AlGaN QWs, and their applications to near-infrared and terahertz devices.
Phosphor-free III-nitride nanowire white-light-emitting diodes for visible light communication
Phosphor-free InGaN/AlGaN core-shell nanowire light-emitting diodes (LEDs) grown by molecular beam epitaxy have been developed and their application in visible light communication (VLC) has been investigated. The electroluminescence spectra of these nanowire LEDs show a very broad spectral linewidth and fully covers the entire visible spectrum. High-brightness phosphor-free LEDs with highly stable white-light emission and high color-rendering index (CRI) of >98 were obtained by controlling the Indium composition in the device active region. Moreover, the phosphor-free nanowire white-LEDs exhibit relatively high 3-dB frequency bandwidth of ~ 1.4 MHz which is higher compared to that of phosphor-based white LEDs at the same measurement condition. Such high-performance phosphor-free nanowire LEDs are being further improved and are ideally suited for future smart lighting applications and communications.
Graphene Reinforced Composites as Efficient Thermal Interface Materials
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