Impact of dislocation density on performance and reliability of 1.3 μm InAs quantum dot lasers epitaxially grown on silicon

This paper reports on the impact of the quality of the epitaxial structure of InAs Quantum Dot (QD) lasers grown on silicon substrates on lifetime. To this aim, a series of current step-stress and constant-current aging experiments were carried out on two sets of Fabry-Pérot QD lasers, emitting at 1.3 μm and featuring two different Threading Dislocations Densities (TDDs) within the epilayers, nominally 6E7 cm-2 (high TDD) grown on Si substrates and 500 cm-2 (low TDD) grown on lattice matched GaAs substrates. The results of the step-stress procedure indicate that i) the high-current optical performance of the lasers is limited by TDD, which reduces the bias range for useful Ground State (GS)-only operation and lowers the roll-off point of the optical output characteristic; ii) TDD contributes to the acceleration of the dominant optical degradation mechanism at high stress current levels, represented for this family of devices by the recombinationenhanced generation of defects in device regions close to the active layers; iii) dislocation density also accelerates optical degradation in GS regime. This process is primarily driven by the diffusion of Non-Radiative Recombination Centers (NRRCs) toward the active region of the devices, as demonstrated by the dependence of threshold current variation on the square root of time. These experimental results show that the presence of TDDs is the main limiting factor for the reliability of QD lasers for epitaxially-integrated silicon photonics applications, further confirming the outcome of previous statistical lifetime analyses carried out on devices featuring similar epitaxial structures.