Spectral-hole burning and carrier thermalization in GaAs at room temperature

Hunsche, S.; Heesel, H.; Ewertz, A.; Kurz, H.; Collet, J.

doi:10.1103/physrevb.48.17818

Cited by 52 publications

(39 citation statements)

References 58 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the same density range, the thermalization of nonequilibrium electrons has been determined to be 200 fs at room temperature and at the same photon energy. 21 However, the dephasing time of the coupled phonon-plasmon oscillations is found to be about three times longer than the thermalization time of 200 fs. We attribute this result to the phononlike part of the coupled mode, which does not lose its coherence even in the presence of much faster momentum scattering rates within the carrier plasma.…”

mentioning

confidence: 97%

Time-resolved observation of coherent phonons by the Franz-Keldysh effect

et al. 1996

Self Cite

View full text Add to dashboard Cite

We report on the time-resolved observation of coherent optical phonons in GaAs by the Franz-Keldysh effect. This effect leads to a modulation of the optical interband transitions with a nonlinear dependence on the macroscopic electric field associated with the coherent phonons. We find that the nonlinear electro-optic effect forms a far more efficient detection mechanism for coherent phonons than the linear electro-optic effect near the band gap.In recent years, the study of coherent phenomena with ultrashort laser pulses has become a matter of growing interest. The use of subpicosecond laser pulses allows a direct observation of coherent vibrations in molecules, 1 phonons in solid-state materials, 2-4 and electronic wave-packet oscillations in quantum-well structures in the time domain. 5 In previous studies the excitation mechanisms and the dephasing of coherent oscillations have been addressed.Recent investigations of coherent phonons in solid-state materials have shown that the excitation results from the impulsive interaction of the material with laser pulses whose durations are shorter than the period of the oscillation. In molecules, coherent vibrations can be excited by impulsivestimulated Raman scattering processes. 1 In narrow-band-gap semiconductors, the strong interband excitation of carriers leads to the excitation of coherent phonons by the impulsive elongation of the bonds. 3 It was found that in these materials the breathing mode of the coherent lattice vibrations modifies the band gap via the deformation potential. 6 In III-V semiconductors, the femtosecond excitation of free carriers results in the impulsive screening of the surface depletion field due to an ultrafast charge separation. This mechanism generates coherent longitudinal optical ͑LO͒ phonons, which are associated with an oscillating macroscopic electric field. 2,7 These field changes have been observed in timeresolved reflectivity measurements via the linear electrooptic effect. 2 In principle, the reflectivity changes induced by coherent phonons in III-V semiconductors arise from the modulation of the optical susceptibility at the phonon frequency, which is expressed by the coupling of the Raman tensor with the coherent motion of the atomic displacement. In a first-order approximation the phonon-induced reflectivity changes ⌬R can be described bywhere is the real part of the optical susceptibility, Q the atomic displacement, and F the macroscopic electric field. The first and second terms at the right-hand side in Eq. ͑1͒ are the deformation potential and the electro-optic contribution, respectively. This first-order Raman tensor determines the usual allowed Raman scattering with its specific polarization selection rules. 8,9 However, in the vicinity of critical points in the electronic band structure, nonlinear effects such as forbidden Raman scattering and electric-field-induced Raman scattering by LO phonons become strongly enhanced. 8,9 The polarization selection rule for these types of Raman tensors is different from that of a...

show abstract

mentioning

confidence: 97%

Time-resolved observation of coherent phonons by the Franz-Keldysh effect

et al. 1996

Self Cite

View full text Add to dashboard Cite

show abstract

“…1,2 Since the density of states in the conduction band is generally much lower than that of the valence band, in most studies the experimental signals are dominated by the dynamics of optically excited electrons. 3 Only in a few specific experiments could information on the hole relaxation dynamics be obtained in special sample structures. [4][5][6][7][8] In these studies, holes were excited with a certain excess energy and subsequent cooling processes were observed.…”

mentioning

confidence: 99%

“…In this case, the hole dynamics at elevated lattice temperatures is expected to be dominated by the absorption of longitudinal optical ͑LO͒ phonons that leads to a heating of the initial hole distribution. 3,7 In this letter, we investigate the intervalence band thermalization of optically excited holes. Femtosecond timeresolved measurements of the bleaching of the heavy-hole ͑HH͒ and light-hole ͑LH͒ exciton transition in a GaAs multi quantum well ͑MQW͒ sample are performed.…”

mentioning

confidence: 99%

“…1 they correspond to transitions between the first HH and LH subbands and the lowest electron subband. In the same figure a typical differential transmission spectrum is shown obtained in a ''white-light'' pump-probe experiment 3,9 at room temperature taken 3 ps after resonant excitation at the E1H1 transition. The spectrum reflects a quasi-equilibrium situation.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Time-resolved study of intervalence band thermalization in a GaAs quantum well

Kim

Hunsche

Dekorsy

et al. 1996

Applied Physics Letters

Self Cite

View full text Add to dashboard Cite

The thermalization of optically excited cold holes in a GaAs quantum well is investigated by femtosecond two-color pump-probe measurements. Clear evidence is found for scattering from heavy-holes into the lowest light-hole band due to LO-phonon absorption. We obtain firm data on scattering times which depend strongly on lattice temperature. They vary from 230 fs at room temperature to 900 fs at Tϭ105 K. The experimental data are well reproduced by numerical calculations. © 1996 American Institute of Physics. ͓S0003-6951͑96͒03021-5͔Firm experimental data on ultrafast carrier dynamics in semiconductors and semiconductor heterostructures are of prime importance for the development of novel ultrafast opto-electronic devices. The development of ultrashort-pulse lasers has stimulated a large number of time-resolved studies addressing the picosecond and subpicosecond dynamics of nonequilibrium carriers in GaAs and other III-V semiconductors. 1,2 Since the density of states in the conduction band is generally much lower than that of the valence band, in most studies the experimental signals are dominated by the dynamics of optically excited electrons. 3 Only in a few specific experiments could information on the hole relaxation dynamics be obtained in special sample structures. [4][5][6][7][8] In these studies, holes were excited with a certain excess energy and subsequent cooling processes were observed. In contrast, optical excitation of excitons close to the band edge will create initially cold holes. In this case, the hole dynamics at elevated lattice temperatures is expected to be dominated by the absorption of longitudinal optical ͑LO͒ phonons that leads to a heating of the initial hole distribution. 3,7 In this letter, we investigate the intervalence band thermalization of optically excited holes. Femtosecond timeresolved measurements of the bleaching of the heavy-hole ͑HH͒ and light-hole ͑LH͒ exciton transition in a GaAs multi quantum well ͑MQW͒ sample are performed. The nonlinear absorption of the excitonic transitions is determined by two contributions, namely the reduction of the oscillator strength and the broadening of the exciton line. 9 It has been shown previously that the reduction of the oscillator strength strongly depends on the subband occupation number, while the intrasubband carrier distribution does not play a significant role. 9,10 In the same work it was found that broadening is not affected by changes of the subband occupation. Furthermore, measurements of absorption changes at the lowenergy edge of the E1H1 transition-which are dominated by broadening-under various excitation conditions only show an ''instantaneous'' signal without any further dynamics on a picosecond time scale, indicating that this signal contribution is not sensitive to the exact intrasubband carrier distribution, either. 11 These facts make it possible to measure changes of the hole subband occupation by choosing sample and excitation parameters that prevent any electron intersubband dynamics.Our experiments are performed...

show abstract

“…The line shape of the PT spectra indicates that one observes only a bleaching of the excitonic absorption but no noticeable broadening or shift of the excitonic resonances. The latter is explained by the fact that the reduction of the exciton binding energy due to screening is compensated by band-gap renormalization [25][26][27] resulting from a change of the single particle states under photoexcitation.…”

Section: Results and Discussion Of The Carrier Capturementioning

confidence: 99%

Carrier capture in ultrathin InAs/GaAs quantum wells

et al. 2000

View full text Add to dashboard Cite

The carrier capture into ultrathin InAs layers embedded in a GaAs matrix has been investigated by timeresolved two-wavelength pump-probe phototransmission at 4.2 K. Using an InAs thickness of 1.2 monolayers, we observe switching of the carrier relaxation from optical to acoustic phonon emission. At the light-hole ͑lh͒ exciton transition we find a constant capture time of 20 ps. In contrast, the capture time decreases abruptly from 50 ps to 22 ps within the heavy-hole ͑hh͒ exciton transition as the energy separation between lh and hh states exceeds the threshold for GaAs LO phonon emission. The combination of both characteristics provides strong evidence for a two-step capture process of the holes. First the holes are captured by the weakly confined lh state and then they cool down to the hh state. We calculated the transient bleaching of the excitonic absorption considering both phase-space filling and exciton screening. The calculations show in agreement with the measurements that the phototransmission transients directly reflect the population of the confined InAs states only at excitation densities below 3ϫ10 8 cm Ϫ2 . At larger excitation densities, the phototransmission rise time becomes significantly smaller than the capture times whereas its decay time appears longer than the carrier lifetime.

show abstract

Spectral-hole burning and carrier thermalization in GaAs at room temperature

Cited by 52 publications

References 58 publications

Time-resolved observation of coherent phonons by the Franz-Keldysh effect

Time-resolved observation of coherent phonons by the Franz-Keldysh effect

Time-resolved study of intervalence band thermalization in a GaAs quantum well

Carrier capture in ultrathin InAs/GaAs quantum wells

Contact Info

Product

Resources

About