Reduced cavity loss for ultra-low threshold vertical cavity surface emitting lasers

We demonstrate the importance of identifying and reducing cavity losses in high Q cavities in order to obtain very low threshold currents with high slope efficiency in vertical cavity surface emitting lasers (VCSELs). Thresholds in the tens of microamps, which may be of interest for highly parallel arrays, have not yet been clearly demonstrated and will most likely require low loss, high Q cavities. Previously, we have used upper dielectric distributed Bragg reflectors (DBRs) and reduced p-doping to achieve low threshold. In the present work, we have removed the Si doping from the lower DBRs and incorporated an intracavity n-contact. As a result, we report to our knowledge the lowest room temperature threshold current density yet achieved in a VCSEL of 98 A/cm ², the highest differential slope efficiency for a sub-100 μA VCSEL of 60 % for a 67 μA threshold and a very low room temperature threshold of 23 μA. We also demonstrate a lasing threshold current of 12 μA (25 A/cm²) for a VCSEL designed and operated at cryogenic temperatures