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    Effect of Au on the crystallization of germanium thin films by electron-beam evaporation
    (Elsevier Science Bv, 2014) Eygi, Zeynep Deniz; Kulakci, Mustafa; Turan, Rasit
    Metal induced crystallization is a widely used method to form crystalline/polycrystalline structures at low temperatures. In this work, Au was applied to enhance the crystallization of amorphous Ge films. Ge films with thicknesses of similar to 1.5 mu m were fabricated by electron beam evaporation on c-Si substrate with and without very thin Au layer. Crystallization properties of Ge films were analyzed for different growth and post annealing temperatures varied between 270 degrees C and 730 degrees C. The structures of polycrystalline Ge films were investigated by employing X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM). The existence of thin Au layer showed significant impact on the crystallization of amorphous Ge films in terms of reducing the crystallization temperature. In post annealing processes, it was noticed that the impact of Au thin layer on crystallization slightly reduces above the temperature of similar to 400 degrees C, and almost no remarkable differences were observed between the films with and without Au layer in this temperature region. It is observed that the growth temperature has a stronger effect on the crystallization than post annealing temperatures in the presence of Au thin film. It is also shown that Au layer catalyzes the axial growth in the presence of planar Ge layer on the substrate surface. (C) 2014 Elsevier BY. All rights reserved.
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    Öğe
    Optimizing emitter-buffer layer stack thickness for p-type silicon heterojunction solar cells
    (Amer Inst Physics, 2013) Eygi, Zeynep Deniz; Das, Ujjwal; Hegedus, Steven; Birkmire, Robert
    p-type silicon heterojunction solar cells are investigated in terms of doping concentration of emitter a-Si: H(n) layer and thickness of emitter-intrinsic buffer a-Si: H(n/i) layers. Control of doping concentration of the amorphous layer is essential to gain sufficient conductivity and junction potential while avoiding an increase in defect density of the a-Si: H(n) layer. Inserting a-Si: H(i) provides high passivation quality by reducing a-Si: H/c-Si interface recombination and leads to a higher open circuit voltage. Properties and thicknesses of both a-Si: H(n) and a-Si: H(i) have a significant role on the performance of silicon heterojunction cell. In this paper, emitter a-Si: H(n) and buffer a-Si: H(i) layers thicknesses are optimized at the optimum gas phase doping concentration in order to obtain high efficiencies. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792510]