| Layered delafossite CuCrO2 is a transparent conducting oxide with wide band gap?3.2 eV?,which consists of close-paced Cu and octahedral CrO6 layers alternately stacking along the c axis.The spontaneously formed Cu vacancies in the crystal structure provide hole carriers which mainly transport within the ab-plane,leading to a large transport anisotropy.The combined research of its transparent conducting and anisotropy proreties can lay the foundation of new applications and device developments basing on this material system.In this thesis,three types of defective CuCrO2 polycrystals/films with Cu,Cr or O stoichiometric ratio deviating from 1:1:2,namely,Cu abundant CuxCrO2?x=0,1.05,1.11,1.25?,Cr abundant CuCryO2?y=0,1.05,1.11,1.25?and Mg doped CuCr1-xMgxO2?0?x?0.08?were prepared,their properties,anisotropies as well as the related mechanisms were studed and discussed.The Cu/Cr stoichiometricly abundant polycrystals were prepared by solid state reaction method with the process of 1100?/12 h+1100?/12 h,which were all of delafossite structure and semiconductive electrical transport behavior with Arrhenius thermal activation mode.Compared with CuCrO2,Cu abundant samples had stronger c-axis preferred orientation with fully grown grains along the ab-plane.The resistivities reduced by 3?4 orders of magnitude,and the thermopower decreased obviously:the room temperature resistivities and thermal activation energies of CuCrO2 and Cu1.25CrO2 were respectively 4.64×105?cm,0.474 eV and70?cm,0.221 eV,and the thermopower at 400 K were 1142.68?V/K and 759.365?V/K,which was mainly due to the increased carrier concentration by Cr vacancies and Cu?Cr?anti-site atoms.Compared with CuCrO2,the density of Cr abundant polycrystals increased slightly,and the resistivities decreased slightly with the same order of magnitude.The lowest room temperature resistivity was 1.58×105?cm for CuCr1.25O2,while the thermal activation energy and thermopoer did not changed obviously.The Cu/Cr abundant c-axis epitaxial films with pure delafossite structure were grown on flat Al2O3?0001?single crystal substrates by PLD with the optimized process:deposition at730?/O2:1 Pa/12 min and annealing at 730?/O2:2000 Pa/20 min.The stoichiometricly deviated films showed rougher surface morphologies than that of CuCrO2.The relative contents and valence states of Cu,Cr in the films were studied by XPS,the results showed that the variation trend of actural Cu/Cr relative content ratios T?Cu/Cr?were consistent with the nominal N?Cu/Cr?,while the value of T?Cu/Cr?=0.8103 is lower than N?Cu/Cr?=1,which was mainly due to the preferential etching of Cu by Ar+sputtering during surface cleaning stage.The binding energies of Cu 2p3/2 and Cr 2p3/2 were 932.5±0.2 eV and 576.5±0.2 eV,respectively,indicating Cu and Cr were of+1 and+3 valence states.The resistivities of Cu/Cr abundant films were lower than CuCrO2 except CuCr1.25O2,which are 62.6?cm and 13.1?cm respectively for CuCrO2 and Cu1.11CrO2 at room temperature due to the increased carrier concentration by Cu,Cr vacancies and Cu?Cr?anti-site atoms.c-axis epitaxial CuCr1-xMgxO2?0?x?0.08?films were grown on 0°?15°inclined Al2O3?0001?single crystal substrates by PLD.The visible light transmittances and optical band gap for films were?60%-80%and Eg?3.08 eV,and decrease with increasing x.The resistivities of Mg doped films were 2 orders of magnitude lower than that of CuCrO2,which were 63?cm and 0.19?cm for x=0 and x=0.08,respectively.The laser induced transverse voltage?LITV?signals were obtained in Mg doped films under pulsed laser irradiation with wavelength?248nm??5 eV?and pulse width?28 ns.The peak voltage was 44.8 mV for x=0.08 and increse with increasing x,which mainly resulted from the enhanced intrinsic thermopower anisotropy?S induced by more hole carriers transporting within the ab-plane after Mg doping.The contribution of photogenerated carriers to LITV effect when laser photon energy is larger than Eg was preliminary discussed,which was 2.75 mV for 15°inclined CuCr0.92Mg0.08O2 film. |
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