Ultrafast heating of silicon on sapphire by femtosecond optical pulses

Downer, Michael; Shank, C. V.

doi:10.1103/physrevlett.56.761

Cited by 158 publications

(68 citation statements)

References 14 publications

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“…This results from the partial occupation of the final and initial states by the photoinjected electrons and holes, respectively, which decreases the absorption at all probe wavelengths and especially near the pump wavelength immediately after excitation. Instead, in the present experiments, we observe photoinduced absorption, which occurs either in indirect-gap semiconductors [23,24] or in amorphous semiconductors [7,25], and is indicative of Drude absorption by free carriers. This confirms recent theoretical [26] and experimental [27] work which also suggested that red-emitting porous silicon is an indirect band gap semiconductor.…”

Section: Resultsmentioning

confidence: 62%

Ultrafast Carrier Dynamics in Porous Silicon

Fauchet

1995

Physica Status Solidi (b)

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The carrier dynamics in porous silicon is investigated by two time-resolved techniques. The blue photoluminescence of oxidized porous silicon is measured with 100 ps time resolution as a function of the oxidation method, emission wavelength, excitation intensity, and measurement temperature. The blue luminescence has a distinct origin from the well-studied rcd luminescence and is attributed to defects in the oxide. Femtosecond photoinduced absorption measurements are performed on thin red-emitting porous silicon films. The wavelength and intensity dependence of the recovery are interpreted in terms of trapping and of Auger recombination at high excitation intensity. It is shown that red-emitting porous silicon is not a direct-gap semiconductor.

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Section: Resultsmentioning

confidence: 62%

Ultrafast Carrier Dynamics in Porous Silicon

Fauchet

1995

Physica Status Solidi (b)

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“…Through Auger processes (at a density of % 10 21 cm À3 ), which take place in a few ps, the carrier density decreases, but the total electronic energy remains unchanged. [13,30,31] The drop in the Coulombic potential along with electron-phonon coupling now drives the system in a reversed motion toward expansion (Figure 3 a). The expansion of the lattice requires 7 ps to define surface-layer temperature and this is evident in the rise of the intensity profile (Figure 3 b); only after this rise can we define the temperature acquired through electron-phonon coupling.…”

Section: Methodsmentioning

confidence: 94%

Ultrafast Electron Crystallography of Surface Structural Dynamics with Atomic‐Scale Resolution

et al. 2004

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Progress over the past two decades has made it possible to study atomic-scale femtosecond molecular dynamics in all phases of matter. The atomic-scale spatial resolution has been achieved with both X-ray and electron diffraction, and only recently has the combination of spatial and temporal resolution [1] been advanced successfully for studies of isolated chemical reactions by ultrafast electron diffraction [2,3] and bulk crystal phonons and melting [4][5][6][7][8][9][10][11][12] by X-ray diffraction. For surface structures and molecules on surfaces, ultrafast electron crystallography (UEC) is unique, and herein we demonstrate its potential for the direct determination of surface structural dynamics of crystalline solids (GaAs), following impulsive fs laser excitation. From the change of Bragg diffraction (shift, width, and intensity), we show, by direct inversion of the diffraction data, that compression and expansion of the atoms occur on the À 0.01 to +0.02 scale, respectively, and that the transient temperature reaches its maximum value (1565 K) in 7 ps. The onset of structural change lags behind the rise in the temperature, demonstrating the evolution of non-equilibrium structures. These structural dynamics results are compared with those of nonthermal fs optical probing, and the agreement for the temperature response from the fluence dependence of the dielectric function is impressive. [13,14] The success in the direct observation of surface (monolayers) structural dynamics with combined ultrafast temporal and atomic-scale spatial resolutions promises many new applications of UEC.GaAs is an ideal system to demonstrate this potential of UEC for surface studies, especially as its crystalline and semiconducting properties are well-quantified.[15] This has allowed a wide range of ultrafast optical experiments that vary from the probing of carrier properties [16] to electronic disordering or change in symmetry.[17] In addition to these optical studies, recent ultrafast X-ray experiments on GaAs revealed bulk lattice dynamics following fs laser excitation. [8] However, these ultrafast X-ray experiments could not probe the surface owing to the large penetration depth into the crystal by X-rays, typically up to several mm. On the other hand, optical techniques that probed the surface on the scale of a few nanometers could not directly determine the structure with atomic-scale resolution, but gave valuable information on the response of the dielectric function and lattice disordering. [13,14,17] The large scattering cross-section of electrons combined with ultrafast time resolution allows the bridging of this gap in addressing the dynamics of surface structures in real time.The experiments were performed in the newly developed UEC apparatus, [18] briefly as follows (Figure 1). Under ultrahigh vacuum (10 À10 Torr), and following surface characterization by low-energy electron diffraction and Auger spectroscopy, the sample was brought to the scattering position where beams of the laser-pulse excitation and electron-pu...

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“…As a result of the existence of these defects there will be absorption of photons corresponding to the energy of these states resulting in the generation of carriers. These photogenerated carriers will result in altering the "steady-state" absorption of the material through affects such as, state filling (SF) [10] or free carrier (FC) induced absorption [11] to higher energy states. SF is a consequence of the occupied available energy states by the photogenerated carriers resulting in a time dependant reduced absorption whose temporal dependence depicts the relaxation of these carriers out of the probing energy states.…”

Section: Discussion and Analysismentioning

confidence: 99%