Showing papers on "Cathodoluminescence published in 1988"

Electron source with micropoint emissive cathodes and display means by cathodoluminescence excited by field emission using said source

Abstract: Electron source with micropoint emissive cathodes and display means by cathodoluminescence excited by field emission and using said source. Each cathode (5) comprises an electrically conductive layer (22) and micropoints (12) and, according to the invention, a continuous resistive layer (24) is provided between the conductive layer and the micropoints. The display means comprises a cathodoluminescent anode (16) facing the source.

Structure and recombination in InGaAs/GaAs heterostructures

Abstract: The defect structure of lattice‐mismatched 1‐μm InxGa1−xAs (x≊012, misfit Δa/a≊85×10−3) epilayers on GaAs was studied with scanning cathodoluminescence (CL), transmission electron microscopy (TEM), high‐voltage electron microscopy, and scanning electron microscopy CL shows that nonradiative recombination lines exist in the GaAs buffer layer as far as 4000 A from the interface The density of these defects is independent of substrate dislocation density Plan‐view TEM analysis indicates that the majority of these dislocations in the buffer layer are sessile edge half‐loops Cross‐sectional TEM shows that loops also extend into the InGaAs epilayer, but the majority of the loops are located on the buffer layer (substrate) side of the interface A model is proposed to explain sessile edge dislocation formation in the buffer layer A comparison of CL and high‐voltage electron microscopy images from the same interface area reveals that the dark nonradiative recombination lines seen in scanning luminescence i

Cathodoluminescence Colours of α-Quartz

Abstract: A new cathodoluminescence-microscope has been developed with a considerably improved detection limit. Time-dependent luminescence intensity changes observed during electron bombardment enabled the recognition of short-lived, long-lived, and brown luminescence colour types in α-quartz. Short-lived bottle-green or blue luminescence colours with zones of non-luminescing bands are very common in authigenic quartz overgrowths, fracture fillings or idiomorphic vein crystals. Dark brown, short-lived yellow or pink colours are often found in quartz replacing sulphate minerals. Quartz from tectonically active regions commonly exhibits a brown luminescence colour. A red luminescence colour is typical for quartz crystallized close to a volcanic dyke or sill. The causes of these different and previously poorly understood luminescence colours were investigated using heat treatment, electron bombardment and electrodiffusion. Both natural and induced brown luminescence colours reflect the presence of lattice defects (nonbonding Si-O) due to twinning, mechanical deformation, particle bombardment or extremely rapid growth. The bottle-green and blue linearly polarized luminescence colour, characterized by a plane of polarization parallel to the c-axis, both depend on the presence of interstitial cations. The yellow and red luminescence colours in α-quartz both exhibit a plane of polarization perpendicular to the c-axis and appear to be related to the presence of trace elements in an oxidizing solution and to ferric iron respectively.

Display unit by cathodoluminescence excited by field emission

Abstract: Display unit by cathodoluminescence excited by field emission. It comprises a plurality of elimentary patterns, each having a cathodoluminescent anode and a cathode able to emit electrons. Each cathode comprises a plurality of electrically interconnected micropoints subject to electron emission by field effect when the cathode is negatively polarized compared with the corresponding anode, the electrons striking the latter, which is then subject to a light emission. Each anode is integrated to the corresponding cathode. Application to the display of stationary or moving pictures.

Investigation of reactive ion etching induced damage in GaAs–AlGaAs quantum well structures

Abstract: We report on the use of a novel technique to study reactive ion etching (RIE) induced damage using multiple quantum wells of 20‐, 40‐, 60‐, and 90‐A widths as in situ probes. Cathodoluminescence (CL) at low temperature, using a finely focused electron beam, allows sensitive determination of the quality of individual quantum wells before and after RIE damage. There is a correspondence between individual luminescence peaks and the depth of the particular quantum well. We can therefore use the CL spectral information to provide a sensitive profile of the depth of RIE induced damage. Various etching conditions and the effects of postetch anneals are examined. Pure Ar sputtering and enhanced chemical etching using CCl2F2/BCl3 at different bias voltages are investigated. Our results reveal that the degree and spatial extent of damage increase with increasing ion energy and decreasing ion mass.

Stress variations and relief in patterned GaAs grown on mismatched substrates

Abstract: Cathodoluminescence scanning electron microscopy studies reveal significant variations in stress across etched patterns of GaAs grown on both InP and Si substrates. The stress in the epilayer is relieved at convex corners and in patterned areas with dimensions on the order of 10 μm. The stress is uniaxial near the edge of a patterned region and changes to biaxial away from the edge, producing nonuniformities in the optical properties of patterned regions.

Blue and Green Cathodoluminescence of Synthesized Diamond Films Formed by Plasma-Assisted Chemical Vapour Deposition

Abstract: Cathodoluminescence study of synthesized diamond films formed by magneto-microwave plasma CVD and usual microwave plasma CVD has been carried out for the first time. The visible luminescence spectra of these diamond films show that peaks occur at different energies between 2.4–2.8 eV (green to purple-blue by visual inspection), depending on the deposition conditions. These spectra can be classified into so-called "band A" luminescence commonly observed in all types of bulk diamond. The growth sectors of {100} (bright visible emission) and {111} (dark) can be differentiated by the intensity of luminescence. These features are analogous to the luminescent properties of high-pressure synthesized diamond.

Selective area growth of InP/InGaAs multiple quantum well laser structures by metalorganic molecular beam epitaxy

Abstract: Selective area growth of InP/InGaAs multiple quantum well laser structures has been demonstrated in openings defined in Si3 N4 layers on InP substrates. Growth was achieved, by metalorganic molecular beam epitaxy, in openings as small as 3 μm wide, but no growth occurred on the dielectric coating. Cathodoluminescence from individual laser stripes was observed at 300 K with a wavelength determined to be 1.57 μm and at 100 K with a wavelength of 1.46 μm.

Band bending and interface states for metals on GaAs

Abstract: We have used soft x‐ray photoemission and optical emission spectroscopies to observe a broad range of Fermi level stabilization energies at metal interfaces with GaAs(100) surfaces grown by molecular beam epitaxy (MBE). The observed metal‐ and As‐related interface cathodoluminescence plus orders‐of‐magnitude differences in bulk‐defect‐related photoluminescence between melt‐ versus MBE‐grown GaAs suggest a role of bulk crystal growth and processing in controlling Schottky barrier formation.

Electron source comprising emissive cathodes with microtips, and display device working by cathodoluminescence excited by field emission using this source

Abstract: Each cathode (5) comprises an electrically conducting layer (22) and microtips (12) and, according to the invention, a continuous resistive layer (24) is provided between the conducting layer and the microtips. The display device comprises a cathodoluminescent anode (16) opposite the source.

Quenching of cathodoluminescence at the centre of hardness indentations on a (100) face of MgO

Abstract: The behaviour of cathodoluminescence (CL) associated with hardness indents in MgO has been examined. Experiments using conical indenters of different included angles show that the luminescence from the deformed zone at the tip of the indenter is quenched by indentations with a representative strain in excess of a critical value, between 5 and 8%. Electron microscopy of the corresponding deformed structure reveals that although the deformed zone is crystalline, it contains a very high dislocation density in the form of a network of loops. This accounts for the characteristic appearance of CL in the neighbourhood of hardness indents, wear tracks, and other regions of localized contact damage.

Cathodoluminescence spectroscopy of metal-semiconductor interface structures

Abstract: Low‐energy cathodoluminescence spectroscopy (CLS) is a powerful new technique for characterizing the electronic structure of semiconductor surfaces and ‘‘buried’’ metal–semiconductor interfaces. This extension of a more conventional electron microscopy technique provides information on localized states, deep‐level defects, and band structure of new compounds at interfaces below the free solid surface. Specifically, CLS provides direct identification of metal‐induced interface states which evolve in energy and density with multilayer metal coverages of the particular metal, extrinsic surface states due to lattice disruption, as well as bulk defect levels—all of which can play a role in Schottky barrier formation. From the energy dependence of spectral features, one can distinguish interface versus bulk state emission and assess the relative spatial distribution of states below the free surface. From the dependence of spectral intensity on injection level, one can spatially resolve large differences in reco...

Cathodoluminescence measurements of high-Tc superconductors

Abstract: Presents some examples of changes in the spectra of high-Tc material during excitation with an electron beam. The temperature dependence of the signals reveals a number of dips in intensity which appear to be related to anomalies in the resistivity and to specific heat data. The features are not apparent in non-superconducting samples. The possibility of probing the defect structure of the material by signals produced at rare-earth ion states is considered. The data suggest cathodoluminescence is potentially a useful characterisation technique of these oxides.

Arsenic‐ and metal‐induced GaAs interface states by low‐energy cathodoluminescence spectroscopy

Abstract: We used optical emission techniques to obtain a direct measure of discrete electronic states at GaAs interfaces. These states depend on surface preparation, metallization, and semiconductor material. The energy of the discrete states found at metal/molecular‐beam epitaxially grown GaAs(100) interfaces integrated within a Schottky formalism provides self‐consistent results for the interface electrostatics. The presence of a large concentration of extrinsic defects causes the pinning behavior observed at metal/melt‐grown GaAs(110) interfaces. These results provide the first direct experimental evidence for the origin of Fermi level ‘‘pinning’’ at metal/melt‐grown GaAs junctions.

Etching and cathodoluminescence studies of ZnSe

Abstract: Epitaxial thin films of ZnSe grown on GaAs substrates were reactive ion etched using BCl3 /Ar gas mixtures. Using an optimized etching process, photolithographically defined micrometer sized structures were etched several micrometers deep with straight sidewalls and smooth surfaces. Cathodoluminescence was measured from both etched and unetched surfaces at room temperature. Luminescence intensities of etched surfaces are shown not to be degraded by the reactive ion etching process. Cathodoluminescence intensities of etched pixels with exposed sidewalls were found to be greater than the intensities measured from unetched flat surfaces. This suggests the possibility of efficient etched light‐emitting structures.

Cathodoluminescence detector utilizing a hollow tube for directing light radiation from the sample to the detector

Abstract: A detector is disclosed which includes an elliptical hollow mirror and a tube having a reflecting inner surface for conducting the light emitted by a specimen under investigation in a scanning electron microscope. A vacuum window is seated at the outer end portion of the tube directly ahead of a receiver.

Origin of donor and acceptor species in undoped ZnSe grown by low‐pressure metalorganic chemical vapor deposition

Abstract: Effects of the [H2 Se]/[Dimethylzinc] source ratio on the electrical properties in the temperature range of 15–300 K and on the cathodoluminescence properties at 77 K have been investigated for undoped ZnSe films grown in one deposition run on (100)GaAs substrates at 350 °C by metalorganic chemical vapor deposition. The properties correlated with each other and depended on the degrees of deviation from stoichiometry. The dominant donor is identified with selenium vacancy from the dependence of donor concentration on the ratio and on the film thickness. Two kinds of acceptors were introduced according to the deviation from stoichiometry. They are tentatively associated with NSe and NaZn . Extended lattice defects which reduce the electron mobility are favored at the high ratios and they seem a principal factor of the high‐resistive property of this material.

A High Resolution Cathodoluminescence Microscopy Utilizing Magnetic Field

Abstract: We propose a new principle to improve spatial resolution of cathodoluminescence microscopy (CL). The resolution of conventional CL is limited by minority carrier lateral diffusion, typically a few microns. The principle, which we named Lorentz force carrier confinement (LC), is to block the lateral diffusion by placing carriers in a circular orbit in terms of the Lorentz force under a vertical magnetic field. Detailed hetero-interface structures of GaAs-AlGaAs quantum wells have been successfully visualized, using the principle. The spatial resolution of LC-CL is improved to be a few thousand Angstrom by applying 0.8 Tesla.

Processing and characterization of GaAs grown into recessed silicon

Abstract: GaAs has been grown by molecular‐beam epitaxy in silicon recesses to form a planar structure suitable for integration of GaAs and silicon devices. The layers were examined using scanning electron microscopy, transmission electron microscopy, and cathodoluminescence. Epitaxial regions inside the well appeared comparable to GaAs grown on unpatterned silicon wafers. Crystal quality of the epitaxial GaAs, determined by cathodoluminescence, appeared to be independent of the distance from the edge of the well; however, (111) stacking faults were present in the GaAs along the sidewalls of the well.

Direct observation of extended monolayer flat islands at metalorganic vapor phase epitaxy grown Al0.5Ga0.5As‐GaAs single quantum well interfaces

Abstract: Extended monolayer flat islands occurring at the heterointerface of metalorganic vapor phase epitaxy grown, growth interrupted Al0.5Ga0.5 As‐GaAs single quantum wells are directly observed for the first time by spatially resolved cathodoluminescence (CL). CL images of growth islands with a lateral size of between 500 nm and 2 μm are shown. The photoluminescence emission peak shows splitting corresponding to exciton transitions in the growth islands of the quantum well with a difference in the well thickness of one atomic layer.

Characterization of oval defects in molecular beam epitaxy Ga0.7Al0.3As layers by spatially resolved cathodoluminescence

Abstract: Oval defects in silicon‐doped Ga07Al03As molecular beam epitaxy grown layers are studied by filtered cathodoluminescence at low temperatures (10 K) in a scanning electron microscope The spectra obtained inside and outside the defects exhibit very different main emission lines which can be explained by an important variation of the Al/Ga ratio at the center of the defects; this hypothesis is confirmed by localized Auger electron spectroscopy

Evolution of the electron acoustic signal as function of doping level in III‐V semiconductors

Abstract: The evolution of the electron acoustic signal has been measured for Be‐ and Si‐doped GaAs and Ga0.28Al0.19In0.53As layers with doping levels from1017 to 1020 at. cm−3. The samples have also been analyzed by cathodoluminescence spectroscopy for near‐band‐edge transition and deep level emission. The results are explained by the reduction of the mean free path of phonons, giving rise to a lattice thermal conductivity decrease. Meanwhile, the electronic part of the thermal conductivity of these compounds is found to be nearly negligible.

Cathodoluminescence observation of metallization‐induced stress variations in GaAs/AlGaAs multiple quantum well structures

Abstract: Cathodoluminescence scanning electron microscopy is utilized to investigate the stresses present underneath 0.4 μm gold layers deposited on GaAs/AlGaAs multiple quantum well structures grown by molecular beam epitaxy on GaAs substrates. Using the known stress dependence of excitonic lines in quantum wells, the magnitude of stress is determined to be about 1 kbar. The stress‐induced change in the refractive index, attributed to photoelastic effect, is about 0.01 for the structures studied in the present work.

Modification of electronic and chemical structure at metal/CdTe interfaces by pulsed laser annealing

Abstract: We have measured the effects of metallization and thermal processing on the chemical interaction, band bending, and deep level formation at Au and In/CdTe interfaces using soft x-ray photoemission, photoluminescence, cathodoluminescence, and surface photovoltage spectroscopies. Metallization and laser processing induce major increases in the intensity of several deep photoluminescence transitions. Core level shifts and cathodoluminescence spectra show Fermi level movements characteristic of both a classical work function model and chemically-induced defect pinning. Both interfaces displayed staged Fermi level movements with the evolving metal-semiconductor interaction. Intermediate and final Fermi energies for both systems correlated with the energies of the processing-enhanced photoluminescence transitions, suggesting that the states associated with these transitions are determining the Fermi level.

Intrawell exciton transport in monolayer‐flat GaAs/AlGaAs single quantum wells grown by molecular‐beam epitaxy

Abstract: During molecular‐beam epitaxy, growth interruption at each heterointerface of single quantum wells results in very narrow multiple peaks in photoluminescence (PL) spectra. These peaks correspond to extended monolayer‐flat regions of the wells, differing in well thickness by one monolayer. PL and PL‐excitation spectroscopies show that excitons tend to diffuse from narrower‐well regions to thicker‐well regions before radiative recombination takes place. This is also observed in time‐resolved PL. The intensity of the higher‐energy peak decreases with time, while that of the lower‐energy peak increases with time. The obtained exciton diffusion time of ≂250 ps is in good agreement with the estimated size (≤1 μm)of the monolayer‐flat islands from spectrally resolved cathodoluminescence.