Dresden 2017 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 6: Ultrafast Phenoma I

HL 6.4: Vortrag

Montag, 20. März 2017, 10:30–10:45, POT 51

Terahertz narrowband-pump broadband-probe spectroscopy of intersubband transitions in a wide single quantum well — •Johannes Schmidt, Stephan Winnerl, Emmanouil Dimakis, Harald Schneider, and Manfred Helm — Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany

Electron relaxation dynamics of intersubband transitions (ISBT) in quantum wells can cover a broad range from ps to ns time scales, dependent on the transition energy compared to the LO-phonon energy [1]. Most of previous studies used various types of narrowband interband or intraband spectroscopy, where only one transition can be studied at a time. We have developed a setup that allows for narrowband THz pumping using the free electron laser FELBE together with broadband THz probing employing time-domain spectroscopy, and thus enabling us to record the full spectral relaxation dynamics under resonant pumping.

We study a 40 nm wide modulation doped single GaAs quantum well; this guarantees a homogeneous intensity over the active structure (which is not the case in multi quantum wells). To improve the sensitivity of the measurements, we modulate the electron density using proper gate voltages.

THz absorption of the 1-2 ISBT is seen at 2.15 THz and the 2-3 transition is observed at 3.4 THz. While pumping the 1-2 transition resonantly, a relaxation time of 1100 ps is probed. We will also report on the full probe spectra, on excitation of the 2-3 transition, and we are searching for pump-induced quantum coherent effects.