Optical Degradation of 845 nm VCSELs With Different Oxide Apertures for Silicon Photonics

In this work, we analyzed the optical degradation of 845 nm VCSELs designed for silicon photonics (SiPh) applications as a function of the oxide aperture. First, we investigated the optical degradation in relation to the stress current. The experimental results showed that devices with a larger oxide aperture exhibit better reliability. From the analysis of the degradation kinetics, we found that the current at which the highly accelerated degradation process occurs depends inversely on the aperture radius. This result was explained by showing that devices with a larger aperture have lower thermal impedance, and therefore operate at lower internal temperatures at similar bias points. This interpretation is supported by isothermal constant current stress tests, which show that when the same internal temperature is maintained during ageing, for all VCSEL geometries under study the onset of degradation occurs at the same time. The equivalent activation energy of the degradation process was found to fall between 0.43 and 0.68 eV. Our analysis demonstrated that using a larger aperture can improve device reliability.