H. Y. Yang

Singapore University of Technology and Design, Singapore

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Publications (63)200.06 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We show that by maximizing the amount of organosilane functional groups, the quantum yield of surface functionalized carbon nanodots (C-dots) dispersed in epoxy can be enhanced to 68% under optical excitation at 450 nm wavelength. This is the highest quantum yield ever recorded for C-dots at such an excitation wavelength. Lasing emission can also be demonstrated from a Fabry–Perot cavity by using C-dots as the gain medium. The lasing threshold is found to be 200 W cm−2 which is 2 orders of magnitude lower than that provided in the recent reports. Furthermore, tunable single-mode lasing over a bandwidth of 60 nm wide is achieved from the Fabry–Perot cavity in the Littrow configuration.
    J. Mater. Chem. C. 01/2014; 2(8).
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    ABSTRACT: A nonvolatile memory based on ink-jet printed In-Ga-Zn oxide (IGZO) thin film transistor with bottom gate bottom contact architecture is reported. The memory device contains SiO2 gate dielectric layer embedded with silicon nanocrystals, which act as charge trapping sites. Memory effects were observed by a clockwise loop in Vgs-Id curves, which is attributed to the charging and discharging of the silicon nanocrystals. The printed IGZO memory exhibits a high (about 1 × 103) on/off ratio.
    Nanoelectronics Conference (INEC), 2013 IEEE 5th International; 01/2013
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    ABSTRACT: Investigation on the room-temperature ultraviolet lasing characteristics of a single ZnS microbelt laser is presented. Lasing emission with peak wavelength at round 335 nm is observed from the hexagonal-wurtzite phase of ZnS microbelt under optical excitation. This is due to the Fabry-Perot resonance along the length of the microbelt. By studying the low-temperature and time-resolved photoluminescence, it is verified that the corresponding lasing characteristics are attributed to the excitonic optical gain process. Furthermore, the rectangular cross-sectional nanostructure of ZnS microbelt suppresses TM polarization for excitation power lower than ~1.4 times the threshold. Hence, ZnS microbelts can be a promising building block to realize ultraviolet semiconductor lasers with control of laser polarization.
    IEEE Journal of Selected Topics in Quantum Electronics 01/2013; 19(4):1501705-1501705. · 4.08 Impact Factor
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    ABSTRACT: Effective control of room-temperature electroluminescence of n-ZnMgO/p-GaN light-emitting diodes (LEDs) over both emission intensity and wavelength is demonstrated. With varied Mg concentration, the intensity of LEDs in the near-ultraviolet region is increased due to the effective radiative recombination in the ZnMgO layer. Furthermore, the emission wavelength is shifted to the green/yellow spectral region by employing an indium-tin-oxide thin film as the dopant source, where thermally activated indium diffusion creates extra deep defect levels for carrier recombination. These results clearly demonstrate the effectiveness of controlled metal incorporation in achieving high energy efficiency and spectral tunability of the n-ZnMgO/p-GaN LED devices.
    Applied Physics Letters 12/2012; 101(26). · 3.79 Impact Factor
  • W F Zhang, H Zhu, S F Yu, H Y Yang
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    ABSTRACT: Lasing is observed from carbon nanodots (C-dots) dispersed into a layer of poly(ethylene glycol) coated on the surface of optical fibers under 266 nm optical excitation. This is due to the enhancement of photoluminescence intensity via the esterification of carboxylic groups of the C-dots, and the formation of high-Q cylindrical microcavities to support second-type whispering gallery modes.
    Advanced Materials 03/2012; 24(17):2263-7. · 14.83 Impact Factor
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    ABSTRACT: Although the dielectric behavior of nanostructured semiconductors has been intensively investigated, the physics behind observations remains disputed with possible mechanisms such as quantum confinement and dangling bond polarization. Here we show that theoretical reproduction of the measured dielectric suppression of Ge nanocrystals asserts that the dielectric suppression originates from the shorter and stronger bonds at the skin-deep surface, the associated local densification and quantum entrapment of energy. Coordination-imperfection induced local quantum entrapment perturbs the Hamiltonian that determines the band gap and hence, the process of electron polarization consequently.
    Nanoscale 02/2012; 4(4):1308-11. · 6.73 Impact Factor
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    ABSTRACT: Room-temperature random lasing is achieved from an n-AlN/p-GaN heterojunction. The highly disordered n-AlN layer, which was deposited on p-GaN:Mg layer via radio frequency magnetron sputtering, acts as a scattering medium to sustain coherent optical feedback. The p-GaN:Mg layer grown on sapphire provides optical amplification to the scattered light propagating along the heterojunction. Hence, lasing peaks of line width less than 0.4 nm are emerged from the emission spectra at round 370 nm for the heterojunction under forward bias larger than 5.1 V. Lasing characteristics of the heterojunction are in agreement with the behavior of random lasers.
    ACS Applied Materials & Interfaces 05/2011; 3(5):1726-30. · 5.90 Impact Factor
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    ABSTRACT: An index-guided zinc oxide random laser array was designed and fabricated to achieve spatial overlapping of random spectral modes between the adjacent random cavities. Hence, the number of lasing spectral modes of the laser array can be limited by the phenomenon of spectral repulsion. In addition, the total spectrally coherent emission power can be enhanced by increasing the number of random cavities.
    IEEE Photonics Technology Letters 04/2011; 23(8):522-524. · 2.04 Impact Factor
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    ABSTRACT: Ag coated ZnO/Al2O3 distributed Bragg reflectors (DBRs), which were fabricated by a modified filtered cathodic vacuum arc technique at room temperature, shown the formation of visible Tamm plasmon polaritons (TPP). By varying the thickness of Ag and top ZnO dielectric layer of the DBR, it can be verified that the excitation of dip at the stopband of the reflection spectrum is related to TPPs. As visible light was used to excite TPPs, the corresponding effective mass can be reduced to 1.3 × 10− 5 of the free electron mass.
    Optics Communications 01/2011; · 1.44 Impact Factor
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    H K Liang, S F Yu, H Y Yang
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    ABSTRACT: DOI: 10.1063/1.3527922 An array of highly disordered i-ZnO:Al(3%) random cavities, which have 1 μm width, 150 nm thickness, and 2 mm length, is sandwiched between n-ZnO:Al(5%) and p-GaN/sapphire substrate to form an array of heterojunctions. The random cavities, which are electrically isolated and optically coupled with the adjacent random cavities, are laterally separated by a 1 μm wide Al₂O₃ dielectric insulator. Stable single-mode operation is observed from the laser diode array under high electrical pumping (i.e., >6×threshold current) at room temperature.
    Applied Physics Letters 12/2010; · 3.79 Impact Factor
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    H. Y. Yang, S. F. Yu, Y. Y. Hui, S. P. Lau
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    ABSTRACT: Aluminum nitride (AlN) nanowires were prepared by the carbothermal reduction method. A heterojunction light-emitting diode (LED) was fabricated by depositing randomly aligned AlN nanowires onto p-type 4H–SiC substrate. When a forward bias voltage greater than 8 V was applied to the LED, a broad band emission peaked at 417 nm could be observed. The peak deconvolution revealed four emission peaks at ∼ 400, 420, 468, and 525 nm. These emission peaks may be attributed to the radiative recombination between electrons from trap-level states and holes from the valence band of the AlN nanowires.
    Applied Physics Letters 11/2010; 97(19):191105-191105-3. · 3.79 Impact Factor
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    ABSTRACT: Room-temperature electroluminescence (EL) has been realized from Sn-doped In(2)O(3) (In(2)O(3):Sn) nanorods. Heterojunction light-emitting diode (LED) was formed by depositing a layer of randomly packed n-In(2)O(3):Sn nanorods onto a p-type 4H-SiC substrate. It is found that the emission intensity of the heterojunction LED under forward bias can be maximized by doping the In(2)O(3) nanorods with 3 mol. % of Sn. Furthermore, two emission peaks of the EL spectra are observed at approximately 395 and approximately 440 nm. These ultraviolet and visible peaks are attributed to the radiative recombination at Sn induced and intrinsic defect states of the In(2)O(3):Sn nanorods.
    Optics Express 07/2010; 18(15):15585-90. · 3.55 Impact Factor
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    H Y Yang, S F Yu, G P Li, T Wu
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    ABSTRACT: Lasing characteristics of randomly assembled ZnO nanowires (NWs) coated with different thickness of MgO layers are investigated. It is found that the MgO coated randomly assembled ZnO NWs demonstrate random lasing action and the formation of coherent optical feedback is dependent on the thickness of MgO coating. Pump threshold of the MgO coated randomly assembled ZnO NWs increases with the increase of MgO thickness. Nevertheless, the appropriate use of MgO coating can reduce the pump threshold by approximately 30% and the corresponding characteristic temperature can be improved by 28 K.
    Optics Express 06/2010; 18(13):13647-54. · 3.55 Impact Factor
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    H. Y. Yang, S. F. Yu, J. Yan, L. D. Zhang
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    ABSTRACT: Wide-bandwidth random lasing action is observed from the randomly assembled ZnS/ZnO biaxial nanobelt heterostructures under optical excitation. This is because optical gain at ultraviolet regime can be obtained from the near-band-edge radiative recombination of ZnS and ZnO. Surface defects related radiative recombination centers of ZnS and ZnO nanostructures also contribute to the visible optical gain. Hence, a broadband optical gain is obtained from the ZnS/ZnO biaxial nanobelt heterostructures. Moreover, a wide bandwidth coherent optical feedback can be achieved from the randomly assembled biaxial nanobelts due to high refractive index contrast between the nanobelts and air.
    Applied Physics Letters 04/2010; 96(14):141115-141115-3. · 3.79 Impact Factor
  • ACS Applied Materials & Interfaces 04/2010; · 5.90 Impact Factor
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    ABSTRACT: Electroluminescence characteristics of a heterojunction light-emitting diode, which was fabricated by depositing a layer of randomly assembled n-SnO(2) nanowires on p-GaN:Mg/sapphire substrate via vapor transport method, were investigated at room temperature. Peak wavelength emission at around 388 nm was observed for the diode under forward bias. This is mainly related to the radiative recombination of weakly bounded excitons at the shallow-trapped states of SnO(2) nanowires, Under reverse bias, near bandedge emission from the p-GaN:Mg/sapphire leads to the observation of emission peak at around 370 nm.
    ACS Applied Materials & Interfaces 04/2010; 2(4):1191-4. · 5.90 Impact Factor
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    H K Liang, S F Yu, H Y Yang
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    ABSTRACT: An edge-emitting ultraviolet n-ZnO:Al/i-ZnO/p-GaN heterojunction light-emitting diode with a rib waveguide is fabricated by filtered cathodic vacuum arc technique at low deposition temperature (approximately 150 degrees C). Electroluminescence with emission peak at 387 nm is observed. Good correlation between electro- and photo- luminescence spectra suggests that the i-ZnO layer of the heterojunction supports radiative excitonic recombination. Furthermore, it is found that the emission intensity can be enhanced by approximately 5 times due to the presence of the rib waveguide. Only fundamental TE and TM polarizations are supported inside the rib waveguide and the intensity of TE polarization is approximately 2.2 time larger than that of TM polarization.
    Optics Express 02/2010; 18(4):3687-92. · 3.55 Impact Factor
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    ABSTRACT: Lasing characteristics of randomly assembled SnO <sub>2</sub> backbone nanowires coated with ZnO nanofins are investigated. It is shown that the hierarchical nanostructures can sustain ultraviolet random lasing action even at substrate temperature higher than 700 K and the corresponding characteristic temperature is found to be about 390 K. This is because the presence of ZnO nanofins improves heat transfer from the SnO <sub>2</sub> backbone nanowires to the surrounding. Hence, some portion of the hierarchical nanostructures can be cooled down and the corresponding optical gain can be maintained even at high substrate temperature.
    Journal of Applied Physics 01/2010; · 2.21 Impact Factor
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    ABSTRACT: Controllable size of silicon (Si) nanocrystals can be achieved by a two-step rapid thermal annealing technique consisting of rapid annealing at 1000°C in nitrogen ambient and rapid oxidation at 600–800°C of a radio frequency magnetron co-sputtered Si-rich oxide/SiO2 superlattice structure. The photoluminescence (PL) spectra related to Si nanocrystals were observed in the visible range (600–900 nm). After rapid oxidation, the size of the nanocrystals was reduced and the quality of the Si nanocrystal/SiO2 interface was improved, resulting in a blue shift and an increase of the PL peak intensity. Finally, annealing in air increases the PL intensity further.
    Applied Physics A 01/2010; 98(4):867-871. · 1.69 Impact Factor
  • H.Y. Yang, S.F. Yu, S.P. Lau
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    ABSTRACT: Transverse optical confinement in zinc oxide (ZnO) random cavities on Si substrate is achieved by a self-generated zinc silicate (Zn2SiO4) layer formed between the interface of ZnO and Si after thermal annealing.
    OptoeElectronics and Communications Conference (OECC), 2010 15th; 01/2010

Publication Stats

556 Citations
200.06 Total Impact Points

Institutions

  • 2010–2014
    • Singapore University of Technology and Design
      • Division of Engineering Product Development
      Singapore
  • 2012
    • The Hong Kong Polytechnic University
      • Department of Applied Physics
      Hong Kong, Hong Kong
  • 2005–2010
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Singapore, Singapore
    • Nagoya Institute of Technology
      • Graduate School of Engineering
      Nagoya, Aichi, Japan
  • 2008
    • Japan Fine Ceramics Center
      Nagoya, Aichi, Japan