Liquid Phase Epitaxy (LPE) method for growth of Si layers at low temperature (<800°C) can be an interesting technique for thin monocrystalline Si photovoltaic applications. LPE has been largely studied at high temperature using solvents like tin or indium but only few works deal with low temperature LPE. The main difficulty is the low solubility of silicon in usual solvent. In this work, we propose the use of a quaternary alloy Al-Cu-Sn-Si. It permits growth at lower temperature, each elements playing a key role: Al reduce Si native oxide prior growth [1]. Cu is used to increase Si solubility. Sn allows growth at low temperature.

Phase equilibria in the Al-Cu-Sn-Si system have been calculated using the Factsage software package and thermodynamic data coming from the SGTE solution database for all solid compounds and the binary interaction in the liquid phase. The ternary interaction has been altered for the calculations. Within the SGTE database, the symmetrical Muggianu model is used by default. This model has the disadvantage that it extrapolates no very well in an unsymmetrical case such as Cu-Si-Sn. Either ternary interaction parameters are needed (with no physical meaning: they are only necessary due to the model chosen) or another extrapolation model has to be chosen. So, the unsymmetrical Toop model, which is implemented in the software package, has been used. Results of these calculations and their implications with respect to Si growth are discussed. We compare effective Si epilayer thickness obtained with expected Si incorporated in the liquid phase, and influence of alloy composition to the growth rate. We also present some electrical characterisation and discuss the use of such epitaxial layer for solar cells.

1- F. Abdo and al. PVSEC-15, Shanghai 2005 pp. 746-747

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