Second-harmonic generation from SiO2/Si(111) interfaces.

Abstract

Second-harmonic generation (SHG) from ${\mathrm{SiO}}_{2}$/Si(111) interfaces was studied. The SHG intensity was measured as a function of azimuthal rotation angle for a 45\ifmmode^\circ\else\textdegree\fi{} incident, s-polarized YAG laser beam (where YAG denotes yttrium aluminum garnet). An interface with a 500-\AA{} thermal-oxide film showed an asymmetric rotational dependence. However, the asymmetry disappeared after hydrogen annealing, whereas the asymmetry did not change for nitrogen annealing. The asymmetry is caused by the nonlinear susceptibility ${\mathrm{\ensuremath{\chi}}}_{\mathit{z}\mathit{x}\mathit{x}}^{(2)}$. Hence, the difference between hydrogen and nitrogen annealing shows that ${\mathrm{\ensuremath{\chi}}}_{\mathit{z}\mathit{x}\mathit{x}}^{(2)}$ decreases by annealing with hydrogen. Because ${\mathrm{\ensuremath{\chi}}}_{\mathit{z}\mathit{x}\mathit{x}}^{(2)}$ reflects the local potential asymmetry along the interface normal direction, the decrease of the asymmetry is related to the passivation by hydrogen of interfacial dangling bonds in this direction. This means that the ${\mathrm{SiO}}_{2}$/Si(111) interface has an intrinsic interface dangling bond normal to the interface which is detectable as a ${\mathrm{\ensuremath{\chi}}}_{\mathit{z}\mathit{x}\mathit{x}}$ contribution to the interface SHG.