Degradation Mechanisms of Monolithic GaAs-on-Si Nano-Ridge Quantum Well Lasers

This work investigates the reliability of a recent demonstration of the III-V laser fully fabricated in imec's 300 mm CMOS pilot line. A two-phase optical degradation is disclosed in such monolithic GaAs-on-Si nano-ridge quantum well lasers. Constant current aging tests reveal a gradual drift of the laser threshold current in phase I, which is attributed to the diffusion of impurities into quantum wells, resulting in a decrease of the non-radiative carrier lifetime. Subsequently, the high current density at metal/p-GaAs contacts induces an abrupt laser failure in phase II. Failure analysis on a device after 1000 h of electrical stress at room temperature reveals elemental interdiffusion in the GaAs nano-ridge under a p-contact plug, eventually punching through the quantum well, creating a leakage current path and inducing a diode breakdown. Detected failure modes are extrinsic and can be alleviated by dedicated contact and nano-ridge engineering (NRE). On the other hand, there is no evidence of recombination-enhanced dislocation reactions taking place close to the GaAs/Si interface, proving the successful confinement of misfit defects using high-aspect oxide trenches. The result sheds light on achieving reliable monolithic lasers for silicon photonics in high- bandwidth datacom applications.