Subpicosecond carrier transport in GaAs surface-space-charge fields

Dekorsy, Thomas; Pfeifer, T.; Kütt, W.; Kurz, H.

doi:10.1103/physrevb.47.3842

Cited by 195 publications

(143 citation statements)

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“…5(d)], indicating the direct relation between the generation and the photoexcited carrier density. B. Pump-polarization dependence at the E0 gap Kurz and coworkers examined the generation mechanisms of the coherent phonons in GaAs by changing the surface fields with external voltage 7,8 . The dependence of the phonon amplitude on the applied field was consistent with the TDFS excitation mechanism.…”

Section: Resultsmentioning

confidence: 99%

“…(7) reproduced well the carrier density dependent frequency by assuming a large plasmon damping, γ > 9 THz 20,21 . At hole densities below 2 × 10 18 cm −3 , the LO-hole coupled mode was not observed as a distinct mode either in Raman scattering 20 or as a coherent oscillation in transient reflectivity 7,8 , because its frequency is very close to Ω LO .…”

Section: Lopc Mode In the Depletion Layermentioning

confidence: 99%

“…(3) describes the ultrafast drift-diffusion current in the surface normal direction j in the presence of surface built-in field within the depletion or accumulation layer of a doped semiconductor. This current can launch coherent phonons polarized along the j direction via ultrafast screening of the built-in field (TDFS mechanism) [6][7][8] . The excitation via TDFS requires photoexcitation of carriers at sufficient density for screening of the field, but does not depend explicitly on the direction of the pump electric field for a zinc blende crystal 7 .…”

Section: Theoretical Background a Generation And Detection Of Comentioning

confidence: 99%

“…The coherent optical phonons have been observed as a periodic modulation in the THz frequency range, most conveniently by linear and non-linear optical techniques 1,2 . The generation mechanisms of the coherent phonons have been studied extensively in a variety of crystals and attributed, depending on the nature of the electron-phonon interaction, to impulsive stimulated Raman scattering (ISRS) 3,4 , displacive excitation of coherent phonons (DECP) 5 , and transient depletion field screening (TDFS) [6][7][8] . The time evolution of coherent phonons is in general determined by the phonon anharmonicity (phonon-phonon scattering) 9 and scattering by defects 10 .…”

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confidence: 99%

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Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

2011

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Detection mechanisms of coherent phonons in variously doped GaAs are investigated by transient reflectivity method with photoexcitation near the E0 gap and probe near either the E0 or E1 gaps. By varying the probe light polarization angle, the coherent amplitudes of both the LO phonon and the LO phonon-plasmon coupled (LOPC) modes show evidence for an interference between their anisotropic and isotropic dielectric response components. We attribute the anisotropic and isotropic components to the reflectivity modulation by lattice and electronic polarizations via dipole-allowed and dipole-forbidden Raman scattering processes. The forbidden processes are resonantly enhanced at the E0 and E1 critical points due to the relaxation of momentum conservation and the strong built-in electric field near the surface. The relative contribution of the anisotropic and isotropic components depends on the modes (LO or LOPC) as well as the probe wavelength (E0 or E1), because of the different Raman scattering mechanisms involved. Reflectivity measurements with the near ultraviolet light, which is used to probe the E1 gap, also enable highly surface sensitive detection of ultrafast LO phonon-plasmon dynamics, which is strongly depth-dependent in the depletion layer of n-doped GaAs.

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Section: Resultsmentioning

confidence: 99%

Section: Lopc Mode In the Depletion Layermentioning

confidence: 99%

Section: Theoretical Background a Generation And Detection Of Comentioning

confidence: 99%

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confidence: 99%

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Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

2011

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“…After above-band-gap photoexcitation, electrons and holes homogeneously generated in the NW bulk are radially separated by the surface field, leading to radial photocurrents j e and j h , respectively. This carrier separation, however, transiently reduces the surface band bending due to screening of the space charge fields 30 , leading to a transient shift of the vacuum level, indicated by the red shaded area in Fig. 3d.…”

Section: Experimental Conceptmentioning

confidence: 99%

Femtosecond electrons probing currents and atomic structure in nanomaterials

Müller¹,

Paarmann²,

Ernstorfer³

2014

Nat Commun

120

158

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The investigation of ultrafast electronic and structural dynamics in low-dimensional systems such as nanowires and two-dimensional materials requires femtosecond probes providing high spatial resolution and strong interaction with small volume samples. Low-energy electrons exhibit large scattering cross-sections and high sensitivity to electric fields, but their pronounced dispersion during propagation in vacuum so far prevented their use as femtosecond probe pulses in time-resolved experiments. Here, employing a laser-triggered point-like source of either divergent or collimated electron wave packets, we developed a hybrid approach for femtosecond point projection microscopy and femtosecond low-energy electron diffraction. We investigate ultrafast electric currents in nanowires with sub-100 femtosecond temporal and few 10 nm spatial resolutions, and demonstrate the potential of our approach for studying structural dynamics in crystalline single-layer materials.

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Electron Transfer Investigated by X‐Ray Spectroscopy

Würth

Föhlisch

2010

Dynamics at Solid State Surfaces and Interfaces

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Electron transfer at surfaces and interfaces plays an important role in many different processes such as catalytic, biophysical, electrochemical, and photoinduced reactions, molecular electronics, and solar energy conversion. Transfer can occur either resonantly or inelastically, involving more than one electron. Transfer processes occur typically on femtosecond and subfemtosecond timescales for systems where the available density of states is high such as metals. To study the fundamental aspects of the dynamics of electron transfer, it is convenient to create an electron wave packet by photoexcitation and follow its evolution by suitable probe techniques. X-rays are particularly well suited in this respect because they allow site-and element-specific localized excitations in complex systems, lead to direct excitation to a specific state, and can probe the subsequent evolution of this particular state.In this chapter, we will focus on two very different approaches using soft X-rays to investigate electron transfer, namely, high-resolution core hole spectroscopy at thirdgeneration synchrotron sources, the so-called core hole clock method [1-3], and stroboscopic pump-probe experiments using ultrashort X-ray pulses from free electron laser sources. The examples that are chosen to illustrate the potential of X-ray spectroscopy to study electron transfer are taken exclusively from our own recent work. Hence, this is by no means meant to be an extensive and representative review of the field. Core Hole Clock SpectroscopyThe term core hole clock spectroscopy reflects the fact that in this type of spectroscopy, the intrinsic lifetime of a core hole state is used as an internal reference against which competing relaxation processes are timed. Basically, the decay of a resonantly excited core hole state is studied spectroscopically (excellent reviews with many references can be found in the literature [4][5][6][7]). We will discuss here only the nonradiative decay channels, which for core hole states created by the absorption of soft X-rays represent the majority of decay channels.

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Subpicosecond carrier transport in GaAs surface-space-charge fields

Cited by 195 publications

References 21 publications

Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

Femtosecond electrons probing currents and atomic structure in nanomaterials

Electron Transfer Investigated by X‐Ray Spectroscopy

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