Showing papers on "Photoexcitation published in 1985"
TL;DR: In this article, the authors combine electron paramagnetic resonance under optical excitation, deep level transient spectroscopy, electron irradiation, annealing, and quenching on LEC semi-insulating GaAs and lightly Si-doped material grown in the same way as the semiinsulating material.
Abstract: Combining electron paramagnetic resonance under optical excitation, deep level transient spectroscopy, electron irradiation, annealing, and quenching on LEC semi‐insulating GaAs and lightly Si‐doped material grown in the same way as the semi‐insulating material, we have shown that (i) the irradiated material contains two types of defects related to the antisite AsGa, one As∇Ga, present before irradiation, identified to EL2 from its characteristic photoquenching behavior and the other As*Ga, created by the irradiation, stable under photoexcitation; (ii) As∇Ga anneals partially under a 850 °C thermal treatment followed by a quench and the remaining defects are transformed into As*Ga; (iii) further annealing around 120 °C converts As*Ga into As∇Ga, the process being thermally activated (0.5±0.2 eV). From these results and using observations of absorption on vibrational modes of the C‐As interstitial pair in electron irradiated material, we are able to conclude that As*Ga is the isolated antisite and As∇Ga, i...
84 citations
TL;DR: The theoretically predicted difference between the dependence of shakeup and shakeoff probabilities on the photon energy near threshold is demonstrated for the first time.
Abstract: Auger satellites have been measured to determine the probability of M-shell excitation accompanying K-shell photoionization of Ar as a function of photon energy. The theoretically predicted difference between the dependence of shakeup and shakeoff probabilities on the photon energy near threshold is demonstrated for the first time. Results are critically compared with calculations.
65 citations
64 citations
TL;DR: In this article, a theoretical analysis is performed for photoexcitation of carriers from a quantum well state into a superlattice subband, where the parameters of the device structure are chosen so that the first excited state of the quantum well lies within the lowest subband of the super lattice and the low subband is narrow.
Abstract: A theoretical analysis is performed for photoexcitation of carriers from a quantum well state into a superlattice subband. The parameters of the device structure are chosen so that (a) the first excited state of the quantum well lies within the lowest subband of the superlattice and (b) the lowest subband is narrow. The degeneracy of the first excited state with the subband provides resonant enhancement of photoexcitation into the subband while the subband extrema provide long‐wavelength and short‐wavelength cutoffs. The response band and bandwidth can be tailored and there is the possibility of high‐temperature operation associated with the narrow band response.
64 citations
15 Aug 1985
TL;DR: In this paper, photoabsorption and fluorescence cross sections of methanol vapor were mearured using synchrotron radiation, and weak structures observed in the 110-140 nm region were classified into three Rydberg series.
Abstract: Photoabsorption and fluorescence cross sections of methanol vapor were mearured using synchrotron radiation. Weak structures observed in the 110–140 nm region are classified into three Rydberg series. Quasidiatomic repulsive potential curves for the states dissociating into CH3 + OH(A2Σ+) are obtained from the measured fluorescence cross section. The photodissociation processes are discussed in accord with the fluorescence observed. The fluorescence quantum yield (< 0.8%) for photodissociation of CH3OH is one order of magnitude smaller than that of H2O, indicating a correlation that the fluorescence quantum yield decreases with increasing number of molecular orbitals.
63 citations
TL;DR: In this article, the long-term photocurrent decay following the steady state photoexcitation was measured in amorphous As 2 Se 3 film as a function of temperature and the data were described empirically by the extended exponential law and are explained by dispersive diffusion-controlled recombination of excess D 0 ; 2D 0 → D + + + D −.
Abstract: The long-term photocurrent decay following the steady state photoexcitation was measured in amorphous As 2 Se 3 film as a function of temperature. The data are described empirically by the extended exponential law and are explained by dispersive diffusion-controlled recombination of excess D 0 ; 2D 0 → D + + D − .
48 citations
TL;DR: A multiconfiguration version of the Tamm-Dancoff approximation (MCTD) is developed to study photoexcitation of atoms in cases where the simultaneous excitation of two atomic electrons is important.
Abstract: A multiconfiguration version of the Tamm-Dancoff approximation (MCTD) is developed to study photoexcitation of atoms in cases where the simultaneous excitation of two atomic electrons is important. Starting from a multiconfiguration Dirac-Fock description of the ground state, the variational principle is applied to give equations for a final-state wave function consisting of both singly excited and doubly excited configurations. To illustrate the method, the MCTD equations are applied to determine the 2pns and 2pnd autoionizing resonances in the low-energy photoionization cross section of Be and the corresponding 3pns and 3pnd resonances in Mg. The predicted cross sections are found to be in good agreement with previous theoretical results as well as with the available experimental data.
41 citations
TL;DR: In this article, a self-energy correction term due to the scattering with magnon-like modes is calculated, and shown to have a part representing the relaxation process through the c-f hybridization.
34 citations
TL;DR: The functional dependencies of the sodium-plasma pumping-line power output and the atomic-level kinetics in the neon which determine gain are examined and a novel way of depleting the lower lasing state in an optically thick laser medium is presented.
Abstract: Two of the most fundamental aspects of the sodium-neon resonantly photopumped x-ray laser system are examined: the functional dependencies of the sodium-plasma pumping-line power output and the atomic-level kinetics in the neon which determine gain. For sodium, the growth of pumping power with size, temperature, and density of the plasma is quantified with numerical and analytic calculations. In the neon an analytic model of the gain kinetics is developed which allows quantitative assessments of the effects of each important rate and process on the gain. Both analytic models should be applicable to similar resonantly pumped systems by using the appropriate rates for those systems. In addition, a novel way of depleting the lower lasing state in an optically thick laser medium is presented.
33 citations
TL;DR: In this article, the authors used the time-dependent formulation of resonant Raman scattering to elucidate the shape of the excited electronic state potential energy surface, and the dynamics which occur on it immediately following photoexcitation.
Abstract: Resonance Raman spectra of NO2 have been recorded as a function of excitation frequency in the range 0–8000 cm−1 above the predissociation threshold. These spectra are interpreted using the time‐dependent formulation of resonant Raman scattering, to elucidate the shape of the excited electronic state potential energy surface, and the dynamics which occur on it immediately following photoexcitation. Our results show that the dominant optical transition in this spectral range is 2B2–2A1. Our Raman spectra reveal a marked decrease in the dynamical time scale of the predissociation of the 2B2 state as excitation frequency increases. At excitation frequencies approximately 4850 cm−1 above the dissociation threshold, the 2B2 predissociative lifetime becomes comparable to a vibrational period. We have analyzed the resonance Raman spectra, along with the absorption spectrum, to determine the magnitudes of the slopes of the potential surface along the symmetric stretch and bending normal coordinates for the 2B2 ex...
28 citations
TL;DR: The existence of a shallow polaron is proposed below the doping level of 3 mol% in this paper, and the evolution of gap states at intermediate doping levels is consistent with the picture of polaron → bipolaron.
Abstract: Absorption spectra, electrical conductivity and ESR of polythiophene during electrochemical cycles are studied. The existence of a shallow polaron is proposed below the doping level of 3 mol%. Drastic change of conductivity is conjectured to the shallow polaron which is also induced by the photoexcitation. The evolution of gap states at intermediate doping levels is consistent with the picture of polaron → bipolaron.
TL;DR: In this paper, the absorption cross section for the lowest-lying, bound excited state (4 2Γ) of Xe2Cl has been measured at several wavelengths in the ultraviolet (UV).
Abstract: The absorption cross section for the lowest‐lying, bound excited state (4 2Γ) of Xe2Cl has been measured at several wavelengths in the ultraviolet (UV). Temporally isolating the excited Xe2Cl species in Xe/Cl2 gas mixtures has been accomplished by producing XeCl molecules in the B state by photoassociation [Xe+Cl+ℏω → XeCl(B)] at λ=308 nm. Collisional mixing of the lowest lying ion pair states of the excimer subsequently forms the XeCl species in its C state. Following the formation of Xe2Cl* from XeCl(B,C) by a three‐body collision, the long radiative lifetime of the trimer (>200 ns) relative to those for the XeCl B and C levels is exploited to ensure that the triatomic molecule is the predominant species when the experiments are performed. A second UV laser pulse depletes the Xe2Cl(4 2Γ) population by photoexcitation [as evidenced by the sudden suppression of the 4 2Γ → 1 2Γ blue‐green (λ∼485 nm) fluorescence] and the absorption cross section is determined from the dependence of the degree of fluorescen...
TL;DR: The electron-emission decay channel for photoexcited fcc Yb 5p/sub 3/2/ and 4f subshell and valence-band electron states in the photon energy range 23--50 eV is observed by measuring the photoionization cross-section curves sigma(.
Abstract: The electron-emission decay channel for photoexcited fcc Yb 5${p}_{3/2}$ and 5${p}_{1/2}$ core levels is observed by measuring the photoionization cross-section curves ${\ensuremath{\sigma}}^{\mathrm{*}}$, for the 4f subshell and valence-band electron states in the photon energy range 23--50 eV ONN Coster-Kronig, 5p-5d resonant photoemission, and 5p-5d giant dipole autoionization decay channels produce well-resolved structures in the photoemission and ${\ensuremath{\sigma}}^{\mathrm{*}}$ curves These processes shed light on the electronic structure of fcc Yb, which is largely hidden in conventional photoemission experiments
TL;DR: In this paper, the first observation of associative ionisation in Rb-K collisions was made using CW laser photoexcitation and mass spectroscopy detection, and the authors measured rate coefficients for the reaction Rb(nL)+K(4S) to KRb++e- at thermal energy.
Abstract: The authors report the first observation of associative ionisation in Rb-K collisions. Using CW laser photoexcitation and mass spectroscopy detection, they have measured rate coefficients for the reaction Rb(nL)+K(4S) to KRb++e- at thermal energy. The measured rates for a few low-lying S and D states show no significant differences from those proviously measured in pure rubidium.
TL;DR: In this paper, the absolute electrofission cross section of /sup 209/Bi was measured in the energy range 40-250 MeV and the data analysis, based on the virtual-photon technique, showed that the excitation mechanism which can cause the fission of ∆/∆/Bi is the Levinger's modified quasi-deuteron, even at energies well above the pion threshold.
Abstract: The absolute electrofission cross section of /sup 209/Bi was measured in the energy range 40--250 MeV. The data analysis, based on the virtual-photon technique, showed that the excitation mechanism which can cause the fission of /sup 209/Bi is the Levinger's modified quasi-deuteron, even at energies well above the pion threshold.
TL;DR: In this paper, a laser-produced plasma was used to resonantly pump C III ions in an adjacent, vacuum arc discharge from the 2s 1S ground level to the 4p1P0 upper level.
Abstract: Line radiation at 310.182 A from Mn VI ions in a laser produced plasma was used to resonantly pump C III ions in an adjacent, vacuum arc discharge from the 2s 1S ground level to the 4p1P0 upper level. Enhanced fluorescence by up to a factor of 150 was measured on the 4p 1P0–3d 1D line at 2177 A. Collisional exchanges between the n=4 levels transfer the pumped 4p population to the 4d and 4f levels. Enhanced fluorescence was also measured on the 4d 1D–3p 1P0 line at 1620 A and on the 4f–3d lines at 2163 A and 1923 A, respectively.
TL;DR: In this paper, the authors report extensive experimental measurements of the nonlinearity in the band-band recombination luminescence in GaAs both broadband and as a function of wavelength, doping, and photoexcitation density.
Abstract: We report extensive experimental measurements of the nonlinearity in the band‐band recombination luminescence in GaAs both broadband and as a function of wavelength, doping, and photoexcitation density. The results of a simple rate equation model which includes the bimolecular term show good qualitative agreement with the data. The implications of the nonlinearity for pump‐probe‐type time‐resolved measurements are discussed.
TL;DR: In this paper, a more rigorous numerical method for determining bulk semiconductor transport properties from photo-Hall data is presented and is used to determine compensation densities in narrow-gap HgCdTe.
Abstract: A more rigorous numerical method for determining bulk semiconductor transport properties from photo‐Hall data is presented and is used to determine compensation densities in narrow‐gap HgCdTe. Previous studies have treated carrier density inhomogeneities by means of a two‐layer approach, assuming a photoexcitation layer of constant thickness associated with either the absorption depth or the ambipolar diffusion length. Here, we show that this approximation can lead to significant error. For arbitrary optical intensities a more detailed integration over depth is required, properly accounting for the variation in the optical and transport of the material with carrier density and optical intensity. In the present technique, the spatial profile of the carrier density, n(z), is calculated as a function of optical intensity Φ0. The electron mobility μ is expanded in known functions of the carrier density. By using this n(Φ0,z) and μ(n), integral expressions for the net conductivity and Hall coefficient are then...
TL;DR: In this article, the decay probability of the Li 1s core exciton through two processes was estimated from the photoelectron spectra and the Li K absorption spectra, and it was found that the latter process is a predominant decay process in lithium halides.
Abstract: The decay process of the Li 1s core exciton was investigated by measuring the photoelectron spectra of LiCl and LiBr. It was observed that the valence-band spectrum as well as the Auger peak is enhanced at photon energies close to the excitation energy of the Li 1s core exciton. To explain these phenomena the following two processes were proposed: A Li 1s core hole and an excited electron which form the Li 1s core exciton may recombine directly with energy transferred to a valence electron. In this case, the valence-band photoelectron spectrum is resonantly enhanced at the photon energy close to the excitation energy of the core exciton, since the final state of this process is the same as that of the direct photoexcitation from the valence band. In the second process, the Li 1s core hole forming a core exciton recombines with a valence electron transferring energy to another valence electron which is excited to the continuum state. This process results in an enhancement of the Auger-electron peak. The decay probability of the Li 1s core exciton through these two processes was estimated from the photoelectron spectra and the Li K absorption spectra. It was found that the latter process is a predominant decay process in lithium halides.
TL;DR: In this paper, photo-Hall results are reported for p-type Hg1−xCdxTe samples (0.22 < x < 0.23) with acceptor densities in the low 1015 cm-3 range.
TL;DR: In this paper, the validity of assuming a constant photon lifetime in the photon conservation equation under steady-state conditions for inhomogeneously pumped lasers was discussed and an expression for photon lifetime was derived which depends on device geometry and the levels of photon fluxes in the device.
Abstract: The letter comments on the validity of assuming a constant photon lifetime in the photon conservation equation under steady-state conditions for inhomogeneously pumped lasers. An expression for photon lifetime is derived which depends on device geometry and the levels of photon fluxes in the device. The effect of this on the I/L characteristics is given.
TL;DR: In this paper, the effect of random frequency fluctuations of a laser field on the process of two-photon absorption was investigated and the laser field which was produced experimentally realized the properties of the phase diffusion model.
Abstract: We report here experimental results on the effect of random frequency fluctuations of a laser field on the process of two-photon absorption. The laser field which we produce experimentally realizes the properties of the phase diffusion model.
TL;DR: In this article, the surface photoconductivity induced by the photoexcitation of bulk traps under sub-band-gap illumination is analyzed and it is shown that the effect is controlled by the trap concentration, the intensity of the illuminating light, the thickness of the semiconductor slab and the surface barrier height.
TL;DR: In this paper, the authors show that the SSH electron-phonon model typically exhibits strong coherent anharmonic excitations, e.g. photoexcitation, in which the energy input is high.
Abstract: Numerical and analytical studies of the dynamic, mean-field, adiabatic Su-Schrieffer-Heeger model of polyacetylene are shown to reveal the typical importance of strong, coherent anharmonicity, e.g. as “breathers”. Examples illustrated include (i) single kink dynamics, (ii) electron-hole (e-h) decay in trans-(CH)x; (iii) e-h decay in cis-(CH)x; (iv) e-h decay in linear polyynes; (v) decay of a photoexcited kink or polaron; (vi) photoexcitation in the presence of bond or site defects. Using a variety of examples we have shown that the adiabatic dynamics of the SSH electron-phonon model typically exhibits strongly coherent anharmonic excitations, e.g. “breathing” modes. We have emphasized situations, e.g. photoexcitation, in which the energy input is high. Breather generation with spallation neutrons should also be considered, as should thermal production in materials with narrower band gaps. Persistent, localized breathers will also be typical in the presence of “confinement” mechanisms –whether du...
01 Jan 1985
TL;DR: In this paper, the use of optical modulation (OM) spectroscopy for studying photoexcited carriers in trans polyacetylene was discussed, and the effective electron correlation energy (Uef) for the soliton defects was measured.
Abstract: Illumination of a semiconductor changes the distribution of electrons which leads to a variety of effects underlying the optoelectronic applications of these materials. These effects can also be used as tools for studying the electron states in the forbidden gap. In this work we discuss the use of optical modulation (OM) spectroscopy for studying photoexcited carriers in trans polyacetylene. We found that interchain photoexcitation mainly produces bound neutral soliton-antisoliton pairs as opposed to well separated charged soliton which is predicted by the theory [1] when electron correlation effects are neglected. Intrachain photoexcitation, which excites electron-hole (e-h) pairs on neighboring chains, can produce charged solitons S± if the e(h) are trapped at neutral soliton defects (So) existing in the sample. Using the OM technique,we directly measure the effective electron correlation energy (Uef) for the soliton defects; we found Uef=0.95eV. This large Uef shows that electron correlation should be included in any realistic model of polyacetylene.
TL;DR: In this article, the authors used the time-dependent formulation of resonant Raman scattering to elucidate the shape of the excited electronic state potential energy surface, and the dynamics which occur on it immediately following photoexcitation.
Abstract: Resonance Raman spectra of NO2 have been recorded as a function of excitation frequency in the range 0–8000 cm−1 above the predissociation threshold. These spectra are interpreted using the time‐dependent formulation of resonant Raman scattering, to elucidate the shape of the excited electronic state potential energy surface, and the dynamics which occur on it immediately following photoexcitation. Our results show that the dominant optical transition in this spectral range is 2B2–2A1. Our Raman spectra reveal a marked decrease in the dynamical time scale of the predissociation of the 2B2 state as excitation frequency increases. At excitation frequencies approximately 4850 cm−1 above the dissociation threshold, the 2B2 predissociative lifetime becomes comparable to a vibrational period. We have analyzed the resonance Raman spectra, along with the absorption spectrum, to determine the magnitudes of the slopes of the potential surface along the symmetric stretch and bending normal coordinates for the 2B2 ex...
TL;DR: In this paper, a defect complex associated with boron having a large configurational relaxation after releasing an electron by photoexcitation is considered as an explanation for the metastable excess conductivity σ(E) observed in hydrogenated amorphous silicon (a-Si:H).
Abstract: The metastable excess conductivity σ(E) observed in hydrogenated amorphous silicon (a-Si:H), that is alternately doped n- and p- type, is compared with the Staebler-Wronski effect and other metastable conductivity changes observed in compensated a-Si:H and in oxidized p- type a-Si:H respectively. We find that Dohler's model of electron-hole pair separation in the pn-junction fields cannot account for the long life of a(E) near and above 300oK. A defect complex associated with boron having a large configurational relaxation after releasing an electron by photoexcitation is considered as an explanation for σ(E).
TL;DR: In this paper, a method for simultaneous determination of trap depths and frequency factors s is derived, which does not depend on the phosphor sample nor on the trap under consideration, but obeys a scaling law.
01 Jan 1985
TL;DR: In this article, the first observation of millimeter and submillimeter wave cyclotron resonance (35, 692, 1364 and 1743 GHz) under an intrinsic photoexcitation has been made in high-quality ZnSe.
Abstract: First observation of millimeter and submillimeter wave cyclotron resonance (35, 692, 1364 and 1743 GHz) under an intrinsic photoexcitation has been made in high-quality ZnSe. The experiment enables us to make a precise determination of the effective mass value and the temperature dependence of the scattering rate of photoexcited electrons. A strong anisotropy in absorption has been observed in the 35 GHz measurement.