An accurate measurement of the refractive index is necessary for the optical design of both deep ultraviolet laser diodes and light-emitting diodes. Generally, the refractive indices along different crystallographic axes of anisotropic thin films are measured using variable angle spectroscopic ellipsometry. However, there are still some limitations concerning this method. Here we proposed a potential method to measure the band edge refractive index of wide bandgap semiconductor. An aperiodic oscillation emission phenomenon due to the Fabry-Perot effect was observed in the fluorescence spectrum of an AlN film with a thickness of 1500 nm. Based on the characteristics of the fluorescence spectrum and the definition of Fabry-Perot effect, we obtained the ordinary refractive index of the AlN thin film near the band edge directly. This refractive index measurement method is a supplement to the variable angle ellipsometry, and it is a more direct and effective method for transferred film and thinner samples to measure the fluorescence spectrum.

深紫外激光二极管和发光二极管的光学设计都需要准确测量折射率。通常，各向异性薄膜沿不同晶轴的折射率是使用变角光谱椭偏仪测量的。然而，这种方法仍然存在一些局限性。在这里，我们提出了一种测量宽带隙半导体带边折射率的潜在方法。在厚度为1500nm的AlN膜的荧光光谱中观察到由于法布里-珀罗效应引起的非周期性振荡发射现象。根据荧光光谱的特点和法布里-珀罗效应的定义，我们直接得到了AlN薄膜在带边附近的寻常折射率。