Reliability investigation and failure analysis of 25Gb/s 850 nm oxide-confined VCSELs

High-speed (25 Gb/s) oxide-confined VCSELs operating at 850 nm have gained widespread use in data communications. However, ensuring their reliability remains a significant challenge. This study investigates the reliability and failure modes of 25 Gb/s 850 nm oxide-confined VCSELs through accelerated life testing and failure analysis. The high-stress life tests are conducted under various temperatures and bias currents. Aging data over a finite period are extrapolated using a power function to determine the life corresponding to the failure criterion. The median life is obtained by fitting a log-normal distribution function to the device life under different stress conditions. The precise junction temperature is determined using the spectral drift method, allowing for the extraction of key life parameters: activation energy (Ea) and current acceleration factor (n). The findings demonstrate a significant increase in the activation energy of InGaAs-based 25 Gb/s VCSELs compared to GaAs-based 10 Gb/s VCSELs. Additionally, high-resolution transmission electron microscopy (TEM) is employed to analyze failure samples subjected to three types of stress tests: high-temperature and high-humidity with bias aging, electrostatic discharge (ESD) damage, and high-temperature and high-current aging. Three main failure modes are identified and analyzed: dark line defects, electrostatic breakdown damage, and dark spot defects. These failure modes predominantly arise from the combined effects of the oxide layer's shrinkage stress and the InGaAs quantum well's compression stress within the device. This study provides detailed insights into the reliability and failure modes of 25 Gb/s 850 nm oxide-confined VCSELs, enhancing our understanding of degradation mechanisms in high-speed VCSELs featuring strained InGaAs quantum wells.