The role of oxygen vacancies in epitaxial-deposited ZnO thin films
The role of oxygen vacancies in epitaxial-deposited ZnO thin films
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DOI：
10.1063/1.2437122
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发表时间：
2007-03-01
影响因子：
3.2
通讯作者：
Shin, B. C.
中科院分区：
文献类型：
--
作者：
Shan, F. K.;Liu, G. X.;Shin, B. C.
采用脉冲激光沉积（PLD）技术在蓝宝石（0001）衬底上外延生长了ZnO薄膜。X射线衍射仪（XRD）被用来研究薄膜的结构特性。结果表明，薄膜均为（0002）取向，且（0002）峰强度随生长温度的升高而增强。薄膜的φ扫描表明，在高于400摄氏度的温度下生长的薄膜与衬底具有外延关系。原子力显微镜（AFM）被用来研究薄膜的表面形貌。薄膜的表面粗糙度和晶粒尺寸随生长温度的升高而增大。用双光束分光光度计测量薄膜的透过率。通过对高质量薄膜的吸收边进行线性拟合，计算了薄膜的带隙能量。利用光谱仪研究了薄膜的光致发光特性。发现所有的薄膜都显示出两种发射。一种是近带边（NBE）发射，另一种是宽深能级（DL）发射。在不同日期检查薄膜的PL之后，观察通过PLD沉积的蓝宝石衬底上的ZnO薄膜的老化效应。结果表明，随着时间的推移，NBE排放量增加，DL排放量减少。为了找到DL发射随时间降低的原因，将沉积的薄膜分别在800 ℃下在N-2和O-2气氛中退火30分钟。用原子力显微镜和分光光度计对退火后薄膜的表面形貌和透过率进行了研究。退火后薄膜的表面粗糙度和透过率均明显降低。对退火薄膜的PL测试表明，在N-2气氛中退火的薄膜的DL发射增强，而在O-2气氛中退火的薄膜的DL发射被猝灭。结果表明，在PLD法制备的ZnO薄膜中，氧空位对DL发射的影响最大，而锌空位对DL发射的影响较小。(c)2007年，美国物理学会。
ZnO thin films were epitaxial deposited on sapphire (0001) substrates at various temperatures by using the pulsed laser deposition (PLD) technique. An x-ray diffractometer (XRD) was used to investigate the structural properties of the thin film. It was found that all of the thin films were (0002) oriented and the intensity of (0002) peak increased with the increasing growth temperature. The phi-scans for the thin films indicated that the thin film grown at a temperature higher than 400 degrees C had an epitaxial relation with the substrate. An atomic force microscope (AFM) was used to investigate the surface morphologies of the thin films. The surface roughness and grain size of the thin films increased with increasing growth temperature. A double-beam spectrophotometer was used to measure the transmittances of the thin films. The band gap energies of the thin films were calculated by linear fitting the absorption edges for high-quality thin films. A spectrometer was used to investigate the photoluminescent (PL) properties of the thin films. It was discovered that all of the thin films showed two emissions. One was the near band edge (NBE) emission; the other was the broad deep-level (DL) emission. After checking the PL of the thin films on a different date, the aging effect of the ZnO thin film on the sapphire substrate deposited by PLD was observed. It was revealed that, the NBE emissions were enhanced and the DL emissions were decreased with time. To find the reason why the DL emission decreased with time, the as-deposited thin films were annealed at 800 degrees C in a N-2 and O-2 atmosphere for 30 min, respectively. The surface morphologies and the transmittances of the annealed thin films were investigated by the AFM and spectrophotometer. The surface roughness and the transmittance decreased much after annealing. The PL measurements for the annealed thin films indicated that, the DL emission of the thin film annealed in N-2 was enhanced and that annealed in O-2 was quenched. It was suggested that the oxygen vacancies, instead of zinc interstitials, played the most important role for DL emissions in ZnO thin films deposited by PLD. (c) 2007 American Institute of Physics.