SiO2/Si interfacial structure on vicinal Si(100) studied with second-harmonic generation

The Evaluation of Interface Quality in HfO2 Films Probed by Time-Dependent Second-Harmonic Generation

Time-dependent second-harmonic generation (TD-SHG) is an emerging sensitive and fast method to qualitatively evaluate the interface quality of the oxide/Si heterostructures, which is closely related to the interfacial electric field. Here, the TD-SHG is used to explore the interface quality of atomic layer deposited HfO2 films on Si substrates. The critical SHG parameters, such as the initial SHG signal and characteristic time constant, are compared with the fixed charge density (Qox) and the interface state density (Dit) extracted from the conventional electrical characterization method. It reveals that the initial SHG signal linearly decreases with the increase in Qox, while Dit is linearly correlated to the characteristic time constant. It verifies that the TD-SHG is a sensitive and fast method, as well as simple and noncontact, for evaluating the interface quality of oxide/Si heterostructures, which may facilitate the in-line semiconductor test.

Silicon nanowire arrays with enhanced optical properties

Vertical silicon nanowire arrays were fabricated leading to an enhanced photoluminescence (PL) emission and second-order nonlinear optical response. PL from the nanowires was increased by a factor of 50 as compared to bulk silicon. The second order nonlinearity was demonstrated in second-harmonic generation and rotational anisotropic measurements. Enhancement by at least a factor of 80 was achieved as compared to bulk silicon for the p-polarized input and s-polarized output. These enhancements in the silicon characteristics should enable highly desired applications using a silicon platform, such as nonlinear and active devices.

Enhancement of second-harmonic generation from silicon stripes under external cylindrical strain

The enhanced second-harmonic (SH) generation from Si (111) stripes induced by external cylindrical strain is investigated. The dependence of the intensity of the strain-induced SH on the sample azimuth shows that the Si under cylindrical strain has 3m symmetry, which is similar to that of the Si (111) surface. Further studies indicate that the intensity of the enhanced SH is a quadratic function of the cylindrical strain within the magnitude that the Si stripe can bear. For the p-polarized and s-polarized SH, the intensities are, respectively, enhanced by 47.9% and 13% at epsilon(0)=2.93x10(-4). The enhancement of SH is due to the contributions from the strain-induced second-order nonlinear susceptibility chi(strain)(2) to the bulk dipole.

Femtosecond carrier-induced screening of dc electric-field-induced second-harmonic generation at the Si(001) SiO(2) interface

Carrier-induced screening of the dc electric field at the Si(001)-SiO(2) interface is observed by intensity-dependent and femtosecond-time-resolved second-harmonic spectroscopy. The screening occurs on a time scale of ~?(p)(-1) , the reciprocal plasma frequency of the generated carriers.

Time-dependent second-harmonic generation from the Si-SiO(2) interface induced by charge transfer

We have observed that the second-harmonic signal generated from oxidized Si(001) varies on a time scale of several seconds in experiments involving a fundamental beam of lambda = 770 nm, 110-fs pulses at 76 MHz. We suggest that the temporal behavior arises from absorption of weak (<100-fW average power) third-harmonic light generated in air or in the sample, inducing charge transfer across the Si-SiO(2) interface and trapping in the oxide layer. Detrapping has been determined to take several minutes.

Optical second-harmonic generation as a probe of electric-field-induced perturbation of centrosymmetric media

Polarization-selective optical second-harmonic generation (SHG) is applied to monitor nonuniform polarization distributions in centrosymmetric media modulated by an external dc electric field. Two different systems are investigated: first, optical SHG from a Au-Si(100) Schottky Barrier is shown to be a direct probe of the electric field polarity near such a metal-semiconductor interface. Second, a poled polymer exhibits a strong anisotropic SHG signal under normal incidence, indicating a nonuniform field enhancement at the edges of the poling electrode. The results demonstrate the sensitivity of SHG to small symmetry perturbations. Consequences for device applications are discussed.

Exact separation of surface and bulk contributions to anisotropic second-harmonic generation from cubic centrosymmetric media

We solve this long-standing problem theoretically by recognizing that the ranks of the tensors that describe the surface and bulk second-order nonlinear susceptibilities differ in this class of media. We show that this implies that the phenomenologies of the anisotropic optical second-harmonic (SH) responses of the two sources differ for all possible crystal facial orientations except (111). To demonstrate the result, we apply the theory to separate the surface and bulk contributions to SH generation from an oxidized vicinal Si(001) wafer for p-polarized 775-nm fundamental and s-polarized SH radiation. It is shown that knowledge of the phase of the SH field is necessary to achieve a unique separation.