Showing papers on "Photoluminescence published in 1990"
TL;DR: In this paper, free standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography using electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers.
Abstract: Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
7,393 citations
TL;DR: In this paper, it was shown that Si microcrystallites were embedded in a Si oxide matrix for the sample which emitted the light, and the inverse relation between emission energy and the square of the crystallite size indicates that carrier confinement in the Si micro-crystallite causes this photoluminescence phenomenon.
Abstract: Visible photoluminescence was observed in ultrafine Si particles at room temperature. Transmission electron microscopy revealed that Si microcrystallites were embedded in a Si oxide matrix for the sample which emitted the light. The emission energy depended on crystallite size in the range from 2.8 to 5 nm. The inverse relation between emission energy and the square of the crystallite size indicates that carrier confinement in the Si microcrystallites causes this photoluminescence phenomenon.
793 citations
TL;DR: In this article, the dynamics of charge recombination following electron injection from the excited state of RuL{sub 3} into the conduction band of the semiconductor were examined under potentiostatic control of the electric field within the space charge layer of the membrane.
Abstract: Transparent titanium dioxide membranes (thickness 2.7 {mu}m) were prepared by sintering of 8-nm colloidal anatase particles on a conducting glass support. The dynamics of charge recombination following electron injection from the excited state of RuL{sub 3} (L = 2,2{prime}-bipyridine-4,4{prime}-dicarboxylic acid) into the conduction band of the semiconductor were examined under potentiostatic control of the electric field within the space charge layer of the membrane. Biasing the Fermi level of the TiO{sub 2} positive of the flat-band potential sharply reduced the recombination rate, a 1,000-fold decrease being associated with a potential change of only 300 mV. Photoelectrochemical experiments performed with the same RuL{sub 3}-loaded membrane in NaI-containing water show the onset of anodic photocurrent to occur in the same potential domain. Forward biasing of the membrane potential impairs photosensitized charge injection turning on the photoluminescence of the adsorbed sensitizer.
693 citations
TL;DR: In this article, the physics of the growth mechanisms, characterization of epitaxial structures and device properties of GaAs and other compound semiconductors on Si are reviewed, and the nontrivial problems associated with the heteroepitaxial growth schemes and methods that are generally applied in the growth of lattice mismatched and polar on nonpolar material systems are described in detail.
Abstract: The physics of the growth mechanisms, characterization of epitaxial structures and device properties of GaAs and other compound semiconductors on Si are reviewed in this paper. The nontrivial problems associated with the heteroepitaxial growth schemes and methods that are generally applied in the growth of lattice mismatched and polar on nonpolar material systems are described in detail. The properties of devices fabricated in GaAs and other compound semiconductors grown on Si substrates are discussed in comparison with those grown on GaAs substrates. The advantages of GaAs and other compound semiconductors on Si, namely, the low cost, superior mechanical strength, and thermal conductivity, increased wafer area, and the possibility of monolithic integration of electronic and optical devices are also discussed.
542 citations
TL;DR: The band-gap luminescence is not from the exciton state, but from a surface trapped state and results in long-lived bleach and induced-absorption features in pump-probe experiments.
Abstract: We use transient optical hole burning and photoluminescence to investigate the static and dynamic electronic properties of 32-\AA{} CdSe quantum dots. We observe a number of discrete electronic transitions, resolve LO-phonon progressions, and obtain homogeneous linewidths and electron--LO-phonon couplings. We find that the band-gap luminescence is not from the exciton state, but from a surface trapped state. Rapid (\ensuremath{\sim}160 fs) trapping into these surface states results in long-lived (\ensuremath{\sim}10--100 ns) bleach and induced-absorption features in pump-probe experiments.
509 citations
TL;DR: In this article, a microscopic model of degradation of both the nonlinear optical and luminescent properties of semiconductor-doped glasses is proposed, where the degradation is due to the process of Auger ionization of microcrystals when some electron-hole pairs are excited.
323 citations
TL;DR: In this paper, the infrared photoluminescence (PL) from InSb, InAs, and InAs1−xSbx (x < 0.3) epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been investigated for the first time over an extended temperature range.
Abstract: Infrared photoluminescence (PL) from InSb, InAs, and InAs1−xSbx (x<0.3) epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been investigated for the first time over an extended temperature range. The values of full width at half maximum of the PL peaks show that the epitaxial layer quality is comparable to that grown by molecular‐beam epitaxy. The observed small peak shift with temperature for most InAs1−xSbx epilayers may be explained by wave‐vector‐nonconserving transitions involved in the PL emission. For comparison, PL spectra from InSb/InSb and InAs/InAs show that the wave‐vector‐conserving mechanism is responsible for the PL emission. The temperature dependence of the energy band gaps, Eg, in InSb and InAs is shown to follow Varshni’s equation Eg(T)=Eg0−αT2/ (T+β). The empirical constants are calculated to be Eg0=235 meV, α=0.270 meV/K, and β=106 K for InSb and Eg0=415 meV, α=0.276 meV/K, and β=83 K for InAs.
277 citations
TL;DR: In this article, the authors studied the optical transient bleaching of ∼40 A, ammonia-passivated CdS clusters in a polymer with nanosecond and picosecond pump-probe techniques.
Abstract: We studied the optical transient bleaching of ∼40 A, ammonia‐passivated CdS clusters in a polymer with nanosecond and picosecond pump‐probe techniques. The transient bleaching spectra behave differently in different time regimes. Within the 30‐ps pump laser pulse width, we tentatively attribute the bleaching to the exciton‐exciton interaction, and the magnitude can be enhanced by surface passivation. On time scales of tens of picoseconds and longer following the pump pulse, when only trapped electron‐hole pairs remain from the pump excitation, the bleaching is due to the interaction between such a trapped electron‐hole pair and a bound exciton produced by the probe light. Experimentally we determined that roughly one trapped electron‐hole pair can bleach the excitonic absorption of the whole CdS cluster. We developed a theoretical model which considers the effects of the trapped electron‐hole pair on the energy of the exciton transition and its oscillator strength. We found that, when a trapped electron and hole are present, the lowest exciton absorption is red‐shifted from the original exciton absorption, and this transition has a weak oscillator strength, which explains the observed efficient bleaching. The model also predicts that a trapped electron is more efficient than a trapped hole for bleaching the excitonic absorption of CdS clusters in the size regime considered here. This is confirmed by pulse radiolysis results. Finally, we discuss the possible effects of charged surface defects on the linear absorption spectra of semiconductor clusters.
239 citations
TL;DR: In this paper, optical absorption and photoluminescence measurements of the 19eV emission, excited by various excitation bands, were carried out on high-purity silica glasses subjected to γ-ray irradiation.
Abstract: Optical absorption measurements of the 20‐eV band and photoluminescence measurements of the 19‐eV emission, excited by various excitation bands, were carried out on high‐purity silica glasses subjected to γ‐ray irradiation Two, and possibly three, different forms of nonbridging oxygen hole centers were deconvoluted from the results of the isochronal annealing experiments The difference in the peak wavelength of the 20‐eV absorption and 19‐eV luminescence bands among various forms of nonbridging oxygen hole centers is reported
215 citations
TL;DR: In this article, the photoluminescence intensity increases in the cavity axis direction, and the spontaneous emission lifetime is experimentally found to decrease with an on-resonance cavity structure.
Abstract: Enhanced spontaneous emission has been observed with wavelength‐sized monolithic Fabry–Perot cavities containing GaAs quantum wells. With an on‐resonance cavity structure, the photoluminescence intensity increases in the cavity axis direction, and the spontaneous emission lifetime is experimentally found to decrease.
184 citations
TL;DR: Ceci conduit a une faible augmentation de luminescence des excitons et a une variation inhabituelle de ce temps d'augmentation, en fonction of the temperature, and of l'excitation.
Abstract: Excitons se forment avec une constante de temps τ≤20 ps apres la creation des paires electron-trou par une excitation optique sous-picoseconde. Les excitons sont initialement formes dans des etats de grands vecteurs d'onde. A basses temperatures, ces excitons se relaxent et se couplent par interaction avec d'autres excitons et phonons acoustiques. Ceci conduit a une faible augmentation de luminescence des excitons et a une variation inhabituelle de ce temps d'augmentation, en fonction de la temperature, et de l'excitation
TL;DR: In this article, a homo-epitaxially grown GaN on a thin GaN buffer layer was shown to have high purity and high crystalline quality, and the magnitude of the strain of the homogeneous GaN was less than half that of a hetero-EPITaxially generated GaN.
TL;DR: In this paper, the integer and fractional quantum Hall effects in GaAs were detected using band-gap photoluminescence, in an ultra-high-mobility single heterojunction at 120 mK.
Abstract: We report a definitive optical detection, using band-gap photoluminescence, of the integer and fractional quantum Hall effects in GaAs by a comprehensive study of integer states from \ensuremath{
u}=1 to 10 and the \ensuremath{
u}=2/3 hierarchy out to the 5/9 daughter state, in an ultrahigh-mobility single heterojunction at 120 mK.
TL;DR: In this paper, low-temperature luminescence spectra of CdS microcrystals grown in a transparent silicate glass matrix have been studied and the effects associated with surface band bending in large micro-crystals have been revealed and studied.
TL;DR: The role of vanadium as minority carrier lifetime killer in SiC-based optoelectronic devices is suggested from these data as discussed by the authors, which suggests that vanadium acts as a deep acceptor, V4+Si(3d1)/V3+Si (3d2)−A0/A−, and possibly also as a donor.
Abstract: Trace impurities of vanadium in Lely‐grown silicon carbide single crystals have been detected by their strong, polytype‐specific photoluminescence in the 1.3–1.5 μm near‐infrared spectral range, as well as by infrared absorption. The spectra arise from the intra‐3d‐shell transitions 2E(3d1)→2T2(3d1) of V4+Si(3d1). Electron spin resonance reveals that VSi in SiC acts as a deep acceptor, V4+Si(3d1)/V3+Si(3d2)−A0/A−, and possibly also as a deep donor. The role of vanadium as minority‐carrier lifetime killer in SiC‐based optoelectronic devices is suggested from these data.
TL;DR: In this paper, the first observation of different nitrogen pair complexes in GaAs was made by carefully tuning the pressure, making one after the other of the NNi pairs (1≤i≤10) appear in the band gap of GaAs and then become the major exciton recombination channel.
Abstract: We report on the first observation of different nitrogen pair complexes in GaAs. These complexes, which have been searched for since the ’60s, are studied under the application of hydrostatic pressure. By carefully tuning the pressure, we make one after the other of the NNi pairs (1≤i≤10) appear in the band gap of GaAs and then become the major exciton recombination channel. We compare our results for nitrogen states in GaAs with the classical case of NNi excitons in GaP.
TL;DR: The role played by oxygen impurities in the optical activation of the 1.54 µm luminescence was demonstrated by implanting oxygen into Er implanted layers in silicon at concentrations comparable to those of Er.
Abstract: Luminescence spectra and SIMS measurements of Er-doped silicon are presented in this paper. Luminescence was found to be stronger in Czochralski-grown Si crystals, known to contain up to 1018 cm-3 of oxygen center. Direct role played by oxygen impurities in the optical activation of the 1.54 µm luminescence was demonstrated by implanting oxygen into Er implanted layers in silicon at concentrations comparable to those of Er. Possible mechanisms of enhancement of photoluminescence are discussed.
TL;DR: In this paper, the authors argue that the discussion of interfacial roughness in terms of "an island size" is too naive, and that a full characterization of an interface requires the description of a "roughness spectrum", specifying the amplitude of the interfacial corrugation versus crugation wavelength over the relevant length scale.
Abstract: Luminescence spectra from quantum wells are routinely interpreted in terms of atomically smooth and atomically abrupt interfaces. Here we show that this interpretation is inconsistent with photoluminescence, photoluminescence excitation, and quantitative microscopic (chemical lattice imaging) results. We argue that the discussion of interfacial roughness in terms of ‘‘an island size’’ is too naive. A full characterization of an interface requires the description of a ‘‘roughness spectrum,’’ specifying the amplitude of the interfacial corrugation versus corrugation wavelength over the relevant length scale.
TL;DR: In this paper, the luminescence induced by the recombination of holes with electrons tunneling into cleaved GaAs/AlGaAs heterostructures is used to image the interface region with nanometer resolution.
Abstract: In a scanning tunneling microscope experiment, the luminescence induced by the recombination of holes with electrons tunneling into cleaved (110) GaAs/AlGaAs heterostructures is used to image the interface region with nanometer resolution.
TL;DR: In this article, anneal treatment was found to be optimal for removal of grown-in defect complexes without creating a significant density of misfit dislocations, and peak energies at 4.2 K varied from 620 to 990 meV for Ge fractions from 0.53 to 0.06.
Abstract: Intense photoluminescence (PL) from strained, epitaxial Si1−xGex alloys grown by molecular beam epitaxy is reported with measured internal quantum efficiencies up to 31% from random alloy layers, single buried strained layers, and multiple quantum wells. Samples deposited at ∼400 °C exhibited low PL intensity, whereas annealing at ∼600 °C enhanced the intensity by as much as two orders of magnitude. This anneal treatment was found to be optimal for removal of grown‐in defect complexes without creating a significant density of misfit dislocations. PL peak energies at 4.2 K varied from 620 to 990 meV for Ge fractions from 0.53 to 0.06, respectively. Efficient PL was due to exciton accumulation in the strained Si1−xGex layers of single and multiple quantum wells, where the band gap was locally reduced. Optical transitions associated with the PL occurred without phonon assistance.
TL;DR: In this article, the temperature dependence of photoluminescence spectra of gas-evaporated CdS microcrystals ranging from 200 to 1500A in average size were measured.
TL;DR: In this article, the authors reported the determination of Auger recombination coefficients in bulk and quantum well InGaAs by time-resolved luminescence measurements, and they found that the Auger coefficient decreases slightly with decreasing well width.
Abstract: We report the determination of Auger recombination coefficients in bulk and quantum well InGaAs by time‐resolved luminescence measurements. In bulk InGaAs the coefficient is C=3.2×10−28 cm6/s and has the temperature dependence of the valence‐band Auger effect involving the split‐off valence band. In 11 nm quantum well InGaAs we find C=0.9×10−28 cm6/s, independent of temperature. The Auger coefficient decreases slightly with decreasing well width.
TL;DR: In this paper, it was shown that photoluminescence in InGaAs/GaAs strained-layer quantum wells is strongly quenched by temperatures above 10−100 K, depending on the well width, and thermal activation of electronhole pairs from the wells into the GaAs barriers, followed by nonradiative recombination through a loss mechanism in bulk GaAs.
Abstract: Photoluminescence in InGaAs/GaAs strained‐layer quantum wells is strongly quenched by temperatures above 10–100 K, depending on the well width. Analysis of this dependence shows that the quenching mechanism is thermal activation of electron‐hole pairs from the wells into the GaAs barriers, followed by nonradiative recombination through a loss mechanism in bulk GaAs. The addition of Al to the barriers to improve confinement eliminates loss through this route but introduces another loss mechanism, characterized by an activation energy independent of well width and with a smaller pre‐exponential factor.
TL;DR: In this paper, the authors used deep-level transient spectroscopy (DLTS) and photoluminescence (PL) techniques to investigate deep impurity centers in 6H-silicon carbide layers.
Abstract: 6H-silicon carbide layers are grown by a liquid phase epitaxy (LPE) process. The layers are doped with boron either by ion implantation or during the LPE process from a B-doped silicon melt. Deep-level transient spectroscopy (DLTS), admittance spectroscopy and photoluminescence (PL) are used to investigate deep impurity centers. Two electrically active defect centers are detected: the isolated boron acceptor at EB=Ev+0.3eV and the boron-related D-center at ED=Ev+0.58eV. The yellow luminescence observed in these layers is proposed to be due to pair recombination via D-center and nitrogen donor. Formation and origin of the D-center are discussed.
TL;DR: Optically transparent CdS membranes have been synthesized as mentioned in this paper, which exhibit different mechanical properties (e.g., rigidity, delayed elasticity, and solubility) in the presence of water depending upon the preparation method employed.
Abstract: Optically transparent CdS membranes have been synthesized. Colloidal Q-CdS particles (particle diameter d{sub p} < 40 {angstrom}) carrying short phosphate chains and excess Cd{sup 2+} ions have been directly converted into a microporous membrane form. By controlling ionic strength and particle concentrations, one can link self-organized fusion-free aggregates and avoid formation of powder-like flocculation products. The resultant unsupported membranes exhibit different mechanical properties (e.g., rigidity, delayed elasticity, and solubility) in the presence of water depending upon the preparation method employed. The membrane form of CdS has distinctively different photophysical properties than the precursor colloidal form. Conversion of weakly red luminescent colloids (broad band at 700 nm) into membranes activated an intense room temperature band edge luminescence (BEL) (narrow bands between 450 and 500 nm) attributed to the recombination of excitons and/or shallowly trapped electron/hole pairs.
TL;DR: In this article, the Schumann-Runge bands were used to estimate the concentration of O2 molecules in the glasses with different concentrations by using a wide variety of preparation conditions, such as vapor phase axial deposition, oxidation of SiCl4 in O2H2 flame, and O2 or O2-Ar plasma method with changing preparation conditions.
Abstract: Silica glasses were prepared by three different techniques, vapor phase axial deposition method, oxidation of SiCl4 in O2‐H2 flame, and O2 or O2‐Ar plasma method with changing preparation conditions. This was done with the expectation that O2 molecules dissolve in the glasses with different concentrations by using a wide variety of preparation conditions. O2 molecules were found to be dissolved in the order of 1017 cm−3 and give an optical absorption above 7 eV, the so‐called Schumann–Runge bands. The estimations of concentrations were done by using a molar absorption coefficient of ≡SiOH at 0.46 eV formed under a reaction of O2 with H2 diffusing from atmosphere at high temperature, 1/2 O2+H2+≡Si−O−Si≡ →2≡Si−OH. The concentration directly estimated from the absorption intensity at above 7 eV was consistent with those estimated from the IR band of ≡SiOH. On the ArF excimer laser irradiation of the glasses which possess the absorption band above 7 eV, the well‐known absorption band at 4.8 eV was induced. Th...
TL;DR: A unified theory of the polarization spectra for undoped and doped quantum wells, which explains the diverse features in the spectra.
Abstract: Valence-hole relaxation by acoustic-phonon emission yields spin relaxation through the spin mixing of the hole-band states. In quantum wells, the hole-spin relaxation is incomplete. This leads to a unified theory of the polarization spectra for undoped and doped quantum wells, which explains the diverse features in the spectra.
TL;DR: In this paper, the authors analyzed the effect of strain on the valence subband of GaxIn1−xAs/InP single-quantum-well structures using the model solid theory of Van de Walle and Martin.
Abstract: Single‐quantum‐well structures were grown by atmospheric pressure organometallic vapor‐phase epitaxy, with GaxIn1−xAs layers (0≤x≤1) coherently strained to match the lattice parameter of the InP barrier layers in the (100) growth plane. The strain effects on the band lineups were analyzed using the ‘‘model solid’’ theory of Van de Walle and Martin. The hydrostatic strain component for alloys with x≊1 is shown to be sufficient to marginally convert the type‐II lineups for the unstrained case to type I. The band lineups remain type I for x≊0. Considering the effect of strain, the ‖ (3)/(2) , (1)/(2) 〉 valence subband becomes a slowly varying function of x. Band offsets are predicted over the entire alloy composition and compared with the reported data. The photoluminescence (10 K) peak energies for the 100‐A GaxIn1−xAs/InP single quantum wells compare quite favorably with the calculated strained band gap versus x. For nominal monolayer quantum wells, the peak energies are slightly above 1.1 eV over the enti...
TL;DR: Since fluorescence occurs in the overtone region from high vibrational states, these results demonstrate that energy can be stored in the adsorbate long enough to allow vibrational up-pumping between neighboring molecules.
Abstract: Infrared fluorescence has been observed from a monolayer of 13 C 16 O on NaCl(100) following vibrational excitation of its fundamental absorption band with ,a pulsed CO gas laser. Direct time-domain measurements of the fluorescence reveal a lifetime of 4.3 ms. Since fluorescence occurs in the overtone region from high vibrational states, these results demonstrate that energy can be stored in the adsorbate long enough to allow vibrational up-pumping between neighboring molecules
TL;DR: In this paper, optically pumped laser action in (Zn,Cd)Se/ZnSe multiple quantum well structures prepared by molecular beam epitaxy on lattice matched bulk (Ga,In)As substrates was reported.
Abstract: We report on studies of optically pumped laser action in (Zn,Cd)Se/ZnSe multiple quantum well structures prepared by molecular beam epitaxy on lattice‐matched bulk (Ga,In)As substrates. Room‐temperature lasing under pulsed excitation with threshold pump intensity at I≊500 kW/cm2 has been achieved, together with high repetition ‘‘quasi‐continuous’’ mode operation at temperatures so far up to 100 K.