Abstract

The Si/SiO₂ interface is the most widely used system in modern electronic devices. Electrically active defects at this interface play an important role in device performance and reliability. In a previous study we have shown that in the case of highly boron doped Si, these interfacial defect states are ionized and result in a built-in interfacial electric field, E₀, which gives rise to an instantaneous electric field induced second harmonic (EFISH) signal, I^(2ω)(E₀), upon irradiation with femtosecond laser pulses (73±5 fs, $35{\text{GW/cm}}^2\le I_{peak}^{(\omega )}\le 115{\text{GW/cm}}^2$) [1]. We now show that the observed power law dependence of the instantaneous EFISH signal on the incident intensity, $I^{(2\omega )}(E_0)\propto {(I_{peak}^{(\omega )})}^n$, reveals 1.2 ≤ n ≤ 2.1 for six fs laser wavelengths 741.2 nm ≤ λ ≤ 801.0 nm. The lowest n value is observed at λ = 752.4 nm (2·hν = 3.3 eV). Its deviation from n = 2 is attributed to shielding of E₀ by electron-hole pairs generated via two-photon absorption (TPA).

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