High-reflectivity AlxGa1-xN/AlyGa1-yN distributed Bragg reflectors with peak wavelength around 350 nm
Al0.49Ga0.51N/Al0.16Ga0.84N 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 353 nm with a stop-band width of 17 nm was obtained at 300 K using a 25 pair DBR. Structures at 6 nm 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. (C) 2004 American Institute of Physics.