W H Lan

National University of Kaohsiung, Kao-hsiung-shih, Kaohsiung, Taiwan

Are you W H Lan?

Claim your profile

Publications (95)139.72 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: GaN p-i-n ultraviolet (UV) photodetectors (PDs) with a low-temperature (LT)-AlN interlayer were proposed and fabricated. It was found that the dark current of such detectors is as small as 28pA even at a high reverse bias of 40 V. Although the high potential barrier at the AlN-GaN interface would slightly reduce the responsivity of PD under low reverse biases, the high UV-to-visible rejection ratio of the PD with an LT-AlN interlayer could be achieved under high reverse biases due to its very low dark current. The rejection ratio of the PD with the LT-AlN interlayer is as large as 735 at the reverse bias of 40 V.
    IEEE Photonics Technology Letters 08/2008; · 2.04 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nitride-based p-i-n ultraviolet (UV) photodetectors with a low-temperature (LT) GaN interlayer were proposed and fabricated. Compared with a conventional GaN p-i-n photodetector, it was found that both the dark current and ideality factor of the p-i-n photodetector with an LT-GaN interlayer became larger whereas the UV-to-visible rejection ratio became smaller because of the poor crystal quality of the LT-GaN interlayer. However, the responsivity of the GaN p-i-n photodetector with an LT-GaN interlayer was larger than that of the conventional GaN p-i-n photodetector under a high reverse bias because of the carrier multiplication effect and/or internal gain that originated from the defect levels.
    IET Optoelectronics 05/2008; · 0.85 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gallium nitride p-i-n ultraviolet photodiodes (PDs) with a titanium dioxide (TiO<sub>2</sub>) nano-particles roughened surface have been fabricated. It was found that the responsivity and external quantum efficiency can be improved 60% on the surface roughened PDs. It was also found that light absorption can be enhanced from various incident angles by the TiO<sub>2</sub> roughened surface. Furthermore, the high detectivity of 9.2 times 10<sup>13</sup> cmldrHz<sup>1</sup> <sup>/2</sup>ldrW<sup>-1</sup> can be achieved from the PD with a rough surface.
    IEEE Photonics Technology Letters 03/2008; · 2.04 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Higher light output intensity and wider polar radiation pattern of InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) with a different nanoscale titanium dioxide (TiO2) textured densities film have been observed. The light output power values and external quantum efficiency of the conventional LEDs at an injection current of 20 mA are 6.34 mW and 11.7%, respectively. The light output power values and external quantum efficiency of the nanoscaled TiO2 textured LEDs at an injection current of 20 mA are 7.55 mW and 14%, respectively. The light output intensity and power values of the nanoscaled TiO2 textured LEDs is approximately 65% and 20% higher than that of the conventional LEDs, respectively.
    Solid-State Electronics 01/2008; · 1.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gallium nitride p-i-n ultraviolet photodiodes with low-temperature (LT)-GaN interlayer have been fabricated. It was found that the dark current of photodiode with LT-GaN interlayer is as small as 143 pA at 5 V reverse bias. It was also found that the responsivity of the photodiode with LT-GaN interlayer can be enhanced at a small electric field ( ∼ 0.4 MV/cm) due to the carrier multiplication effect. The UV photocurrent gain of 13 and large ionization coefficient (α = 3.1×105 cm−1) were also observed in the detector with LT-GaN interlayer. Furthermore, we can achieve a large peak responsivity of 2.27 A/W from the photodiode with LT-GaN interlayer.
    Applied Physics Letters 10/2007; 91(17):173502-173502-3. · 3.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Thin InGaN epitaxial layers and GaN-based light-emitting diodes (LEDs) on conventional and vicinal cut sapphire substrates are prepared. It is found that indium atoms are distributed much more uniformly in the samples prepared on vicinal cut sapphire substrates. It is also found that stronger electroluminescence intensity can be achieved without the band-filling effect of localised states from the LEDs with vicinal cut sapphire substrate. With 20 mA current injection, it is found that 44% electroluminescence intensity enhancement can be achieved by using the 1deg tilted sapphire substrate
    IET Optoelectronics 03/2007; · 0.85 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: InN epitaxial layers were grown on GaN/sapphire templates by metalorganic chemical vapor deposition (MOCVD) at various temperatures. It was found that surfaces of these samples were all reticular and the sample surface became rougher as we increased the growth temperature. It was also found that growth rate increased with increasing growth temperature and the growth rate could reach 470nm/h for the InN epitaxial layer grown at 675°C. Furthermore, it was found that we achieved the highest mobility of 1300cm2/Vs and the lowest carrier concentration of 4.6×1018cm−3 from the InN epitaxial layer grown at 625°C.
    Optical Materials 01/2007; 30(4):517-520. · 1.92 Impact Factor
  • W.-H. Lan, K.-C. Huang, K.F. Huang
    [Show abstract] [Hide abstract]
    ABSTRACT: KOH treatment is investigated as a method to improve the I-V characteristics of AlGaN-based photodiodes. The defects in the photodiode may enhance the dark current, and cause some photocurrents with incident photon energy less than the absorption edge. With the KOH treatment in the process, the defects and whisker-like features could be reduced. High rejection ratio in the spectral responsivity could be achieved. The KOH treatment is a good method to reduce the surface defects in AlGaN-based photodiodes.
    Electronics Letters 08/2006; · 1.04 Impact Factor
  • Journal of Dental Sciences. 01/2006; 1(2):53-58.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of the GaN epilayers and LED structures grown by metalorganic chemical vapor deposition on 1° off c-plane sapphire substrate were studied. Although the 1° off-axis GaN sample has slightly rough surface morphology, it has narrower full-width at half-maximum (FWHM) of X-ray asymmetrical reflection (10–12), higher mobility, lower compensating acceptor concentration and lower etching pits densities (EPD) than the on-axis GaN sample. And it also has lower etching pits densities (EPD). To reduce the threading dislocations in GaN films grown on vicinal substrates is attributed. A very weak yellow luminescence is observed in photoluminescence (PL) spectra of 1° off-axis GaN sample. Finally, comparing to LED structures grown on on-axis c-plane sapphire substrates, the LED structures grown on 1° off substrate show a blue shift of PL wavelength and 2.6 times stronger in PL intensity. The electroluminescence (EL) intensity of 1° LED sample rises faster in small amount of driving current region.
    Materials Science and Engineering B-advanced Functional Solid-state Materials. 01/2006; 128(1):107-110.
  • Chen WP, Lee BS, Lan WH, Lin CP
    Chin Dent J. 01/2005; 24:35-44.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Transforming growth factor-beta (TGF-beta) is important in regulating the repair and regeneration of damaged dental pulp. For further elucidating the roles of different isoforms of TGF-beta in the healing and inflammatory processes of human dental pulp, we found that TGF-beta1, TGF-beta2 and TGF-beta3 inhibited the growth of two human dental pulp cell strains in vitro by 19-29, 18-25 and 23-26%, respectively, at a concentration of 0.5 ng/ml. TGF-beta also differentially stimulated the collagen synthesis of pulp cells. Collagen synthesis increased by 1 ng/ml of TGF-beta1 and TGF-beta2 by 42 and 51%, respectively. TGF-beta3 (0.1-1 ng/ml) lacked of stimulatory effect on collagen synthesis of pulp cells. Pulp cells have the intrinsic capacity to contract collagen lattice, leading to decreasing of lattice diameter. An 8 h exposure to TGF-beta1 and TGF-beta2 enhanced the pulp cell-populated collagen lattice contraction at concentrations ranging from 0.2 to 3 ng/ml. At similar concentrations, TGF-beta3 lacked of this stimulatory effect. When collagen lattice were detached after 24 h of exposure, TGF-beta1 and TGF-beta2 (0.6-3 ng/ml) induced the pulp cells-populated collagen lattice contraction within 4-8h of gel detachment. These results indicate that TGF-beta-induced collagen lattice contraction is a late cellular event. These in vitro results indicate that effects of TGF-beta isoforms on the growth, collagen synthesis and collagen lattice contraction of pulp cells may play crucial roles in the pathobiological processes of dental pulp.
    Archives of Oral Biology 01/2005; 50(5):469-479. · 1.55 Impact Factor
  • Li UM, Lan WH, Lin CP
    Chin Dent J. 01/2005; 26:448-454.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nitride-based GaN/In0.12Ga0.88N heterostructure field effect transistors (HFETs) with semi-insulating Mg-doped GaN current blocking layers were successfully fabricated. The as-grown layers exhibited a very smooth surface. The DC characteristics of these HFETs were substantially improved over those previously reported. Devices with a 0.75 μm gate length showed a maximum drain current (IDS) of 421 mA/mm, and a maximum gm of about 85.6 mS/mm at VGS between −0.5 and −3 V. The device which had a very good pinch-off with source–drain (S–D) leakage current was negligibly small, in the range of 10−1–10−2 mA/mm. The RF characteristic of devices showed the current gain cutoff frequency, fT, was 7.45 GHz and the maximum oscillation frequency, fMAX, was 12.36 GHz.
    Journal of Crystal Growth 12/2004; 272(s 1–4):300–304. · 1.55 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a detailed study of the localized carrier effect and optical characterization of the novel dilute-nitride GaInNP films. These films were grown by metal-organic vapor phase epitaxy on GaAs (1 0 0) substrates. These epitaxial layers were then characterized by a high-resolution X-ray rocking curve (XRC) and photoluminescence (PL) spectra. With nitrogen incorporation, the PL peak red shifts, indicating bandgap reduction, and the line width broadening increases due to the increase of non-radiative centers. The S-shape in temperature dependence of the PL spectra shows a considerable number of carriers detrap from localized states to higher bound exciton states as the increasing temperature. The PR spectrum is used to confirm the nitrogen induced localization. Furthermore, this localization phenomenon observed in low-temperature PL no longer exists after RTA process. This result suggests that the crystal quality is improved significantly by thermal treatment.
    Journal of Crystal Growth 12/2004; 272:765-771. · 1.55 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Nitride-based Al<sub>0.24</sub>Ga<sub>0.76</sub>N/GaN heterostructure field effect transistors (HFETs) with carrier confinement layers were fabricated. The results found that the enhanced 2 dimensional electron gas (2DEG) carrier mobility from 1070 to 1180 cm<sup>2</sup>V<sup>-1</sup>sec<sup>-1</sup> by the insertion of a Mg-doped semi-insulating carrier confinement layer with a Cp<sub>2</sub>Mg flow rate of 2.36×10<sup>-8</sup> mole/min and smoother sample surface. The DC and RF characteristics of these HFETs were also good.
    Semiconductor Device Research Symposium, 2003 International; 01/2004
  • [Show abstract] [Hide abstract]
    ABSTRACT: Photo-enhanced chemical (PEC) wet etching technology was used to etch GaN and AlGaN epitaxial layers. Figure 1 shows PEC etch rate for the GaN and Al<sub>x</sub>Ga<sub>1-x</sub>N epitaxial layers in aqueous KOH and H<sub>3</sub>PO<sub>4</sub> solutions. It was found that the maximum etch rates were 510 nm/min, 1960 nm/min, 300 nm/min and 0 nm/min for GaN, Al<sub>0.175</sub>Ga<sub>0.825</sub>N, Al<sub>0.23</sub>Ga<sub>0.77</sub>N and Al<sub>0.4</sub>Ga<sub>0.6</sub>N, respectively. Nitride-based Schottky diodes and heterostructure field effect transistors (HFETs) were also fabricated by PEC wet etching. As shown in figures 2, 3 and 4, it was found that we could achieve a saturated I<sub>D</sub> larger than 850 mA/mm and a maximum g<sub>m</sub> about 163 mS/mm from PEC wet etched HFET with a 0.5μm gate length. Compared with dry etched devices, the leakage currents observed from the PEC wet etched devices were also found to be smaller.
    Semiconductor Device Research Symposium, 2003 International; 01/2004
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Photo-enhanced chemical (PEC) wet etching technology was used to etch GaN and AlGaN epitaxial layers. It was found that the maximum etch rates were 510, 1960, 300, and 0 nm/mm for GaN, Al0.175Ga0.825N, Al0.23Ga0.77N, and Al0.4Ga0.6N, respectively. It was also found that we could achieve a high Al0.175Ga0.825N to GaN etch rate ratio of 12.6. Nitride-based Schottky diodes and heterostructure field effect transistors (HFETs) were also fabricated by PEC wet etching. It was found that we could achieve a saturated ID larger than 850 mA/mm and a maximum gm about 163 mS/mm from PEC wet etched HFET with a 0.5 μm gate length. Compared with dry etched devices, the leakage currents observed from the PEC wet etched devices were also found to be smaller.
    Materials Science and Engineering: B. 01/2004;
  • Formosan Journal of Medicine. 01/2004; 8:159-167.
  • Chin Dent J. 01/2004; 23(3):175-181.

Publication Stats

633 Citations
139.72 Total Impact Points

Institutions

  • 2003–2008
    • National University of Kaohsiung
      Kao-hsiung-shih, Kaohsiung, Taiwan
  • 1999–2008
    • National Cheng Kung University
      • Department of Electrical Engineering
      Tainan, Taiwan, Taiwan
  • 1995–2008
    • Chung Shan Institute of Science and Technology
      Hsin-chu-hsien, Taiwan, Taiwan
  • 2002–2005
    • Chang Gung Memorial Hospital
      • Department of Dentistry
      Taipei, Taipei, Taiwan
  • 1995–2005
    • National Taiwan University Hospital
      • School of Dentistry
      T’ai-pei, Taipei, Taiwan
  • 1993–2002
    • National Taiwan University
      • • Department of Dentistry
      • • College of Medicine
      T’ai-pei, Taipei, Taiwan
  • 1998–2001
    • Chang Gung University
      • Department of Biomedical Sciences
      Taoyuan, Taiwan, Taiwan