Electronic Transitions at Si(111)/Si${\mathrm{O}}_2$ and Si(111)/S${\mathrm{i}}_3$${\mathrm{N}}_4$ Interfaces Studied by Optical Second-Harmonic Spectroscopy

The existence of both strain and disorder at the interface of thermally grown ${\mathrm{SiO}}_2$ or plasma-deposited ${\mathrm{Si}}_3{N}_4$ films on vicinal Si(111) was ascertained unambiguously by frequency, polarization, and crystal orientation dependent studies of optical second-harmonic generation. The strain was seen to cause a redshift of 40 and 70 meV of the interband critical points $E_0^{\prime }$ and $E_1$ compared with the bulk silicon values. The disorder is observed by the perturbation of states out of the silicon bulk bands into the gap. Both at terraces and at steps, the density of these charge traps is found to be considerably reduced after rapid thermal annealing.