RETRACTED ARTICLE: Hydrogenated nanocrystalline silicon germanium thin films |
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Authors: | A R M Yusoff M N Syahrul K Henkel |
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Institution: | (1) Department of Physics, University Science Malaysia, Penang, Malaysia |
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Abstract: | Hydrogenated nanocrystalline silicon germanium thin films (nc-SiGe:H) is an interesting alternative material to replace hydrogenated
nanocrystalline silicon (nc-Si:H) as the narrow bandgap absorber in an a-Si/a-SiGe/nc-SiGe(nc-Si) triple-junction solar cell
due to its higher optical absorption in the wavelength range of interest. In this paper, we present results of optical, structural
investigations and electrical characterization of nc-SiGe:H thin films made by hot-wire chemical vapor deposition (HW-CVD)
with a coil-shaped tungsten filament and with a disilane/germane/hydrogen gas mixture. The optical band gaps of a-SiGe:H and
nc-SiGe:H thin-films, which are deposited with the same disilane/germane/hydrogen gas mixture ratio of 3.4 : 1.7 : 7, are
about 1.58 eV and 2.1 eV, respectively. The nc-SiGe:H thin film exhibits a larger optical absorption coefficient of about
2–4 in the 600–900 nm range when compared to nc-Si:H thin film. Therefore, a thinner nc-SiGe:H layer of ∼500 nm thickness
may be sufficient for the narrow bandgap absorber in an a-Si based multiple-junction solar cell. We enhanced the transport
properties as measured by the photoconductivity frequency mixing technique. These improved alloys do not necessarily show
an improvement in the degree of structural heterogeneity on the nanometer scale as measured by smallangle X-ray scattering.
Decreasing both the filament temperature and substrate temperature produced a film with relatively low structural heterogeneity
while photoluminescence showed an order of magnitude increase in defect density for a similar change in the process.
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Keywords: | Silicon germanium hot-wire |
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