Abstract
We report on the epitaxial growth of crystalline Si and Ge thin films by standard radio frequency plasma enhanced chemical vapor deposition at 175 °C on (100)-oriented silicon substrates. We also demonstrate the epitaxial growth of silicon films on epitaxially grown germanium layers so that multilayer samples sustaining epitaxy could be produced. We used spectroscopic ellipsometry, Raman spectroscopy, transmission electron microscopy and X-ray diffraction to characterize the structure of the films (amorphous, crystalline). These techniques were found to provide consistent results and provided information on the crystallinity and constraints in such lattice-mismatched structures. These results open the way to multiple quantum-well structures, which have been so far limited to few techniques such as Molecular Beam Epitaxy or MetalOrganic Chemical Vapor Deposition.
Highlights
In the field of solar energy, there is a continuous search for ways to increase the cost-effectiveness of solar cells
Previous studies in our laboratory have shown that plasma conditions leading to hydrogenated microcrystalline germanium films on glass can eventually lead to an epitaxial growth when applied on a (100)-oriented gallium arsenide (GaAs) substrate [16]
We obtained the same results for silicon films, for which conditions known to lead to hydrogenated polymorphous silicon on glass lead to epitaxial growth when applied to (100)-oriented Si substrates [17, 18, 21]
Summary
In the field of solar energy, there is a continuous search for ways to increase the cost-effectiveness of solar cells. Another way to cut costs is to grow the mono or multi crystalline silicon directly on a foreign substrate, using for instance Chemical Vapor Deposition [2], or on a polycrystalline seed layer obtained by the crystallization of an amorphous silicon layer, using a catalyst in the case of aluminium induced crystallization [3] or in a catalyst-free approach using solid phase crystallization [4] These processes usually lead to relatively low solar cell efficiencies since there is a non-monotonic relationship between grain size and solar cell efficiency that implies that in the case of multicrystalline silicon one should have very large grains, as reported by Bergmann [5]
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