面向可见光波段的非周期悬空GaN薄膜光栅

Freestanding non-periodic GaN gratings in visible wavelength region

基于严格耦合波理论,提出了一种在可见光波段能调控入射光相位的非周期悬空氮化镓(GaN)薄膜光栅。首先,采用有限差分时域(FDTD)方法,通过改变光栅的周期、占空比等参数仿真计算非周期悬空GaN薄膜光栅的光响应。然后,采用双面加工工艺和氮化物背后减薄技术在硅基GaN晶圆上制备非周期悬空GaN薄膜光栅,控制入射光束的相移。最后,通过角分辨微反射谱实验和光致发光测量实验表征了该薄膜光栅的光学性能。角分辨微反射谱实验结果显示非周期悬空GaN薄膜光栅的光学性能与FDTD的理论分析一致;光致发光测量实验显示其光致发光(PL)强度比硅衬底GaN光栅大大增强,峰值从364.3nm转移到378.7nm。另外,在可见光波段内,该悬空非周期GaN光栅有较大的入射角容忍度,为-25°~25°。得到的结果表明,研制的悬空非周期GaN光栅有助于提高光提取效率。

On the basis of Rigorous Coupled Wave Analysis（RCWA）,an array of freestanding non-periodic GaN gratings were proposed to control the phase of an incident beam in the visible wavelength region.Firstly,the Finite Difference Time Domain（FDTD）method was used to calculate the optical responses of non-periodic GaN gratings based on the parameters such as period and duty cycle.Then,a double-sided process and nitride back thinning technology were developed to fabricate freestanding non-periodic GaN gratings on a GaN-on-silicon platformand to control the different phase shifts of incident light.Finally,the optical performance of non-periodic GaN gratings was experimentally demonstrated by angular resolved micro-reflectance spectra and photoluminescence spectra.The angular resolved micro-reflectance spectra show that the optical performance of the freestanding non-periodic GaN gratings is in good agreement with that of the theoretical simulations by the FDTD method.The photoluminescence spectra indicate that photoluminescence（PL）intensities of the GaN gratings are greatly improved as compared to that of the GaN-on-silicon,and their emission peaks are from 364.3 nm to 378.7 nm.Moreover,experimental results give that the incident angular tolerance of the GaNgratings is -25°-25°in the visible wavelength region.In conclusion,the gratings are helpful for the improvement of the light extraction efficiency.