Injection-level dependent surface recombination velocities at the Si-SiO2 interface

For determination of the effective surface recombination velocity (SRV) at the Si-SiO2 interface, a new method based on depth- and time-resolved free-carrier absorption measurements is put forward. The proposed technique is more advantageous than conventionally used methods and makes it possible to obtain the SRV and its injection level dependence on a particular sample surface without additional knowledge of other silicon parameters. The experimental measurements have been performed on n-Si with polished facets and a cleaved edge. All surfaces were covered by thermally grown SiO2. The result is that the SRV increases with the injection level followed by saturation. The computer simulation of the excess carrier decay has shown that, for polished surfaces, the value of the SRV should be reduced in the high injection region and not only does depend on the injected level, but also on the initial excitation It is proposed that temporal charging of the Si-SiO2 interface can be responsible for such behavior.