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Compositionally abrupt junctions (interfaces) in Ge-Si heterostructure nanowires can optimize the performance. However, traditional vapor-liquid-solid (VLS) method using Au droplet may cause “reservoir effect”, leading to interface diffuseness. In this case, vapor-solid-solid (VSS) method can be applied along with VLS method. AlAu alloy are used as a catalyst to raise the eutectic temperature. In order to determine which AlAu alloy and temperature are the best for nanowire generation, the Al-Au-Ge-Si quaternary database was established using thermocalc software. Using gibbs free energy expressions for binary systems, the phase diagrams of ternary systems were calculated and compared with experimental data. Calculated Al-Ge-Si and Au-Ge-Si phase diagrams show similar eutectic structures and are in good agreement with experimental data. However, considerable solubility was found in Al2Au compound, raising the eutectic temperature and changing the liquidus lines of the compound. After comparing different AlAu compounds, the alloy that is best for Ge-Si formation are AlAu2 and AlAu alloys because they shows both low solubility of semiconductor and relatively high eutectic temperatures.