单根SnO2纳米线器件的电输运性能及其机理研究

Electrical transport properties and related mechanism of single SnO_2 nanowire device

为探究常态环境下氧空位对单根SnO_2纳米线电输运性能的影响,采用化学气相沉积法合成了SnO_2纳米线,通过光刻微加工技术构筑了Au/单根SnO_2纳米线/Au二端纳米器件.将单根SnO_2纳米器件进行氢化处理,测试其在空气与真空中的伏安特性曲线,发现单根SnO_2纳米线在空气和真空环境中呈现异常不同的电输运特性:在空气中,加偏压注入电子会使通过纳米器件的电流减小,Au电极与SnO_2纳米线之间的接触势垒增大;抽真空后,在偏压的影响下,通过纳米器件的电流增大,Au/SnO_2交界面的接触方式由肖特基接触转变成欧姆接触.实验分析表明,影响单根SnO_2纳米线电输运特性行为的因素与纳米线表面的氧原子吸附与脱吸附所引起的氧空位浓度的变化有关.为进一步分析氧空位浓度变化的作用,利用第一性原理计算方法计算了氧空位浓度对SnO_2纳米线电输运性能的影响,通过分析体系的能带结构、态密度及Au/SnO_2接触界面的I-V曲线和透射谱,发现随着氧空位浓度的增大,SnO_2纳米线的带隙变小.同时,氧空位缺陷使Au/SnO_2接触界面处电子透射率增大,体系电输运能力变强.该研究结果将为集成纳米功能器件的设计提供一种新思路.

Defect engineering in a semiconductor nanowire-based device has aroused intensive attention due to its fascinating properties and the potential applications in nanoelectronics. Here in this work, in order to investigate the effect of oxygen defects on the electrical transport properties in a SnO2-nanowire-based device under normal environment, we synthesize an individual SnO2 nanowire, by a thermal chemical vapor deposition method and further construct a two-terminal Au/SnO2 nanowire/Au device by using optical lithography. The electrical transport properties of a single SnO2 nanowire device are measured under the condition of air and vacuum after hydrogen reduction. It is found that the transport performances in air are unusually different from those in vacuum. Strikingly, the reduction of electric current through the device and the increment of contact barrier of the Au/SnO2 interface in air can be observed with the I-V scan times increasing. While in vacuum, the current increases and a change from Schottky contact to ohmic contact at the interface between Au and SnO2 can be obtained by performing more scans. Our results demonstrate that the oxygen vacancy concentrations caused by the oxygen atom adsorption and desorption on the surface of nanowires play the key role in the transport properties. Furthermore, we calculate the relevant electronic properties, including energy band structure, density of states, as well as I-V characters and transmission spectrum at the interface of Au/SnO2 within the framework of density functional theory. We find that the bandgap of SnO2 nanowires decreases with oxygen vacancy concentration increasing. Also, the existence of oxygen defects enlarges the electron transmission at the interface of Au/SnO2 and enhances electrical transport. Therefore, our results provide a new strategy for designing the integrated nano-functional SnO2-based devices.