Appl. Phys. Lett. 99, 151101 (2011)

Distributed Bragg reflectors that provide high reflectivity in the blue–violet spectral range and are lattice-matched to GaAs substrates are needed for making short-wavelength vertical-cavity surface emitting lasers (VCSELs) and investigating cavity polariton physics. Building on previous work that aimed to realize green VCSELs, Sebastian Klembt and colleagues from the University of Bremen in Germany and the Romanian Academy in Romania now present blue–violet distributed Bragg reflectors that exhibit reflectivities exceeding 99% over a bandwidth of 40 nm. The reflectors are constructed from 21 Bragg-pair layers of high- and low-index group II–VI semiconductors. The Bragg pairs, lattice-matched to the GaAs substrate and grown by molecular beam epitaxy, consist of a 41-nm-thick high-refractive-index ZnMgSSe layer and 2.8-nm-thick low-refractive-index superlattice of MgS and ZnCdSe. The researchers comprised the high-index layer from ZnMgSSe instead of ZnSSe (as in previous work) to shift the onset of optical absorption to shorter wavelengths. They found this onset to occur at 3.25 eV (382 nm) and measured a refractive index step of 0.43. According to the team, the high refractive index step and lattice matching the high- and low-refractive-index layers are both key to constructing high-quality reflectors from a low number of Bragg pairs.