Showing papers on "Photoluminescence published in 1984"
TL;DR: In this paper, a silicon-related intrinsic defect called triplet-to-singlet transitions in the SiO2 optical absorption band was identified. But the most probable model for this center is a silicon atom with only two neighboring oxygens.
286 citations
TL;DR: The detailed structure of porous Si (PS) layers formed in p-type wafers with resistivities 0.01-25 Omega cm has been investigated using reflectance, transmission, ellipsometry and photoluminescence techniques as discussed by the authors.
Abstract: The detailed structure of porous Si (PS) layers formed in p-type wafers with resistivities 0.01-25 Omega cm has been investigated using reflectance, transmission, ellipsometry and photoluminescence techniques. Marked differences were observed in the optical properties of PS formed in degenerate or non-degenerate Si and these results are correlated with the results of other techniques. The optical techniques together with effective medium modelling have been shown to be useful non-destructive methods for either assessment of PS density or detection of unsuspected phases. The degenerate PS layers consistently showed good retention of the single-crystal characteristics of the starting wafer, only c-Si and voids being detected. For these samples, good agreement was obtained between optical and gravimetric densities. However, the non-degenerate PS had much greater variability, with greater loss of crystallinity and significant incorporation of oxygen, due to partial oxidation having occurred on or immediately after anodisation. Oxide fractions have been determined both optically and gravimetrically, with up to 50% oxide being detected in some samples. Non-degenerate PS samples with high oxygen concentrations appeared to be in the form of a chemical mixture, SiOx, from interpretation of the optical constants. Photoluminescence measurements together with the other techniques indicated a complex mixture of phases in the latter samples-voids, alpha -Si:O (and/or alpha -Si:H), an unknown amorphous phase and silicon oxide. This complex structure probably contributes to the observed instability of thick non-degenerate PS layers when heated in UHV as part of the cleaning procedure prior to epitaxial growth, all degenerate samples being able to withstand heat treatment.
272 citations
TL;DR: In this paper, the epitaxial growth of GaAs and AlGaAs on (100) oriented Si substrates by molecular beam epitaxy was studied in situ by reflection high-energy electron diffraction.
Abstract: We have grown GaAs and AlGaAs on (100) oriented Si substrates by molecular beam epitaxy. The epitaxial growth was studied in situ by reflection high‐energy electron diffraction. Low‐temperature photoluminescence, Raman scattering, and scanning electron microscopy were used to characterize the epitaxial layers. It is shown for the first time that antiphase disorder could be suppressed. The doped AlGaAs grown directly on Si substrates exhibited PL efficiency similar to that of AlGaAs grown on GaAs substrates.
213 citations
TL;DR: In this article, a lattice-defect model is invoked to explain the behavior of CdS particles in the presence of acceptors such as methyl viologen (MV2+): 10−8 mol dm−3 MV2+ suffices to quench 50% of the emission.
Abstract: Colloidal particles of CdS are produced by adding H2S to aqueous solutions of Cd(NO3)2(method 1) or rapid mixing of Na2S and Cd(NO3)2 solutions (method 2). Single crystals with cubic structure are obtained, their size being 50 and 20 A, respectively. Type 1 particles are associated as dimers or trimers while type 2 particles form larger clusters of 2000–3000 A size in aqueous solution.Luminescence studies, carried out mainly with type 1 sol, show the presence of a red emission (λmax≈ 700 nm) arising from sulphur vacancies and a very weak green fluorescence (λmax≈ 515 nm) due to free-carrier recombination. The red luminescence is extremely sensitive to the presence of acceptors such as methyl viologen (MV2+): 10–8 mol dm–3 MV2+ suffices to quench 50% of the emission. Kinetic analysis shows that only one MV2+ per CdS aggregate is required to quench completely the red luminescence. This effect is exploited to determine the aggregation number of CdS particles. MV2+ also induces a green emission (λmax≈ 530 nm, ϕ= 4 × 10–3) which is attributed to the formation of Cd vacancies.A green emission (λmax≈ 520 nm) is also obtained by substitutional doping of type 1 sol with chloride, and this arises from interstitial sulphur. Doping with Cu2+ produces the characteristic emission of this activator (λmax≈ 820 nm) only if particles are prepared under aerobic conditions or illuminated in the presence of oxygen. A lattice-defect model is evoked to explain this behaviour.
210 citations
TL;DR: In this paper, the authors studied the picosecond time dependence of luminescence from a two-dimensional electron system following absorption of an ultrashort light pulse, and determined the temporal evolution of the carrier temperature, finding that the cooling of hot carriers is suppressed by a factor 60 below that predicted on a three-dimensional nondegenerate-electron model.
Abstract: We have studied the picosecond time dependence of luminescence from a two-dimensional electron system following absorption of an ultrashort light pulse. From our measurements we determine the temporal evolution of the carrier temperature, finding that the cooling of hot carriers is suppressed by a factor 60 below that predicted on a three-dimensional nondegenerate-electron model. Additionally, we determine the electron-hole radiative life-time and invoke a hole trap to explain shortened luminescence lifetimes at low carrier densities.
200 citations
TL;DR: In this article, the results of low-temperature photoluminescence experiments performed on GaAs single quantum wells grown by metal organic chemical-vapor deposition are presented, showing that the luminescence line is down shifted by a few milli-electron-volts below the heavy-hole exciton absorption peak.
Abstract: We present the results of low-temperature photoluminescence experiments performed on GaAs single quantum wells grown by metal organic chemical-vapor deposition. The luminescence line is down shifted by a few milli-electron-volts below the $n=1$ heavy-hole exciton absorption peak. This behavior is interpreted in terms of exciton trapping on interface defects. A simple model provides reasonable values for the exciton binding energy on these defects as well as insights on the lack of thermalization which characterizes the trapped exciton photoluminescence.
193 citations
TL;DR: In this article, a correlation between impurity trapping and the interface structure in GaAs quantum well (QW) superlattices and single quantum well structures grown by molecular beam epitaxy (MBE) on (100) GaAs was demonstrated.
Abstract: A correlation has been demonstrated between impurity trapping and the interface structure in GaAs quantum well (QW) superlattices and single quantum well structures grown by molecular beam epitaxy (MBE) on (100) GaAs. Using low‐temperature cathodoluminescence, photoluminescence, and transmission electron miscroscopy, we have shown that interface roughness in QW superlattices is related to trapped impurities at interfaces. We have observed that impurities originate from either the substrate or from the GaAlAs MBE layers. A new getter smoothing effect associated with QW structures is shown to produce efficient impurity trapping and yield higher quality GaAs QW with atomically smooth interfaces.
162 citations
TL;DR: In this paper, the role of interfacial quality in the line shape of photoluminescence spectra in quantum wells is investigated. But the authors make use of the Lifshitz theory of disordered alloys to determine the probability of distribution of fluctuations in the well size over the extent of the optical probe, i.e., the exciton.
Abstract: We have developed a simple theory to understand the role of interfacial quality in the line shape of photoluminescence spectra in quantum wells. The interface is described in terms of microscopic fluctuations δ1 and δ2, where δ1 is the local fluctuation in the well width and δ2 is the lateral correlated extent of the fluctuation. We make use of Lifshitz theory of disordered alloys to determine the probability of distribution of fluctuations in the well size over the extent of the optical probe, i.e., the exciton. The line shape is then calculated from this probability distribution. Both δ1 and δ2 are found to be important in controlling the linewidths in quantum wells. The use of this quantitative theory to characterize the microscopic nature of interfaces is discussed.
138 citations
TL;DR: In this paper, changes of absorption spectra in a polythiophene film caused by photo-excitation and electrochemical doping are studied, showing that the formation of a shallow polaron is responsible to the carrier transport.
121 citations
TL;DR: In this paper, the authors interpretation des spectres UV visible and RPE in terms of different pretraitements dans l'oxygene ou dans le vide.
Abstract: Interpretation des spectres UV visible et RPE. Effet de diverses pretraitements dans l'oxygene ou dans le vide
TL;DR: In this paper, low-temperature photoluminescence and excitation spectroscopy measurements on heavily doped (up to 4mmode/times/else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) $n$- and $p$-type silicon are reported.
Abstract: Low-temperature photoluminescence and excitation spectroscopy measurements on heavily doped (up to 4\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) $n$- and $p$-type silicon are reported. From the luminescence spectra values for the optical and the reduced band gap are deduced and compared with theoretical calculations. The shrinkage of the reduced band gap follows an ${n}^{\frac{1}{3}}$ law for carrier concentrations $n$ above the critical Mott density. Both $n$- and $p$-type samples show an identical shift of the reduced gap, whereas the shift of the optical gap is different due to the different density-of-states masses for electrons and holes. From photoluminescence excitation spectra the position of the optical gap is determined independently. A good agreement of the data obtained by these selective absorption measurements with the results from conventional luminescence spectra is found.
TL;DR: In this paper, the observation of one-monolayer well size fluctuations in a superlattice is reported, which is confirmed by the intentional introduction of a larger well in the structure.
Abstract: The observation of one‐monolayer well size fluctuations in a superlattice is reported. Luminescence experiments show that several exciton peaks occur, each of them corresponding to a discrete well width differing by one monolayer from the next one. This attribution is confirmed by the intentional introduction of a larger well in the structure. It is also checked by comparison with the x‐ray diffraction results that confirm the variations of the superlattice parameters observed in luminescence, and by photoluminescence excitation experiments that also show a splitting.
TL;DR: In this article, the first growth of diluted magnetic semiconductor superlattices was reported, and the photoluminescence spectra of the super lattices were found to be over three orders of magnitude more intense when compared to uniform thin films and bulk samples.
Abstract: In this letter we report the first growth of diluted magnetic semiconductor superlattices. Bright and dark field transmission electron microscopy images confirm that the superlattices consist of distinct periodic layers of uniform composition and thickness. The photoluminescence spectra of the superlattices are found to be over three orders of magnitude more intense when compared to uniform thin films (and bulk samples) grown under similar conditions. The reason for this large increase is not clearly understood but this effect may have important consequences for future applications of these novel materials in optoelectronic devices.
TL;DR: By starting with exponential band tails of localized states, it was shown that the photoluminescence of $a$-Si: Hi can be explained with no further assumptions as discussed by the authors, and the spectrum and its changes with temperature, with time, and with pump intensity and energy, and the decay curves and lifetime distributions, are predicted by the model, qualitatively and, when the calculation is feasible, quantitatively.
Abstract: By starting with exponential band tails of localized states, it is shown that the photoluminescence of $a$-Si: Hi can be explained with no further assumptions. The spectrum and its changes with temperature, with time, and with pump intensity and energy, and the decay curves and lifetime distributions, are predicted by the model, qualitatively, and, when the calculation is feasible, quantitatively.
TL;DR: In this article, an As primer layer was successfully used to initiate the polar on nonpolar growth of GaAs on (100) oriented Si by molecular beam epitaxy and have been studied using photoluminescence, photographic, and x-ray measurements.
Abstract: Undoped GaAs layers have been grown on (100) oriented Si by molecular beam epitaxy and have been studied using photoluminescence, photographic, and x‐ray measurements. To minimize antiphase disorder, an As primer layer was successfully used to initiate the polar on nonpolar growth. Photoluminescence spectra show the presence of five bands into which the luminescence from each sample falls. The energy variation within any given band was less than 4 meV. X‐ray and photoluminescence analysis appear to indicate some strain in the crystal. Although very preliminary, the results obtained indicate that GaAs on Si can potentially be used for a number of hybrid ciruits.
TL;DR: In this article, the authors compared the theoretical and experimental emission energy of a single quantum well with the theoretical curves generated from a finite potential square well model and found that the closest agreement between the experimental and theoretical curves occurs when the conduction band discontinuity is taken to be 70% of the band gap discontinuity or 0.52 eV.
Abstract: Photoluminescence studies at 4 K on Ga0.47In0.53As/ Al0.48In0.52As single quantum wells exhibit emission ranging from 1.318 eV for a 15‐A well to 0.82 eV for thick wells. The emission energy of each single quantum well is compared to theoretical curves which are generated from a finite potential square well model. The closest agreement between the experimental curves and the theoretical curves occurs when the conduction band discontinuity is taken to be 70% of the band‐gap discontinuity or 0.52 eV.
TL;DR: In this article, an expression for the excitonic photoluminescence linewidth in intentionally undoped semiconductor alloys is derived and the dominant mechanism for the line broadening is due to the statistical potential fluctuations caused by the components of the alloy.
Abstract: An expression for the excitonic photoluminescence linewidth in intentionally undoped semiconductor alloys is derived. The dominant mechanism for the line broadening is due to the statistical potential fluctuations caused by the components of the alloy. These fluctuations are accounted for by using statistical arguments developed by Lifshitz and then related to the linewidth. Compositional dependence of the linewidth is derived. It is shown that the linewidth is strongly dependent on the short range disorder present in the alloy. The theoretical results are compared with the available low‐temperature photoluminescence data in GaAlAs.
TL;DR: In this article, the growth of epitaxial (100) CdTe films on GaAs substrates by molecular beam epitaxy was discussed, and X-ray diffraction, UV reflectance, photoluminescence, and transmission electron microscopy techniques were employed to characterize the film specimens.
Abstract: Growth of epitaxial (100) CdTe films on (100) GaAs substrates by molecular beam epitaxy is discussed. X‐ray diffraction, UV reflectance, photoluminescence, and transmission electron microscopy techniques were employed to characterize the film specimens. The high structural perfection of the layers was evidenced by line dislocation densities of ≤104/cm2 at the free surface of films ≂6.6 μm thick and by measurable excitonic photoluminescence (∼1.504 eV) at room temperature. The CdTe epilayers were smooth and mirrorlike in appearance.
TL;DR: In this article, the peak energy of a single quantum well was investigated at both 75 and 4.2 K. The peak energy shifts by several meV below the calculated energy, the cause of which may be formation of a two-dimensional free exciton.
Abstract: Photoluminescence of AlxGa1−xAs/GaAs(x=0.54) single quantum wells grown by metal organic chemical vapor deposition has been investigated at both 75 and 4.2 K. AlGaAs/GaAs heterojunction abruptness was estimated to be within a few atomic layers by comparing the peak energy of the quantum well photoluminescence with the values calculated on the assumption that the radiative transition takes place between the n=1 electron subband and the n=1 heavy‐hole subband in the finite square potential well at 75 K. At 4.2 K, however, the peak energy shifts by several meV below the calculated energy, the cause of which may be formation of a two‐dimensional free exciton. The sharp photoluminescence line of the narrower well indicates that the fluctuation in thickness is less than one half the lattice constant. The emission peak shift to lower energy with the increase of excitation intensity may be the result of exchange interaction among carriers.
TL;DR: In this article, the relaxation rate of hot carriers following photoexcitation in GaAs•AlGaAs multiple quantum well structures is found to be significantly slower than the corresponding rate for bulk GaAs under high excitations.
Abstract: The relaxation rate of hot carriers following picosecond photoexcitation in GaAs‐AlGaAs multiple quantum well structures is found to be significantly slower than the corresponding rate for bulk GaAs under high excitations. This is confirmed by a detailed comparison of the hot‐luminescence tails for the two cases using picosecond pulse and cw photoexcitations.
TL;DR: In this article, single crystals of undoped and cerium-doped yttrium aluminum garnet have been pumped with laser radiation of 220 and 266 nm wavelength, and a broadband defect emission at approximately 300 nm was observed, similar to that obtained with cathodoluminescence.
Abstract: Single crystals of undoped and cerium‐doped yttrium aluminum garnet have been pumped with laser radiation of 220‐ and 266‐nm wavelength. A broadband defect emission at approximately 300 nm was observed, similar to that obtained with cathodoluminescence, although decreased in magnitude. Evidence of a transfer of energy from these defect states to the Ce+3 states was inferred from the photoluminescence decay time measurements. We have associated the absorption spectra from 200–300 nm with the defect excitation spectrum, including the peaks at 225 and 270 nm.
TL;DR: A photoluminescence band with unusual spectral properties has been observed in MBE grown CdTe, particularly prominent in single crystal layers containing large concentrations of extended defects generated either by metallurgical imperfections or contamination at the substrate-layer interface.
Abstract: A photoluminescence band with unusual spectral properties has been observed in MBE grown CdTe. It is particularly prominent in single crystal layers containing large concentrations of extended defects generated either by metallurgical imperfections or contamination at the substrate-layer interface. It is suggested that this luminescence results from electron-hole recombination at these extended defects. The weak LO phonon coupling may result from the delocalisation of the electronic binding potential between several nearly equivalent sites, while the spectral breadth of the no-phonon component may result from the influence of small environmental differences between these sites. Similar bands have been observed in ZnSe.
TL;DR: In this article, the metastable alloys covering this entire composition range have been grown by organometallic vapor phase epitaxy (OMVPE) using trimethyl gallium, antimony and -arsenic as the source materials.
Abstract: The system GaAs1−xSbx has a solid phase miscibility gap ranging from x = 0.2 to x = 0.8 at the typical growth temperature of 600 C; however, metastable alloys covering this entire composition range have been grown by organometallic vapor phase epitaxy (OMVPE) using trimethylgallium, antimony and -arsenic as the source materials. The solid composition is studied for various values of growth temperature, the ratio of Sb to total group V elements in the vapor phase and the ratio of group III to group V elements in the vapor phase. The fraction of trimethylarsenic (TMAs) pyrolyzed in the vapor phase is found to be < 1 and to vary with temperature. Taking into account the incomplete pyrolysis of TMAs, solid composition is found to be controlled by thermodynamics. The effects of temperature and vapor composition are all accurately predicted using a simple thermodynamic model assuming equilibrium to be established at the solid-vapor interface. The properties of these metastable GaAs1−x Sbx alloys were explored using interference contrast microscopy, room temperature and 4 K photoluminescence, Hall effect and conductivity measurements. The alloy GaAs0.5Sb0.5 grown lattice matched to the InP substrate has excellent surface morphology, is p-type, and the photoluminescence spectrum consists of a single, intense, fairly broad (23.5 meV half width) peak at a wavelength of 1.54 Μm.
TL;DR: In this paper, CdTe films were found by reflection high-energy electron diffraction analysis to be oriented parallel to the surface of the (001) GaAs and aligned.
Abstract: CdTe films grown by molecular beam epitaxy on a (001) GaAs with a 14% lattice mismatch were found to be a very good crystalline quality. The films were found by reflection high‐energy electron diffraction analysis to be oriented (111) parallel to the surface of the (001) GaAs. Further, the [112] azimuth of CdTe and the [110] of GaAs were aligned. Photoluminescence studies suggest that the films are of high crystalline quality but peaks associated with impurities are observed in the spectra. The optimum growth temperature is about 250 °C.
TL;DR: In this article, high-resolution luminescence studies from individual dislocations and related defects in ZnSe and InP performed in a transmission electron microscope were performed in the presence of complex dislocation tangles.
Abstract: Results are presented of high-resolution luminescence studies from individual dislocations and related defects in ZnSe and InP performed in a transmission electron microscope. In the case of ZnSe unusual luminescence bands (Y at 2.60 eV and S at 2.52 eV) originally observed in photoluminescence studies are attributed to dislocations. In some instances, complete quenching of the excitonic transitions was observed to correlate with the presence of Y emission from complex dislocation tangles. In the case of individual screw dislocations this quenching of the exciton luminescence was found to be variable; for example reduction of the exciton signal was not always observed. For InP, donor-exciton-related transitions were quenched at individual screw dislocations. Donor-acceptor pair/free-to-bound and deep level (band C) transitions were unaffected. For the case of InP, unlike ZnSe, no dislocation-related luminescence was observed within the system detection limit (0.7-4.0 eV).
TL;DR: In this article, the photoluminescence and current transport in the multiple-quantum-well (MQW) heterostructures have been studied by using light illumination, and it has been interpreted in terms of a significant increase in the mobility and lifetime of quasi-two-dimensional electrons.
Abstract: Multiple-quantum-well (MQW) heterostructures consisting of twenty layers of a-Si:H (30∼200 A thick) and a-Si1−xNx:H (30∼200 A thick, x ≅ 0.2) have been studied by photoluminescence and current transport. The luminescence from the MQW structure exhibits a single peak at 1.37 eV originating in the a-Si:H well layers, and there is no emission at ∼1.48 eV arising from the a-Si1−xNx:H barrier layers. This is because the photocarriers generated in the barrier layers flow into the a-Si:H wells. This confinement of photocarriers in the quantum well has been demonstrated by analysing the luminescence quenching in the electric field applied perpendicularly to the MQW heterojunctions. The current transport parallel to the quantum well under light illumination has revealed the remarkable increase of photo-conductance with decreasing the well layer width. This is tentatively interpreted in terms of a significant increase in the mobility and lifetime of quasi-two-dimensional electrons in the a-Si:H well layers.
TL;DR: In this paper, transmission electron microscopy, X-ray diffraction and photoluminescence were evaluated using GaAsP epitaxial layers emitting in the 1.25−1.37 μm wavelength region.
TL;DR: In this paper, the effects of various combinations of prelayers of GaAs and AlGaAs have been investigated and it is shown that it is possible to reduce the sum of the interface recombination velocities to as low as 60 cm/s.
Abstract: From room‐temperature measurements of the photoluminescence decay time, values for the sum of the interface recombination velocities in a series of GaAs/AlGaAs double heterostructures have been obtained. The effects of various combinations of prelayers of GaAs and AlGaAs have been investigated and we show that it is possible to reduce the sum of the interface recombination velocities to as low as 60 cm/s.