The Electrical Transport Properties Of Ta-N Compounds

TaN compound has received particular interest in recent years owing to its excellent physical,chemical and mechanical properties.Because of its high hardness,good wear resistance,chemical inertia,high temperature stability,low resistivity,it has been widely used in the wear-resistant coating on tools,thin-film resistors,diffusion barriers and other fields.In addition,since it has superconducting properties and high carrier concentration,superconductor-insulator transition（SIT）,superconducting fluctuations and anomalous metal phase can be observed in the experiment,and these phenomenons are hot topics in condensed matter physics.Firstly,we study the microstructure and electrical transport properties ofε-TaN bulks,and find thatε-TaN bulk has very low resistivity at room temperature,which is comparable with the resistivity of metals.Electrical transport measurements show that theε-TaN has metallic conductivity property,however,its resistivity rapidly decreases by to 40%as temperature varies from 6 K to 1 K.The magnetic measurements show thatε-TaN has complete diamagnetism which indicates theε-TaN has superconducting property.In addition,its phase structure,grain size and electrical transport properties hardly change after annealed at 973 K,so it has high temperature stability.Secondly,we study the microstructures and transport properties of rock-salt TaN_x thin films.Using RF magnetron sputtering system,two groups of films were deposited onto the quartz grass and Al₂O₃（001）substrates.We studied the crystal structures,microstructures and transport properties of the polycrystalline TaN_x films,which were deposited with different sputtering power and substrate temperature.For the polycrystalline TaN_x films which were deposited on the quartz glass substrate,we have systematically investigated the electrical transport properties of the films from 300 K down to 2 K.It is found that the conductivity varies linearly with ln T from～6 K to～30 K,which can be well explained by the intergrain Coulomb effect which was theoretically proposed in the granular metals.While the fluctuation-induced tunneling（FIT）conduction process dominates the temperature behaviors of the conductivities（resistivities）above～60 K.Normal state to superconductive state transition is observed in the x?1.04 films in low temperature regime.The superconductivity can still be retained at a field of 9 T.The upper critical field increases linearly with decreasing temperature in the vicinity of the superconductive transition temperature,which is the typical feature of granular superconductors or dirty type-II superconductors.The granular-composite-like electrical transport properties of the polycrystalline TaN_x films are related to their microstructure,in which the TaN_x grains with high conductivity are separated by the poorly conductive amorphous transition layers（grain boundaries）.For the TaN_x films prepared on Al₂O₃（001）substrates with different substrate temperatures,the transport measurement shows that the TaN_x thin films have semiconducting conductive properties.And normal state to superconductive state transition is not observed at low temperature,which is influenced by the stress between the substrate and the film.When the temperature is higher than 50 K,the FIT conduction process dominates the temperature behaviors of the resistivity,which describes the transport property of granular metal films.Therefore,the TaN_x films which were prepared on Al₂O₃（001）substrates also have granular-composite-like structure.