Degradation of quantum dot lasers for silicon photonics: role of p-dopant and advanced defect spectroscopy

This thesis addresses the degradation mechanisms of quantum-dot lasers for silicon photonics by means of two different experiments. The first one had the goal of determining how different types of doping schemes, including beryllium, carbon, and unintentional doping, and different type of etching, shallow and deep, affect the behavior of the devices. This was achieved by performing an accelerated stress test under constant current conditions, and by evaluating the variation of the main electro-optical characteristics during aging. We found that, in general, shallow devices perform better than deep ones in terms of degradation of the threshold current and that, in Beryllium-doped devices, the degradation is likely to be caused by the relocation of defects possible related to the dopant, whereas for Carbon and Unintentional doping the optical degradation is much more limited, possibly indicating the lower stability of Be during aging. Additionally, in carbon-doped devices, there is an initial phase during which a recovery of the threshold current is observed. The main objective of the second experiment was to achieve a deeper understanding of the role of defects in the degradation of similar samples, grown on silicon substrate. In particular, by means of capacitance-voltage (C-V),capacitance-temperature (C-T) measurements, as well as Deep Level Transient Spectroscopy (DLTS), the variation in the signatures and concentrations of deep levels related to crystalline defects have been monitored during stress.