Growth and characterization of gasb based semiconductor saturable absorber mirror

The focus of this thesis is the growth of semiconductor saturable absorber mirrors (SESAMs) on GaSb substrates for applications in the mid-infrared region, using a molecular beam epitaxy system. The study involved independent growths of the key constituent layers, such as the distributed Bragg reflector (DBR) and the absorber layers. At the end of the study, high-quality AlAs0.08Sb0.92 layers with defect-free surfaces were successfully obtained for the DBR by optimizing growth conditions at a growth rate of 0.7 ML/s and a group V/III beam equivalent pressure ratio of 12. Besides, it was demonstrated that for the InGaAsSb/AlGaAsSb multiple quantum well (MQW) absorber layers, increasing In content causes a higher defect density and larger defect sizes. A key finding, however, was that these defects could be effectively suppressed by carefully adjusting the As concentration, which led to a significant improvement in overall crystal quality. The knowledge gained from these separate layer studies was then combined with the theoretical studies and subsequent growth of full SESAM structures, including anti-resonant and resonant designs with single or triple QWs were finalized. The optical properties of the grown SESAMs were comprehensively characterized through linear and non-linear reflection measurements. All SESAM structures achieved high reflectivity values exceeding 99%. Notably, one sample (NB-S-2) exhibited a clear nonlinear reflection response with distinct absorption features. For this sample, the saturation fluence (Fsat), the modulation depth (ΔR), and the nonsaturable losses (ΔRns) were determined as 0.26 MW/cm², 1.5%, and 4.75%, respectively.