Minority-carrier lifetime degradation in silicon co-doped with iron and gallium [solar cells]

The effect of Fe-Ga pair defects on minority-carrier lifetime /spl tau/ in high-purity, dislocation-free float-zoned Si solar cells is presented, and their properties are documented by deep-level transient spectroscopy and annealing studies. The typical /spl tau/ of Fe-Ga co-doped crystals (0.4 /spl mu/s) was dramatically lower than /spl tau/ of crystals doped with similar amounts of either Fe alone (12 /spl mu/s) or Ga alone (1,400 /spl mu/s), contrary to the /spl tau/ behavior at low injection of Fe-B pair defects. Thermal dissociation of Fe-Ga pairs increased /spl tau/, confirming a stronger carrier-recombination activity at Fe-Ga pairs than at interstitial Fe. Defect energies (relative to the valance band) equal to 0.10 and 0.21 eV were observed for Fe-Ga co-doped samples, and the corresponding hole-capture cross sections (at T=/spl infin/) were 3/spl times/10/sup -16/ and 6/spl times/10/sup -15/ cm/sup 2/. An estimation of the binding energies resulted in much lower values than expected (0.09 eV and 0.15 eV, respectively).