Fabrication And Electrical Properties Of La_1.8Sr_0.2CuO₄/La_1.9Sr_0.1CuO₄Superconducting Bi-layer Structure

Today superconducting materials are paid more attention to people since it has theadvantages of zero resistance in the nervous energy, the emergence of nano-scale device makepeople give a research on film materials. The aim of applying superconducting thin film for moremicroelectronics devices attracts more and more scientific research workers consideration.In this thesis, pulse laser deposition （PLD） technique was used to fabricate La_1.8Sr_0.2CuO₄film, La_1.9Sr_0.1CuO₄film and La_1.8Sr_0.2CuO₄/La_1.9Sr_0.1CuO₄bi-layer structure. The samples werecharacterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）. We study theproperties including the crystal structure, morphology and electrical transport properties of as-prepared films. The major results and conclusions can be summarized as following:1. In this paper, a traditional solid-state reaction method was used to synthesize La1.8Sr0.2CuO4and La_1.9Sr_0.1CuO₄powder, this powder was then used to prepare ceramic targets for filmdeposition;2. High quality overdoped La_1.8Sr_0.2CuO₄and underdoped La_1.9Sr_0.1CuO₄films were deposited on （001）SrTiO3substrate by pulsed laser deposition technique （PLD）, the optimized parameters are as follows:oxygen pressure30Pa, substrate temperature760℃, the target-substrate distance （the distancebetween target materials and the substrate）4cm, pulse laser energy600mJ;3. A series of films with different thickness were prepared using the optimized parametersmentioned above, and the influence of thickness on superconducting transition temperature werestudied. We found that superconducting transition temperature （9K²0K） gradually increasedwith the increase of the film thickness （20nm²00nm）, and the increasing is not obvious whenthe thickness is above150nm4. La_1.8Sr_0.2CuO₄/Nb-doped SrTiO3（NSTO） and La_1.9Sr_0.1CuO₄/Nb-doped SrTiO3（NSTO）hetero structures were prepared and their electrical transport properties were studied. The resultsshow that both structures have rectifier characteristics and got the change rule of the diffusionpotential, the Vdwas caused by opening of superconducting gap （Eg）;5. La_1.8Sr_0.2CuO₄/La_1.9Sr_0.1CuO₄bi-layer structure were prepared firstly and then the step-structure was fabricated through chemical corrosion methods. The electrical transportproperties were studied. A rectifying property was observed in such structure. Such electricalbehavior of superconducting bilayer film is mainly caused by electric-field-driven migration ofholes.