Excitonic signatures in the photoluminescence and terahertz absorption of aGaAs∕AlxGa1−xAs

Abstract

Measurements of the THz absorption and the time-resolved photoluminescence have been performed on the same GaAs quantum well sample. The strength of the absorption at the internal 1s-2p exciton transition frequency is used as a measure of the density of excitons in the sample. When the interband pump laser is resonant with the 1s exciton frequency, induced absorption at the 1s-2p frequency is clearly seen. If the same density of carriers is created pumping in the continuum, no significant 1s-2p absorption is seen in a time window of 450 ps. Complementary time-resolved photoluminescence experiments, detecting the emission at the exciton energy under the same pump conditions, show the PL intensity in resonant and nonresonant cases to be similar. The counter-intuitive existence of luminescence at the exciton energy simultaneously with the absence of the 1s-2p absorption is consistent with the recent theoretical predictions of Kira et al.,

Far-infrared free-electron lasers and their applications

“…Using synchronised pulses from the FEL and a visible laser internal dynamics of excitons have been investigated, with the visible laser pulses exciting the excitons and the THz pulses tuned to resonance with the 1s-2p transition. It has been experimentally verified that photoluminescence emission can occur at the exciton energy even without the existence of an excitonic plasma [28]. Since by far the majority of experiments concerned with exciton formation and manipulation in the literature have been obtained by PL observed by pumping well above resonance, this is of substantial consequence to both experimenters and theorists in the subject.…”

Semiconductor excitons in strong terahertz fields

“…The absolute value of the complex envelope, 2 , is identical to the usual real-valued temporal envelope of ΔE. Thus, according to Eqs.…”

“…Weak THz fields can, e.g., directly probe internal transitions between different exciton states and thus detect exciton populations [1][2][3][4][5]. Beyond that, strong THz pulses offer the possibility to control and manipulate exciton populations and other many-body states [6].…”

Resonant enhancement of second order sideband generation for intraexcitonic transitions in GaAs/AlGaAs multiple quantum wells

“…The nearby 2p state is optically interband forbidden but should lie around 9 meV above the hh͑1s͒ transition. 13 However, the excitonic intersubband transition between hh͑1s͒ and hh͑2p͒ exciton states is allowed and couples strongly to THz radiation. 2,5 In Fig.…”