Doping dependence of minority carrier lifetime in Ga-doped silicon

The authors present a combination of detailed measurements and modeling to shed light on the lifetime-limiting centers and mechanisms in high-lifetime ( approximately 1 ms) Ga-doped float-zone silicon. A deep level at E_c -0.52 eV was found to limit the lifetime in high-quality silicon prior to intentional doping. Initial addition of a Ga dopant (5.5*10¹⁴ cm^-3) increased the trap density and trap-assisted Auger coefficient by a factor of four; they remained unchanged with further increase in Ga concentration in the range of 6*10¹⁴ to 2.6*10¹⁶ cm^-3. A trap-assisted Auger process was clearly identified and quantified in these samples by deep-level transient spectroscopy and injection-level/doping-dependent lifetime measurements, coupled with lifetime modeling. The observed doping/injection-level dependence of lifetime is explained by a combination of Shockley-Read-Hall, trap-assisted Auger, and band-to-band Auger recombinations. The band-to-band Auger coefficient in highly injected (<10¹⁷ cm^-3) silicon was found to be 1.2*10^-30 cm⁶ s^-1. The-trap assisted Auger coefficients in the undoped and Ga-doped samples were 2*10^-14 and 8*10^-14 cm³ s^-1, respectively.