Optical harmonic generation from interfaces with Group IV semiconductors
Keywords: Physics

Nonlinear optical techniques have been used to investigate the symmetry properties of interfaces between media comprising at least one Group IV semiconductor. Second harmonic generation (SHG) and third harmonic generation (THG) have been performed for s and p polarization states of the fundamental and harmonic beams as a function of sample azimuthal angle at a fixed fundamental wavelength of 775 nm. In addition to these experimental measurements, the thesis contains theoretical calculations of the optical harmonic response from such media with vicinal surfaces, that is surfaces miscut from a low-index face by ${<}{\sim}$10$\sp\circ$.<p> The phenomenological theory of Sipe, Moss and van Driel (Phys. Rev. B 35, 1129 (1987)) for SHG and THG in reflection from the low-index faces of cubic centrosymmetric media has been extended to all faces of both cubic centrosymmetric and cubic noncentrosymmetric media. This theory is applied in many parts of the thesis to interpreting the symmetry information present in nonlinear optical data. Experimentally, measurements of SHG and THG from vicinal semiconductor wafers have been performed, and using the above theory the wafer orientations have been obtained to within $\pm$0.1$\sp\circ$. In addition, the above theory has been applied to achieve an approximate separation of bulk and surface contributions to SHG measurements from vincinal Si(001) and Si(111) surfaces which Sipe et al. showed is not possible on the low-index faces. The SiO$\sb2$/Si interface on vicinal Si(001) has been studied with SHG, and evidence has been obtained for the presence of noncentrosymmetric phases of c-SiO$\sb2$ at this interface whose relative concentrations are influenced by the oxidation conditions. For oxidation temperatures below 600$\sp\circ$C, the SHG data is shown to be consistent with the presence of tridymite at the buried interface, whereas for oxidation at 900$\sp\circ$C the SHG data is consistent with the presence of cristobalite. Finally, SHG has been measured from odd-period Si$\sb{m}$Ge$\sb{n}$ superlattices (n,m both odd) grown on Si(001). The measurements were designed to test the predictions of Ghahramani, Moss and Sipe (Phys. Rev. Lett. 64, 2815 (1990)) of large bulk dipole allowed SHG from such media. The effect is not observed, and this is attributed to the ever-present monatomic height steps on the Si(001) substrate which lead to the formation of antiphased domains on a length scale typically ${\sim}$10$\sp3$ times smaller than the laser spot size. SHG measurements from an odd-period Si$\sb{m}$Ge$\sb{n}$ superlattice grown on a single-domain vicinal Si(001) substrate are shown to be consistent with the presence of a weak bulk dipole-allowed contribution. The contribution is much weaker than would be expected from the ideal superlattice because of the inevitable presence of antiphased domains in the growth direction. The phenomenological theory of Sipe. Moss and van Driel (Phys. Rev. B 55. 1 129 (1087)) for SHG and THG in reflection from the low-index faces of cubic centros\inmetric media has been extended to all faces of both cubic centrosymmetric and cubic noncenirosyminetric media. This theory is applied in many parts of the thesis to interpreting the symmetry information present in nonlinear optical data. Experimentally, measurements of SHG and THG from vicinal semiconductor wafers have been performed, and using the above theory the wafer orientations have been obtained to within ±0.1°. In addition, the above theory has been applied to achieve an approximate separation of bulk and surface contributions to SHG measurements from vicinal Si(001) and S i(lll) surfaces which Sipe et, al. showed is not possible on the low-index faces. The S i0 2/Si interface on vicinal Si(001) has been studied with SHG. and evidence has been obtained for the presence of noncentrosymmetric phases of c-Si()2 at this interface whose relative concentrations are influenced by the oxidation conditions. For oxidation temperatures below GOO °C the SHG data is shown to be consistent with the presence of tridymite at the buried interface, whereas for oxidation at 900 °C the SHG data is consistent with the presence of cristobalite.