Transient gratings and second-harmonic probing of the phase transformation of a GaAs surface under femtosecond laser irradiation

Govorkov, Sergei V.; Schröder, T.; Shumay, I. L.; Heist, P.

doi:10.1103/physrevb.46.6864

Cited by 46 publications

(28 citation statements)

References 7 publications

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“…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%

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: 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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“…The existence of nonthermal, ultrafast phase transitions after strong femtosecond laser excitation has been demonstrated in several materials such as silicon [1][2][3], gallium arsenide [3][4][5][6], indium antimonide [7], and carbon [8]. It is accepted that such transitions are induced by a softening of the lattice structure due to the generation of a very high density electron-hole plasma, as first proposed by Van Vechten [9].…”

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confidence: 97%

Dynamics of Ultrafast Phase Changes in Amorphous GeSb Films

et al. 1998

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Time resolved imaging has been used to analyze structural transformations induced by intense 100 fs laser pulses in amorphous GeSb films. Above a threshold of 19 mJ͞cm 2 the data show the formation of a transient nonequilibrium state of the excited material within 300 fs. The results are consistent with an electronically induced, amorphous-to-crystalline phase transition. [S0031-9007(98) PACS numbers: 61.80. Ba, 61.43.Dq, 68.35.Bs, 68.35.Rh The existence of nonthermal, ultrafast phase transitions after strong femtosecond laser excitation has been demonstrated in several materials such as silicon [1][2][3], gallium arsenide [3-6], indium antimonide [7], and carbon [8]. It is accepted that such transitions are induced by a softening of the lattice structure due to the generation of a very high density electron-hole plasma, as first proposed by Van Vechten [9]. Most of the experimental and theoretical work [10][11][12][13] has concentrated on the solid-to-liquid phase transformation of the above mentioned materials. Some authors [2,11] have also claimed the existence of an ultrafast solid-to-solid phase transition preceding nonthermal melting, although there is experimental evidence [3,7] refusing this hypothesis.In this Letter we present a time resolved study on the dynamics of femtosecond laser induced structural transformations in amorphous GeSb. We describe experimental evidence for the subpicosecond formation of a transient phase of the material and interpret our results as first indication for an ultrafast, nonthermal amorphousto-crystalline phase transition. Sb-rich amorphous GeSb films can be crystallized upon irradiation with ultrashort laser pulses [14] and show a large optical contrast upon transformation [15]. This effect makes GeSb a promising material for the development of rewritable optical memories driven by ultrashort laser pulses [16]. Recently, it has been demonstrated [17] that the energy fluence necessary to induce crystallization in this material decreases significantly for pulses shorter than a picosecond, suggesting the relevance of electronic processes in the amorphousto-crystalline transition.Amorphous Ge 0.06 Sb 0.94 , 50-nm-thick films were grown on glass substrates at room temperature in a multitarget dc magnetron sputtering system from pure (99.999%) Ge and Sb targets. The films were irradiated with 100 fs laser pulses at 620 nm delivered by a 10-Hz amplified colliding-pulse mode-locked (rhodamine 6G͞DODCI) dye laser. The evolution of the reflectivity of the irradiated surface was monitored with both femtosecond time and micrometer spatial resolution by means of ultrafast time-resolved microscopy [18]. A first laser pulse excites the sample. A second time-delayed probe pulse replaces the standard illumination of an optical microscope and provides snapshot pictures of the excited surface with 100 fs time resolution. The optical micrographs are recorded with the help of a charged coupled device detector in conjunction with a computer controlled frame-grabber. Since a single laser pu...

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“…For a carrier density above 20%, disordering occurs too fast to be accounted for by inertial motion, consistent with a carrier driven lattice instability and a repulsive potential. The abrupt onset of potential softening and the appearance of a repulsive potential energy surface at high carrier densities had been predicted by theory [5][6][7], but had not been confirmed by prior experiment [3,10,11,15]. The inertial dynamics observed for a wide range of carrier density can be qualitatively accounted for with a classical Debye model where the crystal dynamics originate from a uniform softening of the phonon distribution.…”

Section: Institut Für Experimentelle Physik Universität Duisberg-essmentioning

confidence: 60%

“…Theoretical, experimental, and simulation studies of these systems indicate that extreme carrier densities destabilize the crystal structure and lead to nonthermal melting [3,[5][6][7][8][9][10][11][12][13][14][15][16][17]. Theoretical studies predict a rapid reduction in the shear restoring force when the excited carrier density exceeds a few percent of the valence band electron density [5][6][7].…”

Section: Institut Für Experimentelle Physik Universität Duisberg-essmentioning

confidence: 99%

Carrier-Density-Dependent Lattice Stability in InSb

Hillyard¹,

Gaffney²,

Lindenberg³

et al. 2007

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The ultrafast decay of the x-ray diffraction intensity following laser excitation of an InSb crystal has been utilized to observe carrier dependent changes in the potential energy surface. For the first time, an abrupt carrier dependent onset for potential energy surface softening and the appearance of accelerated atomic disordering for a very high average carrier density have been observed. Inertial dynamics dominate the early stages of crystal disordering for a wide range of carrier densities between the onset of crystal softening and the appearance of accelerated atomic disordering. DOI: 10.1103/PhysRevLett.98.125501 PACS numbers: 63.20.Kr, 61.10.ÿi, 64.70.Dv, 78.47.+p First-order phase transitions and chemical reactions require crossing a transition state on the potential energy surface (PES). Characterizing the topography of the energy landscape in the vicinity of the transition state represents the key step to understanding the pathway followed during a chemical reaction or first-order phase transition. The experimental and theoretical characterization of these far from equilibrium regions of the PES has proven to be very difficult because of the vanishingly short time spent near the transition state and the multitude of degrees of freedom that influence chemical and physical transformations in the condensed phase. Time-resolved x-ray scattering experiments provide a window for observing the structural dynamics that occur during certain physical transformations. This is achieved by using femtosecond (fs) x-ray pulses to monitor laser initiated dynamics, selectively track the time-dependent evolution of nonequilibrium atomic structures, and extract the shape of a photoinduced PES [1][2][3][4].This approach has proven crucial to investigating the influence of carrier excitation on the stability of tetrahedrally bonded semiconductors. Theoretical, experimental, and simulation studies of these systems indicate that extreme carrier densities destabilize the crystal structure and lead to nonthermal melting [3,[5][6][7][8][9][10][11][12][13][14][15][16][17]. Theoretical studies predict a rapid reduction in the shear restoring force when the excited carrier density exceeds a few percent of the valence band electron density [5][6][7]. A further doubling of the carrier density eliminates the shear restoring force, transforms the room temperature potential energy minimum into a saddle point, and leads to accelerated atomic disordering.The initial ultrafast x-ray diffraction studies of laserexcited InSb at the Sub-Picosecond Pulse Source (SPPS) determined that inertial atomic displacements on a lasersoftened potential energy surface dominate the response to intense optical excitation during the first 500 fs for a range of laser fluences [3]. This predominance of inertial dynamics in a wide fluence range had not been predicted by either theory or simulation. While the studies of Lindenberg et al. [3] and Gaffney et al. [15] covered the mean carrier density range over which theory predicted crystal stability to r...

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Transient gratings and second-harmonic probing of the phase transformation of a GaAs surface under femtosecond laser irradiation

Cited by 46 publications

References 7 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

Dynamics of Ultrafast Phase Changes in Amorphous GeSb Films

Carrier-Density-Dependent Lattice Stability in InSb

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