bluuebunny/crossref_metadata_2025 huggingface dataset:
Raman Scattering of Amorphous Semiconductors Ge–S System under High Hydrostatic Pressure
Authors: Onari Seinosuke , Inokuma Takao , Arai Toshihiro
Published: March 2014

We shall report results on the effects of the hydrostatic pressure on the Raman spectra of the amorphous semiconductors, GexSi1-x (0.2 ≤ x ≤ 0.36). We found that the intensity of low frequency Raman scattering in the wavenumber range of 5∼20 cm-1 for Ge–S system decreased to about one third at 3 GPa pressure compared to that at atmospheric pressure. In order to analyze this anomalously large change of the “Boson peak” band under pressure we tried to use the theory of Martin and Brenig for the elastic continum model. We also observed some anomalous changes in the correlation length for the Ge composition near stoichiometric GeS2. Sharp bands observed near 150 cm'1 and 220 cm-1 for sulfur rich sample disappeared with the increase in pressure.
First Principle Calculation and Photoluminescence Spectroscopy of the DX Center
Authors: Yamaguchi Eiichi , Junnarkar Mahesh R.
Published: March 2014

In order to resolve the controversy (large lattice relaxation or small lattice relaxation?) regarding the origin of DX centers theoretically, ab initio self-consistent pseudopotential method has been applied to 64-atom super cell for donor-doped GaAs under high pressure and donor-doped Al
x
Ga1-x
As alloys. The total energy and force calculations predict that an almost unrelaxed donor atom with T

d
symmetry has the most stable configuration. On the contrary, a negatively charged donor with broken-bond configuration gives a metastable state and not the ground state even under hydrostatic pressures up to 60 kbar. Furthermore, to resolve this controversy experimentally, we have performed photoluminescence (PL) spectroscopy on Si-doped Al
x
Ga1-x
As (x=0.32-0.4). We have observed for the first time band-edge PL for below-gap photoexcitation in these systems at low temperatures (< 50 K). This result strongly suggests the validity of the present theoretical predictions.
Unusual Behaviour of the DX-Centre in GaAs:Ge
Authors: Wisniewski P. , Wel P. van der , Suski T. , Singleton J. , Skierbiszewski C. , Giling L. J. , Warburton R. , Walker P. G. , Mason N. J. , Nicholas R. J. , Eremets M.
Published: March 2014

Magnetotransport measurements have been performed as a function of hydrostatic pressure and temperature to study the effect of deep donor levels on the electron concentration and mobility in bulk GaAs heavily doped with Ge. For the first time, the coexistence of the metastable DX centre and the non-metastable localized A1 level has been unambiguously observed in GaAs. Furthermore, we have determined the energy positions and pressure dependences of both resonant levels (0.07 eV and -7 meV/kbar) for the A1 level and 0.1 eV and -10 meV/kbar for the DX centre) and the energy barrier for electron emission from the DX-centre (0.29 eV). The latter appeared to be pressure independent. From ' the mobility behaviour during depopulation of the DX-centres, an elegant proof for negative U character of DX centres and the positive U character of deep A1 levels has been obtained.
New Results on the EL2 Defect in GaAs
Authors: Dreszer Piotr , Trautman Pawel , Baj Michał
Published: March 2014

In this paper we present a review of our comprehensive high pressure investigations of the EL2 defect in GaAs focusing on the properties of its metastable configuration. We demonstrate that the metastable EL2 possesses an acceptorlike level which can be populated under pressure leading to the negative charge paramagnetic state, (EL2*)-. Based on our experimental results we explain the origin of the pressure-induced optical accessibility and electrical activity of the metastable EL2. We demonstrate that in n-type GaAs thermal EL2 recovery always proceeds via (EL2*)-. Finally, from uniaxial stress studies we conclude that the metastable EL2 has trigonal symmetry.
Transition Metal Deep Level Defects in Silicon
Authors: Pfeiffer G. , Prescha Th. , Weber J.
Published: March 2014

Hydrostatic pressure is employed to investigate the structure of substitutional transition metal defects. The pressure coefficient of the Gibbs free energy for the deep level defects was determined by means of isothermal capacitance transient measurements. The pressure coefficients for the donor and acceptor states of the substitutional transition metal defects Pd, Pt, Au and the A center (oxygen-vacancy pair) relative to the respective energy bands were determined. For the acceptor states, the pressure coefficients vary strongly as a function of the activation energy whereas the variation is smaller for the donor states.
Large Lattice Distortion and Infrared Photoluminescence in Cd1-xMnxTe
Authors: Nakahara Jun'ichirō , Watanabe Junji , Nouchi Taihei
Published: March 2014

The infrared photoluminescence near 1.15eV (IR PL) in Cd1-xMnx Te is investigated under high pressures up to 20kbar and at wide temperature range. Using a configuration coordinate model, we propose that relaxed excited states of Mn2+ have two minima, and the excited states of IR PL has larger lattice relaxation than that of excited states of Mn2+ PL. Also distorted ground state without metastable states is the final states of IR PL. Thermal barrier from Mn2+ excited state to excited state of IR PL is 36meV.
Investigation of Shallow States Related to Si-DX Centers in AlGaAs near the \varGamma-X-L Crossover
Authors: Goutiers B. , Dmowski L. , Ranz E. , Aristone F. , Portal J. C. , Chand N.
Published: March 2014

Using pressure for tuning the band structure we have demonstrated that Si-DX centers in AlGaAs create shallow effective mass states linked to each of the minima (Γ ,L and X) of the conduction band. The presence of the state which we attribute to the L minimum is also confirmed by magnetic freezeout measurements, revealing an interaction (anticrossing effect) between the Γ and L-Like states.
Phase Transformations and p-T Diagram of Some HgX Compounds (X=S, Se, Te)
Authors: Tedenac J. C. , Record M. C. , Ayral-Marin R. M. , Brun G. , Jun J. , Grzegory I. , Krukowski S. , Bockowski M.
Published: March 2014

The paper summarizes recently obtained results on mercury chalcogenides high temperature p-T diagrams 1) 2) 3). Differential thermal analysis (D.T.A) was used to determine the melting curves and phase transitions of mercury chalcogenides at gas pressure up to 2 GPa. Melting as well as zinc blende (B3) - cinnabar (B9) transition temperatures and pressures of HgS, HgSe,HgTe were measured. The resulting p-T diagrams are presented and discussed.
The topotactic interpretation of the zinc blende-cinnabar phase transformation is presented along with the results of elastic properties of zinc blende HgX, close to transition. The influence of Phillips bond ionicity factor 4) 5) on the stabilization of the cinnabar structure with pressure is discussed.
MBE Grown GaSb, AlSb Crystals High Pressure Electrical Characterisation
Authors: Konczewicz L. , Mercy J-M. , Robert J-L. , Dobaczewski L. , Peaker A. R.
Published: March 2014

For growth of GaAlSb layers by MBE method, the new doping Ga2Se3 and Ga2S3 sources have been used for Se and S doping respectively. The electrical transport measurements (Hall effect and resistivity) were used to characterise the grown layers. For GaSb:S layer the role of the two-dimensional electron gas is demonstrated. The Se-donor states in AlSb have been studied and its ionization energy was found to be about 440 meV.
Pressure Dependence of Photoluminescence in Ordered Ga0.5In0.5P Alloys Grown by OMVPE
Authors: Kobayashi Toshihiko
Published: March 2014

Photoluminescence (PL) measurements on Ga0.5 In0.5 P samples grown by organometallic vapor phase epitaxy (OMVPE) on GaAs substrates at various growth temperatures (Tg=600, 650 and 700°C) have been made as a function of pressure up to about 4.5 GPa at 77 K. The PL spectrum shows a rapid shift towards higher energies with pressure, indicating a increase in the direct band gap. In the pressure range 0-3.5 GPa the PL peak energy increases sublinearly with pressure, and a quadratic fit of the pressure dependence was made. The linear pressure coefficient so obtained at low Tg (600°C) is larger than at high Tg (700°C). In addition, at a certain pressure 3.6-4.0 GPa this shift of PL spectra saturates, and then the peak energy shows a tendency to decrease with pressure to about 4.5 GPa at which the emission disappears. These results are explained in terms of repulsion between Γ-folded states in the CuPt-type ordered structure of GaInP alloys.
High Pressure Effects on Photoluminescence Spectra of Color Centers in Diamond
Authors: Kobayashi Michihiro , Nisida Yosio
Published: March 2014

Pressure dependence of vibronic photoluminescence spectra for two types of color centers in diamond: the nitrogen-vacancy `NV' center and the nitrogen-vacancy-nitrogen `H3' center are studied at 77K. By analyzing the spectra, the strength of the electron-lattice interaction, the local vibrational energies, and the energies of the zero-phonon line (ZPL) are determined as a function of pressure. The lattice vibration accompanied by the H3 center shows softening due to pressure. The distribution range of the internal strain which acts as the origin of the inhomogeneous broadening of ZPL is estimated.
Pressure Induced Quantum Confined Excitons in Layered Metal Tri-Iodide Crystals
Authors: Kurisu H. , Tanaka T. , Karasawa T. , Komatsu T.
Published: March 2014

Quantum confined exciton states are analyzed from the absorption, luminescence and Raman spectra under hydrostatic pressure in SbI3 and BiI3 crystals. In SbI3, a new transition line series of excitons suddenly appears below the fundamental absorption edge under the pressure higher than ∼1.4 GPa. In BiI3, the similar line series appears even at atmospheric pressure. The energies of the lines converge to the low energy side revealing a feature of the quantum confinement. The pressure induced quantum confined states are discussed in terms of a phase transition of electronic structure due to the molecular rearrangement.
Pressure-Induced Electronic Phase Transition in CeP
Authors: Môri Nobuo , Okayama Yasushi , Takahashi Hiroki , Haga Yoshinori , Suzuki Takashi
Published: March 2014

High pressure effects on the temperature dependent resistivity of single crystalline CeP were
studied at temperature from 4.2 to 300K under pressure up to 8GPa. The resistivity anomalies associated with the magnetic dense Kondo state are found to change drastically with pressure. A resistivity jump in the residual resistivity is observed at a pressure between 5 and 6GPa. This abrupt change in resistivity clearly indicates a pressure-induced electronic phase transition between a localized to an itinerant state of 4f electron. A pressure-temperature phase diagram of CeP is proposed.
Neutron Diffraction Study of Tl2Ba2CuO6+y under High Pressure
Authors: Takahashi Hiroki , Jorgensen James D. , Hunter Brett A. , Hitterman Richard L. , Pei Shiyou , Izumi Fujio , Shimakawa Yuichi , Kubo Yoshimi , Manako Takashi
Published: March 2014

The crystal structure of Tl2Ba2CuO6+y
has been investigated under high pressure and at low temperature using neutron powder diffraction method. A gas pressure cell is made of aluminum and helium gas is used to generate pressure up to 0.609GPa. The crystal structure at 0.609GPa and 60 K depends systematically on the path in pressure-temperature space by which these conditions are achieved. Lattice parameters obtained by applying pressure at room temperature and then cooling are different from those obtained by cooling first and then applying pressure. Our results support those of Sieburger and Schilling1) who reported that the TC at high pressure for this compound depends markedly on whether the sample is pressurized at room temperature or low temperature.
Pressure Effects on the Antiferroelectric Phase Transition in K3H(SO4)2 and K3D(SO4)2
Authors: Moritomo Yutaka , Tokura Yoshinori
Published: March 2014

Effects of hydrostatic pressure on the antiferroelectric phase transitions of proto-typical hydrogen-bonded antiferroelectrics K3D(SO4)2 as well as its hydrogenerated analog (K3H(SO4)2), which shows no phase transition, have been investigated. The critical temperature (TC) for the D-compounds was found to rise with pressure, making a sharp contrast with the other hydrogen-bonded (anti-)ferroelectrics whose TC's usually decrease under pressure. In contrast, no significant pressure effect was observed for the H-compound. The obtained results are discussed in terms of the electrostatic interaction between the electric dipoles in the crystal.
Pressure-Induced Crossover in Heavy Fermion Compounds
Authors: Kagayama Tomoko , Oomi Gendo
Published: March 2014

Effect of pressure on the electrical resistivity and lattice constant has been studied for three heavy fermion conpounds, CeInCu2, CeCu6 and CeIn3. The resistivity-maximum temperature T
max increases with increasing pressure associated with the large enhancement of the Kondo temperature T
K. This implies that the pressure-induced crossover from the heavy fermion state (low T
K) to intermediate valence state (high T
K). The crossover occurs without any discontinuous change in volume. These results are discussed briefly taking account of the volume dependence of T
K.
Anomalies in the Thermal Expansion and Electrical Resistivity of Fe72Ni28 Alloy under High Pressure
Authors: Oomi Gendo , Iki Keiko
Published: March 2014

The electrical resistivity and thermal expansion of Fe72Ni28 alloy have been investigated under high pressure up to 15 kbar. Anomalous behaviors near the martensitic transformation are found in the temperature dependence of thermal expansion and electrical resistivity. The transformation temperature M
s on cooling process decreases with increasing pressure but its pressure coefficient below 7 kbar, ∂M
s/∂P=-6.7 K/kbar, is different from that above 7 kbar, -10 K/kbar. The discontinuous change in volume and resistance near M
s tends to disappear at high pressure.
III–V Semiconducting Nitrides: Physical Properties under Pressure
Authors: Perlin P. , Gorczyca I. , Porowski S. , Suski T. , Christensen N. E. , Polian A.
Published: March 2014

Results of experimental and theoretical studies of the fundamental electronic properties of III-V nitrides are presented. Single crystals of nitrides grown by means of an equilibrium high-pressure technique have been used for the determination of optical and structural properties. The electronic band structure, its pressure dependence, and high-pressure phase transitions have been calculated using the density functional theory.
InN Thermodynamics and Crystal Growth at High Pressure of N2
Authors: Grzegory Izabella , Jun Jan , Krukowski Stanislaw , Perlin Piotr , Porowski Sylwester
Published: March 2014

InN is a wide direct gap semiconductor, which has not been yet grown in the form of large single crystals. In this work, we report the first synthesis and crystallization of InN from its constituent elements. We have also calculated p-T stability curve for this compound, up to 20 kbar, using low pressure decomposition data1) and equation of state of N2
2). We verified this curve by crystal growth experiments as well as by DTA measurements of decomposition of InN powder at high N2 pressure up to 14 kbar. InN crystals are characterized by SEM and optical absorption.
Design of High Pressure Apparatus to Use at Low Temperature and High magnetic Field
Authors: Oomi Gendo , Kagayama Tomoko , Uwatoko Yoshiya
Published: March 2014

High pressure apparatus has been designed to measure the physical properties of condensed matter at high magnetic field H(T) and at low temperature T(K). It is shown that the apparatus can be used in the ranges of P, T and H, 0<P≤25 kbar, 1.3≤T≤350 K and 0≤H≤5 T, respectively. Some examples of the measurements of electrical resistivity, thermal expansion coefficients, magnetoresistance and magnetostriction are reported briefly. The results
are discussed on the basis of the pressure change of the Kondo temperature T
K. Some difficulties in carrying out the high pressure experiment are pointed out.
Can We Measure a Momentum Change of Conduction Electrons at High Pressure?
Authors: Oomi Gendo , Itoh Fumitake
Published: March 2014

Compton profile of metallic Li has been observed at 1.5 GPa at room temperature. The halfwidth of the peak at 1.5 GPa is found to be larger than that at ambient pressure. The result suggests that the Fermi momentum of Li increases at high pressure. A simple explanation of the present result is given in the framework of free electron model. Some difficulties in obtaining the Compton profile are briefly discussed.
New Development of High-Pressure Brillouin Study for Elastic Properties of Molecular Solid
Authors: Shimizu Hiroyasu , Sasaki Shigeo
Published: March 2014

By using a new diamond-anvil cell having symmetric conical openings with aperture angles of 98°, we have measured the angular dependence of Brillouin acoustic velocities of crystalline H2S at pressures up to 7 GPa. The best fitting of calculations by the Every's expression for elastic waves of an arbitrary direction to the experimental velocities, yielded the orientation of an H2S cubic crystal grown in the diamond cell. In situ determinations of sound velocities for any direction, the refractive index, the density, and the elastic constants could be made as a function of pressure. This method provides a means for the systematic study of elastic properties and phase transitions of condensed gases under ultrahigh pressures.
Image Plate Studies of Tetrahedral Semiconductors Under Pressure: The Implication for Experiment and Theory
Authors: Crain J. , Ackland G. J. , Hatton P. D. , McMahon M. I. , Nelmes R. J. , Piltz R. O.
Published: March 2014

A series of high-pressure synchrotron x-ray powder diffraction experiments on tetrahedral semiconductors have been performed using an image plate area detector system in conjunction with a standard diamond anvil cell (DAC). Initial studies have focused on pressure-induced structural transitions in zincblende semiconductors with emphasis on the previously well-studied InSb compound. Site ordering of the nearly isoelectronic constituents is confirmed in some of the high pressure phases for the first time. Structural solutions are proposed which differ in essential features from previously suggested structures. The results obtained are discussed in the context of present theoretical understanding and data from new total energy calculations will be presented. The experimental evidence for phase transition-induced defects will be presented along with complimentary total energy pseudopotential calculations of their formation energies
Structure of Selenium under High Pressure
Authors: Nagata Kiyofumi , Miyamoto Yasuhiko
Published: March 2014

The high-pressure X-ray structural analysis of rhombohedral selenium has revealed that with increasing pressure, an intermolecular distance decreases rapidly, while an intramolecular covalent bond length increases gradually. On the other hand, the pressure-induced softening of the bond stretching mode, especially A1 mode, has been observed in the Raman spectra of both rhombohedral and α-monoclinic selenium. These findings suggest that the intramolecular covalent bonding in selenium crystal decreases with pressure.
Structural Phase Transitions and Equations of State of Se and Te under High Pressure
Authors: Nishikawa Atsushi , Niizeki Komajiro , Shindo Koichi
Published: March 2014

Selenium and tellurium are known to undergo several structural phase transitions under pressure. We have investigated the band-structures and the total energies of β-P0 type (rhombohedral) structure and body-centered cubic structure of Se and Te within the local density-functional formalism using the norm-conserving pseudopotential method. The calculated equations of state are in good agreement with the experimental ones. We also discuss the structural stability of the high pressure phases.
A Pressure-Induced Isostructural Transition in Black Phosphorus
Authors: Morita Akira , Shibata Kiyotaka , Shindo Koichi
Published: March 2014

The crystal structure of orthorhombic black phosphorus under pressure is calculated as a function of volume using the pseudopotential total-energy method. As a result, it is shown that the anomaly of the lattice constants observed experimentally at the density of 17.5Å3/atom is due to an unusual isostructural second order phase transition and its physical origin is attributed the repulsive force effect due to overlap between valence electron charge clouds of neighboring puckered layers.
Pressure-Induced Type I-Type II Crossover in AlAs/GaAs Short-Period Superlattices
Authors: Minami Fujio , Nakayama Takeshi , Inoue Kuon
Published: March 2014

We have studied the cw and time-resolved photoluminescence spectra of (001)-(AlAs)
n
/(GaAs)
n
(n=8∼15) short-period superlattices under hydrostatic pressure. At atmospheric pressure, the superlattices with n≤12 are of the type-II and the lowest excited state is X exciton, while the samples with n≥13 are type-I materials and the conduction-band minimum occurs at Γ in the GaAs. It is found from decay pattern analysis that the significant Γ-X mixing occurs only near the direct-indirect crossover and dominantly at an odd number of AlAs monolayers.
In the (AlAs)13/(GaAs)13 sample, where the Γ-X crossover just occurs, evidence of the Γ-X mixing can be extracted from energy- and lifetime-versus-pressure data.
Pressure Dependence of the Harmonic Oscillator Levels of AlxGa1-xAs Parabolic Quantum Wells
Authors: Burnett J. H. , Cheong H. M. , Paul W. , Hopkins P. F. , Gossard A. C.
Published: March 2014

We have measured the hydrostatic pressure dependences of the harmonic oscillator spacings of an Al
x
Ga1-x
As parabolic quantum well in a diamond anvil cell, using photoluminescence excitation spectroscopy. From these we determined the pressure dependence of the conduction band offset for GaAs/Al
x
Ga1-x
As heterojunctions and found dΔECB/dP=0.75±0.25 meV/kbar. This has the consequence that the fraction of the band gap difference in the conduction band, QCB, may increase with pressure. Depending on the pressure dependence of the direct gap of Al
x
Ga1-x
As assumed, QCB may increase with pressure for 0-25 kbar from 0-10%. Thus the atmospheric pressure value of QCB=0.70±0.04, determined earlier using hydrostatic pressure, may have been overestimated by as much as 10%.
Can External Perturbation Measurements Provide a Critical Test of Models of the Schottky Barrier Formation?
Authors: Langer Jerzy M.
Published: March 2014

The novel approach to testing the validity of various models of the Schottky barriers is reviewed. It is based on expected different dependence of the barrier on the external perturbation (temperature or pressure shift) for the two competitive contemporary models of the barrier formation, i.e. The metal-induced-gap-states model and the model invoking the presence of real defect states at the interface. In the former the barrier shifts would reflect the individual shifts of the relevant band edges, while in the latter the influence of the external perturbation of the ionization energy of the defect that pins the Fermi level would be reflected on the barrier shifts. The available data on Si-silicide barriers and MBE grown Al/AlGaAs junctions are in a direct conflict with the predictions of the MIGS theory, while at the same time can be positively explained within a frame of the defect model.
Electronic Structure and Optical Properties of (Ga, In)As–(Ga, Al)As Quantum Wells and Superlattices under Internal and External Strain Fields
Authors: Gil Bernard , Boring Philippe
Published: March 2014

We present a detailed study of the electronic structure and optical properties of (Ga,In)As-(Ga,AI)As strained-layer quantum wells and superlattices grown along either the (001) and (111) directions.
Carbon Nanotubes: Optical Absorption in Aharonov-Bohm Flux
Authors: Ajiki Hiroshi , Ando Tsuneya
Published: March 2014

Optical absorption spectra for carbon nanotubes are calculated in the presence of an Aharonov-Bohm flux passing through the cross section. The band gap drastically changes with a period of the magnetic flux quantum because of the Aharonov-Bohm effect. The effect can be seen as a shift of the absorption peaks for light polarization parallel to the tube axis. For perpendicular polarization the absorption is strongly suppressed due to a depolarization effect.
Enhancement of Exciton Exchange Interaction by Quantum Confinement in CdSe Nanocrystals
Authors: Chamarro Maria , Gourdon Catherine , Lavallard Philippe , Ekimov Alexei I.
Published: March 2014

We have investigated the degree of linear polarization and time behaviour of photoluminescence of very small size CdSe nanocrystals under size-selective excitation. At low temperature we observe a luminescence line Stokes-shifted by a few meV and its phonon replica. The degree of linear polarization is positive at short times then becomes negative and remains constant and equal to -15%. The following model is proposed. The exciton state is split by electron-hole exchange interaction into two states with the optically forbidden state at lower energy. Laser light creates excitons in the upper energy state. The luminescence line arises from the lower energy state where excitons have relaxed after a few tens of ps. Recombination is made possible through a phonon assisted virtual transition to the confined B-exciton state. As a result the polarization degree is negative at long times. The value of the exchange energy obtained from the luminescence Stokes shift (8 meV in 40Å-diameter nanocrystals) is much larger than the bulk value (0.1 meV). The enhancement of exchange interaction by quantum confinement and the value of the degree of polarization are in good agreement with theoretical estimates.
Subpicosecond Spectroscopy of CuCl Nanocrystals in NaCl
Authors: Yano Satoshi , Goto Takenari , Iwai Sadayuki , Edamatsu Keiichi , Itoh Tadashi
Published: March 2014

In CuCl nanocrystals, we observed the nonlinear change in the exciton absorption spectra and the appearance of the structures (gain and loss) near the energy region of biexciton luminescence band using the subpicosecond pump-and-probe method under high intensity excitation at 2K and 77K. We observed the decay time of the exciton absorption change at 2K to be about 1ns, twice as large as that at 77K. We found out that the peak positions of the gain and the loss differed in energy at 2K, while they had the same energy at 77K. Taking into account of the luminescence and their time behavior, we got the evidence that the transitions from the biexciton state to “bound” and “free” exciton states occur simultaneously at 2K.
Lamb Shift for an Excitonic Molecule in GaAs Quantum Well
Authors: Ivanov Alex L. , Haug Hartmut
Published: March 2014

We study the influence of the radiative decay of an excitonic molecule (x
x) in quasi-2D quantum well (QW) on the x
x effective binding energy (x
x Lamb shift). For the x
x wave function, the new Schrödinger equation which includes the polariton effects self-consistently is analyzed. In quasi-2D GaAs QW the radiative renormalizations give rise to a “Mexican hat” structure in the x
x dispersion at small momenta together with a considerable increase of both the x
x effective binding energy ε
x
x
and the inverse x
x radiative lifetime Γ
x
x
. Our theory explains a quantitative contradiction between the value of ε
x
x
obtained in the recent experiments and the conventional theoretical one.
Spin Degrees of Freedom and Fermi-Edge Singularity in One-Dimensional Conductors
Authors: Ogawa Tetsuo
Published: March 2014

The Fermi-edge singularity (FES) in optical spectra is studied theoretically for one-dimensional (1D) conductors. In calculation of the FES critical exponent, the electronic correlation and the charge- and spin-density fluctuations of the 1D degenerate electrons are taken into account by the Tomonaga-Luttinger bosonization technique. Spin dependence of the electron-electron and electron-hole pair scatterings is incorporated in the theory. The FES for the 1D systems with spin-split bands is also discussed in terms of the response to a circularly polarized light.
Mesoscopic Semiconductor Switching Element with Giant Electro-Optical Nonlinearities due to Intrinsic Photoconductivity
Authors: Ivanov Alex L. , Haug Hartmut , Knigge Steffen , Jäger Dieter
Published: March 2014

We propose and analyze a new efficient mesoscopic room-temperature electro-optical device consisting of long-period GaAs/AlGaAs
MQW under a vertical voltage bias through a resistor in series. Both the MQW and the substrate are designed to be undoped. Intrinsic photoconductivity, initiated by the photo-active GaAs layers, gives rise to an effective feedback through Kirchhoff's law between the light beam intensity and the voltage drop over MQW. The giant electro-optical nonlinearities of this element stems from (i) Franz-Keldysh effect, (ii) photocarriers accumulation in the GaAs layers due to the charge separation induced by the vertical quasi-static electric field, (iii) dependence of a mean free-path of the ballistic carriers on this electric field. The device operates at light intensities less than 100 mW/cm
2 with a switching time of about 100 ns.
Optical Properties of Excitons in Semiconductor Quantum Wells
Authors: Zhang Baoping , Kano Satoru S. , Ito Ryoichi , Shiraki Yasuhiro
Published: March 2014

Oscillator strength of excitons in various quantum wells is systematically investigated analyzing Fourier transform reflectance spectra. The temperature dependence of the oscillator strength of the zero-phonon line transition is well described by a modified Debye-Waller expression with an averaged phonon mode. This allows us to investigate the exciton-phonon interaction. The oscillator strength in GaAs/AlGaAs quantum wells increases as the well width is reduced in agreement with the existing theory, while in InGaAs/GaAs and GaAs/GaAsP quantum wells takes a maximum at a certain well width, showing the variation from two- to three-dimensional characters. The oscillator strength in InGaAs/GaAs and GaAs/GaAsP quantum wells is differently dependent on the alloy composition variation.
Thiacarbocyanine Dye J-Aggregates as an Example of Restricted Molecular System
Authors: Drobizhev M. A. , Sapozhnikov M. N. , Varnavsky O. P. , Vitukhnovsky A. G. , Argyrakis P.
Published: March 2014

The results of a study of exciton dynamics of thiacarbocyanine derivative J-aggregates in glassy matrices at low temperatures are reported. Temperature dependences of fluorescence spectra and homogeneous absorption linewidth have been experimentally investigated. Spectral hole burning experiments show the homogeneous linewidth to be independent of temperature at T<9 K being as large as 1.7 cm-1 corresponding to the dephasing time 6.2 ps. The results are discussed in a framework of exciton-phonon scattering process. Temperature dependence of coherent length of exciton is considered on the base of fluorescence spectral data.
Large Redshift in Absorption Spectra of Titanylphthalocyanine Thin Films
Authors: Yamashita Akira , Maruno Tohru , Hayashi Takayoshi
Published: March 2014

Titanylphthalocyanine is deposited onto sapphire by organic molecular beam deposition to grow films of 2.5 to 100 nm. The first layer grown on the sapphire surface is not phase II; however, phase II grows on the first layer. The first layer is annealed and changed to phase II during deposition. The Q-band of phase II shows a large redshift. Calculations using molecular exciton theory show that molecular columns grow in two directions parallel to the substrate surface. Each of these columns has a favorable molecular arrangement for a large redshift, such as J-aggregates. The film thickness has a low dependence on the redshift, a result which is consistent with the calculation results.
Electron Transfer between Fullerene and Polysilanes
Authors: Watanabe Akira , Ito Osamu
Published: March 2014

The photoinduced electron transfer between C70 and σ-conjugated polysilanes in solutions was investigated by laser flash photolysis. The absorption band of 3C70
* at 960 nm was quenched effectively in the presence of poly(methylphenylsilylene) (PMePhSi), and new absorption band which can be assigned to the radical cation of PMePhSi appeared. The electron transfer rate constant from PMePhSi to 3C70
* was determined to be 1.90×108 (M-1s-1) based on the concentration of Si-repeating unit by pseudo-first-order plots of 3C70
*.
Theory of Material Design for Third Order Optical Nonlinearity: Symmetric and Asymmetric Cases
Authors: Ohtawara Kazushige , Shinjo Kazumasa
Published: March 2014

A design principle is given to enhance the third order optical nonlinearity for the organic materials, based on the five-types-of-transition-paths model. The validity of the five-types-of-transition-paths model is examined by calculating the electronic structures for a variety of the organic materials. The design principle is established by extracting a set of the material parameters (called dependent parameters) maximizing the third order optical nonlinearity for the other material parameters (called independent parameters) being fixed. The calculations due to the molecular orbital method suggest that the dependent parameters for the existing symmetric molecules are close to those maximizing the third order optical nonlinearity, whereas parameters for the existing asymmetric molecules are far from those maximizing the third order optical nonlinearity.
Modeling of Lateral Hot-Electron Phototransistor for Long-Wave Length Infrared Radiation
Authors: Ryzhii Victor , Khrenov Gregory , Khmyrova Irina , Ryzhii Maxim
Published: March 2014

Analytical and numerical models of a lateral hot-electron phototransistor (LHEPT) are developed. The principle of operation of the LHEPT is associated with intersubband absorption of infrared radiation in the base, which results in stimulation of the hot-electron injection from the emitter to collector. The responsivity of the LHEPTs based on the structures with two-dimensional channels is evaluated as function of the structure parameters, applied voltages and energy of incident photons.
ZnS–ZnSe–ZnS/GaAs (100) Single Quantum Well Structures and ZnS/ZnSe/GaAs (100) Superlattices Grown by Photo-Assisted VPE
Authors: Kovalenko Alexander V. , Tishchenko Valeriy V.
Published: March 2014

It has been shown that photo-assisted VPE (radiation source He-Cd laser hν=2.807eV, P=0.8mW/cm2) at low substrate temperatures (170-350°C) and big temperature gradient (200-250°C/cm) gives results in extremely pure layers II-VI materials such as ZnSe/(100). Using this technology the single quantum well (SQW) structures of ZnS-ZnSe-ZnS/GaAs(100) type and ZnS/ZnSe/GaAs (100) superlattices (SL) have been grown for the first time. Reflection and photoluminescence spectra of the obtained structures have been studied.
Size-Dependent Exciton Densities of States and Exciton Bandwidths in Anthracene Microcrystallites
Authors: Mizuno Ken-ichi , Matsui Atsuo H. , Nishi Osamu , Matsushima Yoshihiro , Shimizu Makoto , Goto Takenari , Takeshima Masumi
Published: March 2014

Applying a technique to determine the k=0 components in the exciton densities of sates (DOS) we found:
(1) The DOS in anthracene microcrystallites appears as sharp bands followed by broad tails extended towards higher energies.
(2) The exciton bandwidth which depends linearly on the size of microcrystallites where the diameter is smaller than 60 Å.
(3) The bandwidth takes its maximum value 340 cm-1 for microcrystallite of 65 Å.
(4) For larger microcrystallites, the bandwidth decreases asymptotically to 300 cm-1.
(5) This width 300 cm-1 is equivalent to the bandwidth for bulk crystal.
(6) Exciton scattering at the surface of microcrystallites is extremely effective.
Time Response of Polariton in Small System by Ultra-Short Pulse Excitation
Authors: Tokihiro T. , Suzuura H. , Tsujikawa T.
Published: March 2014

We develop “tight-binding photon approximation” to investigate time response of a small polariton system. This method is fully quantum mechanical and does not require an additional boundary condition (ABC). The reflection and transmission spectra of thin CuCl films and the response of several femtosecond pulses are demonstrated.
Optical Properties of GaAs Nano-Whiskers
Authors: Katsuyama Toshio , Hirima Kenji , Ogawa Kensuke , Haraguchi Kei-ichi , Yazawa Masamitsu
Published: March 2014

Nanometer-size free-standing GaAs whiskers are fabricated by selective area growth based on reduced-pressure metal-organic vapor-phase epitaxy. Photoluminescence measurements of these GaAs whiskers show a spectral blue shift due to the two-dimensional quantum confinement of the carriers. The spectral blue shift is, however, much smaller than the lowest level energy expected by the square-potential confinement. This is due to a band-gap reduction induced by the charge separation caused by the existence of surface depletion potential, which is confirmed by surface passivation experiments using sulfur compounds. Furthermore, intense light emission is observed during carrier injection to the p-n junction formed in the GaAs whisker. The emitted light shows strong polarization anisotropy, which can be explained by the quantum confinement effect. These results indicate that nano-whiskers offer high-quality quantum wire structures, which can be applied to ultra-small opto-electronic devices.
Time-Resolved Luminescence and Optical Gain in II–VI Quantum Dots
Authors: Woggon Ulrike , Wind Oliver , Langbein Wolfgang , Klingshirn Claus
Published: March 2014

The population and depopulation of the lowest electron-hole pair states have been investigated in CdSe and CdSSe quantum dots by time-resolved luminescence experiments on a picosecond time scale. Auger-like scattering processes within the two-pair system created under high excitation present an efficient relaxation mechanism. In nanosecond pump-and-probe experiments the absorption bleaching has been investigated up to the evidence of gain. Gain has been observed both for quantum dots with radii below and above the Bohr radius.
Temperature Dependence of Exciton Radiative Lifetimes in Quantum Wells and Wires
Authors: Ping Er-Xuan
Published: March 2014

The recently measured temperature dependent (from 10 K to 230 K) radiative lifetimes of one- and two-dimensional excitons in novel GaAs quantum wells and quantum wires prepared by one growth [Akiyama et al, Phys. Rev. Lett. 72, 924 (1994)] are explained in terms of exciton transfer among ground and higher excited states including the continuum states.
Semiconductors Quantum Wells and Microcavities
Authors: Weisbuch Claude
Published: March 2014

The two fields of electron quantization in quantum wells, wires, boxes and of photon mode quantization in microcavities and photonic band gap structures are being actively researched worldwide. We discuss the two approaches in a basic manner. Early results of photon-confined structures are recalled, and we describe in details the recent discovery of the photon-matter strong-coupling situation which develops for quantum wells imbedded in monolithic, planar Fabry-Perot microcavities. The coupled-mode excitations, cavity-polaritons, are reminiscent of the excitonic polaritons of bulk materials at low temperatures. We describe a model of luminescence of cavity-polaritons which allows to map their dispersion curve.
Time-Resolved Photoluminescence of PbI2 Clusters Dispersed in CdI2 Crystals
Authors: Gu Ping , Watanabe Masayuki , Hayashi Tetsusuke
Published: March 2014

Luminescence associated with excitation of Pb2+ ions has been investigated in a wide concentration range of Pb1-x
Cd
x
I2 mixed crystals. Small PbI2 clusters become dispersed in a CdI2 crystal by increasing the Pb2+ concentration from the range of dilute impurity to that of mixed crystals. Time-resolved measurement reveals that luminescence at the absorption edge of crystals consists of emission bands with short and long decay times. The two bands are found to originate from the states related to 3P1 and 3P0 of Pb2+ ions. Energy split between the two states decreases with increase in the size of PbI2 cluster. The result is explained by the change in an exchange energy of electron and hole with the cluster size.
Preparation of Nanometer-Size Crystalline Ge by Chemical Sol-Gel Method and Its Visible Photoluminescence
Authors: Maeda Yoshihito
Published: March 2014

Nanometer-size crystalline Ge (nc-Ge) was made from glassy composites prepared by a chemical sol-gel method and annealing. Room temperature photoluminescence (PL) was observed at 1.6-2.5 eV, and the PL peak energy showed a clear blue shift and the intensity increased as the average size of nc-Ge decreased. These PL behaviors were similar to those for nc-Ge prepared by physical vapor deposition.
Study of Scanning Near-Field Optical Microscopy (SNOM) by Nonlocal Response Theory
Authors: Cho Kikuo , Ohfuti Yasushi , Arima Kiyoshi
Published: March 2014

In the pursuit of higher resolution and signal intensity in SNOM by making use of resonant light, we propose to use a microscopic nonlocal theory of optical response, which allows a microscopic description of EM field down to atomic size. Model calculations are shown for various assemblies of spheres with resonant levels. It is demonstrated that the choice of light frequency at various resonances of the system reveals their characteristic near-field patterns, in contrast to the bias voltage dependence of STM. When the light frequency is resonant to a level of the whole system including probe tip, there can be an extreme distortion of image, because the resonant energy changes quickly as one scans the tip. We make a proposal to make a positive use of this effect as a new type of SNOM.
Optical Properties of the Cylindrical Quantum Wires in the Chrysotile Asbestos Channels
Authors: Poborchii V. V.
Published: March 2014

Optical properties of ultrathin wires (nanocylinders) of a variety of materials incorporated within the chrysotile asbestos nanotubes have been studied. A high anisotropy of the Raman and optical absorption spectra of the asbestos containing guest wires have been observed. A strong quantum size effect have been found for the asbestos-confined GaAs wires with ∼6 nm diameters. An amorphization of the structure of the asbestos-confined wires have been observed for a number of materials (Se, InSb).
Nonlinear Optical Response of Disordered J Aggregates in the Motional Narrowing Limit
Authors: Knoester Jasper
Published: March 2014

We discuss the theory of nonlinear optical response of molecular aggregates with frequency disorder. In contrast to the usual modeling, we allow for spatial correlations in the disorder. We show that the joint distribution of all multi-exciton frequencies can be determined analytically to first order in the disorder. It is demonstrated that, unlike linear absorption measurements, two-color pump-probe experiments may be used to observe intermolecular disorder correlations.
Dynamical Properties of Large Coherence Length Excitons in PIC J Aggregates
Authors: Kobayashi Shunsuke , Sasaki Fumio
Published: March 2014

The dynamical behavior of the J band fluorescence excited to the upper exciton band edge and also vibronic band is investigated. Excitation to upper exciton band edge results superradiant decay which is the same as the superradiant decay from lower exciton band edge excitation. Vibronic band excitation results phonon dressed excitons and their nonradiative decay is depend on the excitation intensity. The excitation wavelength dependent natures of the excitons in J band are also investigated by ns pump-probe method which supports the phonon dressed excitons mechanism.
Nitrogen Doping in GaP Microcrystals: A Photoluminescence Study
Authors: Kim Han-Min , Hayashi Shinji , Yamamoto Keiichi
Published: March 2014

We have attempted to produce GaP microcrystals doped with nitrogen atoms by gas evaporation in Ar and N2 mixture gas. Results of photoluminescence measurements at 10K demonstrate that nitrogen substitution for phosphorus in GaP microcrystals has been achieved successfully. The concentration of N atoms can be varied by a control of N2 partial pressure.
Size Dependence of Exciton Linewidth for CuHal Nanoparticles in Glass
Authors: Onushchenko Aleksei A. , Petrovskii Gurii T.
Published: March 2014

Influence of extra annealing of glass samples on optical properties of CuHal crystallites has been investigated. It has been found that considerable narrowing of exciton lines takes place as result of this low temperature heat treatment. Both annealing of crystallite defects and phase transition are responsible for this effect. Size dependence of exciton linewidth has been obtained. It has been shown that the observed dependence can be explained taking into account increase of surface/volume ratio with decreasing of crystallite size.
Mechanism of Photodarkening Effects in CdS-Doped Glass
Authors: Miyoshi Tadaki , Towata Ken-ichi , Matsuo Naoto
Published: March 2014

Luminescence and electron spin resonance (ESR) were measured in CdS-doped glass. Photoinduced centers were detected by ESR. A correlation between the intensity of the ESR signal and the photodarkening effects was observed. ESR spectrum of CdS-doped glass is different from those of host glass and bare CdS particles. The ESR intensity increases sublinearly with excitation intensity. These results indicate that the centers are induced with one-step excitation process at the glass-semiconductor (CdS) interface.
Optical Bistability in ZnSe–ZnS Superlattices Optical Waveguide
Authors: Zheng Z. H. , Guan Z. P. , Chen L. C. , Fan X. W.
Published: March 2014

The excitonic optical nonlinearities and optical bistability are observed in ZnSe-ZnS superlattices optical waveguide at room temperature for the first time. The excitonic absorption band is broadened and tends to saturating absorption, and has a blue shift towards short wavelength side with increasing incident intensities. At higher incident intensity, the switching response time of the optical bistability is 500 ps. The results suggest that the optical nonlinearities are due to the phase space filling of excitonic states, excitonic saturating absorption and excitonic band broadening, while the major contribution to the optical bistability is due to increasing absorption effect caused by phase space filling of excitonic states and excitonic band broadening.
Absorption Spectra and Electronic Structures in ZnSe–ZnS and ZnTe–ZnSe Strained-Layer Superlattices
Authors: Hohnoki Satoshi , Katayama Shin-ichi , Hasegawa Akira
Published: March 2014

Absorption spectra which originate from vertical valence-band-to-conduction-band transitions in type I ZnSe-ZnS and type II ZnTe-ZnSe strained-layer superlattices (SLSs) are studied theoretically. It has been found that the absorption in the type II SLS is one order of magnitude less than that in the type I SLS, and that in the type II SLS the strength for any transitions to the higher conduction and from the higher valence subbands is greater than that to the lower conduction and from the lower valence subbands, in sharp contrast to the type I SLS.
Stark Localization in ZnSe–ZnCdSe Superlattices under an Electric Field
Authors: Guan Z. P. , Zhang J. Y. , Fan X. W.
Published: March 2014

Photoluminescence measurements have been carried out in ZnSe-ZnCdSe Strained-layer superlattices subjucted to an electric field. It is observed that luminescence quenching and the peak shift toward the lower energy side due to the excitonic Stark effect for small electric fields. Subsequently, we find reversal to a blue shift and the luminescence peak enhancement for higher electric field, which is explained by a field-induced localization of carriers to isolated quantum wells.