Chirped Bloch oscillations in strain-balanced InGaAs/InGaAs superlattices

Först, Michael; Cho, G.C.; Dekorsy, Thomas; Kurz, H.

doi:10.1006/spmi.1999.0762

Cited by 3 publications

(3 citation statements)

References 25 publications

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“…This effect results from the dephasing of the BOs that ͑i͒ reduces the strength of the associated dipole field due to the reduced number of coherently oscillating electrons and ͑ii͒ leads to a drift current of the scattered electrons through the SL which further screens the applied electric field. 21 We should further note that the signals detected in resonant TEOS experiments are typically two orders of magnitude larger. 11 This enlargement is attributed to the resonant enhancement of the electro-optic effect at the WS transitions.…”

Section: Blochmentioning

confidence: 95%

Midbandgap electro-optic detection of Bloch oscillations

et al. 2000

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Bloch oscillations excited in a biased GaAs/Al x Ga 1Ϫx As superlattice are investigated in a time-resolved two-color electro-optic detection scheme. The detection of resonantly excited Bloch oscillations is based on the Pockels effect probed at a wavelength in the center of the band gap. The observed birefringence is induced by the macroscopic polarization of the electronic wave packets relative to the localized holes. The off-resonant detection away from optical transitions directly monitors the spatial dynamics of the electrons in amplitude and phase. The dependence of the amplitudes of the Bloch oscillating electrons on the applied electric fields are in good agreement with the electron-hole dipole lengths calculated by a quantum-mechanical model. Bloch1 and Zener 2 have proposed in their theoretical studies on the dynamics of electronic wave packets in periodic potentials a temporal and spatial oscillation of the carriers in the presence of a static electric field. The frequency and the spatial amplitude L of these Bloch oscillations ͑BO's͒ are ϭeFd/h and Lϭ⌬/eF, ͑1͒respectively, where F is the applied electric field, d the potential period, h Planck's constant, and ⌬ the electronic bandwidth. As proposed by Esaki and Tsu, this intriguing phenomenon can be realized in a biased semiconductor superlattice ͑SL͒.3 Here, BO's are excited by the coherent superposition of several electronic Wannier-Stark ͑WS͒ states 4,5 with a common hole state by short laser pulses. The localization lengths of the electronic wave packets deviate from the semiclassical picture of BO's ͓Eq. ͑1͔͒ if a fully quantum-mechanical calculation of the wave functions in the artificial semiconductor structure is used.6 Additionally, the amplitude of optically excited BO's depends on the exciting laser pulse width and energy that determine the initial conditions of the wave packets. Pathbreaking investigations on BO's have been performed in four-wave-mixing, 8,9 THz emission, 10 and resonant transmittive electro-optic sampling ͑TEOS͒ experiments.11 In recent years, the experimental determination of the spatial amplitude of the oscillating electronic wave packets has become an objective of the studies. The amplitude determination of BO's in a SL has been reported in a THz emission experiment.12 The amplitudes were calculated from the detected THz radiation power by applying a superradiance theory. Subsequently, the BO amplitude has been carefully determined in spectrally and time-resolved four-wave mixing experiments.13 Using this technique, the dependence of the amplitudes on the spectral position of the exciting laser pulses was investigated.14 Resonant TEOS experiments performed with optical detection spectrally integrated over WS transitions can only provide a qualitative analysis of the electronic dynamics due to nonlinearities of the electro-optic effect at the interband resonances.In this paper, we present the off-resonant electro-optic detection of Bloch oscillations in a GaAs/Al x Ga 1Ϫx As SL. BO's are excited resonantly, but detecte...

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Section: Blochmentioning

confidence: 95%

Midbandgap electro-optic detection of Bloch oscillations

et al. 2000

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“…We apply a one-dimensional semiclassical transport model and solve self-consistently the driftdiffusion equation and Poisson's equation along the superlattice growth direction z. 21 The electron mobility is taken as an extension of the well-known Esaki-Tsu semiclassical mobility: 1 e ͑z͒ = q⌬ e e d 2 /2ប 2 ͑1+͑q e dF͑z͒ / ប͒ 2 ͒, where F͑z͒ is the local electric field and e the momentum scattering time for electrons. The effective mobility of holes h is assumed to be independent of the field ͑an analysis considering both hh and lh nonlinear mobilites is under way͒.…”

Section: Time-resolved Photocurrent Spectroscopy Of the Evolution Of mentioning

confidence: 99%

Time-resolved photocurrent spectroscopy of the evolution of the electric field in optically excited superlattices and the prospects for Bloch gain

Lisauskas

Blöser

Sachs

et al. 2005

Applied Physics Letters

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We report on photocurrent spectroscopy on undoped GaAs/AlGaAs semiconductor superlattices subjected to femtosecond optical excitation. The evolution of the carrier-drift-induced inhomogeneity of the electric field is studied by tracing the shifting and broadening of Wannier-Stark transitions as a function of delay time and bias field. Based on experimental data and results of numerical simulations, we find that the superlattice rapidly splits into two moving field regions, one with strong field gradient and low electron density, the other with partially screened field at low gradient and high electron density. Concerning future Bloch-gain measurements, we find that gain is expected in spite of the inhomogeneous field if the electron-rich region is not heavily screened. The time window during which Bloch gain exists is determined by the sweep out of the electrons (10-30 ps)

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“…With an internal electric field of 6.4 kV cm −1 the oscillation frequency is about 1.7 THz. In contrast to measurements on InGaAs/InGaAs superlattices where the field is screened by incoherent electron transport [15], the frequency remains constant within the dephasing time. For the sake of clearness the transients are horizontally separated by an amount corresponding to the value of the excitation power.…”

Section: Resultsmentioning

confidence: 85%