Intersubband relaxation and dephasing in narrow InGaAs/AlAsSb quantum well structures

The InGaAs/AlAsSb heterostructure has been attractive in recent years due to its high conduction band offsets, which is necessary for intersubband transition (ISBT) based devices at short wavelength (< 3 microns) [1]. To achieve this goal, very thin QWs are required, leading to a particular band configuration where a X or L cross-over takes place. Nevertheless it has been shown that intervalley transfer is rather inefficient for ISBT wavelengths as short as 2.3 m [2], indicating that quantum cascade lasers (QCL) at such short wavelength are feasible. Indeed, QCL with wavelength around 3.0 μm [3], using the same material, were recently demonstrated. Besides the intersubband relaxation time, providing the nonradiative lifetime of the QCL, another important parameter for the design of QCL is the homogeneous linewidth, since it would affect the gain profile of the laser. Therefore the study of the dephasing time, being directly relevant for the homogeneous linewidth, is as important as the intersubband relaxation time.
In this work we present a study of the intersubband relaxation dynamics and dephasing time of QW doped InGaAs /AlAsSb samples grown on InP substrate, through, respectively, degenerate pump-probe and four-wave-mixing (FWM) measurements, at wavelengths around 2 m. The measured intersubband relaxation time constants, between 1 and 1.8 ps, increase with the decrease of the temperature due to the reduced LO phonon scattering. The measured FWM time constant increases by a factor of 4, inferring from the increase of the FWM signal intensity with the decrease of the temperature from 300K to13K.
[1] C. V-B. Grimm, M. Priegnitz, S. Winnerl, H. Schneider, M. Helm, Appl. Phys. Lett. 91, 191121(2007).
[2] C.V-B. Tribuzy, S. Ohser, S. Winnerl, J. Grenzer, H. Schneider, M. Helm, J. Neuhaus, T. Dekorsy, K. Biermann, H. Künzel, Appl. Phys. Lett. 89, 171104 (2006).
[3] D. G. Revin, J. W. Cockburn, M. J. Steer, R. J. Airey, M. Hopkinson, A. B. Krysa, L. R. Wilson, and S. Menzel, Appl. Phys. Lett. 90, 021108 (2007).