Study on Dark-line Defect Formation in High-Power Oxide-Confined VCSEL Arrays

Dark-line defect is a common crystal defect in vertical cavity surface emitting lasers (VCSEL) and other semiconductor diodes to cause optical power degradation after long time operation. This work studied the dark-line defect formation and activation mechanism in high-power VCSEL arrays after high-temperature operation life (HTOL) stress up to 2000 hours under high current and short-pulse operation condition. Electrical-optical light-current-voltage testing is used to monitor the power degradation after HTOL stress and slight output power drop is found. Three electrical failure analysis techniques, including reverse IV curves, near-field emission profile images and electron beam induced current (EBIC) images are adopted to study the defect location and reveal that dark-line defect formation and reaching quantum well regions. Subsequently, planar-view transmission electron microscopy (PV-TEM) lamella are prepared to clearly show dark-line defect loops formation at the oxide aperture periphery. Cross-sectional TEM images across a dark-line defect loop find that the dark-line defect origins from the oxide tip. Oxide tip region is a weak location due to the induced interstitial defects between oxide and epitaxy semiconductor layer interface during oxidation process. Nevertheless, the oxide aperture tip has experienced high current density during HTOL overstress condition, and the locally high current and temperature provided sufficient activation energies for the interstitials atom to move around and form dislocation loops. It is consistent with the dark-line defect network location observed from PVTEM and proves that high current density and optical power is responsible for the dark-line defect growth from oxide aperture tip and propagation into active region.