ZnO薄膜表面和边缘的发光特性

研究了分子束外延方法生长的ZnO薄膜的光学特性,首先测量样品反射光谱,然后重点研究其光致发光光谱。实验中通过改变激发光的强度,以及采用波导配置和不同的实验几何配置等手段,观察到了ZnO薄膜中起源于激子-激子散射和电子-空穴等离子体复合发光的受激辐射,同时观察到两种配置下自发辐射谱中存在巨大的差异。通过对实验数据和理论计算结果的分析,初步认为造成了从ZnO薄膜表面和侧面得到的PL谱之间的显著区别原因有两种:一是非对称薄膜波导的吸收损耗造成的波长选择效应,二是薄膜波导对掠出射光的类似薄膜微腔的微腔效应。

Different Luminescence Behavior between the Surface and Edge of ZnO Film

The photoluminescence of ZnO epitaxial film grown by MBE method was investigated. Some obvious interference fringes were observed in the reflection spectrum of ZnO film at room temperature due to Fabry-Perot interference, the Fabry-Perot interference indicates that optical quality of the sample is very good. Using the empirical equation of refractive index, the thickness of the film is estimated about 800 nm. The PL spectrum of the ZnO was investigated under different excitation intensity using waveguide and backward configurations. In PL spectrum of waveguide configuration, six peaks at 383, 390, 392, 406, 438 and 502 nm were observed obviously. The peak at 392 nm appeared when excitation intensity is above certain values and then increased superlinearly. Wide spon- taneous emission was observed in PL spectrum in backward configurations with low intensity. With the increasing of the excitation intensity, a new peak at 392 nm appeared. With further increasing of the excitation intensity, another new peak at 396 nm appeared, its intensity increases rapidly, its location shifts to red and width of the peak is broaden with the increasing of excitation intensity. It is thought that mechanism of the two peaks is identical, which is due to both defect scattering and exciton-exciton scattering. It was analyzed that there are the angle dependence of photoluminescence and striking difference in spontaneous spectrum between the two different configurations. The spectrum using waveguide configuration is more structured. Two effects may be responsible for the experiment results: one is the wavelength selection effect due to the absorption of guided-mode in asymmetric waveguide; the other is Fabry- Perot like interference of the grazing light in substrate (micro-cavity effect). The theory results of the two different explanations are thought to be equal in the film plane.