Dynamics of Photoexcited GaAs Band-Edge Absorption with Subpicosecond Resolution

Shank, C. V.; Fork, R. L.; Leheny, R. F.; Shah, Jagdeep

doi:10.1103/physrevlett.42.112

Cited by 320 publications

(86 citation statements)

References 7 publications

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“…Therefore, the recombination is dominated by the photo-excited electron dynamics in the n-type GaAs. In our previous reports [4,5], it was supposed that the fast decay component is due to the hot electron relaxation in the conduction band because Shank et al reported that the hot carrier distribution approaches to the lattice temperature with a similar time constant of approximately 4 ps [10]. The present experiment shows that the lifetime of the fast decay component was hardly affected by the dopant level, laser power, and sample temperature which change the barrier height of the surface potential and the depth of the band bending region, in other words, the space charge region (SCR).…”

Section: Discussionmentioning

confidence: 98%

Dynamics of photo‐excited carriers on GaAs(100) surface studied by ultrafast time‐resolved photoemission

Azuma

Tokudomi

Takahashi

et al. 2008

Phys. Status Solidi (c)

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Dynamics of the photo‐excited carriers on the GaAs(100) surface have been studied by measuring the surface photo‐voltage effect (SPV) with the ultrafast time‐resolved photoemission spectroscopy. The fast SPV decay with a few picosecond lifetime has been observed on the n ‐type GaAs(100) surface. The lifetime of the fast decay component was almost independent with dopant levels, pump powers, and sample temperatures which mainly change the surface potential barrier in the band bending region. This result supports the SPV relaxation model of the hot electron because the time scale of the electron thermalization is considered to be less affected by the change of the surface potential barrier. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Section: Discussionmentioning

confidence: 98%

Dynamics of photo‐excited carriers on GaAs(100) surface studied by ultrafast time‐resolved photoemission

Azuma

Tokudomi

Takahashi

et al. 2008

Phys. Status Solidi (c)

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“…These observations were noted to be consistent with a simple mechanism in which photointerconversion ofthe isomers occurs via a common twisted excited singlet state intermediate.11 Other workers have also suggested that the photoisomerizations of BR and other pyrrole pigments are "singlet state" reactions (5,6,23 Fluorescence quantum yields for BR were calculated from the integrated fluorescence spectra in comparison with the spectra from solutions of acridine yellow in ethanol at 22°C, for which a yield of 0.86 was previously determined (24 Picosecond Time-Resolved Spectroscopy. The apparatus used in these experiments, described in detail elsewhere, is based on a continuous-wave-pumped, passively mode-locked picosecond dye laser, producing 0.5-ps pulses at 610 nm (25,26). Mode-locked pulses, dumped from the dye laser cavity at 11 Hz, were amplified to an energy of 0.5-1.0 mj per pulse by using a three-stage dye laser amplifier pumped with the second harmonic of a Q-switched Nd:yttrium-aluminum garnet laser.…”

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confidence: 99%

Picosecond primary photoprocesses of bilirubin bound to human serum albumin.

Greene¹,

Lamola²,

Shank³

1981

Proc. Natl. Acad. Sci. U.S.A.

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We measure the fluorescence quantum yield of bilirubin bound to its highest-affinity site on human serum albumin to increase from about 0.001 near room temperature to 0.5 at 77 K. The quantum yield for configurational (Z -+ E) photoisomerization about the meso double bonds concomitantly decreases from about 0.22 to less than 0.01 over the same temperature range in reciprocal relationship to the fluorescence yield. Transient absorption spectra recorded after excitation with a 0.5-ps pulse of 305-nm light decay with a lifetime of 19 ± 3 ps at 220C and 35 ± 7 ps at 2TC. Bilirubin undergoes the same photoisomerization reaction in chloroform solution, in which a similar short-lived (17 ± 3 ps at 220C) transient is observed. From these and other data we conclude that configurational isomerization of bilirubin is the predominant nonradiative pathway that competes with pigment fluorescence, that photoisomerization proceeds via a short-lived (< < 18 ps) partially twisted excited-singlet-state intermediate, and that bilirubin remains relatively unihibited with respect to photoisomerization when bound to human serum albumin.Primary photoprocesses of bilirubin (BR), the product of heme catabolism in humans, is an active area of investigation because of its relevance to the phototherapy of hyperbilirubinemia of the newborn (1). In this therapy jaundiced infants are irradiated with bright visible light, preferably in the blue, in order to reduce the concentration of serum BR and lower the risk of BRassociated brain damage.Electronic relaxation of photoexcited BR in solution near room temperature is dominated by radiationless decay from the exicted singlet manifold to the gound state. This is evidenced by observations of low fluorescence yields (Of < 5 X 10-4) (2, 3), low yields of triplet states (<0.01) (4-6), and the absence of efficient bleaching of the chromophore (7). The same situation pertains to BR bound to the high-affinity site on human serum albumin (hereafter referred to as "albumin") (If = 0.002) (2, 3,5 (15,16). Principles governing the rate of twisting would be those determining diffusional motion of nuclei on an intramolecular potential surface (17)(18)(19). BR contains ethylenic linkages that may effect such relaxation. Although associated spectral changes were observed several years ago (20), the efficient photoisomerization of BR, both in organic solvents and while bound to albumin, was recognized only very recently (1, 21, 22, §). The photoisomerization product, which is a mixture, is called photobilirubin (PBR). The similarity of the optical spectra of BR and PBR and their observed interconversion both thermally and photochemically indicate that PRB consists of one or more E isomers of BC (22, §).Lamola and coworkers have investigated the photoisomerization of BR bound to albumin in buffered saline at room temperature by various spectroscopic methods. §11 They reported that under proper experimental conditions it is possible to observe a photoequilibrium between BR-albumin and PBR-albumin. The fra...

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“…Much attention has been focused on the nonlinear optical response near the bandgap of semiconductors, both for device application and physical insight. In particular, the large nonlinearity of excitons confined in quantum well structures was extensively studied theoretically and experimentally [4][5][6][7][8]. Quasi-two-dimensional excitons in quantum well structures gave rise to the strong nonlinear response in the vicinity of the bandgap.…”

Section: Introductionmentioning

confidence: 99%