ZnO：V薄膜后退火处理前后的微结构与发光特性

利用溶胶-凝胶(Sol-gel)法在单晶硅(100)衬底上分别制备了ZnO:V薄膜和纯ZnO薄膜。为进一步研究后退火对ZnO:V薄膜结构和发光性质的影响,在两段式快速退火后又在800℃下进行了后退火处理。X射线衍射的结果表明:后退火处理前,钒(V)的掺入使ZnO结晶质量变差,而800℃退火处理后,从ZnO的衍射峰中可以看出,相对于无V杂样品其结晶质量变好。扫描电子显微镜形貌图中可以看出制备的样品薄膜颗粒大小均匀,薄膜致密度较高。光致发光(PL)谱的研究表明:ZnO:V薄膜在800℃退火处理后,紫外和绿带发光峰均增强,但紫外发光峰增强得更多;与同样条件下制备的纯ZnO薄膜的PL谱比较,发现V掺杂后样品的紫外激子复合发光峰的强度明显增强且峰位发生蓝移,而缺陷引起的绿带发光峰的强度降低。

Microstructures and Photoluminescence Properties of ZnO:V Thin Films and Effects of Post-annealing

ZnO has attracted great attentions due to its stimulated emission and optically pumped laser behavior.Recent studies proved that the emission properties of ZnO films are dependent on the growth conditions and certain doping of other elements can improve the luminescence properties greatly.Therefore,suitable dopants and proper growth conditions are of great benefit to current research.In this report,V-doped ZnO thin films were investigated including their microstructures,photoluminescence properties and the effects of post-annealing.The undoped ZnO and 1%V-doped ZnO thin films were prepared on single crystalline Si(100) substrates by sol-gel spin coating method.The spin-coating process was repeated 8 times to increase the thickness of the films,with two-step rapid-annealing(300℃ for 300 s and 550℃ for 300 s) in air.A further annealing at 800℃(post-annealing) was performed after the 8th rapid-annealing.The structures,morphologies,and luminescence properties of the films were investigated by X-ray diffraction(XRD),scanning electronic microscopy patterns(SEM),and photoluminescence(PL).According to XRD pattern,no V-related phases were detected in the prepared samples.The crystalline quality of V-doped ZnO thin films was worse than that of undoped sample before post-annealing,in that the doping of V destroyed the structure of ZnO.Whereas,after post-annealing,the crystallinity of V-doped films became better and there appeared diffraction peaks of zinc silicate in the XRD pattern of V-doped films.We attribute the formation of high crystalline of zinc silicate to the catalytic effect of V.Scanning electronic microscopy patterns indicated all samples were compact and homogeneous thin films composed of uniform nano-particulates.The thickness of the films is about 300 nm.As to photoluminescence spectra,measurements of the V-doped samples without post-annealing showed that the intensities of the UV peak and green peak decreased greatly compared with those of pure ZnO films.Nonradiative recombination due to implantation induced damage is obviously dominating.After additional annealing at 800℃ for an hour,the optical quality can be well restored.Both the UV peak and green peak of the V-doped ZnO thin film increased while the former increased more.Moreover,the intensity of UV emission due to exciton recombination for V-doped ZnO films was obviously stronger than that of undoped ZnO thin films,while the intensity of the green peak was on the contrary.During post-annealing,doped V could fill part of defects of ZnO.The origin for the green emission could be attributed to the decrease of defects in the films.At the same time,the post-annealing decreased the quenching centers induced by V-dopant.As a result,the intensity of UV emission for the V-doped ZnO thin film was increased compared with undoped ZnO sample at the same conditions.