Browsing by Author "Lin, D. W."

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Design of distributed amplify-and-forward relay networks for multi-input multi-output transmission
(2012-02-14)
Wu, C-J
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Lin, D. W.
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Sang, T-H
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Relays can potentially enhance the transmission performance of multi-input multi-output (MIMO) systems. A parallel single-antenna relay network has additional advantages in flexibility, diversity and cost, but also poses significant design problems because the absence of inter-antenna connections over different relays makes the underlying mathematical problems much more difficult to solve. In this study, the authors consider the design of parallel amplify-and-forward relay networks. More specifically, the authors consider the design of relay gains to maximise the system capacity. As no closed-form analytic solution can be found, the authors first develop an iterative algorithm to find a locally optimal solution. Since algorithmic optimisation provides little insight into the analytical properties of the solution, they also attempt analytical solutions for several asymptotic noise conditions. It turns out that the solutions involve some methods to select the optimal subsets of relays for signal forwarding. The authors analyse the resulting capacity outage diversity orders and confirm the analysis with simulation results.
Distance dependence of energy transfer from InGaN quantum wells to graphene oxide
(2013-08-01)
Lin, T. N.
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Huang, L. T.
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Shu, G. W.
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Yuan, C. T.
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Shen, J. L.
We report the distance-dependent energy transfer from an InGaN quantum well to graphene oxide (GO) by time-resolved photoluminescence (PL). A pronounced shortening of the PL decay time in the InGaN quantum well was observed when interacting with GO. The nature of the energy-transfer process has been analyzed, and we find the energy-transfer efficiency depends on the 1/d(2) separation distance, which is dominated by the layer-to-layer dipole coupling. (C) 2013 Optical Society of America
Efficiency and Droop Improvement in GaN-Based High-Voltage Light-Emitting Diodes
(2011-08-01)
Wang, C. H.
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Lin, D. W.
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Lee, C. Y.
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Tsai, M. A.
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Chen, G. L.
The efficiency and electrical characteristics of GaN-based high-voltage light-emitting diodes (HV-LEDs) are investigated in detail. The spatial distribution of light output and simulation results showed that 100-V HV-LED with smaller microchips had superior current spreading. As a result, under 1-W operation, the luminous efficiency of 100-V HV-LED with smaller microchips was enhanced by 7.8% compared to that of 50-V HV-LED, while the efficiency droop behaviors were reduced from 28% in 50-V HV-LED to 25.8% in 100-V HV-LED. Moreover, smaller microchips exhibited lower series resistance and forward voltage, leading to higher wall-plug efficiency.
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.
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
Improvement in efficiency droop of GaN-based light-emitting diodes by optimization of active regions
(2011)
Wang, C. H.
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Lin, D. W.
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Chiu, C. H.
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Chang, S. P.
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Li, Z. Y.
We had demonstrated several novel methods to improve efficiency droop behavior in GaN-based light-emitting diodes (LEDs). LEDs with different kinds of insertion layers (ILs) between the multiple quantum wells (MQWs) layer and n-GaN layer were investigated. By using low-temperature (LT, 780. C) n-GaN as IL, the efficiency droop behavior can be alleviated from 54% in reference LED to 36% from the maximum value at low injection current to 200 mA, which is much smaller than that of 49% in LED with InGaN/GaN short-period superlattices (SPS) layer. The polarization field in MQWs is found to be smallest in LED with InGaN/GaN SPS layer. However, the V-shape defect density, about 5.3x10(8) cm(-2), in its MQWs region is much higher than that value of 2.9x10(8) cm(-2) in LED with LT n-GaN layer, which will lead to higher defect-related tunneling leakage of carriers. Therefore, we can mainly assign this alleviation of efficiency droop to the reduction of dislocation density in MQWs region rather than the decrease of polarization field. At second part, LEDs with graded-thickness multiple quantum wells (GQW) was designed and found to have superior hole distribution as well as radiative recombination distribution by simulation modeling. Accordingly, the experimental investigation of electroluminescence spectrum reveals additional emission from the previous narrower wells within GQWs. Consequently, the efficiency droop can be alleviated to be about 16% from maximum at current density of 30 A/cm(2) to 200 A/cm(2). Moreover, the light output power is enhanced by 35% at 20 A/cm(2).
Reduction of Efficiency Droop in Semipolar (1(1)over-bar01) InGaN/GaN Light Emitting Diodes Grown on Patterned Silicon Substrates
(2011-01-01)
Chiu, C. H.
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Lin, D. W.
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Lin, C. C.
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Li, Z. Y.
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Kuo, H. C.
The semi-polar InGaN-based LEDs exhibits low efficiency droop because the reduction of the polarization field not only made the band diagram smoother but also restricted electron overflow to the p-GaN layer as shown in simulations. (C) 2010 Optical Society of America