Modifications of c-Si/a-Si : H/indium tin oxide heterostructures upon thermal annealing

c-Si/a-Si:H/indium tin oxide (ITO) heterojunctions have been prepared by el ectron-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 N-2 atmosphere at temperatures in the range 250-650 degreesC. Thermal annealing effects on s tructural 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 op tical 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 i n terms of a model which combines the Drude model and a double Lorentzian o scillator. Spectroscopic ellipsometry has shown that annealing at T > 450 d egreesC causes hydrogen out-diffusion from the a-Si:H layer into the ITO la yer whose optical and electrical properties are modified. Additionally, dam age of the c-Si/a-Si interface and of the ITO layer by hydrogen diffusion i s detected and seen as a factor affecting performance of c-Si/a-Si/ITO stac ked structure based solar cells. X-ray photoelectron spectroscopy and atomi c force microscopy measurements have corroborated ellipsometric analysis. ( C) 2001 American Institute of Physics.