[show abstract][hide abstract] ABSTRACT: The effect of temperature-dependent electroluminescence (EL) on nitride-based light-emitting diodes (LEDs) with different thicknesses of quantum barrier are studied and demonstrated. It was found that quantum confined stark effect (QCSE) of 6-nm thick barrier was more slightly than that of 9- and 12-nm thick barrier. The results indicated that the polarization field is independent of ambient temperature due to no clearly change of blue-shift value. The results also pointed out that the polarization field within the active region of 12-nm thick barrier was stronger than the others due to larger variation of the wavelength transition position (i.e. blue-shift change to red-shift) from 300 to 350 K, and thus it needed more injection carriers to complete the screening of QCSE. In this study, we reported a simple method to provide useful comparison of electrostatic fields within active region in nitride-based LEDs, specifically for structures consisting of identical active regions with different barrier thicknesses.
Journal of Display Technology 04/2013; 9(4):207-211. · 1.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: This study employed Ar plasma treatment to selectively damage the p-GaN surface under the p-pad electrode as a current-blocking layer (CBL) on nitride-based light-emitting diodes (LEDs). Increasing the resistivity of the p-GaN region under the p-pad electrode can reduce the current flowing vertically downward from the p-pad electrode. At an injection current of 20 mA, the light output power of LEDs with Ar plasma treatment was 13% larger than that of conventional LEDs. At an injection current of 100 mA, the temperature of the p-pad metal on LEDs with Ar plasma treatment is 13 °C lower than that of the LEDs with a SiO2 CBL. However, the electrostatic discharge endurance of LEDs with Ar plasma treatment is the worst due to the surface damage of p-GaN under the p-pad electrode.
Semiconductor Science and Technology 05/2011; 26(8):085005. · 1.92 Impact Factor
[show abstract][hide abstract] ABSTRACT: Nitride-based light-emitting diodes (LEDs) with an n<sup>-</sup> -GaN layer are proposed and fabricated. By providing a larger series resistance in the vertical direction, it was found that the n<sup>-</sup>-GaN layer could enhance LED output intensity due to the enhanced current spreading. It was also found that LEDs with n<sup>-</sup>-GaN layer thicknesses of 0.15, 0.2, and 0.25 μm could endure electrostatic discharge surges up to -1200, - 1800, and -3000 V, respectively.
IEEE Transactions on Device and Materials Reliability 04/2011; · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report the growth of very thick (∼400 nm) quaternary AlInGaN layer on GaN/sapphire template by metalorganic chemical vapor deposition. By properly controlling the trimethylindium molar flow rate, we successfully achieved an Al0.89In0.02GaN layer perfectly lattice matched to the underneath GaN buffer. It was found that we can minimize the number of V-defect pits and the linewidth of X-ray (3 0 2) diffraction peak. Other than the AlInGaN-related photoluminescence peak, we also observed a low-energy band which is originated from indium segregation.
Journal of Crystal Growth 01/2010; 312:1920-1924. · 1.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: An InGaAs buried-heterostructure photodetector (BH-PD) was proposed and fabricated. By introducing etching and refilling with large bandgap and lower concentration semi-insulating InP, it was found that we can reduce the capacitance of P-I-N PDs by 33% without significantly increasing the reverse leakage current. It was also found that we can achieve a 3-dB bandwidth of 11.8 GHz from BH-PD, which was much larger than the 7.1-GHz 3-dB bandwidth observed from conventional InGaAs P-I-N PDs.
IEEE Transactions on Electron Devices 07/2009; · 2.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper, we report the effect of surface HCl treatment on ZnO photoconductive sensors with Ni/Au electrodes after the etching process. Epitaxial ZnO photoconductive sensor film on sapphire substrates was fabricated and then treated with different HCl concentrations. With an incident light wavelength of 370 nm and an applied bias of 10 V, the responsivity of the sensor measured is around 141 mA/W after being treated with 0.7% HCl solution. The result indicates that the a larger surface available for photodetection could be realized by increasing the surface roughness of the ZnO photoconductive sensor. It was also found that the low-frequency and high-frequency noises of the fabricated sensors were dominated by 1/f-type and shot noises, respectively.
Thin Solid Films 01/2009; 517(17):5050-5053. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: The growth, fabrication, and subsequent electroluminescence (EL) characterization of an n-ZnO/p-GaN heterojunction light-emitting diode prepared on c-Al2O3 substrate are presented. The diode-like I–V characteristics and room temperature EL spectrum with an intense broadband emission in the yellow-green spectral region has been observed with forward bias applied. Photoluminescence (PL) and Raman spectra of the n-ZnO and p-GaN films were also measured. By comparing PL and EL spectra, it was concluded that the deep-level defect-related emission mainly originated from the GaN epitaxial layer.
Thin Solid Films 01/2009; 517(17):5054-5056. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: The optical and electrical characteristics of zinc oxide (ZnO) films grown by molecular-beam epitaxy (MBE) on Si substrates were investigated. ZnO epitaxial layer was successfully grown on nitridated Si(100) substrate initially covered with high-temperature GaN and low-temperature ZnO double buffer layers using MBE. X-ray diffraction and photoluminescence results both indicated that a reasonable quality of ZnO epitaxial layer was obtained. As the CV measurement had indicated, the carrier concentration was reduced virtually in a linear fashion from ZnO surface down to GaN buffer layer. A reduction in electron concentration was caused by the carrier depletion due to the presence of the Schottky barrier of Ni/ZnO. The large density of electron accumulated at the ZnO/GaN interface was due to the large conduction band discontinuity and offset.
IEEE Journal of Selected Topics in Quantum Electronics 08/2008; · 4.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: ZnO epitaxial layers were successfully grown on nitridated Si(1 0 0) substrate with high-temperature (HT) GaN and low-temperature ZnO double buffer layers by molecular beam epitaxy. It was found that the HT-GaN buffer was crystalline with both hexagonal and cubic phases. It was also found that numerous cone-shaped nano-islands were formed on the ZnO epitaxial layers with density, average diameter and average height of 1.25 Â 10 9 cm À2 , 300 nm and 150 nm, respectively. X-ray diffraction and photoluminescence results both indicate that quality of our ZnO epitaxial layers was good.
Journal of Crystal Growth 01/2008; 31015(81). · 1.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: Vertical well-aligned and crabwise ZnO nanowires were prepared on patterned ZnO:Ga/glass substrates by reactive evaporation method under different growth conditions. The average length and diameter of vertical well-aligned ZnO nanowires were around 1 mum and 50-100 nm, respectively. In contrast, the average length and diameter of crabwise ZnO nanowires were around 5 mum and 30 nm, respectively. Upon illumination with UV light (lambda = 362 nm), it was found that measured responsivities were 0.015 and 0.03 A/W for the crabwise ZnO nanowire photodetector biased at 10 and 15 V, respectively. Furthermore, a rejection ratio of approximately 10 was obtained for the crabwise ZnO nanowire photodetector with an applied bias of 10 V.
IEEE Transactions on Nanotechnology 12/2007; · 1.80 Impact Factor
[show abstract][hide abstract] ABSTRACT: AlGaN ultraviolet (UV) metal-semiconductor-metal (MSM) photodetectors (PDs) grown on silicon substrates were fabricated and characterized. With 5-V applied bias, it was found that dark current density of Al<sub>0.2</sub>Ga<sub>0.7</sub>N PDs on silicon substrate was only 7.5times10<sup>-9</sup> A/cm<sup>2</sup>. With an applied bias of 7 V, it was found that peak responsivities were 0.09 and 0.11 A/W while UV/visible rejection ratios (i.e., peak wavelength: 420 nm) were 324 and 278 for Al<sub>0.2</sub>Ga<sub>0.8</sub>N and Al<sub>0.3 </sub>Ga<sub>0.7</sub>N MSM PDs, respectively. Moreover, the noise equivalent power of Al<sub>0.2</sub>Ga<sub>0.8</sub>N MSM PDs was estimated to be 3.5times10<sup>-12</sup> W
IEEE Electron Device Letters 05/2007; · 2.79 Impact Factor
[show abstract][hide abstract] ABSTRACT: ZnSe-based white light emitting diodes (LEDs) were homoepitaxially prepared on ZnSe substrates by molecular beam epitaxy. It was found to be possible to simultaneously observe the greenish-blue emission at 483 nm originating from the epitaxial layer and the weaker ZnSe substrate-related orange emission centred at around 595 nm. It was found that the emission wavelength of the LED and the measured chromaticity coordinate were almost independent of the injected current. It was also found that the turn-on voltage and the 20 mA operation voltage of the fabricated LED were 2.25 and 4 V, respectively
[show abstract][hide abstract] ABSTRACT: Low resistivity and high transparent ITO, RuOx
(1<=x<=2) and TiW ohmic contacts to ZnO film was achieved by RF
sputter system and annealing treatment. The transmittance of
450°C-annealing ITO, 650°C-annealing Ru and 200°C-annealing
TiW were measured to be 94, 68 and 61%, with wavelength of 400 nm,
respectively. Moreover, the specific contact resistance of
450°C-annealing ITO, 650°C-annealing Ru and 200°C-annealing
TiW on ZnO films was estimated to be 2.15x10-4,
2.72x10-4 and 2.56x10-4 Ω-cm2 by
circular transmission line model (CTLM) method, respectively. In the
study of ZnO-based photodiodes, high quality and vertical well-aligned
ZnO nanowires were selectively grown on ZnO:Ga/glass templates by
vapor-liquid-solid method. Ultraviolet (UV) photodetectors using these
vertical ZnO nanowires were also fabricated by spin-on-glass technology.
With 2 V applied bias, it was found that dark current density of the
fabricated device was only 3.8x10-9 A/cm2. It was
also found that UV-to-visible rejection ratio and quantum efficiency of
the fabricated ZnO nanowire photodetectors were more than 1000 and
[show abstract][hide abstract] ABSTRACT: We report the fabrication of ZnO photoconductive sensors epitaxially grown on sapphire substrates with interdigitated Ni/Au electrodes. It was found that there exists an electric field-dependent photoconductive gain in the fabricated sensors. With an applied electric field of 500V/cm, it was found that maximum quantum efficiency was around 2.8% while time constant of the decay transient was τ∼0.556ms.
Sensors and Actuators A-physical - SENSOR ACTUATOR A-PHYS. 01/2007; 140(1):60-64.
[show abstract][hide abstract] ABSTRACT: AlGaN ultraviolet metal-semiconductor-metal photodetectors (PDs) with low temperature (LT)-AlN and LT-GaN cap layers were prepared on Si substrates. Unlike PDs prepared on sapphire substrates, no markedly reduction in dark current was observed from the PD with LT-GaN cap layer. With an incident wavelength of 305nm and an applied bias of 5V, it was found that peak responsivities were 0.02, 0.005 and 0.007A/W for the PDs with LT-AlN cap layer, with LT-GaN cap layer and without cap layer, respectively. The corresponding detectivities were 2.2×1010, 1.36×1010 and 1.55×1010cmHz0.5W−1, respectively.
[show abstract][hide abstract] ABSTRACT: We report the fabrication of epitaxial ZnO photoconductive sensors on sapphire substrates. With an incident light wavelength of 370 nm and a 5 V applied bias, we achieved a sensor responsivity of 20.5 mA/W. It was also found that low-frequency and high-frequency noises in the fabricated sensors were dominated by 1/f type and shot noises, respectively. With a 5 V applied bias, it was found that noise equivalent power and normalized detectivity of the fabricated sensors were 1.83 10 −6 W and 6.91 10 5 cm Hz 0.5 W −1 , respectively. Detectors operating in the short wavelength ultraviolet UV re-gion are important devices that can be used in various commercial and military applications. For example, these UV detectors can be used in space communications, ozone layer monitoring, and flame detection. Until very recently, the primary means of UV light detec-tion was the use of silicon photodiodes. However, the most sensitive wavelength of Si-based detector is not located in the UV region because room-temperature bandgap energy of Si is only 1.2 eV. Thus, the responsivity of Si photodiodes is low in UV region. With the advent of optoelectronic devices fabricated on wide direct band gap materials, it becomes possible to produce high-performance solid-state photodetector arrays that are sensitive in UV region. For example, GaN-based photodetectors are already commercially available. 1-6 It has also been demonstrated that ZnSe-based photo-detectors can also be used in sensing optical signal in the blue/UV region. 7-11 ZnO is another potentially useful wide direct bandgap material. 12,13 The large exciton binding energy of 60 meV and wide bandgap energy of 3.37 eV at room temperature make ZnO a prom-ising photonic material for applications such as light-emitting diodes LEDs, laser diodes LDs, and photodetectors. ZnO is also very attractive as UV optical sensors. Compared with GaN, ZnO exhibits higher electron saturation velocity. Thus, we should be able to achieve ZnO-based photo sensors with higher operation speed. Bandgap energy of ZnO and its alloys such as CdZnO, MgZnO, and BeZnO expands from 2.5 eV 496 nm to 10.6 eV 124 nm. Thus, ZnO-based photosensor should perform much better than its GaN-based counterpart in the deep UV region. Compared with GaN and Si, ZnO is exhibits stronger radiation hardness. 14 Indeed, ZnO has attracted much attention in recent years. 15-18 ZnO Schottky diodes and metal semiconductor metal MSM photodetectors, pn-heterojunction diode, ZnO/GaN heterostructure Schottky diodes, ZnO nanowire photodetectors, detecting in the UV region have also been demonstrated. 17,19-22 In this work, we report the fabrication of ZnO photoconductive sensors with Ni/Au electrodes. Optoelectronic and noise properties of the fabricated sensors is also discussed.
Journal of The Electrochemical Society - J ELECTROCHEM SOC. 01/2007; 154(7).
[show abstract][hide abstract] ABSTRACT: Nitride-based light emitting diodes (LEDs) with sidewall texture and pillar waveguides (STPW) were fabricated using conventional lithography method. With 20-mA injection current, it was found that forward voltages were 3.16 and 3.15 V for the conventional LED and the LED with STPW, respectively. It was also found that 20-mA LED output powers were 8.4 and 10.1 mW for conventional LED and the LED with STPW, respectively. The enhancement is attributed to the out-coupling of lateral waveguide mode in the near horizontal directions