W掺杂ZnO透明导电薄膜的理论及实验研究

本文从理论与实验两方面入手, 对高价态差金属W掺杂ZnO (WZO) 薄膜材料的特性进行分析讨论. 采用基于密度泛函理论的平面波赝势方法对WZO材料特性进行理论分析, 计算结果表明: W以替位形式掺入ZnO六角纤锌矿晶格结构中, 由于W-O键的键长较长引起晶格常数增加, 产生晶格畸变; 掺杂后费米能级进入导带, 其附近的导电电子主要由W 5d, O 2p及Zn 3d电子轨道提供, 材料表现出n型半导体的特性; 同时能带简并效应使其光学带隙展宽. 为进一步验证该理论分析结果的适用性, 本文采用脉冲直流磁控溅射技术进行了本征ZnO及WZO薄膜的实验研究, 结果表明: W掺入未改变ZnO的生长方式, 但引起薄膜的晶格常数增加, 电阻率由本征ZnO的1.35× 10^-2 Ω·cm减小到1.55× 10^-3 Ω·cm, 光学带隙由3.27 eV展宽到3.48 eV. 制备的WZO薄膜在400-1100 nm的平均透过率大于83%. 实验结果对理论计算结果进行了验证, 表明WZO薄膜作为透明导电薄膜的应用潜力.

Theoretical and experimental investigation of W doped ZnO

The properties of high valence difference W doped ZnO films (WZO) are investigated by means of plane wave pseudo-potential method based on the density-functional theory (DFT) and pulsed DC magnetron sputtering technique. The theoretical result shows after incorporation of W the Fermi level enters into the conduction band, showing that a typical n-type metallic characteristic and the optical band gap E_g* increase significantly. The carriers originate from the orbits of W 5d, O 2p and Zn 3d. Moreover, the increase of the lattice constant is due to the longer bond length of W-O and lattice distortion. The experimental results demonstrate that the deposited WZO film grows preferentially in the (002) crystallographic direction but the lattice constant increases. The resistivity decreases from 1.35× 10^-2 Ω·cm to 1.55× 10^-3 Ω·cm and the optical bandgap extends from 3.27 eV to 3.48 eV compared with those of ZnO. The average transmittance is over 83 % in a wavelength range from 400 to 1100 nm. The experimental results are in good agreement with the theoretical results, showing that the WZO thin film has a great potential application as transparent conductive oxide.