原子力显微镜在PLD法制备ZnO薄膜表征中的应用

Application of Atomic Force Microscope in the Characterization of ZnO Thin Films Fabricated by Pulsed Laser Deposition

利用脉冲激光沉积(PLD)法在氧压为16Pa、衬底温度为400～700℃时,在单晶Si(100)衬底上制备ZnO薄膜,并通过原子力显微镜(AFM)、X射线衍射(XRD)谱和光致发光谱对制得的薄膜样品进行表面形貌、结构特性和发光性质研究。其中通过原子力显微镜对样品的二维、三维以及剖面线图进行了分析。结果表明衬底温度700℃时得到的薄膜样品表面较均匀致密,晶粒生长较充分,结晶质量较高,相对发光强度高。控制氧压为5.7Pa,在衬底温度为600℃,沉积时间分别为10,20,45min制备ZnO薄膜样品;利用原子力显微镜对样品进行表面形貌观察,得知只有沉积时间足够长才能使薄膜表面晶粒充分生长。

Zinc oxide, which is a direct wide band-gap（3.37 eV） compound semiconductor with the large exciton binding energy（60 meV）, has recently become a very popular material due to its good photoelectric and piezoelectric properties. Besides, the pulsed laser deposition（PLD） technique has its unique advantages such as high controllability of film composition, the easy control of experimental parameters and an inherently clean process which make it easy to deposit high-quality complex compound films. The dependence of the surface morphology, crystalline quality and photoluminescence property of the ZnO films prepared by pulsed laser deposition on the growth temperature and the dependence of the surface morphology of the samples on the different deposition time were investigated in this paper. The ZnO thin films were fabricated on Si （100） substrates by pulsed laser deposition in temperature ranging from 300 ℃ to 700 ℃ at a oxygen ambient pressure of 16 Pa. The surface morphology, the structural characteristics and the optical property of ZnO thin films were characterized by atomic force microscopy（ AFM）, X-ray diffraction （XRD） and PL spectra. The two-dimensional images, three-dimensional images and profiles of the samples were analyzed by AFM. The results indicated that the surface roughness of the films increased at first and decreased later, the quality of crystallization is improved gradually and photoluminescence property is also enhanced. It was found that the film grown at 700 ℃ has a much smoother and denser morphology, ideal crystalline quality and better optical properties. Other ZnO thin films were fabricated at an oxygen ambient pressure of 5.7 Pa in the growth time ranging from 10 to 45 min. Using AFM, we understood that it is important to have crystalline grains grown adequately in a sufficient period of time.