Composition-controlled recovery time of SWIR (2-2.4 µm) GaSb-based SESAMs

SEmiconductor Saturable Absorber Mirrors (SESAMs) have revolutionized the ultrafast laser industry. While SESAMs are well-established in the near-infrared regime, using GaAs-wafer epitaxy, there is an increasing interest for the short-wave infrared (SWIR) regime, for which SESAMs can be fabricated using the GaSb material system. Compared to GaAs-based SESAMs, the nonlinear response of GaSb absorbers has been reported to exhibit inherent ultrafast response and a different interplay between the response time and fabrication process. Here we report new advanced features of this interplay in a detailed study investigating the effects of lattice mismatch (LMM, e.g., strain) in the quantum wells (QWs), and barrier materials of SESAMs designed for a center wavelength between 2 and 2.4 µm. At 2 μm, SESAMs with ternary InGaSb, GaAsSb, and quaternary In(x)Ga(1-x)As(y)Sb(1-y) QWs embedded in GaSb were grown with varying levels of QW LMM, ranging from compressive strain (-1.7% LMM) to tensile strain (+0.9% LMM). We observed a strong dependence of the recovery time on the QW strain. While a maximum interband recovery time of 340 ps was measured for lattice matched QWs (-0.1% LMM), both compressively and tensilely strained QWs exhibit a shorter interband recovery time. Furthermore, a set of In_0.27GaSb QW SESAMs embedded in Al_xGa_1-xAsSb barriers with different Al content have been grown. We observed that an increasing Al content in the barrier significantly slows down the interband recovery time. All findings are consistent for different heterostructures designed for operation at 2-2.4 µm.