Browsing by Author "Lee, Wen-Chin"

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A flatter gallium profile for high-efficiency Cu(In,Ga)(Se,S)(2) solar cell and improved robustness against sulfur-gradient variation
(2016-09-07)
Huang, Chien-Yao
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Lee, Wen-Chin
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Lin, Albert
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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
Co-optimization of the gallium and sulfur profiles in penternary Cu(In,Ga)(Se, S)(2) thin film solar cell and its impacts on device performance and variability are investigated in this work. An absorber formation method to modulate the gallium profiling under low sulfur-incorporation is disclosed, which solves the problem of Ga-segregation in selenization. Flatter Ga-profiles, which lack of experimental investigations to date, are explored and an optimal Ga-profile achieving 17.1% conversion efficiency on a 30 cm x 30 cm sub-module without anti-reflection coating is presented. Flatter Ga-profile gives rise to the higher V-oc x J(sc) by improved bandgap matching to solar spectrum, which is hard to be achieved by the case of Ga-accumulation. However, voltage-induced carrier collection loss is found, as evident from the measured voltage-dependent photocurrent characteristics based on a small-signal circuit model. The simulation results reveal that the loss is attributed to the synergistic effect of the detrimental gallium and sulfur gradients, which can deteriorate the carrier collection especially in quasi-neutral region (QNR). Furthermore, the underlying physics is presented, and it provides a clear physical picture to the empirical trends of device performance, I-V characteristics, and voltage-dependent photocurrent, which cannot be explained by the standard solar circuit model. The parameter "FGa" and front sulfur-gradient are found to play critical roles on the trade-off between space charge region (SCR) recombination and QNR carrier collection. The co-optimized gallium and sulfur gradients are investigated, and the corresponding process modification for further efficiency-enhancement is proposed. In addition, the performance impact of sulfur-gradient variation is studied, and a gallium design for suppressing the sulfur-induced variability is proposed. Device performances of varied Ga-profiles with front sulfur-gradients are simulated based on a compact device model. Finally, an exploratory path toward 20% high-efficiency Ga-profile with robustness against sulfur-induced performance variability is presented. Published by AIP Publishing.
Characterizing the channel backscattering behavior in nanoscale strained complementary metal oxide semiconductor field-effect transistors
(2006-11-01)
Lin, Hono-Nien
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Chen, Hung-Wei
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Ko, Chih-Hsin
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Ge, Chung-Hu
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Lin, Horng-Chih
This work investigates the impact of different uniaxial strain polarities on channel backscattering in nanoscale complementary metal oxide semiconductor field-effect transistor (CMOSFET). Two carrier statistics, nondegenerate and degenerate-limited, are employed to extract the channel backscattering ratio, ballistic efficiency, and related backscattering factors. While the channel length scales down and the channel stress level increases further, the modulation of channel backscattering ratio, i.e., improved (degraded) by uniaxial tensile (compressive) strain, becomes more prominent. This observation holds true under both carrier statistics, which implies that the nondegenerate case with simple mathematics can be fairly used for evaluation. In addition, the correlation between strain-enhanced mobility gain and drain current improvement is found to be predicted well by the ballistic efficiency deduced with the nondegenerate carrier statistics.
Correlating drain-current with strain-induced mobility in nanoscale strained CMOSFETs
(2006-08-01)
Lin, Hong-Nien
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Chen, Hung-Wei
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Ko, Chih-Hsin
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Ge, Chung-Hu
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Lin, Horng-Chih
The correlation between channel mobility gain (Delta mu), linear drain-current gain (AIdlin), and saturation draincurrent gain (Delta I-dsat) of nanoscale strained CMOSFETs are reported. From the plots of Delta I-dlin versus Delta I-dsat and ballistic efficiency (B-sat,B-PSS), the ratio of source/drain parasitic resistance (R-sat,R-PSS) to channel resistance (R-CH,R-PSS) of strained CMOSFETs can be extracted. By plotting Delta mu versus Delta I-dlin, the efficiency of Delta mu translated to Delta I-dlin is higher for strained pMOSFETs than strained nMOSFETs due to smaller R-SD,R-PSS-to-R-CH,R-PSS ratio of strained pMOSFETs. It suggests that to exploit strain benefits fully, the R-SD,R-PSS reduction for strained nMOSFETs is vital, while for strained pMOSFETs the Delta I-dli -to-Delta mu sensitivity is maintained until R-SD,R-PSS becomes comparable to/or higher than R-CH,R-PSS.
Effect of backbone on the biaxial retardation of polyimide films in uniaxial stretch
(2007-05-15)
King, Jinn-Shing
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Whang, Wha-Tzong
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Lee, Wen-Chin
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Chang, Li-Ming
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材料科學與工程學系
A biaxial-retardation film prepared from the uniaxial-stretched polyimide (PI) film was developed for compensating the viewing angle of liquid-crystal displays. Good uniformity of in-plane bireffingence in well-stretched PI films was observed visually with two crossed polarizers. The prism coupling method was used to measure the n(x), n(y), n(z), and thickness of the stretched PI films. The birefringence variations of n, - n, (difference of refractive indices between x- and y-axes) and n(x) - n(z) during the stretching process were highly affected by PI structure. The polarizability tensors and intrinsic birefringences of the PI repeat units were estimated by Gaussian 98W. It was found that the stretch-induced birefringence is more related to the average polarizability per volume at the low elongation period. (C) 2006 Elsevier B.V. All rights reserved.
Strain-induced channel backscattering modulation in nanoscale CMOSFETs
(2006)
Chen, Hung-Wei
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Lin, Hong-Nien
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Ko, Chih-Hsin
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Ge, Chung-Hu
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Lin, Horng-Chih
The channel backscattering ratios as well as the ballistic efficiency of strained CMOSFETs were studied for both nondegenerate and degenerate-limited cases. We found that the simple nondegenerate assumption can predict strain-induced change of ballistic efficiency with fair accuracy. The mechanism of drain current dependence on strain-induced mobility change was also investigated based on channel backscattering theory.
Structural effect on stretch-induced birefringence in polyimide films
(2007-10-01)
King, Jinn-Shing
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Lee, Wen-Chin
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Chang, Li-Ming
;
Whang, Wha-Tzong
;
材料科學與工程學系
Seven polyimides (Pls) of low glass transition temperature were synthesized and their films were uniaxially stretched to observe the variation in their in-plane birefringence (An). The intrinsic birefringences (triangle n degrees) of their polymer chains were also estimated using the experimental average refractive indices and computationally calculated polarizability tensors. The observed stretch-induced An was markedly affected by the PI structure. A model that shows a good fit to experimental data is proposed to predict the orientation degree of PI chains in different PI films. The model, when combined with the analysis of the estimated An's, is useful in explaining the behavior of stretch-induced triangle ns in PI films.