Electrical Transport Properties Of Ultrathin In₂O₃ Films

Indium oxide（In₂O₃）,as a transparent conductive material,has wide bang gap,low resistivity,and high catalytic activity and is widely used in optical electronics devices,gas sensor and catalyzer.In addtion,the discovery of high mobility in undoed epitaxial In₂O₃,open up the application in field of film transistor.As the application of In₂O₃ films are continually expanded and the demand for ultrathin In₂O₃ films is progressively increasing.In this way,it is necessary to research systematically the electrical transport properties of ultrathin films with thickness.We have prepared In₂O₃ films by rf-magnetron sputtering with thickness ranging from⁴ nm to⁴5 nm on the yttrium stabilized ZrO₂ single crystal substrates and systematically investigated the structural and electrical transport properties.The x-ray diffraction measurements indicated that the films with thickness t?17.0 nm are epitaxial.However,the scanning electron microscopy images indicated there are distinct boundaries between In₂O₃ grains.Thus we proposed that the t?17.0 nm films possess structures similar to that of mesocrystal.Those t?11.5 nm films reveal metallic characteristics in electrical transport properties,and electron-electron interaction effects as well as weak localization effect govern the low temperature behaviors of resistance.It is also found that the electron screening factors are nearly zero for the t?11.5 nm films and it may be relative to the low concentration of our In₂O₃ films.For the 6.3 and 3.7 nm thick films,the resistivities variation with temperature curvesρ（T）show insulator behaviors in the temperature range of 2-300 K.In addition,the two-dimensional Mott variable-range-hopping（VRH）and Efros-Shklovskii VRH dominate the temperature behavior of resistivity and a crossover occurs²0 K.For the annealed 6.3 and 3.7nm thick films,theρ（T）data quantitatively satisfy the 2D Mott VRH and 2D Efros-ShklovskiiVRH theories in the corresponding temperature regions.We have deposited t?40 nm In₂O₃ films by rf-magnetron sputtering with substrate temperature T_a varying from 300 to 550℃.The x-ray diffraction measurements indicate all the In₂O₃ films are epitaxial with nice crystal property and have the structure similar to mesocrystal.When T_a reaches 550℃,the particle size increases significantly and the clubbed particles translate to squared and elliptic particles.WhenT_a（27）450℃,the conductivity of films reduce as the time vary due to the oxygen vacancies are filled up,which is unstable conductivity.TheT_a?450℃deposited films reveal metallic conductive properties and the electron-electron interaction effects and weak localization effect dominate electrical transport peocess at low temperature regime.It is also found that small-energy and large-energy transfer electron-electron scatteringdominate the electron dephasing process.At 2 K the dephasing length for theT_a（28）550℃film can reach³50 nm,which is larger than that of other samples and that of reported values in In₂O₃.