Moab Rajan Philip | New Jersey Institute of Technology (original) (raw)

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Papers by Moab Rajan Philip

We present the design of a 4-port photonic crystal-based optical circulator employing ring resona... more We present the design of a 4-port photonic crystal-based optical circulator employing ring resonator cross connect filters, suitable for photonic integrated circuits schemes. This unique design allows the operation in both clockwise as well as counterclockwise directions and shows a calculated normalized transmission of over 80%. Since the spectra ranges cover the whole third communication window, any wavelength in these ranges can be circulated through the proposed photonic crystal-based optical circulator even different wavelengths at the same time. Published by Elsevier GmbH.

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Please cite this article in press as: M. Djavid, et al., Effects of optical absorption in deep ul... more 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 design and fabrication of high performance AlxGa1−xN nanowire ultraviolet (UV) l... more We report on the design and fabrication of high performance AlxGa1−xN nanowire ultraviolet (UV) light-emitting diodes (LEDs) on silicon substrate by molecular beam epitaxy. The emission wavelength and surface morphology of nanowires can be controlled by varying the growth parameters that include substrate temperatures and/or Aluminum/Gallium flux ratios. The devices exhibit excellent current-voltage characteristics with relatively low resistance. Such nanowire LEDs generate strong emission in the UV-B band tuning from 290 nm to 330 nm. The electroluminescence spectra show virtually invariant blue-shift under injection current from 50 mA to 400 mA, suggesting the presence of a negligible quantum-confined Stark effect. Moreover, we have shown that, the AlGaN nanowire LEDs using periodic structures, can achieve high light extraction efficiency of ~ 89% and 92% for emissions at 290nm and 320nm, respectively. The randomly arranged nanowire 290 nm UV LEDs exhibit light extraction efficiency of ~ 56% which is higher compared to current AlGaN based thin-film UV LEDs.

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The development of low density metallic foams is highly intriguing for various applications. More... more The development of low density metallic foams is highly intriguing for various applications. Moreover, the synthesis of hierarchical 3-dimensional structures of graphene is also receiving tremendous attention in recent days because of their unique electrical, thermal, mechanical and chemical properties. Here, we demonstrate a novel method for the bulk production of graphene protected, freestanding, low density (0.03–0.15 g per cc) metallic nickel (Ni) foam (NiG) by a simple polyol assisted chemical route. This hybrid NiG foam is synthesized in air, and during its synthesis, Ni is protected by graphene from its oxidation. These magnetic scaffolds can be used for various energy and environmental applications, and also can be structurally reinforced with other polymers. Polymethyl methacrylate (PMMA) is infiltrated into the Ni/NiG foams and the subsequent annealing of Ni/PMMA composite foam in Ar–H 2 atmosphere at 900 C leads to the formation of large area graphene by the graphitisation of PMMA on Ni. This large area graphene is separated and studied for its properties.

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Phosphor-free InGaN/AlGaN core-shell nanowire light-emitting diodes (LEDs) grown by molecular bea... more 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.

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In this paper, we report our study on high-performance III-nitride nanowire light-emitting diodes... more In this paper, we report our study on high-performance III-nitride nanowire light-emitting diodes (LEDs) on copper (Cu) substrates via the substrate-transfer process. Nanowire LED structures were first grown on silicon-on-insulator (SOI) substrates by molecular beam epitaxy. Subsequently, the SOI substrate was removed by combining dry-and wet-etching processes. Compared to conventional nanowire LEDs on Si, the nanowire LEDs on Cu exhibit several advantages, including more efficient thermal management and enhanced light-extraction efficiency (LEE) because of the usage of metal reflectors and highly thermally conductive metal substrates. The LED on Cu, therefore, has stronger photoluminescence, electroluminescence intensities, and better current−voltage characteristics compared to the conventional nanowire LED on Si. Our simulation results further confirm the improved device performance of LEDs on Cu, compared to LEDs on Si. The LEE of the nanowire LED on Cu is nine times higher than that of the LED on Si at the same nanowire radius of 60 nm and spacing of 130 nm. Moreover, by engineering the device-active region, we achieved high-brightness phosphor-free LEDs on Cu with highly stable white-light emission and high color-rendering index of ∼95, showing their promising applications in general lighting, flexible displays, and wearable applications.

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We present, for the first time, the design of a low-cross talk scalable permutation switch employ... more We present, for the first time, the design of a low-cross talk scalable permutation switch employing photonic crystal ring resonators in an optical network. Through this novel approach, the transition between different states of the 2 × 2 optical switch, as the basic element, is achieved by applying different operating wavelengths. Subsequently, the shuffling mechanisms in 3 × 3 and 4 × 4 optical networks are realized by controlling the position of photonics crystal ring resonators. Lowest cross talk levels of 6 and 5% are obtained for " bar " and " cross " switching states, respectively.

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We report on the achievement of high efficiency green, yellow, and red InGaN/AlGaN dot-in-a-wire ... more We report on the achievement of high efficiency green, yellow, and red InGaN/AlGaN dot-in-a-wire nanowire light-emitting diodes grown on Si(111) by molecular beam epitaxy. The peak emission wavelengths were altered by varying the growth conditions, including the substrate temperature, and In/ Ga flux ratio. The devices demonstrate relatively high (>40%) internal quantum efficiency at room temperature, relative to that measured at 5 K. Moreover, negligible blue-shift in peak emission spectrum associated with no efficiency droop was measured when injection current was driven up to 556 A/cm 2. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

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