High reflectivity ultra-violet AlxGa1-xN/AlyGa1-yN distributed Bragg reflectors

We demonstrate high-reflectivity crack-free Al0.13Ga0.87N/Al0. 56Ga0.44N distributed Bragg reflectors (DBR) for the spectral region around 350 nm grown by molecular beam epitaxy on thick GaN templates. The structural quality of the DBR layers is maintained by compensating the compressive and tensile strains in each l/4 pair. This approach results in the lowest elastic strain energy and allows the growth of thick coherently strained DBRs. A 25 period mirror provides a 26 nm wide stop band centered at 347 nm with the maximum reflectivity higher than 99%.