Abstract

Much recent second harmonic (SH) spectroscopy of the buried Si/SiO₂ interface [1] has been performed without deconvolving the true dipole-allowed strained-interface contribution (~ 10 Å depth) from two comparable, competing bulk contributions: 1) electric-field-induced SHG from the space charge region (~ 100 Å depth) and 2) bulk quadrupole SHG from the SHG from the SH escape depth (~ 1000 Å). Consequently important interface spectral features, such as the strain-induced redshift of the El critical point [1], could be observed qualitatively but not fully quantified. In the current work we have fully separated these three contributions and their corresponding spectra for the first time to our knowledge by performing electromodulated SH spectroscopy on a Si(001) metal-oxide-semiconductor (MOS) structure. The relatively simple tensorial decomposition of nonlinear electroreflectance (NER) at Si(001) interfaces permits full separation of the three contributions through their contrasting dependence on applied bias and sample azimuthal orientation. Moreover field-dependent contributions minimize almost exactly at the independently-measured flatband potential. Finally, SH spectroscopy on unbiased Si₃N₄/Si(001) interfaces confirm the well-known coompressive strain at these interfaces. Simultaneous amplitude and relative phase measurements reveal a blueshift of the surface dipole contribution relative to bulk resonance position.

© 1996 Optical Society of America