Design and fabrication of SiO2/Si3N4 dielectric distributed Bragg reflectors for ultraviolet optoelectronic applications

Abstract

In this paper, we design a SiO2/Si3N4 dielectric distributed Bragg reflector (DDBR) by the transfer-matrix method, which is grown by plasma-enhanced chemical vapor deposition on sapphire (0001). There exists a slight difference between theoretical and experimental results in peak wavelength (～ 10 nm). The peak wavelength is blue shifted with the number of DDBR pairs increasing. The 13-pair DDBR provides a 58 nm wide stop band centered at 333 nm with a maximal reflectivity of higher than 99%, as the refractive index ratio of Si3N4 to SiO2 is relatively high. It is proved by the scanning electron microscope and atomic force microscope measurements that the variations of thickness and roughness of Si3N4 layer with respect to SiO2 layer during growth contribute to the blue shift of peak wavelength. The X-ray reflectivity measurements indicate that the interfacial degradation of the samples has little effect on the maximum reflectivity, and the relatively poor quality of SiO2 compared with Si3N4 may be one of the reasons that cause the difference between the measurements and simulations.