B. S. Ooi

King Abdullah University of Science and Technology, Djidda, Makkah, Saudi Arabia

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Publications (258)332.74 Total impact

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    ABSTRACT: The fabrication of orange-emitting semiconductor laser on interdif-fused InGaP/InAlGaP structure is reported. The lasers lased at 22°C at a wavelength as short as 608 nm with threshold current density of 3.4 KAcm −2 and a maximum output power of ∼46 mW. This is the shortest wavelength electrically pumped semiconductor laser emission from the InGaP/InAlGaP structure. Introduction: Semiconductor visible laser diodes (LDs) cover a wide spectrum of wavelengths. For example, the InGaN/GaN based LDs cover the violet to green spectrum (∼405–530 nm), and InGaP/ InAlGaP system based LDs cover the red spectrum (635–690 nm). The wavelength from ∼530–635 nm is not covered by any commercial LDs yet, which has some important applications in medicine [1, 2], horticulture [3], displays [4] and in optical communication using plastic fibres [5]. LDs in the green-yellow-orange range (530–635 nm) can be grown ideally either by InGaN/GaN or InGaP/InAlGaP based material system. For the InGaN/GaN quantum well (QW) structure, large strain and indium segregation prevent the growth of high quality light emitting devices in yellow and orange spectrum regions. In the case of the InGaP/InAlGaP system, small band offset between the QW and barriers leads small carrier confinement and large carrier leakage to prohibit the growth of high quality QW structures for yellow and orange emissions. The only access to orange, yellow and green regions has been achieved by frequency doubling of diode-pumped solid state lasers [6] or infrared LDs [7] or through the application of high external pressures which cause large blue-shifts of the emission wavelength of diode lasers [5]. However, the frequency doubled diode-pumped semiconductor lasers use non-linear crystals for inefficient second-harmonic generation and require externally distributed Bragg reflector and good heat sink, which makes the overall system more complex. Although InGaN based vertical-external-cavity surface-emitting lasers, also known as optically pumped semiconductor lasers, are worthy contenders for wavelength tuning, high optical output power and a nearly diffraction-limited beam quality means electrical pumping in these devices is challenging [8]. Moreover, the lasers produced by application of external pressure technique are non-practical for any commercial applications. Therefore, there is huge demand for replacements of these complex, expensive and power consuming lasers. In this letter we demonstrate the first room-temperature (RT) orange emission at 608 nm from the interdiffused InGaP/InAlGaP structure. Red laser (∼640 nm) InGaP/InAlGaP structure is known to be very hard to have its bandgap blue-shifted using quantum well intermixing (QWI) technique [9]. Here, a novel QWI technique utilising strain-induced from a thick dielectric cap with cycles annealing at elevated temperature to promote interdiffusion. With this QWI technique, we have successfully tuned the bandgap of InGaP/InAlGaP structure from 640 to 565 nm. Experiment: The single quantum well (SQW) InGaP/InAlGaP laser structure was grown on 10° offcut GaAs substrate using metal-organic chemical vapour deposition as shown in Fig. 1. The structure consists of a 200 nm Si-doped GaAs buffer layer with carrier concentration of 1-2 × 10 18 cm −3 , 1 µm thick n-In 0.5 Al 0.5 P lattice-matched lower cladding layer with carrier concentration of 1 × 10 18 cm −3 , a SQW InGaP sandwiched between two 80 nm undoped In 0.5 Al 0.3 Ga 0.2 P waveguide layers, 1 µm thick Zn-doped In 0.5 Al 0.5 P lattice-matched upper cladding with carrier concentration of 1 × 10 18 cm −3 , 75 nm lattice matched pIn 0.5 Ga 0.5 P barrier reduction layer with carrier concentration of 3 × 10 18 cm −3 and 200 nm highly doped p-GaAs contact layer with carrier concentration of 2-3 × 10 19 cm −3. The emission of the laser was designed to be at 638 ± 2 nm. For the novel QWI process, we studied the effect of the thickness of dielectric encapsulant (external strain), annealing temperature, anneal-ing duration and number of cycles of annealing to identify the optimal process conditions for preserving the surface morphology, photolumi-nescence (PL) characteristics and electrical properties. For the purpose of this work a 1 µm thick SiO 2 cap, 950°C annealing temperature, five cycles of 30 s duration was applied to achieve the desired emission wavelength and optimal process conditions. The bandgap shifts induced by the above procedure were measured at RT using PL spectroscopy equipped with a 473 nm cobalt laser as the excitation source. Wafers were then processed using conventional processing and 1 mm long and 75 µm wide ridge devices were used for opto-electronic characteris-ation. All the devices were mounted on ceramic tiles and probed directly. The measurements were carried out at a tile temperature of 295 K, while pulsed operation (0.5 µs pulsed duration, 0.1% duty cycle) was used to minimise self-heating effects.
    Electronics Letters 06/2015; DOI:10.1049/el.2015.1658 · 1.07 Impact Factor
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    ABSTRACT: Polarized thin film mirror with high reflectivity and broadband characteristics for optoelectronic devices can be realized using subwavelength grating (SWG). 1 For nanoscale SWG, most of the out-of plane emission devices utilized electron beam lithography, however this technique is challenging for SWG fabrication on the facets of in-plane emission devices. Direct SWG patterning at facet of in-plane devices using focused ion beam (FIB) technique has been reported for antireflector in quantum cascade laser (QCL) 2 and plasmonic collimator for QCL 3 , besides the subwavelength slit grating 4 for typical out-of plane emission case. However, these FIB patterned SWG are only demonstrated for III-V compounds and metallic based devices at infra-red spectrum. Here we propose SWG reflector fabrication using FIB technique on dielectric multilayers (Si3N4/SiO2) using GaN-sapphire substrate at visible wavelength. We spin-coated electron dissipation polymer (ESPACER 300Z) on the sample surface to reduce the charging effect of the dielectrics, GaN and sapphire during milling.
    The 59th International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication (EIPBN 2015), San Diego, USA; 05/2015
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    ABSTRACT: We investigated the design and growth of compositionally-graded InGaN multiple quantum wells (MQW) based light-emitting diode (LED) without an electron-blocking layer (EBL). Numerical investigation showed uniform carrier distribution in the active region, and higher radiative recombination rate for the optimized graded-MQW design, i.e. In0→xGa1→(1-x)N / InxGa(1-x)N / Inx→0Ga(1-x)→1N, as compared to the conventional stepped-MQW-LED. The composition-grading schemes, such as linear, parabolic, and Fermi-function profiles were numerically investigated for comparison. The stepped- and graded-MQW-LED were then grown using plasma assisted molecular beam epitaxy (PAMBE) through surface-stoichiometry optimization based on reflection high-energy electron-diffraction (RHEED) in-situ observations. Stepped- and graded-MQW-LED showed efficiency roll over at 160 A/cm2 and 275 A/cm2, respectively. The extended threshold current density roll-over (droop) in graded-MQW-LED is due to the improvement in carrier uniformity and radiative recombination rate, consistent with the numerical simulation.
    IEEE Photonics Journal 05/2015; 7(3). DOI:10.1109/JPHOT.2015.2430017 · 2.33 Impact Factor
  • Chao Shen, Tien Khee Ng, Boon S. Ooi
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    ABSTRACT: We report on a unique area-selective, post-growth approach in engineering the quantum-confined potential-energy profile of InGaN/GaN quantum wells (QWs) utilizing metal/dielectric-coating induced intermixing process. This led to simultaneous realization of adjacent regions with peak emission of 2.74 eV and 2.82 eV with a high spatial resolution (~1 μm) at the coating boundary. The potential profile softening in the intermixed QW light-emitting diode (LED) was experimentally and numerically correlated, shedding light on the origin of alleviated efficiency droop from 30.5% to 16.6% (at 150 A/cm2). The technique is advantageous for fabricating high efficiency light-emitters, and is amenable to monolithic integration of nitride-based photonic devices.
    Optics Express 03/2015; 23(6). DOI:10.1364/OE.23.007991 · 3.53 Impact Factor
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    ABSTRACT: We analyze an epitaxially grown heterostructure composed of InGaN nanodisks inserted in GaN nanowires in order to relate indium concentration to the electronic properties. This study was achieved with spatially resolved low-loss electron energy-loss spectroscopy using monochromated electrons to probe optical excitations—plasmons—at nanometer scale. Our findings show that each nanowire has its own indium fluctuation and therefore its own average composition. Due to this indium distribution, a scatter is obtained in plasmon energies, and therefore in the optical dielectric function, of the nanowire ensemble. We suppose that these inhomogeneous electronic properties significantly alter band-to-band transitions and consequently induce emission broadening. In addition, the observation of tailing indium composition into the GaN barrier suggests a graded well-barrier interface leading to further inhomogeneous broadening of the electro-optical properties. An improvement in the indium incorporation during growth is therefore needed to narrow the emission linewidth of the presently studied heterostructures.
    Applied Physics Letters 03/2015; 106(10):101910. DOI:10.1063/1.4915117 · 3.52 Impact Factor
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    ABSTRACT: We investigated the mechanisms of radiative recombination in a CH3NH3PbBr3 hybrid perovskite material using low-temperature, power-dependent (77 K), and temperature-dependent photoluminescence (PL) measurements. Two bound-excitonic radiative transitions related to grain size inhomogeneity were identified. Both transitions led to PL spectra broadening as a result of concurrent blue and red shifts of these excitonic peaks. The red-shifted bound-excitonic peak dominated at high PL excitation led to a true-green wavelength of 553 nm for CH3NH3PbBr3 powders that are encapsulated in polydimethylsiloxane. Amplified spontaneous emission was eventually achieved for an excitation threshold energy of approximately 350 μJ/cm2. Our results provide a platform for potential extension towards a true-green light-emitting device for solid-state lighting and display applications.
    Applied Physics Letters 02/2015; 106(8):081902. DOI:10.1063/1.4913463 · 3.52 Impact Factor
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    ABSTRACT: The small signal modulation characteristics of an InGaN/GaN nanowire array edge- emitting laser on (001) silicon are reported. The emission wavelength is 610 nm. Lattice matched InAlN cladding layers were incorporated in the laser heterostructure for better mode confinement. The suitability of the nanowire lasers for use in plastic fiber communication systems with direct modulation is demonstrated through their modulation bandwidth of f-3dB,max = 3.1 GHz, very low values of chirp (0.8 Å) and α-parameter, and large differential gain (3.1 × 10−17 cm2).
    Applied Physics Letters 02/2015; 106(7):071108. DOI:10.1063/1.4913317 · 3.52 Impact Factor
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    ABSTRACT: We report on a flat-top and ultrawide emission bandwidth of 125 nm from InGaAsP/InP multiple quantum-well (MQW) superluminescent diode with antireflection coated and tilted ridge-waveguide device configuration. A total output power in excess of 70 mW with an average power spectral density of 0.56 mW/nm and spectral ripple <= 1.2 +/- 0.5 dB is measured from the device. Wall-plug efficiency and output power as high as 14% and 80 mW, respectively, is demonstrated from this batch of devices. We attribute the broad emission to the inherent inhomogeneity of the electron-heavy-hole (e-hh) and electron-light-hole (e-lh) recombination of the ground state and the first excited state of the MQWs and their simultaneous emission.
    IEEE Photonics Journal 02/2015; 7(1):1-1. DOI:10.1109/JPHOT.2015.2399442 · 2.33 Impact Factor
  • IEEE Photonics Journal 12/2014; 6(6):1-12. DOI:10.1109/JPHOT.2014.2374596 · 2.33 Impact Factor
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    ABSTRACT: The advances in lasers, electronic and photonic integrated circuits (EPIC), optical interconnects as well as the modulation techniques allow the present day society to embrace the convenience of broadband, high speed internet and mobile network connectivity. However, the steep increase in energy demand and bandwidth requirement calls for further innovation in ultra-compact EPIC technologies. In the optical domain, advancement in the laser technologies beyond the current quantum well (Qwell) based laser technologies are already taking place and presenting very promising results. Homogeneously grown quantum dot (Qdot) lasers and optical amplifiers, can serve in the future energy saving information and communication technologies (ICT) as the work-horse for transmitting and amplifying information through optical fiber. The encouraging results in the zero-dimensional (0D) structures emitting at 980 nm, in the form of vertical cavity surface emitting laser (VCSEL), are already operational at low threshold current density and capable of 40 Gbp s error-free transmission at 108 fJ/bit. Subsequent achievements for lasers and amplifiers operating in the O–, C–, L–, U–bands, and beyond will eventually lay the foundation for green ICT. On the hand, the inhomogeneously grown quasi 0D quantum dash (Qdash) lasers are brilliant solutions for potential broadband connectivity in server farms or access network. A single broadband Qdash laser operating in the stimulated emission mode can replace tens of discrete narrow-band lasers in dense wavelength division multiplexing (DWDM) transmission thereby further saving energy, cost and footprint. We herein reviewed the progress of both Qdots and Qdash devices, based on the InAs/InGaAlAs/InP and InAs/InGaAsP/InP material systems, from the angles of growth and device performance. In particular, we discussed the progress in lasers, semiconductor optical amplifiers (SOA), mode locked lasers, and superluminescent diodes, which are the building blocks of EPIC and ICT. Alternatively, these optical sources are potential candidates for other multi-disciplinary field applications.
    Progress in Quantum Electronics 11/2014; 38(6). DOI:10.1016/j.pquantelec.2014.11.001 · 4.69 Impact Factor
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    M.Z.M. Khan, T.K. Ng, B.S. Ooi
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    ABSTRACT: We report on the high performance characteristics from superluminescent diodes (SLD) based on four-stack InAs/InGaAlAs chirped-barrier thickness quantum dash (Qdash) in a well structure. The active region exhibits a measured broad gain spectrum of ~140 nm with peak modal gain ~41 cm-1. The non-coated two section gain-absorber broad area and ridge-waveguide device configuration exhibits an output power >20 mW and >12 mW, respectively. The corresponding -3 dB bandwidths span ~82 nm and ~72 nm, with small spectral ripple <0.2 dB, related largely to the contribution from dispersive height dash ensembles of the highly inhomogeneous active region. These C-L communication band devices will find applications in various cross-disciplinary fields of optical metrology, optical coherent tomography, etc.
    IEEE Photonics Journal 08/2014; 6(4). DOI:10.1109/JPHOT.2014.2337892 · 2.33 Impact Factor
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    ABSTRACT: A silicon-based laser, preferably electrically pumped, has long been a scientific and engineering goal. We demonstrate here, for the first time, an edge-emitting InGaN/GaN disk-in-nanowire array electrically pumped laser emitting in the green (λ=533nm) on (001)silicon substrate. The devices display excellent dc and dynamic characteristics with values of threshold current density, differential gain, T0 and small signal modulation bandwidth equal to 1.76kA/cm2, 3x10-17cm2, 232K and 5.8GHz respectively under continuous wave operation. Preliminary reliability measurements indicate a lifetime of 7000 hours. The emission wavelength can be tuned by varying the alloy composition in the quantum disks. The monolithic nanowire laser on (001)Si can therefore address wide-ranging applications such as solid state lighting, displays, plastic fiber communication, medical diagnostics and silicon photonics.
    Nano Letters 06/2014; 14(8). DOI:10.1021/nl5015603 · 12.94 Impact Factor
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    ABSTRACT: The InGaN/GaN quantum-disks-in-nanowire light-emitting diode (LED) with emission centered at ~830nm, the longest emission wavelength ever reported in the InGaN/GaN system, and spectral linewidth of 290nm, has been fabricated with p-side-down on a Cu substrate.
    CLEO: Science and Innovations; 06/2014
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    ABSTRACT: Extraordinary optical transmission (EOT) through arrays of gold nanoholes was studied with light across the visible to the near-infrared spectrum. The EOT effect was found to be improved by bridging pairs of nanoholes due to the concentration of the electromagnetic field in the slit between the holes. The geometrical shape and separation of the holes in these pairs of nanoholes affected the intensity of the transmission and the wavelength of resonance. Changing the geometrical shapes of these nanohole pairs from triangles to circles to squares leads to increased transmission intensity as well as red-shifting resonance wavelengths. The performance of bridged nanohole pairs as a plasmonic sensor was investigated. The bridged nanohole pairs were able to distinguish methanol, olive oil and microscope immersion oil for the different surface plasmon resonance in transmission spectra. Numerical simulation results were in agreement with experimental observations.
    Nanoscale 06/2014; 6(14). DOI:10.1039/c4nr01001a · 6.74 Impact Factor
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    ABSTRACT: Simulating light propagation in anisotropic dynamic gain media such as semiconductors and solid-state lasers using the finite difference time-domain FDTD technique is a tedious process, as many variables need to be evaluated in the same instant of time. The algorithm has to take care of the laser dynamic gain, rate equations, anisotropy and dispersion. In this paper, to the best of our knowledge, we present the first algorithm that solves this problem. The algorithm is based on separating calculations into independent layers and hence solving each problem in a layer of calculations. The anisotropic gain medium is presented and tested using a one-dimensional set-up. The algorithm is then used for the analysis of a two-dimensional problem.
    SPIE Photonics Europe; 05/2014
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    ABSTRACT: Despite the recent progress in gallium nitride (GaN) growth technology, the excessively high threading dislocation (TD) density within the GaN crystal, caused by the reliance on heterogeneous substrates, impedes the development of high-efficiency, low-cost, GaN-based heterostructure devices. For the first time, the chemical exfoliation of completely TD-free, single-crystalline, ultrathin (tens of nanometers) GaN nanomembranes is demonstrated using UV-assisted electroless chemical etching. These nanomembranes can act as seeding layers for subsequent overgrowth of high-quality GaN. A model is proposed, based on scanning and transmission electron microscopy as well as optical measurements to explain the physical processes behind the formation of the GaN nanomembranes. These novel nanomembranes, once transferred to other substrates, present a unique and technologically attractive path towards integrating high-efficiency GaN optical components along with silicon electronics. Interestingly, due to their nanoscale thickness and macroscopic sizes, these nanomembranes may enable the production of flexible GaN-based optoelectronics.
    Advanced Functional Materials 04/2014; 24(16). DOI:10.1002/adfm.201303001 · 11.81 Impact Factor
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    ABSTRACT: We study the enhanced hole confinement by having a large bandgap AlGaN monolayer insertion (MLI) between the quantum well (QW) and the quantum barrier (QB). The numerical analysis examines the energy band alignment diagrams, using a self-consistent 6 $times$ 6 $k cdot p$ method and, considering carrier distribution, recombination rates (Shockley–Reed–Hall, Auger, and radiative recombination rates), under equilibrium and forward bias conditions. The active region is based on $hbox{Al}_{rm a}hbox{Ga}_{1 - {rm a}}hbox{N} hbox{(barrier)}/hbox{Al}_{ rm b}hbox{Ga}_{1 - {rm b}}hbox{N} hbox{(MLI)} /hbox{Al}_{rm c}hbox{Ga}_{1 - {rm c}}hbox{N} hbox{(well)} , / ,hbox{Al}_{rm d}hbox{Ga}_{1 - {rm d}}hbox{N} hbox{(barrier)}$, where b $>$ d $>$ a $>$ c. A large bandgap $ hbox{Al}_{rm b}hbox{Ga}_{1 - {rm b}}hbox{N}$ mono layer, inserted between the QW and QB, was found to be effective in providing stronger hole confinement. With the proposed band engineering scheme, an increase of more than 30% in spatial overlap of carrier wavefunction was obtained, with a considerable increase in carrier density and direct radiative recombination rates. The single-QW-based UV-LED was designed to emit at 280 nm, which is an effective wavelength for water disinfection.
    IEEE Photonics Journal 04/2014; 6(2):1-9. DOI:10.1109/JPHOT.2014.2310199 · 2.33 Impact Factor
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    ABSTRACT: We report on the properties and growth kinetics of defect-free, photoluminescence (PL) efficient mushroom-like nanowires (MNWs) in the form of ~30nm thick hexagonal-shaped InGaN-nanodisk on GaN nanowires, coexisting with the conventional rod-like InGaN-on-GaN nanowires (RNWs) on (111)-silicon-substrate. When characterized using confocal microscopy (CFM) with 458nm laser excitation, while measuring spontaneous-emission at fixed detection wavelengths, the spatial intensity map evolved from having uniform pixelated emission, to having only an emission ring, and then a round emission spot. This corresponds to the PL emission with increasing indium composition; starting from emission mainly from the RNW, and then the 540 nm emission from one MNWs ensemble, followed by the 590 nm emission from a different MNW ensemble, respectively. These hexagonal-shaped InGaN-nano-disks ensembles were obtained during molecular-beam-epitaxy (MBE) growth. On the other hand, the regular rod-like InGaN-on-GaN nanowires (RNWs) were emitting at a shorter peak wavelength of 490 nm. While the formation of InGaN rod-like nanowire is well-understood, the formation of the hexagonal-shaped InGaN-nanodisk-on-GaN-nanowire requires further investigation. It was postulated to arise from the highly sensitive growth kinetics during plasma-assisted MBE of InGaN at low temperature, i.e. when the substrate temperature was reduced from 800 °C (GaN growth) to <600 °C (InGaN growth), during which sparsely populated metal-droplet formation prevails and further accumulated more indium adatoms due to a higher cohesive bond between metallic molecules.
    Proceedings of SPIE - The International Society for Optical Engineering 02/2014; DOI:10.1117/12.2039627 · 0.20 Impact Factor
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    ABSTRACT: In this paper, we assessed the effect of additionally broadened quantum dash (Qdash) optical transitions in the multi-stack dash-in-a-well laser structure at both, material and device level. A broad photoluminescence linewidth of ${sim}{rm 150}~{rm nm}$ demonstrates the formation of highly inhomogeneous InAs-dashes across the stacks. The transmission electron microscopy revealed small (large) average dash height from the Qdash stack with thick (thin) over grown barrier layer. The Fabry–Perot laser diodes fabricated from this chirped structure exhibits unique device physics under the short pulsewidth (SPW) and quasi-continuous wave (QCW) operation. Varying the ridge-width $(W)$ from 2 to 4 $mu{rm m}$ showed quenching of ultrabroad lasing signature in the SPW operation, and consistent even for a wide 15 $mu{rm m}$ oxide strip laser diode. A lasing spectral split with reduced intensity gap in the center is observed in the QCW operation with the gap decreasing with increasing ridge-width. Such atypical lasing operation, influenced by the waveguiding mechanism is qualitatively realized by associating to the reduced vertical coupling effect of the Qdash stacks in the operation of small ridge-width lasers compared with large ridge-width and oxide stripe lasers, and leading to varying non-uniform distribution of carriers among the inhomogeneously broadened Qdash stacks in each case. Our chirped 2$,times,$830 $mu{rm m}$ ridge laser demonstrated marked improvement in the internal quantum efficiency $({sim}{80%})$x> and ${-}{rm 3}~{rm dB}$ lasing bandwidth, ${>}{rm 50}~{rm nm}$ centered at ${sim}{1.61}~mu{rm m}$.
    IEEE Journal of Quantum Electronics 02/2014; 50(2):51-61. DOI:10.1109/JQE.2013.2294092 · 2.11 Impact Factor
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    ABSTRACT: A theoretical investigation of AlGaN UV-LED with band engineering of hole and electron blocking layers (HBL and EBL, respectively) was conducted with an aim to improve injection efficiency and reduce efficiency droop in the UV LEDs. The analysis is based on energy band diagrams, carrier distribution and recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates) in the quantum well, under equilibrium and forward bias conditions. Electron blocking layer is based on AlaGa1-aN / Alb → cGa1-b → 1-cN / AldGa1-dN, where a < d < b < c. A graded layer sandwiched between large bandgap AlGaN materials was found to be effective in simultaneously blocking electrons and providing polarization field enhanced carrier injection. The graded interlayer reduces polarization induced band bending and mitigates the related drawback of impediment of holes injection. Similarly on the n-side, the Alx → yGa1-x → 1-yN / AlzGa1-zN (x < z < y) barrier acts as a hole blocking layer. The reduced carrier leakage and enhanced carrier density in the active region results in significant improvement in radiative recombination rate compared to a structure with the conventional rectangular EBL layers. The improvement in device performance comes from meticulously designing the hole and electron blocking layers to increase carrier injection efficiency. The quantum well based UV-LED was designed to emit at 280nm, which is an effective wavelength for water disinfection application.

Publication Stats

1k Citations
332.74 Total Impact Points

Institutions

  • 2010–2015
    • King Abdullah University of Science and Technology
      • • Division of Computer, Electrical and Mathematical Sciences and Engineering (CEMSE)
      • • Division of Physical Sciences and Engineering (PSE)
      Djidda, Makkah, Saudi Arabia
  • 2004–2011
    • Lehigh University
      • Department of Electrical and Computer Engineering
      Bethlehem, Pennsylvania, United States
  • 1997–2003
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Tumasik, Singapore
  • 2000
    • Université de Sherbrooke
      Шербрук, Quebec, Canada
  • 1994–1998
    • University of Glasgow
      • Division of Electronics and Electrical Engineering
      Glasgow, SCT, United Kingdom