Efficiency optimization of high power broad-area lasers and investigation of their power saturation mechanisms

High power semiconductor lasers are the most efficient light sources in converting electrical energy into optical output. However, their maximum achievable optical power and efficiency are limited by thermal and non-thermal power saturation. The main objective of this thesis is to investigate power saturation mechanisms in GaAs-based broad-area lasers. The study targets vertical design optimization by increasing the confinement in the quantum well (QW) at room temperature to enhance power and efficiency and investigates the impact of capture time on power and efficiency at high bias. Experimental results reveal that low-confinement devices (Γ<0.8%) performance are strongly affected by front facet reflectivity Rf, driven by Longitudinal spatial hole burning (LSHB), which is mitigated by using higher confinement designs. The optimum confinement design (Γ~0.8%) enables high power (~26 W) and a best balance of confinement (Γ~0.5%) and reflectivity (Rf ~ 3%) enables very high efficiency (η > 70%) at high powers. Further study reveals that a finite capture time in the QW contributes almost half of the total resistance, even for highly optimized vertical designs, limiting the efficiency. Furthermore, the presence of a finite capture time can lead to high hole accumulation in the n-doped region at extremely high bias, increasing free carrier absorption, non-stimulated recombination rates, and leakage currents, ultimately leading to power saturation.