Browsing by Author "Wang, C. M."

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Dynamics of phonons in Sr3Ir4Sn13: an experimental study by ultrafast spectroscopy measurements
(2016-07-26)
Luo, C. W.
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Cheng, P. C.
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Tu, C. M.
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Kuo, C. N.
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Wang, C. M.
We report a study of ultrafast dynamics of photoexcited electrons and phonons in Sr3Ir4Sn13 using dual-color transient reflectivity change (Delta R/R) measurements. Time resolved optical spectroscopy of collective excitations reveal the marked features near its structural phase transition temperature T* similar or equal to 147 K. Two distinctive oscillatory timescales in Delta R/R have been clearly resolved. The rapid THz-range oscillations are attributed to the dynamics of the optical phonons which strongly correlate to the structural phase transition. The slow GHz-range oscillatory phenomenon which only occurs below about 150 K is associated with the dynamic response of the longitudinal-acoustic phonons. These low-energy phonons show a softening feature on approaching the transition temperature, also indicating a strong relevance to the structural phase transition. The information that we demonstrated would provide a deeper understanding of the structural phase transition in Sr3Ir4Sn13.
Influence of Hydrogen on the Germanium Incorporation in a-Si1-xGex:H for Thin-Film Solar Cell Application
(2010-01-01)
Wang, C. M.
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Huang, Y. T.
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Yen, K. H.
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Hsu, H. J.
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Hsu, C. H.
In this work, we examined the Ge incorporation and the accompanied defect formation during PECVD deposition of hydrogenated amorphous silicon-germanium alloys (a-Si1-xGex:H). In particular, we studied the effect of hydrogen on film growth, defect formation, Ge and Si incorporation efficiencies, and the H-bonding configuration. Our results indicate that hydrogen has a strong effect on improving the a-Si1-xGex:H film quality and the Ge incorporation in a-Si1-xGex:H. With adequate hydrogen dilution, the a-Si1-xGex:H thin-film quality significantly improved. However, excessive hydrogen dilution degraded the film properties. A number of analytical tools were employed, including FTIR, XPS, UV-Visible spectroscopy, photoconductivity, etc. The a-Si1-xGex:H material having 24% Ge content and a bangap of 1.61ev produced the solar cell with a conversion efficiency of 7.07%.
Optimization of the absorber layer for a-Si:H and a-Si1-xGex:H single-junction solar cells
(2011)
Tsai, C. C.
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Hsu, C. H.
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Hsu, H. J.
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Cheng, P. H.
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Wang, C. M.
This paper focuses on the optimization of the absorber layers in single-junction a-Si:H and a-Si1-xGex:H solar cells. For a-Si:H thin-film solar cells, we have found the electrode-to-substrate (E/S) spacing is an important parameter. By optimizing the E/S spacing, the cell effi-ciency was improved from 7.62% to 8.70% due to an improvement in material quality and JSC. For a-Si1-xGex:H solar cells, by optimizing the Ge-content, the microstructure parameter and the graded bandgap, we were able to improve the cell efficiency to 8.15%. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim