Picoseconds carrier spin relaxation in In 0.8 Ga 0.2 As/Al 0.5 Ga 0.5 As/AlAs 0.56 Sb 0.44 coupled double quantum wells

InGaAs/AlAsSb coupled double quantum wells (CDQWs) have been attracting much attention for their use in all-optical switches at 1.55 µm wavelength because of their large conduction band offset of 1.7 eV. In this study, we have investigated the spin relaxation in In 0.8 Ga 0.2 As/Al 0.5 Ga 0.5 As/AlAs 0.56 Sb 0.44 CDQWs using time-resolved spin-dependent pump and probe reflectance measurements to observe the time evolution of the spin polarization. By the double-exponential fitting of the time evolution of spin polarization, we obtained the spin relaxation times of 4.2 ps and 50.2 ps at room temperature. The observed spin relaxation time of 4.2 ps at room temperature indicates high potential for applications to high-speed optical devices.