Interband Relaxation Dynamics of Photo-Excited Carriers in InSb Quantum Wells

As the switching rates in electronic and optoelectronic devices are pushed to higher frequencies, it is important to understand carrier dynamic phenomena in semiconductors on femtosecond time- scales. Here we present carrier dynamics, using several pump/probe schemes, in doped and undoped InSb quantum wells (QWs) with Al$_{x}$In$_{1-x}$Sb barrier layers. In one scheme, the carriers were created by NIR pulses fixed at 800 nm, above the band gap of Al$_{x}$In$_{1-x}$Sb and InSb, and probed by MIR pulses, tuned in the vicinity of several interband transitions. We observed that the carriers were captured in the QWs in a time scale of $\sim$ 800 fs and not fully relaxed in a time scale longer than 20 ps. Electrons that are sufficiently energetic have the possibility to scatter between the X, L, and $\Gamma$ valleys in the conduction band, resulting in more complex dynamics. We probed the influence of the initial distribution function by employing a degenerate pump/probe scheme close to several interband transitions. We will discuss several mechanisms describing the observed dynamics, important for developing long-wavelength optoelectronic devices.