Hot-phonon effects in femtosecond luminescence spectra of electron-hole plasmas in CdS

Klimov, Victor I.; Bolívar, P. Haring; Kurz, H.

doi:10.1103/physrevb.52.4728

Cited by 71 publications

(104 citation statements)

References 19 publications

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“…Here T is the common electron/hole temperature, m is the electron momentum relaxation time due to phonon-or carrier-induced scattering processes, and E ៝ is an electric field that arises from charge density imbalance e͑N h − N e ͒ and from J. The space-charge and current sources produce scalar ͑⌽͒ and vector potentials ͑A͒ which can be calculated using Green function techniques 17 for the appropriate boundary conditions; the electric field is then given by E =−١⌽ − ‫ץ‬A / ‫ץ‬t. For our experiments where the illuminated spot sizes are W ϳ 100 m full width at half maximum ͑FWHM͒ in diameter and the relative dielectric constants 15 are ⑀ = 9.3 ͑8.7͒ for CdSe ͑CdS͒, respectively; the time scales ͑ϳ100 fs͒ for current evolution areϽW ͱ ⑀ / c therefore the electrostatic approximation is inappropriate; and the electric field arises mainly from current sources through A if one uses the Coulomb gauge.…”

Section: B Current Evolutionmentioning

confidence: 99%

Ultrafast shift and injection currents observed in wurtzite semiconductors via emitted terahertz radiation

Laman

Bieler

Driel

2005

Journal of Applied Physics

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Shift and injection currents are generated in the wurtzite semiconductors CdSe and CdS at 295 K using above-band-gap ͑ប Ͼ E g ͒ femtosecond pulses and detected via the emitted terahertz radiation; the optical beams are normally incident on samples with the optic axis in the plane of the surface. For optical intensities up to 75 MW cm −2 ͑or carrier density Ͻ10 18 cm −3 ͒ the terahertz radiation amplitude shows the expected linear dependence and also varies with optical polarization and sample orientation consistent with the third-rank tensors that govern the current generation processes in the wurtzite structure. The largest shift currents are generated along the optical axis for light polarized along that axis. In CdSe with ប = 1.80 eV ͑690 nm͒, the electron shift distance is ϳ40% of the 0.25 nm bond length and the peak current density is 5 kA cm −2 for an optical intensity of 10 MW cm −2 ; for CdS the corresponding experiment at ប = 3.0 eV ͑410 nm͒ gives a shift distance ϳ80% of the 0.26 nm bond length with a peak current density of 50 kA cm −2 for an incident intensity of 75 MW cm −2 . For injection current produced in CdSe with circularly polarized 690 nm excitation, electrons are injected with an average speed of 9 km s −1 ; this is ϳ3% of the group velocity for electrons excited with the same energy. The corresponding values for CdS excited at 410 nm are 20 km s −1 and 2%. From the temporal characteristics of the terahertz emission for injection currents in CdS we deduce that the electron momentum scattering time is Ͻ100 fs, consistent with mobility studies.

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Section: B Current Evolutionmentioning

confidence: 99%

Ultrafast shift and injection currents observed in wurtzite semiconductors via emitted terahertz radiation

Laman

Bieler

Driel

2005

Journal of Applied Physics

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“…3. Estimations show that the threshhold for saturation of the EЈ(2 2 ) phonon mode is at carrier densities of ϳ5ϫ10 16 cm Ϫ3 , which is in the range of the excitation densities used in the present experiments.…”

Section: A Carrier Cooling Dynamicsmentioning

confidence: 95%

“…The free-exciton formation rate is determined by the exciton binding energy (E B X ϭ19 meV in GaSe͒ and the thermal energy of the carriers 3 2 k B T C . When the thermal energy of the carriers becomes smaller than the exciton binding energy, the attractive Coulomb interaction between electrons and holes is strong enough to bind them into excitons and prevent the thermal dissociation of the exciton.…”

Section: B Exciton Formation Dynamicsmentioning

confidence: 99%

Carrier cooling and exciton formation in GaSe

et al. 1997

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The initial cooling of hot carriers and the subsequent exciton formation in GaSe are studied by time-resolved photoluminescence ͑PL͒ using femtosecond up-conversion techniques. From the time-resolved PL spectra of this layered III-VI semiconductor two different energy relaxation channels are derived. After an initial subpicosecond cooling due to Fröhlich-type interaction of carriers with longitudinal optical EЈ(2 2 ) phonons a slower regime follows, which is dominated by deformation potential interaction with the nonpolar optical A 1 Ј(1 2 ) phonons. The coupling constant for nonpolar optical phonon scattering is derived. The subsequent formation of excitons is studied at different carrier densities and detection energies. A cross section for the free-exciton formation is determined based on a rate equation model. ͓S0163-1829͑97͒01132-6͔

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“…Furthermore, it is well-known that the highly excited carriers rapidly relax energy toward the LO-phonon system, creating large nonequilibrium phonon populations. A build-up of the nonequilibrium phonons creates a bottleneck in the relaxation channel carrier-phonon LO that may influence considerably the carriers' cooling rate [2,[5][6][7][8][9][10][11]. The diminished effectiveness of the process of relaxation in the carrier system, with an accompanied slowing down in the rate of energy loss has been mainly ascribed to this so-called hotphonon effect [12].…”

Section: Introductionmentioning

confidence: 98%

Numerical analysis of the relaxation of photoexcited carriers and the hot-phonon effect in GaN

Silva

Nascimento

2004

Journal of Luminescence

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Hot-phonon effects in femtosecond luminescence spectra of electron-hole plasmas in CdS

Cited by 71 publications

References 19 publications

Ultrafast shift and injection currents observed in wurtzite semiconductors via emitted terahertz radiation

Ultrafast shift and injection currents observed in wurtzite semiconductors via emitted terahertz radiation

Carrier cooling and exciton formation in GaSe

Numerical analysis of the relaxation of photoexcited carriers and the hot-phonon effect in GaN

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