Coherent surface phonon at aGaAs(100)−c(8×2)surface

Abstract

Coherent surface phonon at a GaAs(100)-c(8ϫ2)-Ga reconstructed surface has been investigated by timeresolved second-harmonic generation ͑TRSHG͒. The phonon mode is impulsively excited by an ultrashort laser pulse and subsequent coherent nuclear motion is monitored through the intensity modulation of the second harmonics of a probe pulse. Oscillatory traces are clearly observed in TRSHG signals and their Fourier transformation show two peaks at 8.2-8.6 and 8.9 THz. Fitting these traces with two oscillatory components shows that the oscillatory signals are contributed by the bulk LO phonon at 8.8 THz and the surface phonon at 6.0-8.6 THz. The relative amplitude of the surface phonon modes is sensitive to sputtering and annealing of the surface. Clear dips appear at 8.7 THz in the Fourier spectra, which is caused by the initial phase difference between the surface phonon and the bulk phonon modes. The frequency of the surface component shows red shifts as the pumping power increases. The shifts are indicative of a marked electron phonon interaction or anharmonicity of the surface phonon modes.

Coherent Vibrations of Adsorbates Induced by Femtosecond Laser Excitation

“…The peak is significantly reduced by Ar + -ion sputtering and annealing, indicating that TRSHG is sensitive to the coherent phonon modes in a few monolayers of the surface. A similar surface sensitivity also has been demonstrated for GaAs(100)-c(8 × 2) 5 TRSHG trace from native-oxide-covered GaAs(100).…”

“…A similar surface sensitivity also has been demonstrated for GaAs(100)-c(8 × 2). 127 As pointed out in Section 3.5, the excitation mechanism for coherent phonons observed on those semiconductor surfaces is attributed to DECP associated with carrier-induced screening of the depletion field. In fact, the Fourier power spectrum of the oscillatory part in a TRSHG signal depends on pump fluence, i.e., the injected carrier density.…”

“…TRSHG was first applied to GaAs surfaces by Tom and co-workers 55 and proved to be very versatile for the investigation of coherent motions of ions near the surface and interface regions. This method also has been applied to various GaAs surfaces in ultrahigh vacuum conditions, including GaAs(110)-(1 × 1), -(1 × 6), -(4 × 6) and -(4 × 1), ,, and GaAs(100)-c(8 × 2) …”

Phonon damping in ferromagnetic semiconducting thin films

“…For CdCr 2 Se 4 the first case is more realistic. At a solid surface, the crystal symmetry is broken, and the anharmonicity is expected to be a factor of 2-3 greater than in the bulk as shown experimentally by Baddorf and Plummer [17] and Watanabe et al [18]. In Ref.…”

Applications of Time‐Domain Spectroscopy to Electron–Phonon Coupling Dynamics at Surfaces

“…Ultrafast screening of the surface depletion field by photoexcited carriers creates LO‐phonon–plasmon modes . Coherently excited phonon modes were observed on various semiconductor surfaces including GaAs, InN, and Bi 2 Te 3 . As described in the Introduction, at metal surfaces the empty electronic level of a molecule hybridizes with metal electronic states as the molecule approaches the surface.…”