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5 October 2015 Effect of surface stoichiometry and interfacial interactions on ultrafast carrier dynamics of crystalline CdTe (Presentation Recording)
Xing He, Napat Punpongjareorn, Chengyi Wu, Karjini Rajagopal, Ding-Shyue Yang
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Proceedings Volume 9549, Physical Chemistry of Interfaces and Nanomaterials XIV; 954917 (2015) https://doi.org/10.1117/12.2190460
Event: SPIE Nanoscience + Engineering, 2015, San Diego, California, United States
Abstract
To improve the efficiency of optoelectronic devices, it is critical to understand the carrier dynamics of photoactive materials and the mechanisms involved, including those effects caused by different surface stoichiometry and/or interfacial interactions. A good example is CdTe, which exhibits cost-effective high performance in thin-film photovoltaic cells; it is also known to show surface oxidation, which may affect device efficiency and hence limit the production methods used. In this contribution, we present ultrafast carrier dynamics of crystalline CdTe specimens with different surface conditions using transient reflectivity measurements, following a femtosecond above-gap excitation. The distinct differences observed in the dynamics and the time constants for oxidized and stoichiometrically restored specimens indicate the major role of surface tellurium oxide on the relaxation of photoinduced carriers. The much slower recovery observed on oxidized surfaces is attributed to a transfer (and trapping) of electrons to the tellurium atoms with a high oxidation state, which signifies a charge separation near the surface. To distinguish the effect caused by oxygen adsorption, we also examined the carrier dynamics of CdTe surfaces covered by a thin layer of water molecules for comparison. These results, which show clear interfacial effects, may have broader implications for the understanding of carrier dynamics in nanostructured and polycrystalline specimens under different chemical environments, as such materials exhibit a high surface-to-volume ratio.
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Xing He, Napat Punpongjareorn, Chengyi Wu, Karjini Rajagopal, and Ding-Shyue Yang "Effect of surface stoichiometry and interfacial interactions on ultrafast carrier dynamics of crystalline CdTe (Presentation Recording)", Proc. SPIE 9549, Physical Chemistry of Interfaces and Nanomaterials XIV, 954917 (5 October 2015); https://doi.org/10.1117/12.2190460
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KEYWORDS
Carrier dynamics
Crystals
Ultrafast phenomena
Oxidation
Tellurium
Optoelectronic devices
Photoactive materials
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