B. S. Ooi

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

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Publications (286)401.37 Total impact


  • No preview · Article · Jan 2016
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    ABSTRACT: High-quality nitride materials grown on scalable and low-cost metallic substrates are considerably attractive for high-power light emitters. We demonstrate here, for the first time, the high-power red (705 nm) InGaN/GaN quantum-disks (Qdisks)-in-nanowire light-emitting diodes (LEDs) self-assembled directly on metal-substrate. The LEDs exhibited a low turn-on voltage of ~2 V without efficiency droop up to injection current of 500 mA (1.6 kA/cm(2)) at ~5 V. This is achieved through the direct growth and optimization of high-quality nanowires on titanium (Ti) coated bulk polycrystalline-molybdenum (Mo) substrates. We performed extensive studies on the growth mechanisms, obtained high-crystal-quality nanowires, and confirmed the epitaxial relationship between the cubic titanium nitride (TiN) transition layer and the hexagonal nanowires. The growth of nanowires on all-metal stack of TiN/Ti/Mo enables simultaneous implementation of n-metal contact, reflector and heat-sink, which greatly simplifies the fabrication process of high-power light emitters. Our work ushers in a practical platform for high-power nanowires light emitters, providing versatile solutions for multiple cross-disciplinary applications that are greatly enhanced by leveraging on the chemical stability of nitride materials, large specific surface of nanowires, chemical lift-off ready layer structures, and reusable Mo substrates.
    Full-text · Article · Jan 2016 · Nano Letters
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    Full-text · Article · Jan 2016 · Journal of Physical Chemistry Letters

  • No preview · Article · Dec 2015 · Optics Express
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    ABSTRACT: An advanced light-fidelity (Li-Fi) system based on the blue Gallium nitride (GaN) laser diode (LD) with a compact white-light phosphorous diffuser is demonstrated for fusing the indoor white-lighting and visible light communication (VLC). The phosphorous diffuser adhered blue GaN LD broadens luminescent spectrum and diverges beam spot to provide ample functionality including the completeness of Li-Fi feature and the quality of white-lighting. The phosphorous diffuser diverged white-light spot covers a radiant angle up to 120o with CIE coordinates of (0.34, 0.37). On the other hand, the degradation on throughput frequency response of the blue LD is mainly attributed to the self-feedback caused by the reflection from the phosphor-air interface. It represents the current state-of-the-art performance on carrying 5.2-Gbit/s orthogonal frequency-division multiplexed 16-quadrature-amplitude modulation (16-QAM OFDM) data with a bit error rate (BER) of 3.1 × 10−3 over a 60-cm free-space link. This work aims to explore the plausibility of the phosphorous diffuser diverged blue GaN LD for future hybrid white-lighting and VLC systems.
    Full-text · Article · Dec 2015 · Scientific Reports
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    ABSTRACT: The high optical gain and absorption of organic-inorganic hybrid perovskites have attracted attention for photonic device applications. However, owing to the sensitivity of organic moieties to solvents and temperature, device processing is challenging, particularly for patterning. Here, we report the direct patterning of perovskites using chemically gas-assisted focused-ion beam (GAFIB) etching with XeF2 and I2 precursors. We demonstrate etching enhancement in addition to controllability and marginal surface damage compared to focused-ion beam (FIB) etching without precursors. Utilizing the GAFIB etching, we fabricated a uniform and periodic sub-micron perovskite subwavelength grating (SWG) absorber with broadband absorption and nanoscale precision. Our results demonstrate the use of FIB as a sub-micron patterning tool and a means of providing surface treatment (after FIB patterning to minimize optical loss) for perovskite photonic nanostructures. The SWG absorber can be patterned on perovskite solar cells to enhance the device efficiency through increasing light trapping and absorption.
    Full-text · Article · Dec 2015 · Journal of Physical Chemistry Letters
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    ABSTRACT: We demonstrate ultra-air- and photostable CsPbBr3 QDs by using an inorganic-organic hybrid ion pair as the capping ligand. This passivation approach to perovskite QDs yields high photoluminescence quantum yield with unprecedented operational stability in ambient conditions (60 ± 5% lab humidity) and high pump fluences, thus overcoming one of the greatest challenges impeding the development of perovskite-based applications. Due to the robustness of passivated perovskite QDs, we were able to induce ultra-stable amplified spontaneous emission (ASE) in solution processed QD films not only through one photon but also through two-photon absorption processes. The latter has not been observed before in the family of perovskite materials. More importantly, passivated perovskite QD films showed remarkable photostability under continuous pulsed laser excitation in ambient conditions for at least 34 hours (corresponds to 1.2 × 108 laser shots), substantially exceeding the stability of other colloidal QD systems in which ASE has been observed.
    Full-text · Article · Dec 2015 · Journal of Physical Chemistry Letters
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    Full-text · Article · Nov 2015 · Optics Express
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    ABSTRACT: III-nitride nanowire diode heterostructures with multiple In0.85Ga0.15N disks and graded InGaN mode confining regions were grown by molecular beam epitaxy on (001)Si substrates. The aerial density of the 60 nm nanowires is ∼3 × 1010 cm-2. A radiative recombination lifetime of 1.84 ns in the disks is measured by time-resolved luminescence measurements. Edge-emitting nanowire lasers have been fabricated and characterized. Measured values of Jth, T0, and dg/dn in these devices are 1.24 kA/cm2, 242 K, and 5.6 × 10-17 cm2, respectively. The peak emission is observed at ∼1.2 μm.
    No preview · Article · Nov 2015 · Applied Physics Letters
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    ABSTRACT: Nanoscale periodic patterning on insulating materials using focused-ion beam (FIB) is challenging because of charging effect, which causes pattern distortion and resolution degradation. In this paper, the authors used a charging suppression scheme using electron conducting polymer for the implementation of FIB patterned dielectric subwavelength grating (SWG) reflector. Prior to the FIB patterning, the authors numerically designed the optimal structure and the fabrication tolerance for all grating parameters (period, grating thickness, fill-factor, and low refractive index layer thickness) using the rigorous-coupled wave analysis computation. Then, the authors performed the FIB patterning on the dielectric SWG reflector spin-coated with electron conducting polymer for the anticharging purpose. They also performed similar patterning using thin conductive film anticharging scheme (30 nm Cr coating) for comparison. Their results show that the electron conducting polymer anticharging scheme effectively suppressing the charging effect during the FIB patterning of dielectric SWG reflector. The fabricated grating exhibited nanoscale precision, high uniformity and contrast, constant patterning, and complied with fabrication tolerance for all grating parameters across the entire patterned area. Utilization of electron conducting polymer leads to a simpler anticharging scheme with high precision and uniformity for FIB patterning on insulator materials.
    Full-text · Article · Nov 2015 · Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures
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    ABSTRACT: We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser structure based on seven dielectric capping layers. Compared to the typical SiO2 and Si3N4 films, HfO2 and SrTiO3 dielectric layers showed superior enhancement and suppression of intermixing up to 725°C, respectively. A QD peak ground-state differential blue shift of >175 nm (>148 meV) is obtained for HfO2 capped sample. Likewise, investigation of TiO2, Al2O3, and ZnO capping films showed unusual characteristics, such as intermixing-control caps at low annealing temperature (650°C) and interdiffusion-promoting caps at high temperatures (≥675°C). We qualitatively compared the degree of intermixing induced by these films by extracting the rate of intermixing and the temperature for ground-state and excited-state convergences. Based on our systematic characterization, we established reference intermixing processes based on seven different dielectric encapsulation materials. The tailored wavelength emission of ∼1060-1200 nm at room temperature and improved optical quality exhibited from intermixed QDs would serve as key materials for eventual realization of low-cost, compact, and agile lasers. Applications include solid-state laser pumping, optical communications, gas sensing, biomedical imaging, green-yellow-orange coherent light generation, as well as addressing photonic integration via area-selective, and postgrowth bandgap engineering. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
    No preview · Article · Oct 2015 · Optical Engineering
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    ABSTRACT: We experimentally demonstrate a record high-speed underwater wireless optical communication (UWOC) over 7 m distance using on-off keying non-return-to-zero (OOK-NRZ) modulation scheme. The communication link uses a commercial TO-9 packaged pigtailed 520 nm laser diode (LD) with 1.2 GHz bandwidth as the optical transmitter and an avalanche photodiode (APD) module as the receiver. At 2.3 Gbit/s transmission, the measured bit error rate of the received data is 2.23×10<sup>-4</sup>, well below the forward error correction (FEC) threshold of 2×10<sup>-3</sup> required for error-free operation. The high bandwidth of the LD coupled with high sensitivity APD and optimized operating conditions is the key enabling factor in obtaining high bit rate transmission in our proposed system. To the best of our knowledge, this result presents the highest data rate ever achieved in UWOC systems thus far.
    No preview · Article · Sep 2015 · Optics Express
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    ABSTRACT: We experimentally demonstrate an underwater wireless optical communications (UWOC) employing 450-nm TO-9 packaged and fiber-pigtailed laser diode (LD) directly encoded with an orthogonal frequency division multiplexed quadrature amplitude modulation (QAM-OFDM) data. A record data rate of up to 4.8 Gbit/s over 5.4-m transmission distance is achieved. By encoding the full 1.2-GHz bandwidth of the 450-nm LD with a 16-QAM-OFDM data, an error vector magnitude (EVM) of 16.5%, a signal-to-noise ratio (SNR) of 15.63 dB and a bit error rate (BER) of 2.6 × 10<sup>-3</sup>, well pass the forward error correction (FEC) criterion, were obtained.
    No preview · Article · Sep 2015 · Optics Express
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    ABSTRACT: Impurity free vacancy disordering induced highly intermixed InAs/ GaAs quantum-dot lasers are reported with high internal quantum efficiency (>89%). The lasers are shown to retain the device characteristics after intermixing and emitting in the important wavelength of ∼1070-1190 nm. The non-coated facet Fabry-Perot post-growth wavelength tuned lasers exhibits high-power (>1.4W) and high-gain (∼50 cm-1), suitable for applications in frequency doubled green- yellow-orange laser realisation, gas sensing, metrology etc.
    Full-text · Article · Sep 2015 · Electronics Letters
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    ABSTRACT: The coherent amplified spontaneous emission and high photoluminescence quantum efficiency of organolead trihalide perovskite have led to research interest in this material for use in photonic devices. In this paper, the authors present a focused-ion beam patterning strategy for methylammonium lead tribromide (MAPbBr3) perovskite crystal for subwavelength grating nanophotonic applications. The essential parameters for milling, such as the number of scan passes, dwell time, ion dose, ion current, ion incident angle, and gas-assisted etching, were experimentally evaluated to determine the sputtering yield of the perovskite. Based on our patterning conditions, the authors observed that the sputtering yield ranged from 0.0302 to 0.0719 lm3/pC for the MAPbBr3 perovskite crystal. Using XeF2 for the focused-ion beam gas-assisted etching, the authors determined that the etching rate was reduced to between 0.40 and 0.97, depending on the ion dose, compared with milling with ions only. Using the optimized patterning parameters, the authors patterned binary and circular subwavelength grating reflectors on the MAPbBr3 perovskite crystal using the focused-ion beam technique. Based on the computed grating structure with around 97% reflectivity, all of the grating dimensions (period, duty cycle, and grating thickness) were patterned with nanoscale precision (>63 nm), high contrast, and excellent uniformity. Our results provide a platform for utilizing the focused-ion beam technique for fast prototyping of photonic nanostructures or nanodevices on organolead trihalide perovskite.
    Full-text · Article · Aug 2015 · Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures
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    ABSTRACT: We present a detailed study on the effects of dangling bond passivation and the comparison of different sulfides passivation process on the properties of InGaN/GaN quantum-disk (Qdisk)-in-nanowire based light emitting diodes (NW-LEDs). Our results demonstrated the first organic sulfide passivation process for nitride nanowires (NWs). The results from Raman spectroscopy, photoluminescence (PL) measurements, and X-ray photoelectron spectroscopy (XPS) showed octadecylthiol (ODT) effectively passivated the surface states, and altered the surface dynamic charge, thereby recovered the band-edge emission. The effectiveness of the process with passivation duration was also studied. Moreover, we also compared the electro-optical performance of NW-LEDs emitting at green wavelength before and after ODT passivation. We have shown that the Shockley-Read-Hall (SRH) non-radiative recombination of NW-LEDs can be greatly reduced after passivation by ODT, which led to a much faster increasing trend of quantum efficiency, and higher peak efficiency. Our results highlighted the research opportunity in employing this technique for further design and realization of high performance NW-LEDs and NW-lasers.
    Full-text · Article · Jul 2015 · Nanoscale
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    Full-text · Dataset · Jul 2015
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    ABSTRACT: With increasing interest in visible light communication, the laser diode (LD) provides an attractive alternative, with higher efficiency, shorter linewidth and larger bandwidth for high-speed visible light communication (VLC). Previously, more than 3 Gbps data rate was demonstrated using LED. By using LDs and spectral-efficient orthogonal frequency division multiplexing encoding scheme, significantly higher data rates has been achieved in this work. Using 16-QAM modulation scheme, in conjunction with red, blue and green LDs, data rates of 4.4 Gbps, 4 Gbps and 4 Gbps, with the corresponding BER/SNR/EVM of 3.3 × 10<sup>-3</sup>/15.3/17.9, 1.4 × 10<sup>-3</sup>/16.3/15.4 and 2.8 × 10<sup>-3</sup>/15.5/16.7were obtained over transmission distance of ~20 cm. We also simultaneously demonstrated white light emission using red, blue and green LDs, after passing through a commercially available diffuser element. Our work highlighted that a tradeoff exists in operating the blue LDs at optimum bias condition while maintaining good color temperature. The best results were obtained when encoding red LDs which gave both the strongest received signal amplitude and white light with CCT value of 5835K.
    Full-text · Article · Jul 2015 · Optics Express
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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.
    Full-text · Article · Jun 2015 · Electronics Letters
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    M S Alias · H-. Y Liao · T K Ng · B S Ooi
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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.
    Full-text · Conference Paper · May 2015

Publication Stats

2k Citations
401.37 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
  • 2012
    • The University of Sheffield
      Sheffield, England, United Kingdom
  • 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
  • 1994-1998
    • University of Glasgow
      • Division of Electronics and Electrical Engineering
      Glasgow, SCT, United Kingdom