Propagation velocity of excitonic polaritons confined in GaAs thin films

Abstract

We report on the dependence of exciton‐polariton propagation on film thickness in GaAs thin films using a reflection‐type pump‐probe technique. The rise time of the transient signal under exciton excitation conditions increases with an increase in the film thickness. In order to reveal the origin of the change in signal rise time, we have compared the propagation velocities estimated from values of the signal rise time and effective film thickness with the calculated group velocity of the exciton‐polaritons in bulk GaAs crystals. The propagation velocities are almost consistent with the group velocity in the bulk crystals. Therefore, we conclude that the propagation of exciton‐polaritons in a confined system coincides with that in the bulk crystal (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dephasing of Excitonic Polaritons Confined in GaAs Thin Films

“…In the transientgrating and pump-probe signals under exciton resonant conditions, a slow rise of the signals much longer than the pulse width was observed in the negative-time region. [17][18][19] The propagation velocity estimated from the film thickness and the rise time Rise almost agrees with the group velocity of excitonic polaritons in a bulk GaAs crystal. 18,19) In this study, we investigated the dynamics of excitonpolaritons in GaAs thin films at various temperatures using reflection-type pump-probe techniques.…”

“…19) Therefore, the experimentally evaluated velocity of the propagation of excitonic polaritons approximately originates from the group velocity of the lower polaritons. While the signal in the positive-time region does not show a clear change with an increase in temperature, Rise clearly decreases as shown in Fig.…”

Observation of quantum beat oscillations and ultrafast relaxation of excitons confined in GaAs thin films by controlling probe laser pulses

“…The signal measured in the negative time region originates from the polariton propagation. [20][21][22] The signal clearly varies with DE of the probe pulse. The signals obtained by using a probe pulse with DE > 1:2 meV show ultrafast components around zero delay, which had not been observed by a pump-probe technique in our previous studies, which employed a pump-probe technique with the broadband pulses to probe the response of the several exciton states.…”

“…The Al 0:3 Ga 0:7 As barrier layer has sufficient thickness to confine the excitons in the GaAs thin films. 11,[19][20][21] The GaAs layer thickness is larger than the exciton Bohr radius (11 nm); therefore, the center-of-mass motion of excitons is confined. The transient response was measured at 4 K by using a reflection-type pump-probe technique.…”

“…RESULTS AND DISCUSSION Figure 1(a) shows the PL spectrum for the evaluation of exciton energies. By comparison of their peak energies with the calculation results for exciton energies based on the model of quantization of the center-of-mass motion of excitons, 20,21 we determined the origins of the PL peaks. This calculation does not include the effect of the radiative shift caused by coupling with light fields.…”