退火温度对同质缓冲层ZnO薄膜微观结构和光学特性的影响

Effects of annealing temperature on structural and optical properties of homo-buffer layer ZnO thin films

采用射频磁控溅射法在300℃真空退火处理过的同质缓冲层上制备了不同退火温度下的ZnO薄膜.使用X射线衍射仪(XRD)和光致发光(PL)等表征技术,研究了ZnO薄膜的微观结构和发光特性.结果表明:在6min缓冲层上制备的ZnO薄膜有较好的结晶质量,并且在适当的退火温度下薄膜的结晶质量进一步提高.薄膜在可见光范围内的平均透过率均超过90%,光学带隙值随退火温度的增加由3.221eV减小为3.184eV.在光致发光谱(PL)中观测到了5个主要的发光峰位,分别是紫外光(384nm)、紫光(420nm)、蓝光(455nm和473nm)和绿光(530nm).对发光机制进行详细讨论认为,紫外光是自由激子复合形成的,紫光与晶界缺陷的辐射跃迁有关,蓝光与氧空位和间隙锌缺陷有关,绿光发射主要是电子从氧空位深施主能级向锌空位浅受主能级上的辐射跃迁.退火温度从400℃增加到600℃时,455nm处的蓝光峰蓝移至447nm处,发光强度随退火温度增加而增加.继续升高退火温度至700℃,530nm处的绿光峰强度降低,认为和锌空位的减少有关.

ZnO thin film was deposited on Si substrate with the insertion of ZnO buffer layer,which was annealed at 300 ℃ in vacuum.ZnO thin film was grown by RF magnetron sputtering deposition technique and the ZnO/ZnO-buffer/Si films have been further annealed with different annealing temperatures.The microstructure and luminescence properties of ZnO thin films were investigated by X-ray diffraction（XRD） and photoluminescence（PL） spectrum,respectively.The results reveal that the sample,which was grown on buffer layer of the deposition time is 6 min,has the best crystalline quality.The crystalline quality is markly improved with annealing temperature increasing.All films have an average optical transparency over 90% in the visible range.The optical band gaps gradually decrease from 3.221 eV to 3.184 eV within the increase of annealing temperature.Five main peaks located at about 384 nm（UV）,420 nm（violet）,455 nm（blue）,473 nm（blue） and 530 nm（green） photoluminescence are observed from the PL spectra.The UV emission is attributed to free exciton-related activity.The violet luminescence is associated with radiative defects.The blue emission is ascribed to oxygen vacancies and interstitial Zn.The green emission is due to electron transition from deep donor levels of oxygen vacancies to shallow acceptor levels of Zn vacancies.The 455 nm blue peak shifts from 455 nm to 447 nm as the annealing temperature increases from 400 ℃ to 600 ℃.The intensity of 530 nm green first increases then decreases as annealing temperature increases,which attributes to the reduce of Zn vacancies.