Addressing the oxide-aperture dependency of the degradation of 845 nm VCSELs for silicon photonics

Discrete NIR III-As VCSELs have been used for a long time in the datacom industry. Recently, the integration of such devices onto SiN substrates was successfully achieved by means of micro-transfer printing techniques, thus allowing the use of these devices as the laser sources of next generation PICs for silicon photonics applications. Despite the maturity of modern III-V epitaxy, previous reports investigating the reliability of these so-called vertical-cavity silicon-integrated lasers (VCSILs) identified the stress-induced relocation of point defects as the main cause for the electrical and optical degradation exhibited by the LDs during accelerated ageing. In this work, we further analyze these processes by evaluating through EL imaging, TEM, numerical modeling and simulations, the variation in the properties of III-V bottom-emitting VCSELs based on the very same epitaxy and structure. The results indicate that i) the adopted aging procedure does not cause the formation of extended defects in proximity of the oxide aperture, ii) that the observed spreading in the optical beam of the laser is strongly correlated with the increase in series resistance, iii) that the electrical degradation is stronger for smaller oxide apertures, due to the more pronounced crowding of injected current occurring at the top DBR, which determines the overall series resistance of the device. These results further confirm our previous findings and help identify guidelines for the design of reliable VCSELs for future SiPh applications.