Ultrafast dynamics of photoexcited charge carriers in In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As superlattices under femtosecond laser excitation

The results of experimental studies of the time dynamics of photoexcited charge carriers in In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As superlattices grown by molecular-beam epitaxy on a GaAs substrate with a metamorphic buffer are reported. On the basis of the results of the numerical simulation of band diagrams, the optimal thickness of the In$_{0.52}$Al$_{0.48}$As barrier layer (4 nm) is chosen. At this thickness, the electron wave functions in In$_{0.53}$Ga$_{0.47}$As substantially overlap the In$_{0.52}$Al$_{0.48}$As barriers. This makes it possible to attain a short lifetime of photoexcited charge carriers ($\tau\sim$ 3.4 ps) at the wavelength $\lambda$ = 800 nm and the pumping power 50 mW without doping of the In$_{0.53}$Ga$_{0.47}$As layer with beryllium. It is shown that an increase in the wavelength to $\lambda$ = 930 nm (at the same pumping power) yields a decrease in the lifetime of photoexcited charge carriers to $\tau\sim$ 2 ps. This effect is attributed to an increase in the capture cross section of trapping states for electrons with lower energies and to a decrease in the occupancy of traps at lower excitation densities.