Browsing by Author "Lai, W. C."

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A side-by-side comparison of Daya Bay antineutrino detectors
(1970-01-01)
An, F. P.
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An, Q.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
"The Daya Bay Reactor Neutrino Experiment is designed to determine precisely the neutrino mixing angle theta(13) with a sensitivity better than 0.01 in the parameter sin(2) 2 theta(13) at the 90% confidence level. To achieve this goal, the collaboration will build eight functionally identical antineutrino detectors. The first two detectors have been constructed, installed and commissioned in Experimental Hall 1, with steady data-taking beginning September 23, 2011. A comparison of the data collected over the subsequent three months indicates that the detectors are functionally identical, and that detector-related systematic uncertainties are smaller than requirements. (C) 2012 Elsevier B.V. All rights reserved."
Characterization of n-GaN with Naturally Textured Surface for Photoelectrochemical Hydrogen Generation
(2010)
Liu, Shu-Yen
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Sheu, J. K.
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Ye, Jhao-Cheng
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Tu, S. J.
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Hsu, Che-Kang
To reduce light reflection and enlarge the effective reaction surface area at the n-GaN/electrolyte interface, n-GaN epitaxial layers with naturally textured surface are utilized. The layers are combined with Cr/Au ohmic contacts on n-GaN to form working electrodes that generate hydrogen by direct photoelectrolysis of water. Although the surface reflection on the naturally textured n-GaN samples is lower than that on n-GaN epitaxial layers with flat surface, our results reveal that the photocurrent (I(ph)) and gas generation rates (R(gas)) obtained from the naturally rough n-GaN samples are lower than those from the flat samples. The results can be attributed to the fact that the rough n-GaN surface caused by dense surface pits leads to significant recombination of photogenerated carriers with charged defects; this occurs before carriers reach the ohmic contacts, thereby resulting in lower I(ph) and R(gas). Related analyses have been performed and presented in this paper to initially explain the possible mechanism. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3499327] All rights reserved.
GaN-Based LEDs Grown on HVPE Growth High Crystalline Quality Thick GaN Template
(2011)
Lin, D. W.
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Lin, C. C.
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Chiu, C. H.
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Lee, C. Y.
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Yang, Y. Y.
In this study, high crystalline quality 30 mu m thick gallium nitride (GaN) films were grown by hydride vapor phase epitaxy (HVPE) on sapphire substrate, and the thick GaN films were used for developing high performance light-emitting diodes (LEDs). By using high-resolution X-ray diffraction, the full width at half-maximum (FWHM) of the rocking curve shows that this 30 mu m thick GaN template had high crystalline quality. In addition, the transmission electron microscopy (TEM) images suggest that threading dislocation densities (TDDs) are almost free in multiple quantum wells (MQWs) for LEDs grown on 30 mu m thick GaN template. Compared with conventional LEDs grown on sapphire, LEDs grown on 30 mu m thick GaN template exhibit 26% enhancement of light output at 20 mA. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.003111jes] All rights reserved.
GaN-Based Light-Emitting-Diode With a p-InGaN Layer
(2014-03-01)
Chen, P. H.
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Kuo, Cheng-Huang
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Lai, W. C.
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Chen, Yu An
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Chang, L. C.
GaN-based LEDs with a p-InGaN layer was proposed and fabricated. By inserting the 50-nm-thick p-In0.01Ga0.99N layer, it was found that we could reduce the 20 mA forward voltage from 3.34 to 2.99 V. It was found the inserted p-InGaN layer could also reduce the efficiency droop from 36.7% to 23.8%.
High responsivity of GaN p-i-n photodiode by using low-temperature interlayer
(2007-10-22)
Lin, J. C.
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Su, Y. K.
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Chang, S. J.
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Lan, W. H.
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Huang, K. C.
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 (similar to 0.4 MV/cm) due to the carrier multiplication effect. The UV photocurrent gain of 13 and large ionization coefficient (alpha = 3.1 X 10(5) 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. (C) 2007 American Institute of Physics.
Improved carrier injection in GaN-based VCSEL via AlGaN/GaN multiple quantum barrier electron blocking layer
(2015-10-19)
Hsieh, D. H.
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Tzou, A. J.
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Kao, T. S.
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Lai, F. I.
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Lin, D. W.
In this report, the improved lasing performance of the III-nitride based vertical-cavity surface-emitting laser (VCSEL) has been demonstrated by replacing the bulk AlGaN electron blocking layer (EBL) in the conventional VCSEL structure with an AlGaN/GaN multiple quantum barrier (MQB) EBL. The output power can be enhanced up to three times from 0.3 mW to 0.9 mW. In addition, the threshold current density of the fabricated device with the MQB-EBL was reduced from 12 kA/cm(2) (9.5 mA) to 10.6 kA/cm(2) (8.5 mA) compared with the use of the bulk AlGaN EBL. Theoretical calculation results suggest that the improved carrier injection efficiency can be mainly attributed to the partial release of the strain and the effect of quantum interference by using the MQB structure, hence increasing the effective barrier height of the conduction band. (C) 2015 Optical Society of America
Improved measurement of electron antineutrino disappearance at Daya Bay
(2013-01-01)
An, F. P.
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An, Q.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
We report an improved measurement of the neutrino mixing angle theta(13) from the Daya Bay Reactor Neutrino Experiment. We exclude a zero value for sin(2)2 theta(13) with a significance of 7.7 standard deviations. Electron antineutrinos from six reactors of 2.9 GW(th) were detected in six antineutrino detectors deployed in two near (flux-weighted baselines of 470 m and 576 m) and one far (1648 m) underground experimental halls. Using 139 days of data, 28909 (205308) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to the expected number of antineutrinos assuming no oscillations at the far hall is 0.944 +/- 0.007(stat.)+/- 0.003(syst.). An analysis of the relative rates in six detectors finds sin(2)2 theta(13)= 0.089 +/- 0.010(stat.)+/- 0.005(syst.) in a three-neutrino framework.
Improved Power Conversion Efficiency of InGaN Photovoltaic Devices Grown on Patterned Sapphire Substrates
(2011-04-01)
Yang, C. C.
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Sheu, J. K.
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Kuo, C. H.
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Huang, M. S.
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Tu, S. J.
The InGaN/sapphire-based photovoltaic (PV) cells with Al(0.14)Ga(0.86)N/In(0.21)Ga(0.79)N superlattice structures that serve as absorption layers were grown on patterned sapphire substrates (PSSs). Under global air-mass 1.5 conditions, the short-circuit current density, the open-circuit voltage, and the fill factor obtained from the PV cells were 1.21 mA/cm(2), 2.18 V, and 0.65, respectively, corresponding to a conversion efficiency of 1.71%. Compared with PV devices grown on flat sapphire substrates, the photocurrent of PSS-grown PV devices was enhanced by 26%. The improved PV performance was attributable to the positive effects of the PSS on the material quality.
Independent measurement of the neutrino mixing angle theta(13) via neutron capture on hydrogen at Daya Bay
(2014-10-03)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A new measurement of the theta(13) mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely different systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of the theta(13) measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GWth reactors, the rate deficit observed at the far hall is interpreted as sin(2)2 theta(13) = 0.083 +/- 0.018 in the three-flavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain sin(2)2 theta(13) = 0.089 +/- 0.008 as the final result for the six-antineutrino-detector configuration of the Daya Bay experiment.
Low operation voltage of GaN-based LEDs with Al-doped ZnO upper contact directly on p-type GaN without insert layer
(2015-07-01)
Chen, P. H.
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Chen, Yu An
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Chang, L. C.
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Lai, W. C.
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Kuo, Cheng Huang
Al-doped ZnO (AZO) film was evaporated on double-side polished sapphire, p-GaN layers, n(+)-InGaN-GaN short-period superlattice (SPS) structures, and GaN-based light-emitting diodes (LEDs) by e-beam. The AZO film on the p-GaN layer after thermal annealing exhibited an extremely high transparency (98% at 450 nm) and a small specific contact resistance of 2.19 x 10(-2) Omega cm(2), which was almost the same as that of as-deposited AZO on n(+)-SPS structure. With 20 mA injection current, the forward voltages were 3.30 and 3.27 V, whereas the output powers were 4.32 and 4.07 mW for the LED with AZO on insert n(+)-SPS upper contact and the LED with AZO on p-GaN upper contact (without insert layer), respectively. The small specific contact resistance and low operation voltage of LED with AZO on p-GaN upper contact was achieved by rapid thermal annealing (RTA) process. (C) 2015 Elsevier Ltd. All rights reserved.
Observation of Electron-Antineutrino Disappearance at Daya Bay
(2012-04-23)
An, F. P.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
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Beavis, D.
The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle 0(13) with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GW(th) reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With a 43 000 ton-GW(th)-day live-time exposure in 55 days, 10 416 (80 376) electron-antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is R = 0.940 +/- 0.011(stat.) +/- 0.004(syst.). A rate-only analysis finds sin(2)2 theta(13) = 0.092 +/- 0.016(stat.) +/- 0.005(syst.) in a three-neutrino framework.
Results from the Daya Bay Reactor Neutrino Experiment
(2014-01-01)
Tsang, K. V.
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An, F. P.
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An, Q.
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Bai, J. Z.
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Balantekin, A. B.
The Daya Bay Reactor Neutrino Experiment was designed to achieve a sensitivity on the value of sin(2) 2 theta(13). to better than 0.01 at 90% CL. The experiment consists of eight antineutrino detectors installed underground at different baselines from six nuclear reactors. With data collected with six antineutrino detectors for 55 days, Daya Bay announced the discovery of a non-zero value for sin(2) 2 theta(13) with a significance of 5.2 standard deviations in March 2012. The most recent analysis with 139 days of data acquired in a six-detector configuration yields sin(2) 2 theta(13) = 0.089 +/- 0.010(stat.) +/- 0.005(syst.), which is the most precise measurement of sin(2) 2 theta(13) to date.
Search for a Light Sterile Neutrino at Daya Bay
(2014-10-01)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines from six 2.9 GW(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10(-3) eV(2) < vertical bar Delta m(41)(2)vertical bar < 0.3 eV(2) range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin(2) 2 theta(14) cover the 10(-3) eV(2) less than or similar to vertical bar Delta m(41)(2)vertical bar less than or similar to 0.1 eV(2) region, which was largely unexplored.
Spectral Measurement of Electron Antineutrino Oscillation Amplitude and Frequency at Daya Bay
(2014-02-10)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A measurement of the energy dependence of antineutrino disappearance at the Daya Bay reactor neutrino experiment is reported. Electron antineutrinos ((v) over bar (e)) from six 2.9 GW(th) reactors were detected with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls. Using 217 days of data, 41 589 (203 809 and 92 912) antineutrino candidates were detected in the far hall (near halls). An improved measurement of the oscillation amplitude sin(2) 2 theta(13) = 0.090(-0.009)(+0.008) and the first direct measurement of the (v) over bar (e) mass-squared difference vertical bar Delta m(ee)(2)vertical bar = (2.59(-0.20)(+0.19) x 10(-3) eV(2)) is obtained using the observed (v) over bar (e) rates and energy spectra in a three-neutrino framework. This value of vertical bar Delta m(ee)(2)vertical bar eejis consistent with vertical bar Delta m(mu mu)(2)vertical bar measured by muon neutrino disappearance, supporting the three-flavor oscillation model.
The detector system of the Daya Bay reactor neutrino experiment
(2016-03-01)
An, F. P.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
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Beavis, D.
The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of (nu) over bar (e) oscillations over km-baselines. Subsequent data has provided the world\'s most precise measurement of sin 2 2013 and the effective mass splitting Delta m(ee)(2). The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world\'s most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors\' baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking. (C) 2015 Elsevier B.V. All rights reserved.
The muon system of the Daya Bay Reactor antineutrino experiment
(2015-02-11)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
The Daya Bay experiment consists of functionally identical antineutrino detectors immersed in pools of ultrapure water in three well-separated underground experimental halls near two nuclear reactor complexes. These pools serve both as shields against natural, low-energy radiation, and as water Cherenkov detectors that efficiently detect cosmic muons using arrays of photomultiplier tubes. Each pool is covered by a plane of resistive plate chambers as an additional means of detecting muons. Design, construction, operation, and performance of these muon detectors are described. (C) 2014 Elsevier By. All rights reserved.