Impurity Segregation in LPE Growth of Silicon from Cu-Al Solutions

Al segregation at the solid-liquid interface and Cu segregation at the free silicon surface were studied in liquid-phase epitaxy (LPE) of silicon thin layers from mixtures of Cu-Al-Si. Using the multi-component regular solution model and experimental results, we found that Si-Al and Si-Cu interactions in the liquid solution are repulsive, and Al-Cu interaction is attractive. As a result, Aldoping in silicon epitaxial layers is controlled by both Cu and Al compositions in the growth solution to allow epitaxy at about 900 degrees C, with a substantial amount of Al present in the liquid for substrate surface-oxide removal. On the other hand, Cu concentration in the growth layers is determined by both the solid-liquid interface segregation during growth and segregation at the siliconsurface after growth. The surface segregation phenomenon can be used to getter Cu from the bulk of silicon layers so that its concentration is much lower than its solubility at the layer growth temperatures and the reported 10 th the 17th CM-3 degradation onset for solar-cell performance.