Ultrafast Dynamics of Photoexcited Charge Carriers in In0.53Ga0.47As/In0.52Al0.48As 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 (τ ~ 3.4 ps) at the wavelength λ = 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 λ = 930 nm (at the same pumping power) yields a decrease in the lifetime of photoexcited charge carriers to τ ~ 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.