磁控濺鍍製備鋯、鈦共摻氧化鋅薄膜之結構研究與光電特性分析

Study on the Structure and Optoelectronic Properties of Zr, Ti co-doped ZnO Thin Films Prepared by Magnetron Sputtering

本研究以磁控濺鍍系統，鈦靶在DC功率固定為10 watt （W），氧化鋅靶在RF功率固定為150 W，鋯靶在RF功率改變為0、25、50、60、75和100 W下濺鍍2小時，在200℃之玻璃基材上成功製備出不同鋯含量的鋯、鈦共摻氧化鋅（Zr, Ti co-doped zinc oxides, ZTZO）薄膜。經由感應耦合電漿質譜儀（inductively coupled plasma mass spectrometry; ICP-MS）分析結果顯示：鈦靶在DC功率10 W下，鍍膜所得鈦摻雜量變化不大（0.70 ~ 0.72 at. %）；而鍍膜中鋯摻雜量則隨著濺鍍功率的增加而遞增。薄膜之化學狀態經由X光光電子能譜儀（X-rayphotoelectron spectrometer; XPS）分析得知，位於458.8 （Ti 2p3/2） eV，為TiO2狀態之正四價鈦。位於182.2 （Zr 3d5/2）與184.5 （Zr 3d3/2） eV束縛能則屬於ZrO2正四價鋯之峰值。X光繞射分析（X-ray diffractometer; XRD）結果顯示：所有的ZTZO薄膜皆為六方纖鋅礦晶體結構，在（002）晶面具優選性，此優選晶面的波峰強度隨著鋯含量由0.00增加到3.82 at. %而增強，但鋯含量達6.12 at. %時，（002）強度減弱且峰值向小角度偏移約0.04°。場發射式掃瞄式電子顯微鏡（Field Emission Scanning Electron Microscope；FE-SEM）觀察結果顯示：濺鍍ZTZO薄膜的膜厚為350 nm，隨著摻鋯量增加，柱狀晶粒直徑大小由112 nm下降至57 nm。原子力顯微鏡（Atomic force microscopy; AFM）分析結果顯示：隨著摻鋯量增加，薄膜表面更平滑。光學分析顯示：薄膜在可見光的平均穿透率均為90 %以上。隨摻鋯量增加，薄膜在紫外光區的吸收緣往短波長移動（藍移現象），且光學能隙隨之增加。霍爾量測結果顯示：ZTZO薄膜的載子濃度，隨著摻鋯量增加而增加；而載子移動率則隨摻鋯量增加而下降，當鋯含量在3.46 at. %時，薄膜得到最低值之電阻率（5.54×10-3Ω􀁸cm）。於3.5 wt. %NaCl水溶液中由電化學法分析薄膜腐蝕特性發現:隨ZTZO薄膜中摻鋯量增加，其腐蝕電流密度減小，顯示抗蝕性增強。

Transparent conductive Zr, Ti codoped ZnO (ZTZO) films were prepared on glass substrate by three-target magnetron sputtering system in this work. The glass substrate was heated to 200 ℃, and under the working pressure at 5×10-2 Torr in the chamber. In the sputtering process, the pure Ti target was bombarded by direct current power fixed at 10 watt (W), the pure ZnO target was bombarded by radio frequency power fixed at 150 W and the pure Zr target was bombarded by radio frequency varying in the power at 0, 25, 50, 60, 75 and 100 W. After sputtering for 120 minutes, the thickness of the films were varying in Zr-contents which were measured to be about 350 nm. The composition of ZTZO thin film was analyzed with the inductively coupled plasmamass spectrometer (ICP-MS) to show that the Zr-content raising with increasing the RF power for Zr target in the order: 0 at. % (0 W) < 1.61 at. % (25 W) < 2.76 at. % (50 W) < 3.46 at. % (60 W) < 3.82 at. % (75 W) < 6.12 at. % (100 W), and the Ti-content of the films were around 0.7 at. %. Through the examination by X-ray photoelectron spectroscopy (XPS), the TZTO films revealed TiO2 with binding energy of tetravalent Ti (IV) at 458.8 eV for Ti 2p3/2 ; ZrO2 with binding energy of tetravalent Zr (IV) at 182.2 and 184.5 eV for Zr 3d5/2 and 3d3/2, respectively. Analysis of X-ray diffraction (XRD) indicated that all the films were belonged to wurtzite structure textured on (002). The surface morphology and cross section of the films were examined by using field emission scanning electron microscope (FE-SEM). Through the examination by atomic force microscopy (AFM), the films displayed their average surface roughness (Ra) decreased from 9.67 to 5.58 nm with increasing the Zr-dopant. The carrier concentration of the films, determined by Hall effect analyzer, increased but the carrier mobility decreased with increasing the Zr-dopants so that the lowest resistivity was found at 5.54×10-3 Ω􀁸cm for the ZTZO doped with 0.71 at. % Ti and 3.46 at. % Zr. Average optical transmittance of the films was analyzed, which higher than 90 ± 5 % by UV-vis spectra. Estimating by electrochemical measurements in 3.5 wt. % NaCl, the ZTZO films depicted their corrosion current density decreased with increasing the Zr-dopants. Therefore, ZTZOs were more corrosive resistance with higher Zr-dopants. The features are found with the Zirconium content is increased and the corrosion current density is smaller, and enhancing the phenomenon of corrosive resistance.