La掺杂浓度对PLZT薄膜红外光学性质的影响

采用溶胶-凝胶法在Pt/Ti/SiO2/Si衬底上制备了不同La掺杂浓度PLZT(x/40/60)薄膜- x射线衍射分析表明制备的PLZT(x/40/60)薄膜是具有单一钙钛矿结构的多晶薄膜- 通过红外椭圆偏振光谱仪测量了波长为2-5—12-6μm范围内PLZT薄膜的椭偏光谱，采用经典色 散模型拟合获得PLZT薄膜的红外光学常数，同时也拟合获得PLZT薄膜的厚度- 随着La掺杂浓 度的增大，折射率逐渐减小- 而消光系数除PLZT(4/40/60)薄膜外，呈现逐渐增大的趋势- 分析表明这些差异主要与PLZ 关键词： PLZT薄膜 红外光学性质 红外椭圆偏振光谱

Investigations of concentration effects of La on the infrared optical properties of PLZT thin films

Lead lanthanum zirconate titanate (PLZT) thin films with different La concentrations (x), whose composition is x/40/60, have been grown directly on Pt/Ti/SiO₂/Si substrates by a modified sol-gel method. x-ray diffraction analysis shows that the PLZT thin films are polycrystalline with a single perovskite p hase. The infrared optical properties of the PLZT thin films are investigated us ing the infrared spectroscopic ellipsometry in the spectral range of 2.5—12.6μ m. By fitting the measured ellipsometric parameters, and a classical dispers ion relation for the thin films, the optical constants and thickness of the thin films have been obtained. The refractive index of the PLZT thin films decreases with increasing La concentration; however, the extinction coefficient increases with increasing La concentration except for the PLZT (4%) thin films. It is bel ieved that the decrease in the refractive index for the PLZT thin films with inc reasing La concentration is mainly due to the crystallinity and the electronic b and structure of the PLZT thin films. The absorption coefficient of the PLZT thi n films is larger than that of the PZT thin films. The values of the effective s tatic charge in the PLZT thin films, which are smaller than those of the purely ionic materials for the PLZT thin films, decrease with increasing La concentrati on. This indicates that PLZT belongs to a mixed ionic-covalent compound.