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Microcrystalline silicon (μc-Si:H) solar cells were prepared in a wide range of deposition parameters using 13.56 MHz plasma-enhanced chemical vapour deposition (PECVD). The best μc-Si:H solar cells were prepared close to the transition to amorphous silicon (a-Si:H) growth at very high deposition pressures (∼10 Torr) showing solar cell efficiencies up to 8.0 % at a deposition rate of 5ÊÅ/s. Investigations of the solar cells were performed by Raman spectroscopy and transmission electron microscopy (TEM). TEM measurements revealed similar structural properties with similar high crystalline volume fractions for these cells although they showed distinctly different efficiencies. However, an increased amorphous volume fraction was detected by Raman spectroscopy for the low efficiency cells prepared at low deposition pressures. This result is attributed to an increased ion bombardment at low pressures.
In this paper we report lateral variation of Si and Ge concentration profiles measured in SiGe layers grown on mesa shaped Si(001) substrates. Si(001) substrate was patterned using conventional lithography process in forms of mesa with two crystal planes: (001) top plane and the etched (111) side plane. 50 nm thick Si0.7Ge0.3 strained epitaxial layer was grown using Molecular Beam Epitaxy (MBE), on top of the substrate. Thickness on the center of both crystal planes agrees with the expected values. Lateral image of composition profiles has been obtained from Micro Raman spectra taken at various locations on the mesa. Lower concentration of Ge was found at the vicinity of the edges of the (001) planes relative to the centers. We introduce a diffusion model using stress enhanced activation energy to explain our data, taking into account stress profiles along the mesas, by modifying the activation energy for planar diffusion model. The planar diffusion length was used as a fitting parameter in the model, with good agreement to known values from the literature.
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