Intersubband relaxation dynamics in InGaAs/AlAsSb multiple quantum wells


Intersubband relaxation dynamics in InGaAs/AlAsSb multiple quantum wells

Tribuzy, C. V.-B.; Schneider, H.; Ohser, S.; Sellesk, M.; Winnerl, S.; Grenzer, J.; Helm, M.; Neuhaus, J.; Dekorsy, T.; Biermann, K.; Künzel, H.

Intersubband transitions in semiconductor quantum wells (QW) are crucial for mid-infrared lasers, detectors, and modulators. New compound materials such as lattice matched InGaAs/AlAsSb and strain compensated InGaAs/AlAs, both grown on InP, feature large conduction band discontinuities (>1eV) and allow the extension of the available wavelength range into the near infrared. Such short wavelengths require narrow QWs (<3 nm) where the first excited state inside the QW may be raised above indirect (X or L) valleys within the Brillouin zone. Quantum cascade lasers involving subbands above the indirect minimum have recently been reported [1].
We have studied intersubband relaxation dynamics in In0.53Ga0.47As/AlAs0.56Sb0.44 multiple QWs with thicknesses from 2.9 to 4 nm (corresponding to absorption wavelengths of 2.4 to 3.2 µm) by femtosecond pump-probe experiments [2]. At early delay times, all samples show an exponential decay of the transient transmission occurring with time constants of 0.8 to 1.5 ps. The relaxation dynamics at later delay times strongly depends on the QW thickness and doping. For very narrow QWs the observed bi-exponential decay indicates several competing relaxation channels. Here transfer of electrons to X- and L-states in the barriers, which exist in the case of n-type modulation doping, or in the wells is energetically possible. The data are analyzed in terms of an effective three-level configuration. Our results indicate that intervalley scattering in QWs is in the ps regime, much slower than in a bulk semiconductor. This observation suggests that intersubband lasing involving states above indirect minima of the well material should be possible, as also confirmed by the results of [1].
[ ] D. G. Revin et al., Appl. Phys. Lett. 90, 021108 (2007).
[2] C. V.-B. Tribuzy et al., Appl. Phys. Lett. 89, 171104 (2006).

Keywords: lattice matched InGaAs/AlAsSb; multiple quantum wells; intersubband relaxation; indirect valleys

  • Poster
    ITQW07 - The Ninth International Conference on Intersubband Transitions in Quantum Wells, 14.09.2007, Ambleside, Cumbria, United Kingdom

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Publ.-Id: 10237