Degradation of 1.3 μm Quantum Dot Laser Diodes for Silicon Photonics: Dependence on the Number of Dot-in-a-Well Layers

For the first time, we analyze the optical degradation of 1.3 mu m InAs quantum dot laser diodes (QD LDs) epitaxially grown on silicon as a function of the number of dot-in-a-well layers (DWELLs). To this aim, we tested the reliability of two kinds of devices differing only in the number of DWELLs in the active region: QD LDs with three vs. five quantum dot layers (3 vs. 5 QDLs). To induce degradation, we submitted the devices to highly accelerated stress tests: in the current step stress, we tested the degradation of the devices as a function of the stress current, whereas with a constant current stress, we evaluated the degradation as a function of the stress time. Both experiments confirmed that the device with more QDLs (5xQDLs) has better reliability than the structure with a lower number of DWELLs (3xQLDs), while exhibiting the very same degradation modes. We hypothesize that a higher number of active layers favors the redistribution of carriers across the active layers, lowering carrier density and therefore non-radiative recombination rates. This is beneficial in terms of reliability, as the non-radiative recombination lowers the radiative efficiency of the laser and, in turn, can enhance degradation via recombination-enhanced defect reaction (REDR). To support our assumption, we employed a quantum-corrected Poisson-drift-diffusion simulation tool to evaluate the carrier distribution and the Shockley-Read-Hall (SRH) recombination rate within the active region. The simulation results confirmed that the device with five QDLs has a lower carrier concentration per DWELLs and, therefore, a lower SRH recombination rate per active layer, thus resulting in a lower degradation rate.