【作者】 张志广；

【导师】 满宝元；

【作者基本信息】 山东师范大学 ， 原子与分子物理， 2006， 硕士

【摘要】 ZnO是宽带隙II-VI族化合物半导体材料,由于其光电特性受缺陷影响较小,激子束缚能较高(60 meV, GaN为25 meV),体材料可得,生长温度较低(可在200-700℃左右成膜,比GaN低几百度),并且材料来源广泛、价格低廉,而成为继GaN之后在光电研究领域,极有希望用于紫外和蓝色发光器件的新型光电子材料。ZnO薄膜具有良好的透明导电性、压电性、光电性、气敏性、压敏性、且易于与多种半导体材料实现集成化。由于这些优异的性质,使其具有广泛的用途和许多潜在用途,如制作紫外探测器、紫外发光管和激光器、高频表面声波器件、透明导电电极、微型传感器等,其在航天、通讯、卫生等高新技术领域和广阔民用领域都具有广泛的用途。制备ZnO薄膜的方法有很多,包括:磁控溅射(sputtering)、金属有机化学气相沉积(MOCVD)、分子束外延(MBE)、原子层外延(ALE)、化学气相沉积(CVD)、电子束蒸发沉积(e-beam evaporation)、喷涂热解法(spray pyrolysis)、溶胶-凝胶法(Sol-gel)、脉冲激光沉积(pulsed laser deposition, PLD)法等。激光脉冲沉积是近年来发展起来的先进的薄膜生长技术,它是在高真空背景下用高能激光烧蚀ZnO靶材生成蒸发物淀积在加热衬底上生长晶体薄膜的。脉冲激光沉积法与其它沉积方法相比有沉积时可以有较高的氧气压强,薄膜生长温度低等优点。本论文是采用脉冲激光沉积的方法,在单晶Si(111)衬底上外延生长了沿c轴高度取向的ZnO薄膜。本文分析研究了薄膜生长条件(不同的衬底温度、不同的入射激光能量密度和不同的氧气压强)对ZnO薄膜性质的影响。通过X射线衍射( XRD)、扫描电镜(SEM)、原子力显微镜(AFM)、光致发光和拉曼( Raman)散射技术对不同条件下生长的ZnO薄膜的性质进行了研究。在其它参量保持不变的情况下,通过改变衬底温度来研究它对ZnO薄膜的影响。结果显示,较高的温度时生长的薄膜具有较好的结晶质量,最佳生长温度为400oC。薄膜的光致发光谱中有两条发光峰,一条为紫外峰,另一条为蓝光峰。紫外峰的强度强烈依赖于薄膜的结晶度。蓝光峰是由氧空位引起的,其强度随衬底温度的升高变强。原因是,较高的温度会导致薄膜中氧原子的脱附,从而导致薄更多还原

【Abstract】 ZnO is a promising wide band-gap semiconductor (Eg =3.37eV) and attracts asmuch attention as GaN for its potential utilization in short-wavelength light-emitting/detecting devices. In comparison to GaN, its optoelectronic characteristics are littleaffected by the defects, and it has higher exciton binding energy (60 meV at roomtemperature), lower growth temperature and cost. Due to their excellent physical andchemical properties, ZnO films have many realized and potential applications such asdisplay devices, sensors, piezoelectric transducers, transparent conductor, surfaceacoustic wave devices and lasers operating in the near ultraviolet and blue spectralrange.ZnO thin films can be deposited by various methods, such as sputtering, metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), atomiclayer epitaxy (ALE), chemical vapor deposition (CVD), e-beam evaporation, spraypyrolysis, sol-gel, pulsed laser deposition (PLD), etc. PLD is a newly developed filmgrowth technique. In this technique, high density laser ablates the target and producesZnO plume depositing on heated substrate in high vacuum background. PLD hasadvantages in comparison with other methods, such as deposition in relatively highoxygen pressure, lower temperature of film crystallization because of high particleenergy in laser produced plasma plume. In this paper, a pulsed laser deposition system was used for the epitaxy of ZnO thinfilms on Si (111) substrate. The influences of different growth conditions on features ofZnO thin films in several aspects are studied, especially in the impacts of differentsubstrates temperatures, laser energy density and oxygen pressure, respectively. Thecharacteristics of ZnO film grown on different growth conditions were studied bymeasurements of X-ray diffraction (XRD), scanning electron microscopy, atomic forcemicroscopy (AFM), photoluminescence and Raman scattering.We investigate the effects of the substrate temperature on the crystal andluminescent quality of the ZnO thin films by depositing films at variable substratetemperature keeping all the rest of the parameters unchanged. It is found that arelatively high substrate temperature induces high quality films. The substratetemperature of 400 ℃ is the optimum condition of crystalline for the Si (111) substrate.Photoluminescence (PL) results indicate that the thin films show the UV and blueemissions. The blue emission is related to the oxygen vacancies in the ZnO film. Theintensity of the blue emission increases with the increases of substrate temperature. Thereason is that high substrate temperature increases the opportunity for the oxygenoutgassing of the film which induced increase of oxygen vacancies.We investigate the effects of the laser energy density on the crystal andluminescent quality of the ZnO thin films by depositing films at variable laser energydensity keeping all the rest of the parameters unchanged. It is found that the laser energydensity of 62.5 J/cm2 is the optimum condition of crystalline for the Si (111) substrate.Photoluminescence (PL) results indicate that the intensity of the blue emission increaseswith the increases of laser energy density. The reason is that high laser energy densityincreases the opportunity for the interdiffusion between ZnO film and Si substrate andthe formation of SiO2, which results in the increase of oxygen vacancy.ZnO thin films were deposited at different oxygen pressures. After deposition, thesamples were investigated by XRD, AFM and Raman spectroscopy. It is found that theintensity of ZnO (002) peak increases while the FWHM of ZnO (002) peak decreaseswith the increase of the oxygen pressure. This means that the crystallinity of thespecimens is improved when increase the oxygen pressure. The Raman results indicatethat oxygen ambient plays an important role in removing defects due to oxygen vacancy.It is found that the oxygen pressure of 1.3 Pa is the optimum condition of crystalline forthe Si (111) substrate.更多还原