Doping dependence of second harmonic generation from native oxide/Si(111) interfaces

Optical second harmonic generation (SHG) was studied on native oxide/Si(111) substrates with both n- and p-type dopings of various doping concentrations. With the rotation about the (111) azimuth, six peaks were observed in SHG intensity at every 60° with C3v symmetry for all substrates. However, the strong peaks appeared at 0, 120, and 240° on p-type Si substrates, whereas these peaks were small on n-type Si substrates. We found that the reduction of the peaks at 0, 120 and 240° had a correlation with the change of the doping type and the doping concentration from the p+ to the n+ region. Analysis of the azimuthal rotation dependence of the SH intensity indicates that the observed change is caused by the change of the 2nd order non-linear susceptibility tensor components, χzxx. We think that this is due to the change of the interface dangling bond occupation and the resulting change of the interface dipole with the dopings.