低温磁控溅射法制备氧化锌薄膜的光学性能研究

Optical Properties of ZnO Thin Films Deposited by Magnetron Sputtering at Low Temperature

采用射频磁控溅射法,在较低的衬底温度(100℃)下,改变溅射时间,制备了一组氧化锌(ZnO)薄膜。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)、X射线能谱仪(EDS)、傅里叶红外光谱(FTIR)、拉曼光谱和紫外-可见分光光度计对制备的ZnO薄膜的微观结构、形貌和光学特性进行了研究。XRD图谱表明,制备的ZnO薄膜具有良好的结晶性和c轴择优取向,随着溅射时间的增加,(002)衍射峰的强度先增大后降低,溅射时间为40 min时,(002)衍射峰的强度达到最大,衍射峰半高宽最小;AFM测试表明制备的ZnO薄膜表面呈现球状颗粒,随着溅射时间的延长,薄膜的颗粒尺寸和表面均方根粗糙度均逐渐变大;EDS结果显示溅射时间较长(40min和60 min)的ZnO薄膜,O和Zn的原子比更接近1∶1。FTIR光谱中,发现位于408 cm-1附近的ZnO的E1(TO)声学模式和位于380 cm-1处的A1(TO)模式;拉曼光谱中,观测到了分别位于99 cm-1和438 cm-1处的ZnO的E2(Low)和E2(high)模式拉曼特征峰;紫外-可见透过光谱显示,在可见光范围,ZnO薄膜具有高的透光率,平均透光率高于90%,ZnO薄膜的光学禁带宽度范围为3.27~3.28 e V,溅射时间为40 min时,ZnO薄膜的光学禁带宽度最接近单晶ZnO的。

ZnO thin films were deposited under low substrate temperature for different times by radio frequency magnetron sputtering.The microstructure,morphology,and optical properties of the films were investigated by X-ray diffraction(XRD),scanning electron microscope(SEM),atom force microscopy(AFM),energy dispersive spectrometer(EDS),Fourier transform infrared(FTIR)spectroscopy,Raman spectroscopy,and ultraviolet-visible(UV-vis)spectrophotometer.XRD patterns results show that the prepared ZnO thin films possess well crystal quality and highly c axis preferred orientation.The(002)diffraction peak intensity of the ZnO thin film first increases and then decreases as the sputtering times increases.When the sputtering time is 40 min,the intensity of the(002)diffraction peak reaches the maximum value and the position of the(002)peak is closer to that of the ZnO single crystal.AFM results verify that the grain size and the root-mean-square(RMS)roughness of the ZnO thin film become bigger when the sputtering time is increased.EDS results show that the atomic ratios of O to Zn of the ZnO thin films deposited for longer times(40 min and 60 min)are close to 1∶1.Typical ZnO infrared vibration peak located at 408 cm-1 and 380 cm-1 is found in the FTIR spectra and are attributed to E 1(TO)and A 1(TO)phonon modes.The major peaks at 99 cm-1 and 438 cm-1 were observed in Raman spectra of all prepared films and are identified as E 2(low)and E 2(high)modes,respectively.UV-vis spectra indicate that the average transmittance of the ZnO thin film is higher than 90%in visible light range.The optical band gap energy of ZnO thin film extracted from the absorption edge of transmission spectra is in the range of 3.27-3.28 eV.The optical band gap energy of the ZnO thin film deposited for 40 min is closer to that of the single crystal ZnO.