Minority-Carrier Lifetime Degradation in Silicon Co-Doped with Iron and Gallium

The effect of Fe-Ga pair defects on minority-carrier lifetime ..tau.. in high-purity, dislocation-free float-zoned Si is presented, and their properties are documented by deep-level transient spectroscopy and annealing studies. The typical ..tau.. of Fe-Ga co-doped crystals (0.4 ..mu..s) was dramatically lower than ..tau.. of crystals doped with similar amounts of ither Fe alone (12 ..mu..s) or Ga alone (1,4000 ..mu..s), contrary to the ..tau.. behavior at low injection of Fe-B pair defects. Thermal dissociation of Fe-Ga pairs increased ..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 correspondinghole-capture cross sections ( at T = ..infinity..) were 3 x 10-16 and 6 x 10-15 cm2. An estimation of the binding energies resulted in much lower values than expected (0.09eV and 0.15eV, respectively).