Electrical magneto- and spintransport properties of wide bandgap oxide semiconductors
ABSTRACT :
Wide bandgap oxide semiconductors are promising materials for optoelectronic devices. Most of these oxides such as ZnO, InGaZnO4, In2O3 etc. exhibit n-type conduction due to presence of native defects. Electrical conductivity in these oxides can be tuned over a wide range by doping different elements. We have studied electrical and magnetotransport on PLD (pulsed laser deposition) grown pure and doped ZnO thin films. Different dopants (Eu, Sb and Ga) have been explored to understand the transport mechanism. While pure and Sb doped ZnO exhibits strong localization, Eu and Ga doped samples show weak localization phenomena. Among different dopants, Ga doped ZnO (Ga:ZnO) possesses highest conductivity. Therefore, we have studied the effect of thickness on transport properties of Ga:ZnO films and observe thickness dependent metal insulator transition (MIT). Magnetotransport measurement and density functional theory (DFT) calculations further confirm the MIT. The generation and detection of pure spin currents has stimulated theory and experiments reaching from spin pumping over spin Seebeck effect to spin Hall magnetoresistance (SMR).We have experimentally investigated the flow of a pure spin current through ultrathin Ga:ZnO layer sandwiched between an insulating bismuth doped yttrium iron garnet (Bi:YIG) layer and a platinum (Pt) layer via SMR measurements. The observed SMR amplitude is reduced when inserting Ga:ZnO layer between Pt and Bi:YIG. Amorphous InGaZnO4 (a-IGZO) is another excellent material for thin film transistors (TFTs) owing to high mobility (>10 cm2/v-s). We have also studied disorder dependent metal-insulator transition (MIT) in a-IGZO thin films. From the magnetoresistance experiment, phase coherence length was estimated. Phase coherence length scales with temperature as T-3/4 confirming that the electron-electron scattering dominates the dephasing mechanism.