Compositional grading in distributed Bragg reflectors, using discrete alloys, in vertical-cavity surface-emitting lasers

We present experimental results on a technique for alloy composition grading within distributed Bragg reflectors (DBRs) for use in vertical-cavity, surface-emitting lasers (VCSELs). This technique, implemented using molecular beam epitaxy (MBE), employs multiple group-III sources, with different fluxes, to realize a set of AlxGa1−xAs compositions without changing cell temperatures. By varying the source combination and layer thickness, different functional forms of compositional grading, such as linear and parabolic, can be closely approximated. This method, in combination with modulated doping profiles, was used to grow 980 nm VCSELs with low threshold currents, high output powers, and threshold voltages less than 1.45 V.