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 si licon 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, Al doping in silicon epitaxia l layers is controlled by both Cu and Al compositions in the growth so lution to allow epitaxy at about 900 degrees C, with a substantial amo unt of Al present in the liquid for substrate surface-oxide removal. O n the other hand, Cu concentration in the grown layers is determined b y both the solid-liquid interface segregation during growth and segreg ation at the silicon surface after growth. The surface segregation phe nomenon can be used to getter Cu from the bulk of silicon layers so th at its concentration is much lower than its solubility at the layer gr owth temperature and the reported 10(17) cm(-3) degradation onset for solar-cell performance.