Impact of illumination level and oxide parameters on Shockley-Read-Hall recombination at the Si-SiO2 interface
Abstract
The experimentally observed dependence of effective surface recombination velocity S(ind eff) at the Si-SIO2 interface on light-induced minority carrier excess concentration is compared with theoretical predicitions of an extended Shockley-Read-Hall formalism. The calculations of SRH-recombination rates at the Si-SiO2 interface are based on the theory of a surface space charge layer under non-equilibrium conditions and take into account the impact of illumination level, gate metal work function, fixed oxide charge density and the energy dependence of capture cross secctions sigma(ind n),sigma(ind p) and interface state density D(ind it). Applying this theory to p-type silicon surfaces covered by high quality thermal oxides, the experimentally observed strong increase of S(ind eff) with decreasing minority carrier excess concentration could quantitatively be attributed to the combined effect of the sigma(ind n)/sigma(ind p)-ratio of about 1000 at midgap and the presence of a positive fi xed oxide charge density Q(ind f) of about 1x10(exp 11) charges/qcm. Due to the favorable work function of aluminum, surface recombination velocities below 1 cm/s can be obtained at Al-covered Si-SiO2 interfaces for minority carrier densities above 10(exp 13) cm(exp -3).
