High-reflectivity AlxGa1−xN∕AlyGa1−yN distributed Bragg reflectors with peak wavelength around 350nm

Al 0.49 Ga 0.51 N ∕ Al 0.16 Ga 0.84 N distributed Bragg reflectors (DBRs), designed for the ultraviolet spectral region, are reported. The crack-free structures are grown on sapphire substrates by metalorganic chemical vapor deposition. A peak reflectivity of 91% at 353nm with a stop-band width of 17nm was obtained at 300K using a 25pair DBR. Structures at 6nm shorter wavelength show asymmetric spectra, a narrower stop band, and slightly decreased peak reflectivity. By studying the spectra as a function of temperature, the degradation is shown to arise from internal absorption at short wavelengths. Simulations based on transfer matrix theory agree well with the experimental data.