THz spectroscopy of optically excited InGaAs quantum wells in the high charge-carrier density regime


THz spectroscopy of optically excited InGaAs quantum wells in the high charge-carrier density regime

Schmidt, J.; Teich, M.; Wagner, M.; Winnerl, S.; Stehr, D.; Schneider, H.; Helm, M.

In this work we study the THz transmission of a 40 nm wide undoped In0.1Ga0.9As quantum well (QW) under optical excitation. Carriers are photoexcited by a near-infrared (NIR) fs pulse and probed in the frequency range from 0.1 to 3 THz by electro-optic sampling using the modified setup of Ref. [1]. The THz pulse is focused on a side facet of the QW sample such that the THz electric field is mostly polarized perpendicular to the QW layer. Fig. 1a depicts the THz field transients for modulated (signal) and un-modulated (reference) NIR excitation. The presence of the carriers which were photoinjected several ps prior to the THz pulse creates a large amount of THz signatures in the QW. Our present goal is to disentangle the various possible contributions to the THz signal: electron intersubband, heavy-hole intersubband, 1s-2p intraexciton and free-carrier absorption. In addition we search for a Fano-like behavior, similar as has been observed in narrower QWs in the mid infrared [2], which is supposed to arise from the interplay between the intersubband absorption and the purely reactive ponderomotive contribution. The different phase of the associated dielectric functions results in a (non-quantum like) interference between these two polarizations, which is only visible in the differential transmission but not in the absorption. We will also report experiments where we use wavelength tuning of the near-infrared pulse using an optical parametric amplifier in order to selectively pump optically either into the barrier or into the QW. Polarization resolved measurements are underway which should help us to reveal the various contributions.
[1] M. Wagner et. al. , Appl. Phys. Lett. 99, 131109 (2011).
[2] D. Golde, M. Wagner et. al., PRL 102, 127403 (2009).

Keywords: quantum well; THz time domain; photoexcitation

  • Poster
    OTST 2013: International Workshop on Optical Terahertz Science and Technology 2013, 01.-05.04.2013, Kyoto, Japan

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Publ.-Id: 18710