Showing papers on "Photoluminescence published in 1985"
TL;DR: In this paper, the photoluminescence peak energies of the epilayers with the best experimental relation of band gap versus composition for unstrained layers were determined by comparing the peak energy of the Epilayers.
Abstract: Interfacial elastic strain induced by the lattice parameter mismatch between epilayer and substrate results in significant energy–band‐gap shifts for III‐V alloys. The epilayers used in this study are GaxIn1−xAs on (100) InP and GaxIn1−xP on (100) GaAs prepared by organometallic vapor phase epitaxy. For layer thicknesses between 1 and 1.5 μm, and Δas.f./a0≤3.5×10−3 the misfit strain is assumed to be accommodated elastically. The energy–band‐gap shifts are determined by comparing the photoluminescence peak energies of the epilayers with the best experimental relation of band gap versus composition for unstrained layers. A calculation of the energy–band‐gap shift due to biaxial stress made for GaxIn1−xAs is found to agree with the photoluminescence measurements. In addition, a comparison of the energy–band‐gap shift for GaxIn1−xP shows a clearly different dependency for tensile and compressive strain, in good agreement with calculated results.
244 citations
TL;DR: In this article, the optical absorption edge is blue shifted approx.0.9 eV for the CdS colloid; for PbS colloids the shift is approx.2 eV.
Abstract: Optical effects due to size quantization in three dimensions have been observed for CdS and PbS colloids with particle diameters less than 50 A and 20 to 200 A, respectively. The optical absorption edge is blue shifted approx.0.9 eV for the CdS colloid; for PbS colloids the shift is approx.2 eV for particle diameters 20 to 30 A, and approx.1 eV for particle diameters 50 to 200 A. The results are consistent with perturbation of the semiconductor band structure due to carrier confinement resulting in an increase in the effective band gap. 14 refs., 3 figs.
221 citations
TL;DR: In this paper, the time dependence of photoluminescence due to carrier recombination and the gratings created by degenerate four-wave mixing were measured in semiconductor-doped color filter glasses.
Abstract: The time dependence of both the photoluminescence due to carrier recombination and the gratings created by degenerate four‐wave mixing were measured in semiconductor‐doped color‐filter glasses. Values ranging from 80 to less than 16 ps (laser pulse width limited) are measured in several different samples at various excitation levels. A slower mechanism, believed to be thermal in nature, is also observed with a lifetime in excess of 9 ns.
191 citations
TL;DR: In this article, the authors used molecular beam epitaxy to grow GaAs/AlGaAs on (100) oriented Ge and Si substrates, and showed that the antiphase disorder was contained within the 250-Athick initial layer which was grown at a 0.1-μ/h growth rate at a substrate temperature of 500 °C.
Abstract: Using molecular beam epitaxy, we have successfully grown device quality GaAs/AlGaAs on (100)‐oriented Ge and Si substrates. Modulation doped field effect transistors have been fabricated from these layers which exhibit room‐temperature transconductances as high as 160 and 170 mS/mm for layers on Ge and Si, respectively, and showed no looping in either case. At 77 K, these values rose to 345 and 275 mS/mm for Ge and Si, respectively. Analysis by transmission electron microscopy of layers grown on Ge showed that the antiphase disorder was contained within the 250‐A‐thick initial layer which was grown at a 0.1‐μ/h growth rate at a substrate temperature of 500 °C. For both the layers grown on Si and Ge specular surface morphologies were obtained. The photoluminescence of GaAs/AlGaAs quantum wells grown on Si and Ge was similar in intensity to the same quantum well structures grown on GaAs. In quantum wells grown on Ge, the luminescence was dominated by a donor‐acceptor recombination at 1.479 eV, which appears to be Ge0Ga ‐Ge0As. These results show that high‐quality GaAs/AlGaAs is obtainable on nonpolar substrates, which has important implications for the monolithic integration of III‐V’s with Si.
188 citations
TL;DR: In this paper, the absorption and photoluminescence of n-type InP were examined as a function of free-carrier concentration and it was found that concentration dependent band gap at 300 K is given by the empirical relation: Eg = 1.344−(2.25±0.25)10−8n1/3 (eV).
Abstract: The absorption and photoluminescence of n‐type InP are examined as a function of free‐carrier concentration. It is found that concentration dependent band gap at 300 K is given by the empirical relation: Eg =1.344−(2.25±0.25)10−8n1/3 (eV). The photoluminescence results are interpreted using the model taking into account nonparabolicity of the conduction band. Calculations of the peak position and photoluminescence line shape for band‐to‐band transitions are performed. Both the band filling as well as band tailing due to the Coulomb interaction of free carriers with ionized impurities and band shrinkage due to the exchange interaction between free carriers are considered in order to properly account for observed features of photoluminescence spectra. It is proposed that room temperature photoluminescence linewidth can be used for determination of the free carrier concentration in n‐type InP. This method can be used to estimate free carrier concentration ranging from 1016 to 1020 cm−3.
181 citations
TL;DR: In this paper, the authors examined the correlation of the interface roughness with the measured intensity oscillations of reflective high energy electron diffraction (RHEED) during the growth of 10 or more atomic layers and found that the growth interruption of 10−100 seconds prior to the interface formation is effective in achieving an atomically flat interface.
Abstract: Photoluminescence spectra of GaAs-AlAs quantum wells are studied to evaluate the flatness of heterointerfaces prepared by molecular beam epitaxy. We examine the correlation of the interface roughness with the measured intensity oscillations of reflective high energy electron diffraction (RHEED) during the growth. The crystal surface is found to roughen after the growth of 10 or more atomic layers. The growth interruption of 10–100 seconds prior to the interface formation is effective in achieving an atomically flat interface, leading to sharp photoluminescence with the linewidth <30 A at 77 K even when the quantum well width is reduced to 40 A.
170 citations
TL;DR: In this article, the quantum-confined Stark effect on the photoluminescence of the lowest free exciton for electric fields perpendicular to the quantum well layers is investigated.
Abstract: We report on picosecond luminescence studies of GaAs/AlGaAs quantum wells in the regime of the quantum-confined Stark effect. A drastic increase of the recombination lifetime is accompanied by a Stark shift of the photoluminescence of the lowest free exciton for electric fields perpendicular to the quantum-well layers. A consistent picture of the quantum-confined Stark effect is presented.
170 citations
TL;DR: In this paper, the compositional dependence of the band gap energy was determined and the free and bound exciton lines for x = 0 and 1 and only broadened bound excititon peaks for other compositions were quantitatively explained based on compositional fluctuations of the cations.
Abstract: Photoluminescence (PL) experiments were carried out at 300 and 12 K to investigate the electro‐optical properties of Cd1−xZnxTe grown by molecular beam epitaxy on GaAs substrates. The compositional dependence of the band‐gap energy was determined. It has a quadratic dependence on x. The near band edge PL spectra at 12 K show free and bound exciton lines for x=0 and 1 and only broadened bound exciton peaks for other compositions. The bound exciton broadenings are quantitatively explained based on the compositional fluctuations of the cations. The PL line shapes give indications of the high quality of the layers.
170 citations
TL;DR: In this paper, the effect of the electron-electron correlation on inter-metal sites has been investigated in detail in the visible or infrared energy regions, and the dependence of the CT excitation energies on the species M and X is shown to be consistent with the prediction by the Peierls-Hubbard model.
Abstract: Polarized reflection and luminescence have been measured for the single crystals of [MA 2 ][MX 2 A 2 ](ClO 4 ) 4 (M=Pt, Pd, X=Cl, Br, I and A=ethylenediamine, cyclohexanediamine). The strong absorption bands due to the charge-transfer (CT) exciton transitions between the mixed-valent metal ions have been investigated in detail in the visible or infrared energy regions. The dependence of the CT excitation energies on the species M and X is shown to be consistent with the prediction by the Peierls-Hubbard model which incorporates the effect of the electron-electron correlation on inter-metal sites. The oscillator strength of the CT excitons are observed to be enhanced by substituting heavier halogen ions. This enhancement is interpreted by a halogen-linked super-transfer mechanism. The unusually large values of the oscillator strength can be qualitatively explained in terms of the trimer CT model.
161 citations
TL;DR: In this paper, a series of crystals with different magnesium-doping levels and Li/Nb ratios were investigated, and the defects were introduced either by x-ray irradiation at low temperatures (10−85 K) or by reduction at high temperature in a vacuum.
Abstract: Optical absorption, electron spin resonance (ESR), thermoluminescence, and x‐ray‐induced luminescence techniques have been used to characterize point defects in LiNbO3. A series of crystals with different magnesium‐doping levels and Li/Nb ratios were investigated, and the defects were introduced either by x‐ray irradiation at low temperatures (10–85 K) or by reduction at high temperature in a vacuum. The samples may be classified into two groups, according to their response to radiation and reduction. A threshold (i.e., a sharp change in behavior due to a small change in composition) marks the change from one type of response to the other. The concentrations of both magnesium and lithium affect the threshold level. An electron trap, represented by an optical absorption band peaking at 1200 nm and a broad ESR spectrum centered at gc=1.82, is observed in several of the heavily‐doped crystals after irradiation. A corresponding hole trap produced during the same irradiation has an optical absorption peak near...
138 citations
TL;DR: In this paper, the authors clarified that UV irradiation of the small TiO2 particle in the presence of H2O leads to the formation of \overset•OH radicals, which are formed by trapping of photo-formed holes by the surface OH− groups.
Abstract: ESR and photoluminescence studies have clarified that UV irradiation of the small TiO2 particle in the presence of H2O leads to the formation of \overset•OH radicals, which are formed by trapping of photo-formed holes by the surface OH− groups.
TL;DR: In this paper, the molecular beam epitaxial growth of GaAs on Si(211) has been investigated and the experimental results support the theoretical prediction, and the (211) layer growth is initiated with a thin (GaAs/Al, GaAs) superlattice buffer (0.1 μm), consisting of 10 periods of 5+5 nm.
Abstract: The molecular beam epitaxial growth of GaAs on Si(211) has been investigated. Theoretical considerations had suggested the (211) orientation to be particularly suitable for the nucleation and growth of a zincblende‐type compound semiconductor on a diamond‐type elemental one. The experimental results support the theoretical prediction. Morphologies of thin (≤0.1 μm) (211) layers are substantially better than for (100) layers, which nucleate poorly and require large layer thicknesses (≂1μm) to yield good morphologies. When the (211) layer growth is initiated with a thin (GaAs/Al, Ga)As superlattice buffer (0.1 μm), consisting of 10 periods of 5+5 nm, the (211) morphology rivals that of GaAs(100) homoepitaxial growth. Chemical etching studies as well as transmission electron microscope investigations show the layers to have the (211)B orientation and to be free of antiphase domains, both as predicted. The (211) layers show strong photoluminescence at 4 K. Not intentionally doped layers are n type, with elect...
TL;DR: Time-resolved photoluminescence measurements at room temperature of the n=1 heavy hole transition in a GaAs/AlxGa1−xAs multiple quantum well structure reveal a single-exponential decay with τ≊1 ns over a wide range of excitation densities.
Abstract: Time‐resolved photoluminescence measurements at room temperature of the n=1 heavy hole transition in a GaAs/AlxGa1−xAs multiple quantum well structure reveal a single‐exponential decay with τ≊1 ns over a wide range of excitation densities. Time‐integrated photoluminescence increases as the square of excitation energy density. These data indicate that the observed decay rate is due to nonradiative recombination. Free carriers, not excitons, govern radiative recombination in this sample.
TL;DR: In this paper, the emission spectrum of Tb3+ substituted in YAG to various concentrations (x in Y3−xTbxAl5O12 ranges from 3×10−5 to 3x10−1) has been measured on samples prepared by two different methods.
Abstract: The emission spectrum of Tb3+ substituted in YAG to various concentrations (x in Y3−xTbxAl5O12 ranges from 3×10−5 to 3×10−1) has been measured on samples prepared by two different methods. These methods are powder preparation by coprecipitation and growth of crystalline layers by liquid‐phase epitaxy. The spectrum consists of two groups of lines, one group around 550 nm originating from the 5D4 level and one group around 450 nm from the 5D3 level. The intensity of the two groups of lines depends on the method of excitation. In the case of UV excitation (λ=254 nm) the emission intensity for low Tb concentrations is mainly governed by the absorption of the incident radiation. With electron excitation, the energy loss of incoming electrons to ‘‘killer sites’’ in the lattice is found to influence the emission. The ratio, however, of 5D4 to 5D3 intensity is independent of the excitation mode. This ratio tends to a constant value at low concentrations and increases strongly with increasing concentration. These ...
TL;DR: In this paper, extensive characterizations of nominally undoped, Ga-doped, and P-Doped ZnSe grown on (001)GaAs substrate have been made, and the free exciton emission line split into two lines due to the residual strain.
TL;DR: In this paper, the photoluminescence of the semiconducting titanates (TiO 2 (rutile), SrTiO 3, MgTiO3, K 1.8 Mg 0.9 Ti 7.1 O 16, and La 2 Ti 2 O 7, which are known to act as photoanodes in a photoelectrochemical cell was investigated.
TL;DR: In this article, the effects of surface preparation, substrate temperature, and film thickness were studied in detail for homoepitaxial films grown on the (111)A and (100) planes of CdTe.
Abstract: Photoluminescence (PL) studies of bulk and epitaxial CdTe samples obtained from several sources are discussed. Steady state PL measurements were carried out at temperatures ranging from 16–300 K. The effects of surface preparation, substrate temperature, and film thickness were studied in detail for homoepitaxial films grown on the (111)A and (100) planes of CdTe. PL studies of epitaxial CdTe films grown on (0001) sapphire by molecular beam epitaxy (MBE), by hot wall MBE, and by metal‐organic chemical vapor deposition (MOCVD), and on the (111)B and (100) planes of GaAs by MBE have also been completed. The CdTe epilayers on sapphire and GaAs substrates typically display a bright PL spectrum dominated by the near edge peak at 1.58 eV (77 K). In addition, a number of films exhibit a near edge peak at 1.503 eV at 300 K, which is indicative of high quality epitaxy and which allowed direct measurement of the room temperature band gap of CdTe. PL studies of epitaxial Cd1−x MnxTe films grown by MBE on 5.0 μm thic...
TL;DR: In this paper, the luminescence properties of several Bi3+-activated lanthanide borates (LnBO3) were investigated and two luminescent centers were observed.
TL;DR: In this paper, a new band was assigned to an interligand charge-transfer excited configuration in which electronic charge has been transferred from the coordinated thiol ligand(s) to the N-heterocycle via the metal ion.
TL;DR: In this paper, the results of optical absorption, infrared absorption, electron spin resonance and photoluminescence measurements are presented for hydrogenated amorphous Si-N films prepared by three different methods.
Abstract: The results of optical absorption, infrared absorption, electron spin resonance and photoluminescence measurements are presented for hydrogenated amorphous Si-N films prepared by three different methods; magnetron sputtering of an Si target in an Ar+N2+H2 gas mixture, glow-discharge decomposition of SiH4+N2, and glow-discharge decomposition of SiH4+NH3 The improvement in the properties of films prepared by the third method, eg, the sharp band tail and low dangling-bond density, is explained mainly in terms of the structual softening due to the existence of N-H bonds The fatigue of the photoluminescence due to illumination is found to be more prominent and the recovery due to annealing less prominent in N-incorporated film than in a-Si:H
TL;DR: In this article, the structure of the intermediate layers between GaAs and Si by metalorganic chemical vapor deposition was investigated and it was found that the insertion of AlP and AlGaP layers makes the crystallinity and the surface morphology better, and the PL (photoluminescence) intensity with two superlattice layers is about one order of magnitude stronger than that without these layers.
Abstract: GaAs grown on Si substrate with AlP, AlGaP, GaP/GaAs0.5P0.5 superlattice, and GaAs0.5P0.5/GaAs superlattice was investigated by varying the structure of the intermediate layers between GaAs and Si by metalorganic chemical vapor deposition. It was found that (1) the insertion of AlP and AlGaP layers makes the crystallinity and the surface morphology better, (2) PL (photoluminescence) intensity with two superlattice layers is about one order of magnitude stronger than that without these layers, (3) the crack formation in the GaAs surface layer can be avoided by the strained superlattice layers, (4) the PL intensity has a maximum at about 20 nm for each layer thickness in the superlattices, and (5) the PL intensity increases and the carrier concentration decreases while increasing the thickness of the surface GaAs and saturates over 3 μm. The PL intensity of GaAs on Si substrates is about 80% of that grown on GaAs substrates.
TL;DR: In this paper, the photoluminescence spectra of two GaAs/GaAs heterojunctions were analyzed and the location of the spectrum peak and shoulders agreed well with the calculated energies using Dingle's connection rule.
Abstract: Quantum‐mechanically coupled well systems consisting of two GaAs wells 30 A thick separated by an Al0.5Ga0.5As barrier whose thickness was varied from 12 to 40 A have been grown by metalorganic chemical vapor deposition. The photoluminescence spectra of these systems indicated the splitting of a degenerate single well state into a doublet state, a symmetrical state, and an antisymmetric state. The location of the spectrum peak and shoulders agreed well with the calculated energies using Dingle’s connection rule which assumes 85% conduction band offset and the continuous first derivative of the wave function across the AlGaAs/GaAs heterojunction. Two other connection rules were tried, but the agreement was worse.
TL;DR: In this article, time-resolved photoluminescence measurements of excitons in GaAs−Ga1−xAlxAs quantum wells subject to an electric field perpendicular to the well plane have been made.
Abstract: Time‐resolved photoluminescence measurements of excitons in GaAs‐Ga1−xAlxAs quantum wells subject to an electric field perpendicular to the well plane have been made. With increasing field, both integrated luminescence (as previously reported) and luminescence lifetime decrease. Thus the electric field increases the exciton nonradiative decay rate. Estimates of several possible mechanisms suggest that Fowler–Nordheim tunneling is responsible for the quenching. With increasing pump laser intensities, larger electric fields are required to quench the lifetime because of exciton screening of the field.
TL;DR: In this paper, an unusual new line has been observed in the low-temperature photoluminescence spectrum of GaAs/AlGaAs epilayers grown by liquid phase epitaxy, which represents a unique probe of the heterointerface.
Abstract: An unusual new line has been observed in the low‐temperature photoluminescence spectrum of GaAs/AlGaAs epilayers grown by liquid‐phase epitaxy, which represents a unique probe of the heterointerface. A very strong, broad and asymmetric line is seen, with peak energy ranging from that of the bound exciton to that of the shallowest acceptor, increasing roughly linearly with the logarithm of the excitation power. The intensity is seen to exhibit a very strong temperature dependence as the temperature is varied from 1.4 K up to about 20 K where the line falls below the background luminescence intensity. Intensity and energy dependence of the luminescence as a function of the Al mole fraction on one side of the junction is also investigated. By employing a novel step‐etching technique, this transition is shown to originate from the GaAs/AlGaAs heterojunction. A qualitative model is proposed to explain the observed data.
TL;DR: In this article, the effect of various MBE growth conditions on the sample morphology, the defect density, and the optical properties of GaAs and Ge epilayers is examined.
Abstract: Epitaxial GaAs/Ge films are grown by molecular beam epitaxy (MBE) on Si substrates. The effect of various MBE growth conditions on the sample morphology, the defect density, and the optical properties of GaAs and Ge epilayers is examined. Scanning electron microscopy, plan‐view and cross‐sectional transmission electron microscopy, reflection high‐energy electron diffraction, and photoluminescence are used to characterize epitaxial layers. It is found that the defect density decreases with increasing epilayer thickness. This is due to an annihilation process that affects both threading dislocations and stacking faults. The substrate temperature during Ge growth is found to affect the properties of both the Ge and GaAs films. GaAs surface morphology degrades and the stacking fault density increases at high Ge buffer‐layer substrate temperatures; however, the threading dislocation density remains unchanged. Variations in growth conditions are correlated with defect densities and luminescence efficiencies to determine material quality and optimize growth conditions.
TL;DR: In this article, optical properties of single and multiple quantum well structures grown by gas source molecular beam epitaxy were described, and it was estimated that over 50% of the InGaAs/InP band discontinuity resides in the conduction band.
Abstract: We describe optical properties of single and multiple quantum well structures grown by gas source molecular beam epitaxy. Absorption and photoluminescence were used in conjunction with x‐ray and transmission electron microscopy techniques to determine the confined particle energy levels and well thicknesses. Well defined exciton transitions were observed in the ternary and quaternary well superlattices even above room temperature. In single well structures energy shifts as large as 260 and 370 meV were observed for GaInAs and GaInAsP wells, respectively. On the basis of these results we estimated that over 50% of the InGaAs/InP band discontinuity resides in the conduction band.
TL;DR: In this article, two possible broadening mechanisms of the quantum well photoluminescence were found to dominate: one mechanism for thin well and one for thick well, respectively.
Abstract: GaInAs/AlInAs single quantum wells have been grown lattice matched to InP substrates by molecular beam epitaxy. The quantum well thicknesses ranged from 15 to more than 100 A. The low‐temperature photoluminescence exhibited a monotonically increasing spectral linewidth with decreasing well thickness. Of the several possible broadening mechanisms of the quantum well photoluminescence, two mechanisms were found to dominate: one mechanism for thin wells and one for thick wells. Quantum wells thicker than 50 A were found to have their low‐temperature photoluminescence spectra broadened primarily by a transfer of electrons from the AlInAs cladding layers into the GaInAs quantum well. Wells thinner than 50 A had their photoluminescence broadened mainly by interface roughness.
TL;DR: In this article, a method of detecting optical waveguide modes of semiconductor epitaxial layers is presented, where the modes are excited by photoluminescence and coupled out of the semiconductor wafer by a grating etched on the surface of the guiding layer.
Abstract: A new method of detecting optical waveguide modes of semiconductor epitaxial layers is presented. The modes are excited by photoluminescence and coupled out of the semiconductor wafer by a grating etched on the surface of the guiding layer. As a consequence of this coupling, the spectrum of optical emission from the sample at fixed angles has "mode lines" superimposed on the spontaneous emission spectrum. This method is used to measure the refractive indexes of eight InGaAsP layers of different compositions. These data together with published data for the refractive index of InP were fit with a two-oscillator model to yield an algebraic description of the refractive index of the InGaAsP/InP system. The method was also used to measure the change in mode index of a laser in going from low current up to threshold. The observed change was measured to be -0.023 ± 0.006.
TL;DR: The photoluminescence (PL) and excitation spectra of various TLD phosphors were measured at temperatures of 6, 17, 80 and 300 K as discussed by the authors.
Abstract: The photoluminescence (PL) and excitation spectra of various thermoluminescence dosimetry (TLD) phosphors were measured at temperatures of 6, 17, 80 and 300 K. Their PL spectra at 300 K consist of a single band in the vicinity of 380 nm. The emission bands and their excitation bands are ascribed to the electronic 4f6 5d ↔4f7 transitions in the Eu2+ ions. In the PL spectra of MgSO4:Eu2+, SrSO4:Eu2+ and BaSO4:Eu2+, the emission lines due to the electronic 4f7 →4f7 transition in the Eu2+ ion were also observed near 360 nm, in addition to the broad band. No line emission due to the Eu3+ center was observed in any of the phosphors prepared in the present work. In CaSO4:Eu2+ cooled to low temperatures, phonon structures are observed on the emission band and the low-energy excitation band. The TL emission spectra of BaSO4:Eu2+ at various temperatures were also measured.