Dynamics of exciton-polariton recombination in CdS

Wiesner, P.; Heim, U.

doi:10.1103/physrevb.11.3071

Cited by 90 publications

(15 citation statements)

References 29 publications

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“…Heim and Wiesner measured a frequencydependent decay of EP luminescence in CdS and observed a prolonged polariton decay time in the region below ftr. 4,5 On the assumption of a spatially homogeneous distribution of polaritons, their results were analyzed and found to be direct evidence of the accumulation of EP's in the bottleneck region. 6 In analyses of polariton dynamics, the spatially homogeneous distribution is often assumed for simplicity.…”

Section: Pulsed Propagation Of Polariton Luminescencementioning

confidence: 99%

Pulsed Propagation of Polariton Luminescence

et al. 1988

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Pulsed luminescence is observed in time-and frequency-resolved measurements of the Z3 exciton luminescence of CuCl single crystals under excitation at the highly absorptive region of the Zn exciton resonance. A high-repetition-rate tunable picosecond uv light source was used. The pulse traveling time coincides well with the time calculated from the corresponding polariton group velocity. It is found that the redistribution of polaritons due to intraband relaxation is not important to the temporal behavior of the free-exciton luminescence, but the polariton propagation effect is essential, in contrast to the discussions found in previous work.PACS numbers: 71.36.+C, 42.65.Re, 78.47.+p, 78.55.Hx The optical properties of a dipole-allowed exciton are described well with the exciton-polariton (EP) concept. 1 ' 2 In this description, the radiative recombination process of photocreated excitons is regarded as a combined process of propagation to a sample surface as polaritons and subsequent conversion into photons. Thus the spectral shape of the EP luminescence is determined by the population distribution function of the EP's and the boundary conditions at the sample surface. The EP's are nonequilibrium in nature, since there is no lower energy limit in the EP state. However, Toyozawa 3 studied the population dynamics of EP's taking into account a phonon scattering rate in the sample and an escape rate at the surface, and pointed out that the polaritons can accumulate in the region, named "bottleneck," that is situated just below the energy Cl j of the transverse exciton at k =0. As long as the extrinsic nonradiative recombination rate is small, one may expect formation of a thermal-equilibrium distribution of excitons in the energy region above the bottleneck. This effect is often quoted as the origin of a peak found in EP luminescence spectra. Heim and Wiesner measured a frequencydependent decay of EP luminescence in CdS and observed a prolonged polariton decay time in the region below ftr. 4,5 On the assumption of a spatially homogeneous distribution of polaritons, their results were analyzed and found to be direct evidence of the accumulation of EP's in the bottleneck region. 6 In analyses of polariton dynamics, the spatially homogeneous distribution is often assumed for simplicity. In actual experiments, however, the EP's are inhomogeneously created in space, because the incident photon energy is usually in a highly absorptive region, e.g., in the region of a band-to-band transition. It has already been pointed out that this spatial dependence of the EP distribution causes a forward-backward variation of the line shapes of steady-state EP luminescence from platelet samples with finite thickness. 7,8 If such a spatial inhomogeneity exists, it should also be reflected in the temporal behavior of the EP luminescence. Therefore, it is clear from this argument that one has to take into account the space and time evolution of the polariton distribution in order to understand correctly the temporal profile of the EP l...

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Section: Pulsed Propagation Of Polariton Luminescencementioning

confidence: 99%

Pulsed Propagation of Polariton Luminescence

et al. 1988

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“…The FFT signal shown in figure 3(c), which was obtained by the same evaluation as in The output P out as a function of the time delay also closely coincides with the simulated response from figure 1(c) (see SI figure S4). We note that our measurement technique scans over relative short time delays (~ 80 ps) relative to the spontaneous recombination times in CdS (~ 1 ns) [27]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 In particular, we note a peak in the output power for a given time delay, t max , which is attributed to absorption saturation in the nanowire following the first pump pulse.…”

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confidence: 99%

Ultrafast Dynamics of Lasing Semiconductor Nanowires

et al. 2015

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Semiconductor nanowire lasers operate at ultrafast timescales; here we report their temporal dynamics, including laser onset time and pulse width, using a double-pump approach. Wide bandgap gallium nitride (GaN), zinc oxide (ZnO), and cadmium sulfide (CdS) nanowires reveal laser onset times of a few picoseconds, driven by carrier thermalization within the optically excited semiconductor. Strong carrier-phonon coupling in ZnO leads to the fastest laser onset time of ∼1 ps in comparison to CdS and GaN exhibiting values of ∼2.5 and ∼3.5 ps, respectively. These values are constant between nanowires of different sizes implying independence from any optical influences. However, we demonstrate that the lasing onset times vary with excitation wavelength relative to the semiconductor band gap. Meanwhile, the laser pulse widths are dependent on the optical system. While the fastest ultrashort pulses are attained using the thinnest possible nanowires, a sudden change in pulse width from ∼5 to ∼15 ps occurs at a critical nanowire diameter. We attribute this to the transition from single to multimode waveguiding, as it is accompanied by a change in laser polarization.

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“…6 ' 7 Much work has been reported on the dynamics of polaritons in semiconductors by use of picosecond-laser spectroscopic techniques. 8 ' 12 However, to our knowledge direct demonstration of the time evolution of the secondary emission process mentioned above has not been reported in the time domain within the experimental time resolution.…”

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confidence: 84%

Observation of Time Evolution from Resonant Raman Scattering to Excitonic-Polariton Luminescence in ZnTe

Oka¹,

Nakamura²,

Fujisaki³

1986

Phys. Rev. Lett.

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We report the evolution from resonant Raman scattering (RS) due to longitudinal-optical and acoustic phonons to excitonic-polariton luminescence in ZnTe at low temperature by picosecond time-resolved spectroscopy. The resonant RS lines deform with decay time of 300 ps into the ordinary polariton luminescence. The finite decay time of the RS lines shows evidence of a real transition on the polariton branch in the resonant RS process.PACS 78.30.Gt, 78.55.Hx The relation between light scattering and luminescence under resonant optical excitation has been discussed by many authors. 1 " 4 A unified picture of secondary emission processes developed by Toyozawa leads us to the understanding of the processes as follows 2 : The secondary photon which is emitted by the electron after interaction with a few optical (acoustic) phonons in the resonant intermediate state is characterized by light scattering. Such photons are normally investigated in Raman (Brillouin) spectroscopy. The photon arising after full thermalization of the electron system by phonons in the intermediate state has the character of ordinary luminescence (OL). The correlation between the excitation photon and the secondary photon is completely lost in this case. The secondary photon emitted from the electron before full thermalization in the intermediate state is denoted as hot luminescence (HL). In these three emission processes, RS, HL, and OL, the difference is only the degree of the relaxation by phonons (either the longitudinal or the dephasing relaxation) in the intermediate states. In RS, when the relaxation of the intermediate electron takes place it is possible to identify which phonon causes the relaxation because the relevant phonons are limited. However, in HL and OL processes a number of phonons are related with the relaxation so that we cannot distinguish individual phonons in the relaxation. In this case the phonon system plays the role of a thermal bath for the electrons. From the above argument we see that these three secondary emission processes cannot be separated from each other with clear boundaries and only the phonon relaxation rate determines the character of the emitted photons.The secondary emission process under resonant excitation therefore transforms from RS type to OL through HL, which takes place usually in a time range of less than 10 ~1 2 s in most solids even at low temperature. Thus the time-resolving measurement in the picosecond time domain could not reveal this transformation in solids.The excitonic-polariton state in direct semiconductors, however, has the possibility of displaying the above evolution of the emission process because the polariton populated around the knee region in the lower branch at low temperature interacts with the acoustic and optical phonons with a much lower rate than an electron in the ordinary electronic state because of the k dependence of the deformation-potential and Frohlich interactions: This is the bottleneck of the polariton. 5 Recent studies on the resonant Brillouin and Raman sc...

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Dynamics of exciton-polariton recombination in CdS

Cited by 90 publications

References 29 publications

Pulsed Propagation of Polariton Luminescence

Pulsed Propagation of Polariton Luminescence

Ultrafast Dynamics of Lasing Semiconductor Nanowires

Observation of Time Evolution from Resonant Raman Scattering to Excitonic-Polariton Luminescence in ZnTe

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