Degradation mechanisms of InAs quantum dot 1.3 um laser diodes epitaxially grown on silicon

This paper reports on a preliminary investigation of the gradual degradation processes that may affect the lifetime of InAs quantum dot (QD) lasers epitaxially grown on silicon substrates. To this aim, a series of identical Fabry-Pérot lasers emitting at 1.31 μm have been subjected to current step-stress and constant-current aging experiments at an ambient temperature of 35°C. With the adopted stress conditions, the optical characteristics of the devices exhibited an increase in the threshold-current and a decrease in the slope efficiency. This latter process was found to be well correlated with the variation in the threshold current, suggesting that this specific degradation mode may be ascribed to a stress-induced reduction in the injection efficiency. Moreover, the linear dependence of the threshold-current variation on the square root of time observed for longer stress time highlighted the possible role of a charge/defects diffusion process in the optical degradation of the devices. Consistent with this hypothesis, the electrical characteristics of the devices exhibited an increase of the forward leakage current in the bias regime dominated by defect-assisted current conduction mechanisms. The degradation process was found to be heavily accelerated for bias values allowing excited-state operation: this peculiar behavior was ascribed to the higher rate of carriers escaping from the quantum dots that undergo Recombination Enhanced Defect Reactions (REDR) in proximity of the active region of the device.