退火对溶胶-凝胶法制备的ZnO薄膜结构和光致发光的影响

采用溶胶-凝胶法在n-Si(100)衬底上制备ZnO薄膜并从三个方面对其研究。X射线衍射结果表明,在含氧气氛中退火的ZnO薄膜为多晶六角纤锌矿结构,有明显的c轴择优结晶取向;退火时间的长短和温度的高低对结晶取向性和粒径均有较大影响,通过进一步的研究发现最佳处理温度在500℃左右。用扫描电子显微镜观察样品的表面和侧面形貌,晶体的生长比较均匀,粒径平均在70~160nm范围内,与XRD测量结果相一致。室温下ZnO胶体的光致发光谱表明,随着胶体老化时间的延长,胶体的紫外峰位发生了蓝移。室温下ZnO薄膜的光致发光谱表明,紫外部分的发光峰位在365,390nm,发光强度较强;在可见光区的发光强度相对较弱,但是还没有被氧完全抑制掉。

Influence of Annealing on the Structure and Photoluminescence of ZnO Thin Films Made by Sol-gel Method

Zinc oxide with high stability and a direct band gap of 3.37eV has attracted tremendous attention in recent years because of its high potential for application as short wavelength optical devices. Several techniques such as pulsed laser deposition, reactive thermal evaporation, sol-gel have been employed to synthesize high quality ZnO thin films. Sol-gel method was adopted to make ZnO thin films on n-Si (100) and they could be investigated from three parts. The X-ray diffraction spectra indicates that the structure of the ZnO thin films is polycrystal wurtzite structure with c axis preferred orientation. The annealing time and the annealing tempe-rature has great effect on the structure and particle size of the films, the proximate annealing temperature is around 500℃ by comprehensive experiments. The surface and profile character of the ZnO thin films can be observed by the Scanning Electrical Microscopy, which indicates that the growth of the films is uniform, the polycrystalline dimensions were determined to be in the range of 70~160 nm, consistent with the X-ray diffraction results. The optical properties of ZnO nanowires were investigated by room-temperature photoluminescence spectroscopy using a Xe lamp with an excitation wavelength of 230 nm. The photoluminescence of the ZnO sol indicates that as the aging time went on, the ultraviolet peak position moved to the short wavelength, from 342 to 340, 339 nm. The photoluminescence spectrum of the ZnO thin films at room temperature indicates that the ultraviolet peak positions were at 365, 390 nm, and the intensities of the emission were stronger, while the visible emission at 435 nm didn’t change obviously. The stronger peak positions at 460 and 690 nm are twice and three times frequency multiplication of the excitation light. The visible emission showed a weaker deep-level green emission than UV emission without being completely restrained. The PLspectra showed a strong peak around 390 nm at room temperature, corresponding to the ZnO free exciton emission.