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Showing papers on "Photoluminescence published in 1988"


Journal ArticleDOI
TL;DR: Amorphous carbon nitride thin films have been grown by plasma decomposition of a feedstock of CH4 and N2 as mentioned in this paper, and the optical absorption and photoluminescence spectra show that nitrogen incorporation decreases the bandgap and increases the structural order of these thin films.

321 citations


Journal ArticleDOI
TL;DR: In this paper, the surface migration is effectively enhanced by evaporating Ga or Al atoms onto a clean GaAs surface under an As-free or low As pressure atmosphere, which is utilized by alternately supplying Ga and/or Al and AS4 to the substrate surface for growing atomically-flat GaAs-AlGaAs heterointerfaces, and also for growing high quality GaAs and AlGaAs layers at very low substrate temperatures.
Abstract: Surface migration is effectively enhanced by evaporating Ga or Al atoms onto a clean GaAs surface under an As-free or low As pressure atmosphere. This characteristic was utilized by alternately supplying Ga and/or Al and AS4 to the substrate surface for growing atomically-flat GaAs-AlGaAs heterointerfaces, and also for growing high-quality GaAs and AlGaAs layers at very low substrate temperatures. The migration characteristics of surface adatoms have been investigated through reflection high-energy electron diffraction measurements. It was found that different growth mechanisms are operative in this method at both high and low temperatures. Both these mechanisms are expected to yield flat heterojunction interfaces. By applying this method, GaAs layers and GaAs-AlGaAs single quantum-well structures with excellent photoluminescence were grown at substrate temperatures of 200 and 300degC, respectively.

311 citations


Journal ArticleDOI
TL;DR: In this article, thin layers of ZnO were grown on (0001) oriented sapphire by organometallic chemical vapor deposition, and low-temperature photoluminescence indicates that near-band edge luminescence dominates the spectrum.
Abstract: Thin layers of ZnO were grown on (0001) oriented sapphire by organometallic chemical vapor deposition. Low‐temperature photoluminescence indicates that near‐band‐edge luminescence dominates the spectrum. In contrast to bulk grown material deep level luminescence for the layers is relatively weak.

284 citations


Journal ArticleDOI
TL;DR: This work has studied the spontaneous emission of light from electron-hole recombination in optically thin GaAs double heterostructures and found the spontaneous-emission rate can be markedly increased or decreased depending on whether the surrounding refractive index is higher or lower than that of GaAs.
Abstract: Inhibited spontaneous emission in atomic physics has been intensively investigated recently. In solid-state physics these effects are no less important. We have studied the spontaneous emission of light from electron-hole recombination in optically thin GaAs double heterostructures. The electron-hole radiative recombination rate coefficient $B$ is not purely a property of the GaAs itself, but depends strongly on the optical-mode density and refractive index of the medium in which it is immersed. The spontaneous-emission rate can be markedly increased or decreased depending on whether the surrounding refractive index is higher or lower than that of GaAs.

278 citations


Journal ArticleDOI
TL;DR: In this article, the photoluminescence properties of CdS superclusters in zeolites have been studied and three different emission bands, all attributed to defects rather than carrier recombination, are observed.
Abstract: Photoluminescence properties of CdS superclusters in zeolites have been studied. Three different emission bands, all attributed to defects rather than carrier recombination, are observed. The yellow-green emission, which can be observed in zeolites X, Y, and A, is attribued to Cd atoms. The red emission is attributed to sulfur vacancies, following previous works on colloidal CdS. The blue emission is due to shallow donors, the nature of which is not yet clear but we suggest it is sulfur related. Both red and blue emissions can be observed only in zeolite A

268 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that the exciton-trapped carrier interaction is mainly responsible for the observed bleaching of the excitonic absorption, and the recovery time of the absorption bleaching is determined by the trapped carrier relaxation time, which is sensitive to fabrication methods and can be controlled by surface chemistry.
Abstract: We report a picosecond pump–probe study of 55 A cadmium sulfide microcrystallites embedded in polymer films. Large negative absorbance changes at wavelengths corresponding to energies near the band gap are observed. This absorption bleaching and the associated changes in refractive index are mainly responsible for the large nonlinearity observed in degenerate four‐wave mixing experiments. Based on photoluminescence data, the known electron‐trapping cross section of defects, and these pump–probe experiments, we show that the conventional carrier density‐dependent band‐filling mechanism cannot account for the data, and the absorption bleaching is due to the saturation of the excitonic transition. We further show that the phase‐space filling and exchange effects from exciton–exciton and exciton‐free carrier interactions fail to account for the observed data. Instead, we propose that the exciton‐trapped carrier interaction is mainly responsible for the observed bleaching of the excitonic absorption. This interaction is unique for small semiconductor clusters since the presence of a high density of defects (most likely on the surfaces) causes the extremely rapid trapping of free carriers. According to this model, the recovery time of the absorption bleaching is determined by the trapped‐carrier relaxation time, which is sensitive to the fabrication methods and can be controlled by surface chemistry. Our study also demonstrates that one needs to understand the effects of surfaces and control the surface chemistry before the important question of size effects on the nonlinear optical properties can be addressed.

216 citations


Journal ArticleDOI
TL;DR: In this article, a dynamical model of the temporal dependence of photostimulated luminescence of the storage phosphor BaFBr:Eu2+ as a result of preceeding x-ray irradiation is presented.
Abstract: A dynamical model of the temporal dependence of photostimulated luminescence of the storage phosphor BaFBr:Eu2+ as a result of preceeding x‐ray irradiation is presented The model is based on a monomolecular recombination mechanism The commonly used bimolecular mechanism leads to contradictions with experimental observations The monomolecular recombination is explained by the existence of a photostimulable luminescence complex with a recombination center and an electron trap in close proximity Charge transfer after optical excitation occurs through tunneling The simulation of the transient charge carrier dynamics is performed through rate equations Good agreement wih experimentally determined temporal responses for different x‐ray doses applied and stimulating light intensities is obtained

190 citations


Journal ArticleDOI
TL;DR: In this paper, the photoluminescence from GaAs/AlxGa1−xAs single and multiple quantum well (QW) heterostructures grown by molecular-beam epitaxy (MBE) has been studied in the temperature range 10
Abstract: The photoluminescence (PL) from GaAs/AlxGa1−xAs single and multiple quantum well (QW) heterostructures grown by molecular‐beam epitaxy (MBE) has been studied in the temperature range 10

183 citations


Journal ArticleDOI
TL;DR: In this article, an explicit model to explain the radiative recombination in noble metals, arising from transitions between electrons in the spconduction band and holes in the d-band generated by optical excitation, was developed.
Abstract: We have developed an explicit model to explain the radiative recombination in noble metals, arising from transitions between electrons in the spconduction band and holes in the d-band generated by optical excitation. We find that the observed photon distribution has its shape from two competing factors. The first is due to the optics and the final density of states for the exiting photons. This is off-set by a d-band density of states factor increasing as the number of available d-states increase. We give a satisfactory account of the observed spectrum, using constant matrix elements, and find that luminescence can be used as a complementary tool to the ordinary elastic light scattering, giving detailed information about occupied and unoccupied states, provided the elastic optical constants are measured on the same sample.

167 citations


Journal ArticleDOI
TL;DR: In this article, a many-body calculation of the electron-hole correlation enhancement is presented, which identifies this peak with the Mahan exciton, the result of the Coulomb interaction between the photoexcited hole in the valence band and the sea of electrons in the conduction band.
Abstract: The temperature-dependent optical absorption and luminescence spectra of GaAs/AlGaAs and InGaAs/InAlAs n-doped modulation-doped quantum wells is discussed with emphasis on the peak seen at the edge of the absorption spectra of these samples A many-body calculation of the electron-hole correlation enhancement is presented, which identifies this peak with the Mahan exciton-the result of the Coulomb interaction between the photoexcited hole in the valence band and the sea of electrons in the conduction band This calculation accounts for the strong dependence of the absorption edge peak on both the temperature and carrier concentration, in good qualitative agreement with experimental data and with previously published results The changes induced by the carriers on the subband structure through self-consistent calculations are also analyzed, and it is concluded that in these symmetric structures, the changes are small for achievable carrier densities >

156 citations


Journal ArticleDOI
TL;DR: In this article, a consistent set of data for the band-gap narrowing in n and p-type material at low temperatures as well as at room temperature was given, and a good agreement was found between the optical and electrical data removing the discrepancies existing so far.
Abstract: The band‐gap narrowing in heavily doped silicon has been studied by optical techniques—namely, photoluminescence and photoluminescence excitation spectroscopy—and by electrical measurements on bipolar transistors. The optical experiments give a consistent set of data for the band‐gap narrowing in n‐ and p‐type material at low temperatures as well as at room temperature. A good agreement is found between the optical and electrical data removing the discrepancies existing so far in the literature.

Journal ArticleDOI
TL;DR: In this article, low-temperature photoluminescence studies of 26 cubic SiC films, ranging in thickness from 600 A to 25 microns, grown by CVD on (100)Si are presented.
Abstract: Low-temperature photoluminescence studies of 26 cubic SiC films, ranging in thickness from 600 A to 25 microns, grown by CVD on (100)Si are presented. It is suggested that the G band near 1.90-1.92 eV and its phonon side bands G1 and G2 are related to dislocations and extended defects. Formulas for the band-gap shift due to an axial stress have been obtained and applied to the CVD 3C-SiC/Si system. The results indicate that a 1-3-micron transition layer greatly reduces the interface misfit strain, and that biaxial stress in the SiC/Si system depresses the intensity of the no-phonon line.

Journal ArticleDOI
TL;DR: In this article, the capture of electrons and holes by quantum wells in multiple quantum well samples of InGaAs/InP was investigated using subpicosecond luminescence spectroscopy.
Abstract: The capture of electrons and holes by quantum wells in multiple quantum well samples of InGaAs/InP is investigated using subpicosecond luminescence spectroscopy. For samples with thin barriers, quantum capture or carrier thermalization dominates. For thicker barriers (>500 A), transport of carriers to the well dominates. We show that quantum capture time is <0.3 ps for holes and <1 ps for electrons. No significant dependence on well thickness is observed. Finally, Coulomb interaction between electrons and holes is shown to ‘‘trap’’ the electrons in unbound states in InGaAs before they are captured by the well.

Journal ArticleDOI
TL;DR: In this paper, a planar magnetron-based sputtering technique was used to fabricate mostly crystallized Si:H with a wide optical band gap and visible photoluminescence at room temperature.
Abstract: The mostly crystallized Si:H having a wide optical band gap and showing a visible photoluminescence at room temperature, has been fabricated by means of a planar magnetron rf sputtering technique in hydrogen gas onto a low temperature (about 100 K) substrate. The materials consist of very small crystalline silicon particles (average diameters: 2–5 nm) surrounded by =SiH2 groups. The observed macroscopic physical properties are explained by the three-dimensional quantum size effects in the ultrafine silicon particles.

Journal ArticleDOI
TL;DR: In this article, the authors describe fabrication and photoluminescence excitation of InGaAs/InP quantum wires with a lateral dimension of ∼350 A. The exciton energies agree with the theoretical predictions based on a new method of solving the two-dimensional effective mass Schrodinger equation.
Abstract: We describe fabrication and photoluminescence excitation of InGaAs/InP quantum wires with a lateral dimension of ∼350 A. Transverse confinement results in the splitting of the n=1 heavy hole‐electron transition. Three of these levels are observed in the excitation spectrum. The exciton energies agree with the theoretical predictions based on a new method of solving the two‐dimensional effective mass Schrodinger equation.

Journal ArticleDOI
TL;DR: In this paper, GaAs epitaxial layers (0.5 μm
Abstract: GaAs epitaxial layers (0.5 μm

Journal ArticleDOI
TL;DR: In this paper, a GaAs/AlGaAs superlattices were partially intermixed via the impurity-free vacancy diffusion process, which allowed continuously variable energy shifts of at least 61 meV while still maintaining clearly resolved excitonic behavior.
Abstract: Substantial increases are observed in the energies of room‐temperature exciton transitions in GaAs/AlGaAs superlattices which have been partially intermixed via the impurity‐free vacancy diffusion process. Localized intermixing of the layered structure was accomplished by selective deposition of a SiO2 capping layer followed by rapid thermal annealing at temperatures between 850 and 950 °C for 15 s. In the samples studied, the above process allows continuously variable energy shifts of at least 61 meV while still maintaining clearly resolved excitonic behavior. Shifting and broadening of the exciton transitions are studied using room‐temperature photoluminescence and photocurrent spectroscopies. A transmission resonance calculation is used to determine the interdiffusion coefficient as a function of temperature from the measured energy shifts.

Journal ArticleDOI
TL;DR: In this paper, rare-earth ions have been systematically incorporated into the cores of silica-based optical fibers, and the absorption and fluorescence spectra have been measured to provide basic data for a wide range of possible future fiber-based devices.
Abstract: Rare-earth ions have been systematically incorporated into the cores of silica-based optical fibers, and the absorption and fluorescence spectra have been measured. The results provide basic data for a wide range of possible future fiber-based devices. For specific telecommunications applications, ions that could be useful for sources in the 1.3- mu m and 1.5- mu m low-loss windows are identified. It is suggested that Er/sup 3+/, Nd/sup 3+/, and Tm/sup 3+/ are the most promising ions for semiconductor pumping with GaAs-based laser diodes. >

Journal ArticleDOI
TL;DR: In this paper, the III-V metastable alloy InP1−x Sbx has been grown for the first time with compositions well inside the miscibility gap, and the bowing parameter for the band gap energy of the InP 1−x sbx was estimated to be 1.9±0.1 eV.
Abstract: The III‐V metastable alloy InP1−x Sbx has been grown for the first time with compositions well inside the miscibility gap. Despite the large miscibility gap at the growth temperatures of 480–600 °C, epilayers with compositions covering the entire range from x=0 to 1.0 have been grown successfully by organometallic vapor‐phase epitaxy at atmospheric pressure using the reactants trimethylindium, trimethylantimony, and phosphine. The 10‐K energy band gap as a function of composition was determined from photoluminescence measurements combined with x‐ray diffraction and electron microprobe analysis. The bowing parameter for the band‐gap energy of the InP1−x Sbx was estimated to be 1.9±0.1 eV. The lattice dynamics have been studied using Raman spectroscopy in the frequency range from 150 to 400 cm−1. Long wavelength optical phonons display a ‘‘two‐mode’’ behavior throughout the entire composition range. The InP‐like longitudinal‐optical and transverse‐optical modes shift to lower frequency with increasing Sb co...

Journal ArticleDOI
TL;DR: In this article, the first p-type conversion in ZnSe grown by molecular beam epitaxy was reported, which is the first report of p−type conversion for ZnS.
Abstract: Molecular beam epitaxy has been used to grow Li‐doped ZnSe on (100)GaAs substrates, resulting in material which exhibits a low‐temperature photoluminescence spectrum dominated by emission from acceptor‐bound excitons, with no evidence of emission from residual donors. Electrical measurements on these films indicate that, while the resistivity of the material is high, the majority carriers are holes. This is the first report of p‐type conversion in ZnSe grown by molecular beam epitaxy.

Journal ArticleDOI
TL;DR: In this article, the authors studied the optical properties of Tm 3+ ions in indium-based heavy metal fluoride glasses and presented absorption and emission spectra as a function of temperature.

Journal ArticleDOI
TL;DR: In this paper, the authors performed photoluminescence spectroscopy of the plasma plume during plasma assisted laser deposition of YBa2Cu3O7−x and found that both atomic and molecular components were present.
Abstract: Photoluminescence spectroscopy of the plasma plume during plasma‐assisted laser deposition of YBa2Cu3O7−x was performed. The spectrum in the range of 355–900 nm was measured at several spatial positions using an optical multichannel analyzer. It was found that both atomic and molecular components were present. Rich emission lines of O, O+, Y, Y+, Ba, Ba+, and Cu were observed, from which the plasma temperature could be estimated. Cu+ emission was conspicuously absent. The mechanism of the plasma process and its relevance to thin‐film formation is discussed.

Journal ArticleDOI
TL;DR: In this article, it was shown that the excitation thresholds of these luminescence bands are located at the transition energies from the outermost core band to the conduction band.
Abstract: Excitation spectra of visible luminescence in CsF (2.5-5.6 eV), CsCl (3.9-6.0 eV), CsBr (4.4-6.2 eV), and RbF (2.6-6.2 eV) have been measured at room temperature with use of synchrotron radiation for the energy range up to 40 eV. It is shown that the excitation thresholds of these luminescence bands are located at the transition energies from the outermost-core band to the conduction band. This fact provides direct evidence for the radiative decay of valence electrons into outermost core holes in which the Auger decay process is energetically impossible in these materials.


Journal ArticleDOI
TL;DR: In this paper, it was shown that samarium in the form of Sm3+ ion acts as a thermally stable electron trap in MgS:Ce,Sm and Mg S:Eu,Sm, while the free hole is captured by a Ce3+ (or Eu2+).
Abstract: Optically stimulated luminescence and thermally stimulated luminescence in MgS:Ce,Sm and MgS:Eu,Sm have been investigated. It appears that samarium in the form of Sm3+ ion acts as a thermally stable electron trap in MgS:Ce,Sm and MgS:Eu,Sm. A Sm3+ ion becomes a Sm2+ ion capturing an electron when these materials are exposed to UV radiation at room temperature, while the free hole is captured by a Ce3+ (or Eu2+). On optically stimulating an UV treated sample, the trapped electrons are released from Sm2+ ions and are recaptured by Ce4+ (or Eu3+) ions leading to the luminescence which is characteristic of Ce3+ (or Eu2+) emission. However, thermal stimulation of these UV treated samples results in luminescence which is characteristic of Sm3+ emissions, indicating that the thermoluminescence results from the release of holes from Ce4+ (or Eu3+) and Sm3+ acts as a luminescence center.

Journal ArticleDOI
TL;DR: In this paper, the photoluminescence spectrum of MgO degassed at high temperature has been reinvestigated using a standard JRC-MgO sample because the contribution of low-coordination surface sites (Mg2+LC-O2-LC) to the observed photolumininescence of the degassed Mg O samples has been recently questioned.
Abstract: The photoluminescence spectrum of MgO degassed at high temperature has been reinvestigated using a standard JRC-MgO sample because the contribution of low-coordination surface sites (Mg2+LC—O2–LC) to the observed photoluminescence of the degassed MgO samples has been recently questioned. The JRC-MgO-I sample exhibits two different types of photoluminescence, i.e. one short-lived with a lifetime of ca. 10–4 s, the other long-lived with a lifetime of 1–104 s. The effect of the degassing temperature of the sample and of added quencher molecules indicates that the short-lived photoluminescence observed under u.v. excitation is a radiative decay process from the charge-transfer-excited complex (Mg+LC—O–LC)* with a lower coordination number of four. However, the luminescence observed after u.v. excitation, i.e. a long-lived emission, is a radiative recombination process of photo-produced electrons and holes via defects such as F+centres. Thus, both charge transfer and defect mechanisms account for the photoluminescence of the MgO degassed at high temperatures, although the long-lived emission is not directly measured in the present work owing to its much smaller contribution.

Journal ArticleDOI
TL;DR: In this article, the authors have grown ZnSe single crystals having various concentrations of Te atoms from a mixture of Te and Se solutions and observed an emission band having phonon structure and peaking at 2.67 eV in slightly Te-doped specimens.

Journal ArticleDOI
TL;DR: In this article, the N-doped ZnSe/n-GaAs heterojunctions were grown on (100) GaAs substrates by metalorganic vapor phase epitaxy using NH3 as the doping material.
Abstract: Nitrogen-doped ZnSe layers have been grown on (100) GaAs substrates by metalorganic vapor phase epitaxy using NH3 as the doping material. The N-doped layers exhibit a strong free-to-acceptor transition emission at 77 K and a strong acceptor bound-exciton emission line at 15 K. The layers with a high doping level, which exhibit broader excitonic emission lines, indicate p-type conduction with low resistivities from 102 to 103 Ω·cm, carrier concentrations of the order of 1014 cm-3 and mobilities from 20 to 50 cm2/Vs. Current-voltage characteristics of the N-doped ZnSe/n-GaAs heterojunctions conform to the p-type conduction.

Journal ArticleDOI
TL;DR: In this paper, InAs1−xSbx films have been successfully prepared by molecular beam epitaxy on (100) InAs substrates and long-wavelength photoluminescence has been investigated over the complete compositional range.
Abstract: InAs1−xSbx films have been successfully prepared by molecular beam epitaxy on (100) InAs substrates. Long‐wavelength photoluminescence has been investigated over the complete compositional range. Luminescence peak wavelengths as long as 8 μm have been obtained for the first time among III‐V compound semiconductor materials in spite of the existence of a large lattice mismatch. These results are indicative of high‐quality material.

Journal ArticleDOI
TL;DR: In this paper, the relationship between sample quality and exciton emission spectra is discussed, and the change in exciton photoluminescence power dependence with excitation wavelength indicates that the superlinear power dependence is due to the formation of excitons from photoexcited electrons and holes.