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Showing papers on "Photoluminescence published in 1991"


Journal ArticleDOI
01 Sep 1991-Nature
TL;DR: In this paper, the structure of the porous layers that emit red light under photoexcitation was revealed, which constitutes direct evidence that highly porous silicon contains quantum-size crystalline structures responsible for the visible emission.
Abstract: LIGHT-emitting devices based on silicon would find many applications in both VLSI and display technologies, but silicon normally emits only extremely weak infrared photoluminescence because of its relatively small and indirect band gap1. The recent demonstration of very efficient and multicolour (red, orange, yellow and green) visible light emission from highly porous, electrochemically etched silicon2,3 has therefore generated much interest. On the basis of strong but indirect evidence, this phenomenon was initially attributed to quantum size effects within crystalline material2, but this interpretation has subsequently been extensively debated. Here we report results from a transmission electron microscopy study which reveals the structure of the porous layers that emit red light under photoexcitation. Our results constitute direct evidence that highly porous silicon contains quantum-size crystalline structures responsible for the visible emission. We show that arrays of linear quantum wires are present and obtain images of individual quantum wires of width <3 nm.

1,285 citations


Journal ArticleDOI
TL;DR: In this paper, the average radius of the Ge microcrystals in SiO2 was determined by means of Raman spectroscopy and high resolution electron microscope, which is consistent with quantum confinement of electrons and holes.
Abstract: Ge microcrystals embedded in SiO2 glassy matrices were formed by a radio‐frequency magnetron cosputtering technique and then annealed at 800 °C for 30 min. The average radius of the Ge microcrystals in SiO2 was determined to be about 3 nm by means of Raman spectroscopy and high resolution electron microscope. The annealed sample showed a strong room temperature luminescence with a peak at 2.18 eV. This is consistent with quantum confinement of electrons and holes.

573 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of impurity coimplantation in MeV erbium-implanted silicon is studied and a significant increase in the intensity of the 1.54μm Er3+ emission was observed for different coimplants.
Abstract: The effect of impurity coimplantation in MeV erbium‐implanted silicon is studied. A significant increase in the intensity of the 1.54‐μm Er3+ emission was observed for different coimplants. This study shows that the Er3+ emission is observed if erbium can form an impurity complex in silicon. The influence of these impurities on the Er3+ photoluminescence spectrum is demonstrated. Furthermore we show the first room‐temperature photoluminescence spectrum of erbium in crystalline silicon.

383 citations


Journal ArticleDOI
TL;DR: In this article, the photoluminescence (PL) intensity and Fourier transform infrared spectroscopy were performed concurrently on porous Si and it was shown that SiH2 is essential to the visible luminescence in porous Si.
Abstract: Thermal annealing studies of the photoluminescence (PL) intensity and Fourier‐transform infrared spectroscopy have been performed concurrently on porous Si. A sharp reduction in the PL intensity is observed for annealing temperatures ≳300 °C and this coincides with desorption of hydrogen from the SiH2 surface species. A brief etch in HF can restore the luminescence of the samples annealed below 400 °C. We conclude that SiH2 is essential to the visible luminescence in porous Si.

303 citations


Journal ArticleDOI
TL;DR: In this article, the p-n junction GaN junction LED, which emits UV light and violet-blue light at RT, is fabricated for the first time, and the LEEBI treatment is found to be effective to lower the resistivity of the GaN:Mg, and to get the p type GaN.

288 citations


Journal ArticleDOI
TL;DR: The luminescence from excitons confined in fully strained SiGe quantum wells is reported, and quantum-confinement effects shift the observed free-exciton edge above the bulk strained band-gap energy.
Abstract: We report the first well-resolved band-edge luminescence from excitons confined in fully strained SiGe quantum wells grown on Si. At liquid-He temperatures the photoluminescence is due to shallow bound excitons, and in addition to a no-phonon line, phonon-assisted transitions involving TA phonons and Si-Si, Si-Ge, and Ge-Ge TO phonons are observed At higher temperatures the spectra are dominated by free-exciton luminescence. Quantum-confinement effects shift the observed free-exciton edge above the bulk strained band-gap energy, and also influence the relative intensities of the three TO-phonon replicas.

272 citations


Journal ArticleDOI
TL;DR: A coherent undrestanding of spin relaxation of electrons, holes, and excitons in quantum wells is obtained by investing subpicosecond dynamics of luminescence polarization.
Abstract: We have obtained a coherent understanding of spin relaxation processes of electrons, holes, and excitons in quantum walls by investigating subpicosecond dynamics of luminescence polarization. We show that the spin behavior for electrons and holes in quasi-two-dimensional systems is distinct from that in bulk semiconductors and that many-body effects and formation process play an important role in exciton spin relaxation.

245 citations


Journal ArticleDOI
TL;DR: In this article, the dependence of a near-band edge emission on the indium mole fraction of InGaN has been investigated, and the photoluminescence has been observed for the first time.
Abstract: InGaN single‐crystal films were grown on (0001) plane sapphire substrates at 800 °C by metalorganic vapor phase epitaxy. By using such a high temperature for growth, the crystalline quality has been greatly improved. But a high nitrogen over pressure and high indium source flow rate were necessary to achieve significant indium incorporation during growth. For the first time, photoluminescence has been observed in InGaN, and near‐band edge emission is seen in the photoluminescence at 77 K. From this photoluminescence, the dependence of a near‐band edge emission on the indium mole fraction of InGaN has been investigated.

232 citations


Journal ArticleDOI
TL;DR: The surace structure gives rise to lateral quantum-size effects which result in increased exciton continuum energies, in strong exciton-phonon interaction, and in pronounced optical anisotropy.
Abstract: We report on the direct synthesis of superlattices with lateral corrugation of the interfaces on (211), (311), and (111) GaAs substrates by moelcular-beam epitaxy. Reflection electron diffraction directly shows the formation of arrays of macrosteps during epitaxial growth. High-resolution transmission electron microscopy confirms the transfer of the surface structure to the GaAs/AlAs interface which results in distinct energy shifts in the luminescence of GaAs/AlAs multilayer structures. The surace structure gives rise to lateral quantum-size effects which result in increased exciton continuum energies, in strong exciton-phonon interaction, and in pronounced optical anisotropy.

216 citations


Journal ArticleDOI
TL;DR: Relaxation of a nonequilibrium distribution of electrons and holes in GaAs following femtosecond photoexcitation is investigated via spectrally and time-resolved luminescence, demonstrating carrier-carrier scattering rates higher than predicted by calculations with a statically screened interaction potential.
Abstract: Relaxation of a nonequilibrium distribution of electrons and holes in GaAs following femtosecond photoexcitation is investigated via spectrally and time-resolved luminescence. A rapid onset of luminescence over a broad spectral range shows that both electrons and holes are redistributed over a wide energy range within 100 fs, even at excitation densities as low as ${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. The data demonstrate carrier-carrier scattering rates higher than predicted by calculations with a statically screened interaction potential. Monte Carlo simulations using dynamical screening account for the experimental results.

214 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that strong visible photoluminescence can be obtained directly from as-formed high-porosity porous silicon samples, without need for subsequent chemical dissolution.

Journal ArticleDOI
TL;DR: Variational calculations of the ground-state exciton energy in quantum wells have been done, and the results agree with the experimental data, providing evidence for exciton confinement in organic quantum-well structures.
Abstract: Multiple-quantum-well structures based on two crystalline organic semiconductors, namely, 3,4,9,10 perylenetetracarboxylic dianhydride and 3,4,7,8 naphthalenetetracarboxylic dianhydride, have been grown by organic molecular-beam deposition. Both optical-absorption and time-resolved photoluminescence measurements reveal a significant effect on the binding energy and the radiative recombination probability of excitons due to localization of carriers. Variational calculations of the ground-state exciton energy in quantum wells have been done, and the results agree with the experimental data. This provides evidence for exciton confinement in organic quantum-well structures.

Journal ArticleDOI
TL;DR: Metal-insulator-semiconductor structures with poly (3-hexyl thienylene) as the active semiconductor are fabricated and the strong confinement deduced for the polaron is contrasted with the weak confinement observed for bipolarons.
Abstract: We have fabricated metal-insulator-semiconductor structures with poly(3-hexyl thienylene) as the active semiconductor. Optical-absorption bands due to injected carriers seen near 0.4, 1.80, and 2.16 eV are assigned to the optical transitions of the singly charged polaron, which is expected to be the thermodynamically favored excitation under these experimental conditions. Additional absorption bands at 0.5 and 1.18 eV are assigned to optical transitions of doubly charged bipolarons. We contrast the strong confinement deduced for the polaron (gap states separated by 1.80 eV) with the weak confinement observed for bipolarons (gap states separated by 0.7 eV).

Book ChapterDOI
01 Jan 1991
TL;DR: In this paper, the authors used luminance spectra for activator identification in calcite and dolomite, and found that 10-20 ppm Mn2* in solid solution is sufficient to produce visually detectable luminescence, if total Fe contents are below about 150 ppm.
Abstract: Luminescence in calcite and dolomite is governed by physical phenomena that are common to all oxygen-dominated crystalline substances, including other carbonates and silicates. Absorption of excitation energy, energy transfer, and emission involve predictable transitions between electronic energy levels. Strong emission in various colors is always caused by impurities which function as activators of luminescence. Visible luminescence is not expected from pure, undistorted insulators, including carbonates. However, a faint blue 'intrinsic' luminescence, with a broad emission peak (band) around 400 nm, presumably caused by lattice defects, occurs in pure calcite and dolomite, and even in some samples containing impurities. The most important activators in carbonates are transition elements and rare earth elements. Luminescence spectra can be used for activator identification. These spectra are largely independent of the type of excitation, e. g., electron beam (cathodoluminescence = CL), photon (photoluminescence = PL), X-Ray (radioluminescence = RL) excitation, and others. Emission intensities depend on activator, sensitizer, and quencher concentrations, and on the method of excitation. At a given activator concentration, the luminescence intensity generally increases with an increase in excitation energy from PL (relatively weak) to CL (strong). Changes in visual luminescence color between different excitation methods are caused by relative changes in emission peak heights. Mn2* appears to be the most abundant and important activator in natural calcite and dolomite. Substituting for calcium in both minerals, its emission is orange-red to orange-yellow, with a fairly broad band between 570-640 nm (maximum between 590-620 nm). The emission band maximum of Mn2* substituting for Mg2* (in dolomite) is located around 640-680 nm. As little as 10-20 ppm Mn2* in solid solution are sufficient to produce visually detectable luminescence, if total Fe contents are below about 150 ppm. Sm3* activated luminescence can be visually indistinguishable from that activated by Mn2*. The spectrum of Sm3* emission, however, is quite distinct from that of Mn2* and consists of three narrow bands at 562 nm, 604 nm, and 652 nm. Tb3+ and Dy3+ activate green and cream-white luminescence, respectively. The main emission of Tb3* is at 546 nm. The emission of Dy3t consists of three bands, located at 484 nm, 578 nm, and 670 nm. Emission from Eu-containing calcite is red or blue. Narrow spectral bands of 590 nm, 614 nm, and 656 nm are caused by Eu3* and correspond to the red emission. A broad emission spanning a large range of shorter wavelengths is caused by Eu2* and corresponds to the blue emission. As in the case of Sm3*-activated luminescence, the red Eu3* luminescence can be mistaken visually for Mn2*-activated luminescence. Visual luminescence detection limits for rare earths are on the order of 10 ppm. Pb2* is an activator, with an emission band around 480 nm, but it also is a sensitizer of Mn2*-activated luminescence in carbonates. Another recognized sensitizer for Mn2* in carbonates is Ce3*. Sensitizers appear to be effective at concentrations as low as 10 ppm in calcite. Quenchers of Mn2*-activated luminescence in carbonates are Fe2*, Co2*, Ni2*, and Fe3*. The concentrations at which quenchers appear to be effective may vary from element to element and with host mineralogy. Effective minimum concentrations as low as 30-35 ppm have been reported for calcite. The interplay of Mn2* and Fe2*, commonly regarded to be the most important activator and quencher, respectively, in determining the luminescence characteristics of natural carbonates is not well understood because the available data are partially inconsistent. The Mn/Fe ratio may exert a control on luminescence intensity. Mn and Fe concentrations at which 'bright' CL changes to 'dull' can be determined only semi-quantitatively. The available data on the concentration of Mn2* at which quenching starts are partially inconsistent Consequently, the Mn2* concentration at which concentration extinction occurs has not been determined unequivocally. The data presented and summarized in this paper can be used as a basis for the interpretation of luminescence of geological materials. Li particular, knowledge of the possibilities and complexities of activation, sensitization, and quenching has great potential for the interpretation of diagenetic carbonate cements.

Journal ArticleDOI
TL;DR: In this paper, MeV erbium ion implantation into micron-thick silica and phosphosilicate glass films and 1200-Athick Si3N4 films was studied with the aim of incorporating the rare earth dopant on an optically active site in the network.
Abstract: Implantation of MeV erbium ions into micron‐thick silica and phosphosilicate glass films and 1200‐A‐thick Si3N4 films is studied with the aim of incorporating the rare‐earth dopant on an optically active site in the network. Implantation energies and fluences range from 500 keV to 3.5 MeV and 3.8×1015 to 9.0×1016 ions/cm2. After proper thermal annealing, all implanted films show an intense and sharply peaked photoluminescence spectrum centered around λ = 1.54 μm. The fluorescence lifetime ranges from 6 to 15 ms for the silica‐based glasses, depending on annealing treatment and Er concentration. Silicon nitride films show lower lifetimes, in the range <0.2–7 ms. Annealing characteristics of all materials are interpreted in terms of annealing of ion‐induced network defects. These defects are identified using photoluminescence spectroscopy at 4.2 K. Concentration quenching, diffusion and precipitation behavior of Er is also studied.

Journal ArticleDOI
TL;DR: In this article, the steady-state photoluminescence of (100)-oriented GaAs has been studied using x-ray photoelectron spectroscopy and steadystate photodynamic properties of GaAs surfaces exposed to inorganic and organic donors.
Abstract: Steady-state photoluminescence, time-resolved photoluminescence, and x-ray photoelectron spectroscopy have been used to study the electrical and chemical properties of GaAs surfaces exposed to inorganic and organic sulfur donors. Despite a wide variation in S2–(aq) concentration, variation of the pH of aqueous HS–solutions had a small effect on the steady-state n-type GaAs photoluminescence intensity, with surfaces exposed to pH=8, 0.1-M HS–(aq) solutions displaying comparable luminescence intensity relative to those treated with pH=14, 1.0-M Na2S·9H2O(aq). Organic thiols (R-SH, where R=–CH2CH2SH or –C6H4Cl) dissolved in nonaqueous solvents were found to effect increases in steady-state luminescence yields and in time-resolved luminescence decay lifetimes of (100)-oriented GaAs. X-ray photoelectron spectroscopy showed that exposure of GaAs surfaces to these organic systems yielded thiols bound to the GaAs surface, but such exposure did not remove excess elemental As and did not form a detectable As2S3 overlayer on the GaAs. These results imply that complete removal of As0 or formation of monolayers of As2S3 is not necessary to effect a reduction in the recombination rate at etched GaAs surfaces. Other compounds that do not contain sulfur but that are strong Lewis bases, such as methoxide ion, also improved the GaAs steady-state photoluminescence intensity. These results demonstrate that a general class of electron-donating reagents can be used to reduce nonradiative recombination at GaAs surfaces, and also imply that prior models focusing on the formation of monolayer coverages of As2S3 and Ga2S3 are not adequate to describe the passivating behavior of this class of reagents. The time-resolved, high level injection experiments clearly demonstrate that a shift in the equilibrium surface Fermi-level energy is not sufficient to explain the luminescence intensity changes, and confirm that HS– and thiol-based reagents induce substantial reductions in the surface recombination velocity through a change in the GaAs surface state recombination rate.

Journal ArticleDOI
TL;DR: In this article, a low-pressure metalorganic chemical vapor deposition of high quality single-crystal GaN layers over basal plane sapphire substrates was reported, achieving a carrier densities of 1017 /cm3 at room temperature and corresponding mobilities around 350 cm2 /V
Abstract: We report on the low‐pressure metalorganic chemical vapor deposition of high quality single‐crystal GaN layers over basal plane sapphire substrates. Optimization of growth conditions resulted in material with carrier densities of 1017 /cm3 at room temperature and corresponding mobilities around 350 cm2 /V s. The photoluminescence linewidths improved from 160 meV [full width at half maximum (FWHM)] to 25 meV (FWHM). With improved material quality we were able to observe the polar optical mode and the ionized impurity scattering regimes in the mobility versus temperature data. Good quality Schottky barriers were formed on the as‐grown material using a tungsten probe and an alloyed indium contact. Our observations indicate a direct correlation between electrical and optical characteristics of good material and strongly question nitrogen vacancies as the sole explanation for the high carrier densities observed in poor quality GaN growths.

Book
01 Jan 1991
TL;DR: In this article, a model system for new Phenomena is presented for new properties of polyaniline: charge transfer crystals and molecular conductors, non-linear optical Spectroscopy of Conjugated Polymers, Pulsed Neutron Studies of Materials, Photoluminescence Spectrography of Thin Film Semiconductor Materials Vibrational Spectrograms of Polyconjugated Materials.
Abstract: Charge Transfer Crystals and Molecular Conductors Non-linear Optical Spectroscopy of Conjugated Polymers Pulsed Neutron Studies of Materials Photoluminescence Spectroscopy of Thin Film Semiconductor Materials Vibrational Spectroscopy of Polyconjugated Materials: Polyacetylenes and Polyenes Spectroscopy and Photoexcitation Spectroscopy of Polyaniline: A Model System for New Phenomena.

Journal ArticleDOI
TL;DR: In this paper, it was shown that UV-excited porous Si (PS) exhibits an efficient visible photoluminescence (PL) at room temperature, which can be interpreted as a result of quantum size effects in PS.
Abstract: It is shown that UV-excited porous Si (PS) exhibits an efficient visible photoluminescence (PL) at room temperature. The PS layers were formed by anodization of p-type and n-type single-crystal Si wafers in aqueous HF solutions. The peak wavelength of PL spectra depends on the anodization parameters including the resistivity and the conduction type of Si substrates. The PL spectra can be tuned to a higher energy side by either adjustment of the anodizing conditions or chemical etching after anodization. These remarkable results can be interpreted as a result of quantum size effects in PS.

Journal ArticleDOI
TL;DR: In this article, the optical properties of ZnSe/Zn0.86Cd0.14Se single quantum well have been investigated under direct and indirect excitation, and the temperature dependence of photoluminescence and resonant Raman scattering are investigated.
Abstract: The optical properties of strained‐layer ZnSe/Zn0.86Cd0.14Se single quantum wells have been studied. The photoluminescence under direct and indirect excitation is investigated in detail. The temperature dependence of photoluminescence and resonant Raman scattering are investigated. Very strong 2LO‐phonon Raman scattering has been observed with Zn0.86Cd0.14Se quantum wells, where the scattered photon energy is in resonance with an exciton transition. Experimental exciton energies are compared with a finite‐square‐potential quantum‐well model including band nonparabolicity and the strain effect. Based on Hill’s theory [J. Phys. C 7, 521 (1974)] we have computed the band gap of Zn1−xCdxSe as a function of composition x.

Journal ArticleDOI
TL;DR: The p-type ZnSe layers exhibited the 2.616-eV emission from recombination between free electrons and acceptor holes (FA) in room-temperature photoluminescence measurement as mentioned in this paper.
Abstract: p-type ZnSe layers have been grown by molecular beam epitaxy using nitrogen radical doping. We have employed Pt as the electrode material for p-type ZnSe. The Pt electrodes markedly reduced contact resistances. The p-type conduction was confirmed by Hall measurement. Carrier concentration was 4.4×10 15 cm −3 . Hall mobility was a high as 86 cm 2 /V•s because of good crystallinity. The p-type ZnSe layers exhibited the 2.616-eV emission from recombination between free electrons and acceptor holes (FA) in room-temperature photoluminescence measurement. The FA emission provides evidence that the layers are p-type ZnSe

Journal ArticleDOI
TL;DR: The first example of a dilute magnetic semiconductor confined in all three dimensions (DMS quantum dot) was reported in this paper, where Zn0.93Mn 0.07S clusters of not, vert, similar 25 A diameter were successfully synthesized inside a glass matrix and fully characterized by chemical analysis, x-ray diffraction, extended xray absorption fine structure (EXAFS), and photoluminescence spectroscopy.

Journal ArticleDOI
TL;DR: In this paper, the authors used anodization techniques to process porous surface regions in p-type Czochralski Si and in P-type Si0.85Ge0.15 epitaxial layers grown by molecular beam epitaxy.
Abstract: We have used anodization techniques to process porous surface regions in p-type Czochralski Si and in p-type Si0.85Ge0.15 epitaxial layers grown by molecular beam epitaxy. The SiGe layers were unrelaxed before processing. We have observed strong near-infrared and visible light emission from both systems. Analysis of the radiative and nonradiative recombination processes indicate that the emission is consistent with the decay of excitons localized in structures of one or zero dimensions.

Journal ArticleDOI
TL;DR: In this paper, needle-shaped quantum size microcrystals as thin as 10 nm have been selectively grown by employing reduced pressure organometallic vapor phase epitaxy using trimethylgallium and arsine as source materials.
Abstract: Needle‐shaped quantum size microcrystals as thin as 10 nm have been selectively grown by employing reduced pressure organometallic vapor phase epitaxy using trimethylgallium and arsine as source materials. The microcrystals grown within a SiO2 window area have their growth axes along the [111] direction. Transmission electron diffraction analysis shows that the crystal structure of microcrystals is consistent with the zinc‐blende structure of GaAs. The mechanism for growing the needle‐shaped crystals is similar to a vapor‐liquid‐solid (VLS) equilibrium phase growth model. From photoluminescence measurements at 4.2 K, it is found that the microcrystals show a very distinct spectra for free exciton and neutral acceptor‐bound exciton recombinations, meaning good crystal quality.

Journal ArticleDOI
TL;DR: In this article, a new method of doping for ZnSe was attempted by using a neutral radical beam during the MBE growth, which dominantly consisted of N2 molecular radicals at A3σ+u state.

Journal ArticleDOI
TL;DR: In this article, optical absorption and luminescence studies of Cr3+-doped silicate glasses with compositions chosen to vary the octahedral crystal-field splitting at the Cr 3+ site are presented.
Abstract: This paper reports optical absorption and luminescence studies of Cr3+-doped silicate glasses with compositions chosen to vary the octahedral crystal-field splitting at the Cr3+ site. The extensive site-to-site disorder in the glasses is signalled by the inhomogeneous broadening of radiative transitions and by non-exponential fluorescence decay patterns. Laser-excited luminescence shows that the octahedral crystal-field splitting Dq varies between the different sites occupied by Cr3+ ions. Both R-line and 4T2 to 4A2 emissions are inhomogeneously broadened by site-to-site disorder. Fluorescence line narrowing (FLN) of the R line gives a particularly dramatic demonstration of the site multiplicity. Measurement of the width of the FLN component of the R line as a function of temperature has been used to probe the density of two-level vibrational systems coupled to the electronic levels of the Cr3+ ion.

Journal ArticleDOI
TL;DR: The first observation of near-UV vertical-cavity stimulated emission from a photopumped GaN epilayer at room temperature was reported in this article, where an AIN-coated basal plane sapphire substrate using low-pressure metalorganic chemical vapor deposition.
Abstract: We report the first observation of near‐UV vertical‐cavity stimulated emission from a photopumped GaN epilayer at room temperature. The epilayer was deposited over AIN‐coated basal plane sapphire substrate using low‐pressure metalorganic chemical vapor deposition. Epitaxy quality of a 1.5‐μm‐thick GaN layer was high enough to achieve stimulated emission at room temperature. The observed near‐UV optical emission power was a nonlinear function of the pump power density. At threshold power density, we also observed line narrowing and a shift of the peak UV emission towards longer wavelengths. Data comparing the UV emission for the vertical‐cavity and the edge emission geometry are also presented.

Journal ArticleDOI
TL;DR: In this paper, strong photoluminescence with sub-band-gap photon energies has been observed in fine Si particles prepared by the gas-evaporation technique, the band tail covering the visible light region.
Abstract: Strong photoluminescence with sub‐band‐gap photon energies has been observed in fine Si particles prepared by the gas‐evaporation technique. After surface oxidation, the Si particles show above‐band‐gap photoluminescence, the band tail covering the visible light region. The amount of the increased apparent band gap (0.3 eV) estimated from this blueshift can be explained by a quantum‐size effect expected to be observed in Si quantum dots with a diameter of 50 A.

Journal ArticleDOI
TL;DR: Photoluminescence and resonant-Raman-scattering studies of single GaAs/AlAs quantum-well structures show that there is a large-scale island structure at the interfaces and shifts in the absolute exciton energies of quantum wells grown at different substrate temperatures indicate that there also exists a small-scale structure on the interfaces.
Abstract: We report photoluminescence and resonant-Raman-scattering studies of single GaAs/AlAs quantum-well structures. Splittings of the exciton peaks show that there is a large-scale island structure at the interfaces. Shifts in the absolute exciton energies of quantum wells grown at different substrate temperatures and also the form of the optical-phonon energies as a function of both mode index and quantum-well width indicate that there also exists a small-scale structure on the interfaces.