Femtosecond Excitation of Nonthermal Carrier Populations in GaAs Quantum Wells

Knox, Wayne H.; Hirlimann, Charles; Miller, D. A. B.; Shah, Jagdeep; Chemla, D. S.; Shank, C. V.

doi:10.1103/physrevlett.56.1191

Cited by 401 publications

(110 citation statements)

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“…In bulk GaAs it is known that under high densities of excitation, carriercarrier scattering plays an important role in the thermalization of hot carriers (carriers with high excess energy with respect to the bottom of the conduction or valence band [3]), and it has been shown with both photon echo [4] and time-resolved polarization rotation measurements 2 [5,6] that it is also the dominant mechanism for momentum redistribution. In QW structures the carrier therrnalization has been extensively studied in undoped [7,8] and doped [9,10] structures, where the imponance of collisions between carriers was found to be the main process for the redistribution of energy through inelastic carrier-carrier scattering.Recent work [8,9,10] has also shown that phase space filling due to the Pauli exclusion principle dominates over the long-range Coulomb screening in bleaching of the exciton. This was clearly demonstrated by the appearance of exciton bleaching only when the carriers occupy the lowest energy states of the fIrst QW sub-band.…”

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“…Recent work [8,9,10] has also shown that phase space filling due to the Pauli exclusion principle dominates over the long-range Coulomb screening in bleaching of the exciton. This was clearly demonstrated by the appearance of exciton bleaching only when the carriers occupy the lowest energy states of the fIrst QW sub-band.…”

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“…The fast decay times deduced from our dara are consistent with the fact that the phase coherence between an electron and a hole is lost long before the carrier thermalization is reached. Thermalization of an initial non-thermal carrier distribution is known to occur on a time scale of 200 fs in similar QW structures [8].…”

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Two-dimensional carrier-carrier screening in a quantum well

et al. 1991

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Abstract:The behavior of carrier-carrier screemng IS investigated in a GaAs-GaAIAs quantum well structure by measuring the band-to-band polarization dephasing with femtosecond photon echoes. The variation of the electron-hole polarization dephasing time with the carrier concentration reveals the two-dimensional character of the short range screening between the interacting carriers. 1The phase coherence time between an electron and the corresponding hole created during a band-to-band optical transition in a semiconductor decreases with increasing carrier density due to the effects of carrier-carrier scattering. At low carrier densities, ignoring the Coulomb interaction between carriers, the carrier-carrier scattering time is expected to scale inversely with the carrier density. At higher densities, screening due to the Coulomb potential of the charged particles will act to suppress the process of carrier-carrier scattering. Coulomb screening, which was originally studied in metals [1], depends on the electron and hole environment and therefore is a function of the dimensionality of the system under study.We report here measurements that show the influence of carrier-carrier interactions on the dephasing processes which occur in a GaAs-GaAlAs Quantum Well (QW) structure. Due to the confmement of the carriers in the well, they are expected to behave like a two-dimensional (2D) electron gas. Indeed, our measurements performed at different carrier densities indicate a screening behavior that reveals the bi-dimensionality of the system. The 2D screening that we deduce from the experiment is well understood if we assume that a given carrier interacts only with its nearest neighbors, indicating that the range of the screened Coulomb interaction is of the order of the average inter-carrier spacing. We discuss the validity of this nearest-neighbor interaction picture with respect to the experimental conditions in which a nonequilibrium, nondegenerate electron-hole population is created over a large range of energies and wave vectors.Femtosecond optical spectroscopy now allows the dynamics of energy relaxation and dephasing of excited carriers in bulk semiconductors or 2D QW structures to be studied with 10 fs resolution [2]. In bulk GaAs it is known that under high densities of excitation, carriercarrier scattering plays an important role in the thermalization of hot carriers (carriers with high excess energy with respect to the bottom of the conduction or valence band [3]), and it has been shown with both photon echo [4] and time-resolved polarization rotation measurements 2 [5,6] that it is also the dominant mechanism for momentum redistribution. In QW structures the carrier therrnalization has been extensively studied in undoped [7,8] and doped [9,10] structures, where the imponance of collisions between carriers was found to be the main process for the redistribution of energy through inelastic carrier-carrier scattering.Recent work [8,9,10] has also shown that phase space filling due to the Pauli exclusion principle...

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Two-dimensional carrier-carrier screening in a quantum well

et al. 1991

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“…Laser ablation of material is a complex process involving several phases and multiple length and time scales [2,3,4]. Ultrashort laser pulses are especially promising for micromachining of various materials, since high energy density can be transferred to the materials in such a short timeframe, that thermal effects on the material are minimal.…”

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Periodic surface structure creation by UV femtosecond pulses on silicon

Gilicze¹,

Moczok²,

Madarász³

et al. 2017

AIP Conference Proceedings

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Abstract. Laser-induced periodic surface structures are created on Si (100) and Si (111) wafers by 500 fs laser pulses at 248 nm. The periodic structure is concentric and highly regular. The spatial period is consistently varying between 1.1 μm and 3.3 μm in the radial direction. It is shown that the fluence of the irradiation at the same pulse number determines the size of the area where the periodic structure is created and for the same fluence the pulse number determines the regularity of the created grooves by melting processes. The origin of this structure is identified as the inhomogeneity of the laser beam profile caused by Fresnel diffraction close to the focal plane. Further improvement of the formation of periodic structure with femtosecond laser pulses is suggested.

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“…This assumption is justified at electron densities above 10 18 cm-3 based on both theoretical considerations and experimental evidence . 19 Although this assumption may not be valid at lower densities; it does not affect the rate at which LO phonons are produced. The cooling of the electron and LO phonon temperatures calculated within this single conduction band valley model are shown as continuous curves in Fig.…”

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Subpicosecond Raman Study of Hot Electrons and Hot Phonons in GaAs

Kim

1991

Light Scattering in Semiconductor Structures and Superlattices

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Femtosecond Excitation of Nonthermal Carrier Populations in GaAs Quantum Wells

Cited by 401 publications

References 16 publications

Two-dimensional carrier-carrier screening in a quantum well

Two-dimensional carrier-carrier screening in a quantum well

Periodic surface structure creation by UV femtosecond pulses on silicon

Subpicosecond Raman Study of Hot Electrons and Hot Phonons in GaAs

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