W掺杂ZnO透明导电薄膜的理论及实验研究

Theoretical and experimental investigation of W doped ZnO

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.

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 Eg 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 x 10-2 ^2.cm to 1.55 x 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.