|Modifications of c-Si/a-Si:H/indium tin oxide heterostructures upon thermal annealing
|Articolo su Rivista peer-reviewed
|Year of Publication
|Losurdo, M., Giangregorio M., Capezzuto P., Bruno G., Varsano F., Tucci M., and Roca F.
|Journal of Applied Physics
c-Si/a-Si:H/indium tin oxide (ITO) heterojunctions have been prepared by electron-beam deposition of an (ITO) thin film on a plasma enhanced chemical vapor deposition grown c-Si/a-Si:H heterojunction. These heterostructures, which are the basis of solar cells, have been annealed in N2 atmosphere at temperatures in the range 250-650 °C. Thermal annealing effects on structural and optical properties of the ITO, the a-Si:H layer, and of the c-Si/a-Si interface have been detected by spectroscopic ellipsometry. The optical response of ITO is described in the energy range 1.5-5.0 eV, where a high transparency is required for ITO, by analyzing ellipsometric spectra in terms of a model which combines the Drude model and a double Lorentzian oscillator. Spectroscopic ellipsometry has shown that annealing at T>450 °C causes hydrogen out-diffusion from the a-Si:H layer into the ITO layer whose optical and electrical properties are modified. Additionally, damage of the c-Si/a-Si interface and of the ITO layer by hydrogen diffusion is detected and seen as a factor affecting performance of c-Si/a-Si/ITO stacked structure based solar cells. X-ray photoelectron spectroscopy and atomic force microscopy measurements have corroborated ellipsometric analysis. © 2001 American Institute of Physics.
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