Intersubband relaxation of heavy-hole excitons in GaAs quantum wells

Höpfel, R. A.; Rodrigues, Rosana; Iimura, Yasufumi; Yasui, Takanari; Segawa, Y.; Aoyagi, Yoshinobu; Goodnick, Stephen M.

doi:10.1103/physrevb.47.10943

Cited by 21 publications

(15 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The former process is known to take place on a time scale of 130 ps. 4 The latter is quite inefficient due to the large momentum change required. We note that the bleaching dynamics after resonant LH excitation does not show any fast changes which could be assigned to ionization of the LH excitons.…”

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

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

mentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

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

Kim

Hunsche

Dekorsy

et al. 1996

Applied Physics Letters

View full text Add to dashboard Cite

show abstract

“…The slower relaxation time is consistent with the energy separation between lh states and these hh states being smaller than the threshold energy for LO phonon emission. In such a case relaxation occurs via a cascade of acoustic phonons [31][32][33] with relaxation times larger than 40 ps. We therefore conclude, that a change in the relaxation mechanism from LO phonon emission to an acoustic phonon cascade, at the threshold energy of 36 meV, is sufficient to explain the observed sudden increase of the hh transient rise time accompanied by the decrease of the lh transient decay time and a constant decay time of the hh transient.…”

Section: Results and Discussion Of The Carrier Capturementioning

confidence: 99%

“…In contrast, when the hh-lh level separation becomes smaller than the LO phonon energy, relax lhϪhh should increase to several tens of picoseconds. [31][32][33] In order to demonstrate that a change of relax lhϪhh from 1-2 ps to several tens of picoseconds is responsible for the observed increase of the capture time within hh exciton transition, we performed a systematic study of the parameters entering the rate equations ͑see Appendix B͒. This is necessary because rise and decay times of the populations p hh (t) and p lh (t) are determined by a combination of the individual hole capture times to the hh and lh level, the relaxation time for intersubband relaxation from the lh to the hh level, and the band-band recombination time.…”

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

“…It is interesting to note that in addition to the An=O transitions (el-> hhl, e2->hh2 and the complementary light hole transitions), we have also observed the e2 -> hhl transiliion, whichis forbidden in a symmetric QW. In the barrier-doped samples, however, the quantum well potential is highly asymmetric due to the electric field induced by the doping layer and hence otherwise forbidden transitions are also observed [5].…”

Section: Resultsmentioning

confidence: 98%

The influence of delta-doped sheet position on the optical properties of InGaAs/GaAs single quantum wells

Dao

Gál²,

Li³

et al.

2000 International Semiconducting and Insulating Materials Conference. SIMC-XI (Cat. No.00CH37046)

View full text Add to dashboard Cite

We found that the time integrated (CW) and time resolved photo-lunhescence (PL) spectra of Si &doped In~.zGao.sAs/GaAs quantum wells (QW's) depended signiticantly on the position of the doping sheet. Using time resolved PL we measured the various relaxation times into and out of the well and found strong correlation between the position of the doping sheet and the values of the relaxation times. A. IntroductionDelta doping (&doping) is known to achieve effective and efficient doping of semiconductor quantum wells (QWs) [l-2]. While the effect of the position of the 6-doped layer on the transport properties of QW's has been carefully studied and is well documented, its effect on the optical properties of the QW is less well known. We expect, for example, the heshape, energy and intensity of radiative transitions to depend on the position of the doping layer since the internal electric field created by the doping is a strong function of the position of the doping layer.Similarly, in these systems at low temperatures, ionised impurity scattering is the: dominant scattering mechanism, hence we anticipate the relaxation rates in the quantum wells to depend decisively on the position of the doping layer. Optical studies can also be used to help iunderstand the nature of the electronic states involved, as well as provide a direct non-contact tool to study the carrier dynamics into and out of the quantum wells. For these reasons we undertook to study the photoluminescence properties of centre and barrier &doped InGaAs/GaAs QWs and measure its temporal evolution. The time resolved PL measurements were spectrally resolvcd so the various excited state emissions could separately be studied. B. ExperimentsThe samples used in this study were grown by metal-organic chemical vapour deposition (MOCVD) and consisted of a single lOnm I~.~G~.~A s quantum well between GaAs baniers, grown on a semi-insulating GaAs substrate. The position of the Si &doped layers was varied between samples: some samples were doped in the well, while others were doped 0ui:side of the well, on either side of the quantum well, at lOnm From the side of the well. In this report we shall concentrate on the centre-doped and the (substrate-side and surface-side) barrier-doped samples.The samples discussed in this report had a sheet electron density which varied between 2~1O'~cm'~ and 4~10'~ cm". Other details of the Si S-doping can be found in our previous publications[ 31.

show abstract

Intersubband relaxation of heavy-hole excitons in GaAs quantum wells

Cited by 21 publications

References 36 publications

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

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

Carrier capture in ultrathin InAs/GaAs quantum wells

The influence of delta-doped sheet position on the optical properties of InGaAs/GaAs single quantum wells

Contact Info

Product

Resources

About