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04/2011: pages 125 - 149; , ISBN: 9783527636280
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ABSTRACT: We have measured the electrical, optical and morphological properties of as-grown Hg1-xCdxTe films prepared by r.f. sputtering. The Hg1-xCdxTe films were grown at substrate temperatures ranging from 25°C to 150°C. Films grown at temperatures lower than or equal to 70°C were highly resistive (≥105 Φ-cm) and were not measurable by our Hall apparatus. Optical transmission data show that the band gap of these films ranged from 0.8 eV-1.5 eV, satisfying the optimum band gap criteria. Plan view and cross sectional SEM studies indicate that the films grown at 85°C and 100°C have larger grains with compact grain boundaries and these films typically yield the best cell performance. Spectroscopic ellipsometry studies are being used to estimate the band-gap as a function of substrate temperature.We have also studied the effect of various back contacts and have fabricated complete solar cells. We found that Cu-Au serves as the best ohmic back contact to CdS/HgCdTe solar cell. Our preliminary results of J-V analyses on the complete solar cell show that the efficiency is mainly limited by the short-circuit current. Electrical-bias-dependent QE measurements indicate voltage-dependent current collection mainly in the long wavelength region. Further optimization of growth parameters and CdCl2 treatment needs to be carried out to improve the cell performance.
MRS Proceedings. 12/2006; 1012.
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ABSTRACT: Plasmonic films have become important for many applications including photonics, energy conversion, and chemical sensing, but the fabrication of these films often requires special equipment, great care, and skill. Colloidal metal nanoparticles offer an alternative as they have been shown to self-assemble into highly-ordered monolayer films by the simple and inexpensive technique of drop casting. Using this technique, we fabricated wafer-scale films of highly-ordered 6 nm Au nanoparticles and evaluated them as candidates for plasmonic applications. These colloidal films were found to support uniform and high-quality plasmon modes over the entire area of the wafer. A combination of microscopy and spectroscopy was used to evaluate and correlate the structural and optical qualities of the films. Electron and atomic force microscopy showed that the nanoscale structure of the films was compact and highly ordered, with few defects or bilayers. Spectroscopic ellipsometry showed that the majority of the film was optically quite uniform with some bilayer patches and voids. These were subsequently confirmed by microscopy. Optical analysis of the thin film showed a prominent plasmon resonance band across the entire wafer. The plasmon frequency was quite insensitive to the presence of voids or bilayers. The width of the plasmon band was more sensitive to bilayers, however, and was found to be as much as 15% wider than in monolayer regions. These results indicate that self-assembled colloidal thin films should be suitable for large-scale plasmonic applications.
Thin Solid Films 519(18):6077-6084. · 1.89 Impact Factor
