Time-resolved second-harmonic study of femtosecond laser-induced disordering of GaAs surfaces

Govorkov, Sergei V.; Shumay, I. L.; Rudolph, W.; Schröder, T.

doi:10.1364/ol.16.001013

Cited by 55 publications

(23 citation statements)

References 10 publications

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“…Experiments were performed on Bi 2 Se 3 thin films that were 6,8,10,12,15,20,25,30,35, and 40 nm thick. The films were grown on 0.5 mm Al 2 O 3 (0001) substrates by molecular beam epitaxy, with a 10 nm thick MgF 2 capping layer to protect against oxidation.…”

Section: Methodsmentioning

confidence: 99%

“…One of the most intriguing effects regarding the SHG sensitivity to interfaces is the laser-induced phase transitions in semiconductors with either diamond (Si) or zinc-blende (GaAs) lattice structure, which has been the scope of intensive experimental and theoretical studies since the discovery of pulsed-laser annealing [8][9][10][11][12][13][14][15][16][17][18]. Because Si is a centrosymmetric semiconductor, the electric-dipole contribution to the SHG process is allowed by symmetry only at the surface of the crystal.…”

Section: Introductionmentioning

confidence: 99%

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Resonance-type thickness dependence of optical second-harmonic generation in thin films of the topological insulatorBi2Se3

et al. 2015

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Optical second-harmonic generation (SHG) has been measured in a reflection from the nanometer-thick films (6 to 40 nm) of the topological insulator Bi 2 Se 3 using 1.51 eV (820 nm) Ti:Sapphire laser photons and revealed a strong dependence of the integral SHG intensity on the film thickness. The integral SHG intensity was determined by area integration of the SHG rotational anisotropy patterns measured for different input-output light polarization geometries. A ∼100-fold enhancement of the integral SHG intensity with decreasing film thickness has been suggested to result from the dc-electric-field-induced SHG (EFISHG) effects. Two sources of dynamically created dc electric field were proposed: (i) the capacitor-type dc electric field that gradually increases with decreasing film thickness from 40 to 6 nm due to a dynamical imbalance of photoexcited long-lived carriers between the opposite-surface Dirac surface states and (ii) a dc electric field associated with a nonlinearly excited Dirac plasmon, which is responsible for the resonant enhancement of the integral SHG intensity for the 10 nm thick film with a Lorentz-shaped resonance of ∼1.6 nm full width at half maximum. In addition to the general SHG enhancement trends with decreasing film thickness, a relative decrease of the out-of-plane contribution with respect to the in-plane contribution was observed. Using a theoretical treatment of the measured SHG rotational anisotropy patterns, this effect has been suggested to result from the joint contributions of the linear and quadratic dc electric field effects to the EFISHG response.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Resonance-type thickness dependence of optical second-harmonic generation in thin films of the topological insulatorBi2Se3

et al. 2015

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“…Several conclusions can be drawn from this observation. The system disorders; however, the hypothesis [1,4,5] that this happens while the lattice remains relatively cold can be rejected. Furthermore, melting does not proceed via a mechanical instability due to phonon softening [1,15].…”

Section: (Received 21 May 1996)mentioning

confidence: 99%

“…However, for very short irradiation times ͑ϳ100 fs͒, recent time-resolved experiments have strongly strengthened the PA model. In fact several groups [4] have observed laser-induced melting of a GaAs crystal under high laser irradiation. Tom, Aumiller, and Brito-Cruz [5] have reported a loss of cubic order in crystalline Si only 150 fs after an intense 100 fs optical pulse.…”

Section: (Received 21 May 1996)mentioning

confidence: 99%

Ab initioMolecular Dynamics Simulation of Laser Melting of Silicon

et al. 1996

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The method of ab initio molecular dynamics, based on finite temperature density functional theory, is used to simulate laser heating of crystal silicon. We have found that a high concentration of excited electrons dramatically weakens the covalent bond. As a result, the system undergoes a melting transition to a metallic state. In contrast to ordinary liquid silicon, the new liquid is characterized by a high coordination number and a strong reduction of covalent bonding effects. [S0031-9007(96)01372-5] PACS numbers: 61.20. Ja, 64.70.Dv, 65.50.+m The phenomenon of laser-induced annealing in semiconductors has attracted, over the years, considerable attention and contradictory explanations [1,2]. One of the first attempts to explain the observed phenomenology has been the "plasma annealing" (PA) model [1]. In this model it is suggested that a tetrahedral semiconducting material, subject to intense laser irradiation, can be driven directly into a disordered state, long before the system has time to become vibrationally excited. In fact, laser irradiation induces electronic transitions from the bonding to the antibonding states, thus depleting the bond charges. A high level of electronic excitation could severely weaken the interatomic bonds so that room temperature atomic motions can lead to the disordering of the lattice. The alternative explanation [2] was that direct energy transfer between the excited electrons and the ions leads to ordinary thermal melting (TM).For laser pulses lasting 20 ps and longer, TM appears to be [2,3] the dominant mechanism. However, for very short irradiation times ͑ϳ100 fs͒, recent time-resolved experiments have strongly strengthened the PA model. In fact several groups [4] have observed laser-induced melting of a GaAs crystal under high laser irradiation. Tom, Aumiller, and Brito-Cruz [5] have reported a loss of cubic order in crystalline Si only 150 fs after an intense 100 fs optical pulse. Shank, Yen, and Hirlimann [6] have observed melting of silicon on a time scale of less than 1 ps after a 90 fs pump pulse, as evidenced by reflectivity and second-harmonic generation. In spite of this strong experimental evidence, a clear understanding of the processes that take place is still missing.Since reasonable estimates [7] suggest that the relaxation time for the electrons, t ee ϳ10 214 sec, is much shorter than the electron-ion relaxation time, t eI ϳ10 212 sec, we can treat the subsystems of electrons and ions in a different way. We assume that, after irradiation and for times smaller than t eI , the electron subsystem remains in internal equilibrium at the initial laser-induced temperature, which is different from that of the ions. The ions instead are allowed to evolve freely. In order to describe this situation we used the ab initio molecular dynamics (MD) simulation technique introduced by Alavi et al. [8]. This method is based on finite temperature density functional theory (DFT), and incorporates self-consistently the effects of thermal electronic excitations and fractiona...

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“…Many studies have been performed to characterize and understand temporal evolution of GaAs properties upon intense optical laser excitation. For instance, several all-optical pump-probe experiments were carried out to investigate nature of high-speed melting3031 and to characterise nonlinear optical absorption phenomena32. While numerous studies have been performed to characterize free carrier generation and relaxation dynamics in multi-photon absorption regimes, it is still primarily unknown how they alter lattice properties of the material.…”

mentioning

confidence: 99%

Direct measurements of multi-photon induced nonlinear lattice dynamics in semiconductors via time-resolved x-ray scattering

Williams

Lee

Walko

et al. 2016

Sci Rep

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Nonlinear optical phenomena in semiconductors present several fundamental problems in modern optics that are of great importance for the development of optoelectronic devices. In particular, the details of photo-induced lattice dynamics at early time-scales prior to carrier recombination remain poorly understood. We demonstrate the first integrated measurements of both optical and structural, material-dependent quantities while also inferring the bulk impulsive strain profile by using high spatial-resolution time-resolved x-ray scattering (TRXS) on bulk crystalline gallium arsenide. Our findings reveal distinctive laser-fluence dependent crystal lattice responses, which are not described by previous TRXS experiments or models. The initial linear expansion of the crystal upon laser excitation stagnates at a laser fluence corresponding to the saturation of the free carrier density before resuming expansion in a third regime at higher fluences where two-photon absorption becomes dominant. Our interpretations of the lattice dynamics as nonlinear optical effects are confirmed by numerical simulations and by additional measurements in an n-type semiconductor that allows higher-order nonlinear optical processes to be directly observed as modulations of x-ray diffraction lineshapes.

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Time-resolved second-harmonic study of femtosecond laser-induced disordering of GaAs surfaces

Cited by 55 publications

References 10 publications

Resonance-type thickness dependence of optical second-harmonic generation in thin films of the topological insulatorBi2Se3

Resonance-type thickness dependence of optical second-harmonic generation in thin films of the topological insulatorBi2Se3

Ab initioMolecular Dynamics Simulation of Laser Melting of Silicon

Direct measurements of multi-photon induced nonlinear lattice dynamics in semiconductors via time-resolved x-ray scattering

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