Degradation Processes and Aging in Quantum Dot Lasers on Silicon

We discuss the physical processes responsible for the degradation of quantum-dot (QD) lasers epitaxially grown on silicon, based on combined electro-optical measurements and deep-level transient spectroscopy. The results shown that: a) during long-term operation, QD lasers show an increase in threshold current, correlated to a decrease in slope efficiency; b) the degradation is faster when the devices are stressed at high current levels, i.e. when the carriers occupy both the ground and the excited state; c) degradation can be explained by considering a recombination-enhanced defect reaction process, promoted by the escape of electrons from the quantum dots; d) the degradation rate is significantly dependent on the density of dislocations, as demonstrated by tests carried out on devices grown on native and silicon substrate; e) by modeling the degradation as due to defect diffusion, threshold voltage instability is ascribed to the recombination-enhanced diffusion of Be; f) through the use of a defect-trapping layer, degradation rate can be significantly reduced. The results provide relevant information for understanding the degradation physics of QD lasers for silicon photonics.