Magneto-transport Properties Of Semiconductors And Optical Properties Of HgTe Crystals

The spin-orbit interaction(SOI) and Zeeman spin splitting are two important physical mechanisms of the electron spin dynamics. In this paper, their competition is studied and developed by investigations of Alx Ga1-x N/Ga N quantum wells and Hg1-x Cdx Te inversion layers. In addition, the three-dimensional weak localization and anisotropic magnetoresistance in Mg Zn O thin film, as well as the strained Hg Te plates on Sr Ti O3 are investigated. The following results are obtained:(1) The transport properties of Alx Ga1-x N/Ga N quantum wells are studied. By focused research on weak antilocalization(WAL) effects in the in-plane magnetic field for two Alx Ga1-x N/Ga N quantum wells, in which the WAL effects are dominated by the SOI originating from the structural inversion asymmetry and the bulk inversion asymmetry, respectively, their dependence of spin dynamics on in-plane magnetic field are found the same. By fitting the weak antilocalization magnetoconductance, the phase coherence time and spin-orbit scattering time are obtained. With the increase of in-plane magnetic fields, the phase coherence time decreases quadratically while the spin-orbit scattering time increases quadratically. The value of the effect g-factor obtained are the same as that from the Sd H oscillations, indicating this phenomenon attributed to the competition between the SOI and Zeeman splitting rather than the microroughness scattering.(2) Two different Hg1-x Cdx Te films are used and inversion layers on their surfaces are induced by anodic oxidation. Their WAL effects are found to be in the diffusion and ballistic regimes, respectively, i.e., strong SOI and weak SOI. By investigation of the WAL effects in the in-plane magnetic field and fitting by the Golub model, the phase coherence time is found to decrease quadratically with increasing in-plane magnetic fields too, while the spin-orbit scattering time show no obvious change, due to small variation of phase coherence time for structural inversion asymmetry as well as relatively big SOI in Hg Cd Te. The value of the effect g-factor obtained are the same as that from the Sd H oscillations, indicating the same competition between the SOI and Zeeman splitting in systems of big SOI.(3) Hg1-x Cdx Te inversion layer with microroughness scattering are studied, the WAL effect is enhanced and then suppressed with the in-plane magnetic field in relatively high in-plane magnetic field. In relatively high in-plane magnetic field, no microroughness scattering is observed, the phase coherence time is found to decrease quadratically as well, this dependence is found to be independent on the temperature.(4) Magnetotransport properties of Mg Zn O thin film grown on Zn O substrate are investigated. The three-dimensional weak localization effect is found and fitted by the Kawabata theory as well as analyzing the different changing rate of the magnetoresistance. The obtained phase coherence length ranges from 38.4 ?1 nm at 50 K to 99.8 ?3.6 nm at 1.4 K, its temperature dependence is found to scale as 3/ 4T-. Meanwhile, we study the anisotropic magnetoresistance resulting from the geometric effect as well as the Lorentz force induced path-length effect. It enhances in high magnetic fields, roughly linear dependents on the temperatures and differs with the direction of current.(5) Hg Te plates have been grown on Sr Ti O3 substrates. Examination of the plates using the micro-Raman mapping shows that the Hg Te plates exhibit unusual strain patterns: the Raman peaks from the transverse-optical(117.1cm-1) and longitudinal-optical(137.3cm-1) phonons for the thicker(central) parts of the Hg Te plates are at the same frequency as that of bulk Hg Te, while the Raman peaks for the thinner parts of the Hg Te plates, which surround the thicker parts and can hardly be seen in a scanning electron microscope, are significantly larger in frequency(125.8cm-1 and 144.5cm-1, respectively). Theoretical analysis shows that the Hg Te plates on Sr Ti O3 substrates suffer from compressive stress, this may be sufficient to induce the three-dimensional topological insulator behavior in Hg Te.