<title>VCSELs for 640- to 1100-nm emission</title>

Despite their complexity, vertical cavity surface emitting lasers (VCSELs) have become key devices for future low cost optical interconnections. The high quality dielectric distributed Bragg reflectors (DBRs) mirrors possible in the AlGaAs system have made GaAs based devices the most successful and most studied VCSELs. This paper reviews the work carried out at the University of Sheffield on devices which employ AlGaAs mirrors and emit at wavelengths across the range 640 to 1100 nm. The active layers in the different designs contain variously quantum wells of InGaAs, GaAs, AlGaAs, and AlGaInP. A major limitation of using Al based compounds, particularly AlGaAs, at shorter wavelengths has previously been the presence of oxygen and other impurities. But by improving the crystal quality and purity, respectable performance of arsenide compounds has been extended to the sub 700 nm wavelength region and further improvements are expected through structural optimization and the application of strained AlInGaAs layers. Issues regarding the growth, device resistance and reproducibility of emission wavelength are also discussed.