Browsing by Author "Wang, Lei"

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GaN Schottky Barrier Diodes on Free-Standing GaN Wafer
(2017-01-01)
Liu, Xinke
;
Gu, Hong
;
Li, Kuilong
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Wang, Jianfeng
;
Wang, Lei
In this paper, vertical GaN Schottky barrier diodes (SBDs) have been demonstrated on the freestanding (FS) GaN wafer. Room temperature photoluminescence shows no emission of yellow luminescence, due to the eliminating the point defects (O-N, V-Ga). The average full width half maximum (FWHM) value of.-scans for (0001) and (10-12) planes is 53 and 103 arcsec, respectively, as measured by high resolution X-ray diffraction; the average dislocation density at the top surface measured by cathodoluminescence is similar to 7.7 x 10(5) cm(-2). The vertical GaN SBDs fabricated on this FS-GaN wafer achieve a breakdown voltage of 1200 V, an on-state resistance R-on of 7 m Omega.cm(2), and a current on/off ratio I-on/I-off of similar to 2.3 x 10(10), which leads to a power device figure-of-merit V-BR(2)/R-on of 2.1 x 10(8) V-2 Omega(-1) cm(-2). TCAD simulation was employed to study the device breakdown mechanism, and shows the breakdown mechanism is due to the impact ionization at the edge of the Schottky gate. (c) 2017 The Electrochemical Society. All rights reserved.
Highly efficient and stable sky blue organic light-emitting devices
(2006-09-18)
Lin, Mei-Fang
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Wang, Lei
;
Wong, Wai-Kwok
;
Cheah, Kwok-Wai
;
Tam, Hoi-Lam
A highly efficient and stable sky blue organic light-emitting device doped with a sky blue dopant BUBD-1 has been fabricated, achieving an electroluminescence efficiency of 13.2 cd/A and 6.1 lm/W at 20 mA/cm(2) and 6.7 V, with Commission Internationale del'Eclairage coordinates of (0.16, 0.30) and a half-decay lifetime of 1815 h at an initial brightness of 2640 cd/m(2). This performance is one of the best blue devices ever reported without using hole blocking layer or any p or n dopant in hole or electron transport layer. (c) 2006 American Institute of Physics.
Highly efficient and stable white light organic light-emitting devices
(2007-08-13)
Lin, Mei-Fang
;
Wang, Lei
;
Wong, Wai-Kwok
;
Cheah, Kok-Wai
;
Tam, Hoi-Lam
A highly efficient two-element white light organic light-emitting device with a sky blue dopant BUBD-1 and a yellow dopant TBRb was fabricated. The device achieved an electroluminescence efficiency of 17.1 cd/A and 7.9 lm/W at 20 mA/cm(2). From 112 to 32 010 nits, the CIEx,y coordinates variation was Delta(x,y)<+/-(0.01,0.01), which is superior to common white light organic light-emitting devices (OLEDs) that tend to change color with drive conditions. Moreover, the device reached a half-decay t(1/2) lifetime over 40 000 h at an initial luminance of 300 cd/m(2). This result is among the best records of fluorescent white light OLEDs. (C) 2007 American Institute of Physics.
Highly efficient white light organic light-emitting device
(2007-01-01)
Lin, Mei-Fang
;
Wang, Lei
;
Wong, Wai-Kwok
;
Cheah, Kok-Wai
;
Tam, Hoi-Lam
A highly efficient white organic light-emitting device (OLED) with a novel sky blue dopant BUBD-1 in a two-color emission system was fabricated. The device achieved an EL efficiency of 17.1 cd/A and 7.9 lm/W at 20 mA/cm 2 with CIEx,y coordinates of (x=0.29, y=0.41) which was not changed with drive conditions. The white light OLED reached a half-decay t(1/2) lifetime over 40,000 hours at an initial luminance of 300 cd/m(2).
Highly efficient white organic light-emitting diodes with single small molecular emitting material
(2007-10-29)
Wang, Lei
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Lin, Mei-Fang
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Wong, Wai-Kwok
;
Cheah, Kok-Wai
;
Tam, Hoi-Lam
We demonstrate a highly efficient white organic light emitting device with fluorescent small molecule 4,4'-bis(9-(1-naphthyl)anthracene-10-yl)biphenyl (BUBH-3). With a simple device architecture of indium tin oxide/tris 4,4',4'-tris-N-naphthyl-N-phenylamino-triphenylamine (60 nm)/N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (10 nm)/BUBH-3 (45 nm)/Alq(3) (15 nm)/LiF (1 nm)/Al (150 nm), a white light with CIEx,y color of (0.31,0.36) was generated. The device achieved one of the best single-emitting-material electroluminescence performance of white organic light-emitting devices with efficiencies of 7.0 cd/A and 3.17 lm/W at 6.9 V. (C) 2007 American Institute of Physics.
Novel host materials for single-component white organic light-emitting diodes based on 9-naphthylanthracene derivatives
(2008)
Wang, Lei
;
Wong, Wai-Yeung
;
Lin, Mei-Fang
;
Wong, Wai-Kwok
;
Cheah, Kok-Wai
A series of 9-naphthylanthracene based dimers and trimers were synthesized and characterized. TGA studies reveal that they are all thermally stable with decomposition temperatures well above 500 degrees C. Upon optical excitation, all of these dimers and trimers show intense blue emission in common organic solvents, accompanied by a new peak at long wavelength in the solid state. They exhibit nanosecond transient lifetimes consisting of two decay components, suggesting the formation of excimers. Single-component light-emitting electroluminescent devices based on these robust materials have been fabricated. The device based on 4,4'-bis(9-(1-naphthyl)anthracen-10-yl)biphenyl exhibits a maximum luminance efficiency of 7.0 cd A(-1) with CIE coordinates of (0.31, 0.36) and luminance of 1396 cd m(-2) at 6.9 V. The device based on 1,3,5-tris(9-(1-naphthyl)anthracen-10-yl)benzene exhibits a maximum luminance efficiency of 5.78 cd A(-1) with CIE coordinates of (0.33, 0.43) and luminance of 1156 cd m(-2) at 7.8 V.
Regional surface mass anomalies from GRACE KBR measurements: Application of L-curve regularization and a priori hydrological knowledge
(2012-11-08)
Tangdamrongsub, Natthachet
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Hwang, Cheinway
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Shum, C. K.
;
Wang, Lei
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土木工程學系
We present a method of directly estimating surface mass anomalies at regional scales using satellite-to-satellite K-band Ranging (KBR) data from the Gravity Recovery and Climate Experiment (GRACE) twin-satellite mission. Geopotential differences based primarily on KBR measurement are derived using a modified energy integral method with an improved method to calibrate accelerometer measurements. Surface mass anomalies are computed based on a downward continuation process, with optimal regularization parameters estimated using the L-curve criterion method. We derive the covariance functions in both space-and space-time domains and use them as light constraints in the regional gravity estimation process in the Amazon basin study region. The space-time covariance function has a time-correlation distance of 1.27 months, which is evident that observations between neighboring months are correlated and the correlation should be taken into account. However, most of the current GRACE solutions did not consider such temporal correlations. In our study, the artifact in the regional gravity solution is mitigated by using the covariance functions. The averaged commission errors are estimated to be only 6.86% and 5.85% for the solutions based on the space-covariance function (SCF) and the space-time covariance function (STCF), respectively. Our regional gravity solution in the Amazon basin study region, which requires no further post-processing, shows enhanced regional gravity signatures, reduced gravity artifacts, and the gravity solution agrees with NASA/GSFC's GRACE MASCON solution to about 1 cm RMS in terms of water thickness change over the Amazon basin study region. The regional gravity solution also retains the maximum signal energy while suppressing the short wavelength errors.