Band-gap engineered digital alloy interfaces for lower resistance vertical-cavity surface-emitting lasers

We report on a technique of grading the heterobarrier interfaces of a p-type distributed Bragg reflector mirror to reduce the operating voltages of vertical-cavity surface-emitting lasers (VCSELs). We report VCSELs with lower operating voltages (2–3 V) and record continuous-wave room-temperature power-conversion efficiencies (17.3%). We experimentally demonstrate that by using a parabolic grading and modulating the doping correctly, a flat valence band is generated that provides low voltage hole transport. The low resistance mirrors are achieved using low Be doping, digital-alloy grading and 600 °C growth temperatures.