Showing papers on "Cathodoluminescence published in 1983"

Improvements on the electrical and luminescent properties of reactive molecular beam epitaxially grown GaN films by using AlN‐coated sapphire substrates

Abstract: The electrical and luminescent properties of the GaN epitaxial films grown on AlN‐coated sapphire by reactive molecular beam epitaxy have been studied. The GaN films on AlN epitaxial films have larger Hall mobilities and show more intense cathodoluminescence peaks at a wavelength of 360 nm than those of the GaN films grown directly on sapphire, which suggests that the crystal qualities of GaN films are improved by use of AlN‐coated sapphire as substrates. The lattice matching and small difference of the thermal expansion coefficients between GaN and AlN are considered to result in the improvements.

Epitaxial growth of GaN/AlN heterostructures

Abstract: GaN/AlN heterostructures were grown on sapphire by reactive molecular beam epitaxy. The electrical and luminescent properties of the GaN have been studied. The GaN films on AlN have larger Hall mobilities and show more intense cathodoluminescence at the peak of 360 nm, compared with GaN films grown on sapphire. This suggests that the crystalline quality of the GaN is improved by making GaN/AlN heterostructures. The improvement is thought to result from the small mismatch of lattices and the small difference of thermal expansion coefficients between GaN and AlN.

Preparation and Cathodoluminescence of CaS: Eu and Ca1-xSrxS: Eu Phosphors

Abstract: Red emitting phosphors, CaS: Eu and Ca1-xSrxS: Eu, have been prepared by the sulfurizing flux method. The products consist of well-crystallized and non-aggregated particles with smooth surfaces. CaS: Eu had the highest luminescence efficiency at 0.04 mole% of europium. The energy efficiency was about 50%, and the visual efficiency about 20% when compared with the standard red phosphor, Y2O2S: Eu. The relation between cathodoluminescence properties and activator concentration is discussed.

The Low‐Energy‐Electron (LEE) Excitation of SnO2 : Eu Powder Phosphor; Fundamental Characteristics

Abstract: The physicochemical properties and fundamental luminescent characteristics of powder were examined for use as low‐energy‐electron (LEE) excitation phosphor. Solubility limit of Eu into was 0.05–0.06 a/o and smaller mean diameter, higher resistivity (order of 106 Ω cm), and more intensive diffused reflectance were observed with increased Eu addition. Although the same emission spectra by f‐f transition of Eu ( strongest peaks) were observed in u.v., high and low‐energy‐electron excitation, broad intrinsic emission from matrix, which coexist with the f‐f transition emission, was different for each excitation method. In LEE excitation, the maximum intensity wavelength of the intrinsic emission was longer than in high‐energy‐electron excitation. The intrinsic emission was not observed at room temperature in u.v. excitation. Excitation spectrum with a peak at 300 nm was attributed to matrix excitation, i.e., electron hole generation. Optimal addition of 0.1 a/o Eu for brightness, 5.9 msec decay , and an efficiency of 2 lm/W at 9 ~ 10 V were observed under LEE excitation. Efficiency increased with lower voltage and current excitation due to sublinearities of brightness‐voltage and current dependences.

Cathodoluminescence from deformed CaO

Abstract: The cathodoluminescence (CL) emission from deformed and undeformed CaO single crystals has been studied in the scanning electron microscope. Deformation enhances the emission which appears, in the CL image, localized in the deformed regions of the crystal. The CL spectrum depends on the kind of deformation applied to the crystal and is unstable under the electron beam. The results are discussed in terms of impurities and of vacancy defects generated during the plastic deformation.

The optoelectronic properties of donors in organo-metallic grown zinc selenide

Abstract: Organo-metallic chemical vapour deposited (MO CVD) ZnSe grown on 〈100〉 GaAs and on glass was assessed by photoluminescence (PL) and cathodoluminescence (CL) between 4.2°K and 300°K. Material quality is established by the small ratio of deep centre (DC) to near gap (NG) luminescence, much larger for ZnSe/glass. Low temperature PL reveals axial strain of heteroepitaxial ZnSe/GaAs. Selectively excited PL shows Cl and Ga dominant shallow donors for ZnSe/GaAs, mainly Cl for ZnSe/Ge. The ZnSe/glass shows more contamination by shallow Li acceptors, while Cu may be responsible for much of the DC luminescence for both substrates. Growth doping by Ga and Al donors is contrasted with comparison of PL and electrical data, and a threshold effect discovered for Al.

Excitation and decay of H4 luminescence in diamond

Abstract: Photoluminescence and cathodoluminescence decay time measurements have been carried out for the H4 (2.499 eV) centre in diamond. The photoluminescence decay time increases progressively from approximately= 19 to 23 ns as the energy of the exciting light is increased from 2.6 to 4.0 eV, and the cathodoluminescence decay curves are non-exponential. Luminescence excitation measurements reveal a previously unreported absorption band peaking at about 3.2 eV in the ultraviolet spectral region; absorption of light in this band produces H4 luminescence. The range of decay times noted above is believed to be due, at least in part, to transitions from the higher excited levels via the 2.499 eV excited state. The decay time of 19+or-1 ns measured with photoexcitation at 2.6 eV shows no significant variation with temperature, and this represents the most likely value of the radiative lifetime of the 2.499 eV centre.

Thermally induced changes in the cathodoluminescence image of deformed MgO

Abstract: The effect of annealing of the cathodoluminescence (CL) from deformed MgO single crystals has been investigated. Annealing at 1200 °C for a short time changes the bright slip bands into dark bands and also produces CL rosettes in indented crystals. The behaviour is attributed to annihilation and diffusion of point defects responsible for the CL emission. Es wird der Einflus der thermischen Behandlung auf die Kathodolumineszenz von verformten MgO-Einkristallen untersucht. Kurzes Anlassen bei 1200°C andert die Leuchtgleitbander in Dunkelgleitbander um und cryzeugt dunkle KL-Rosetten um Mikroharteeindrucke herum. Die Ergebnisse weisen darauf hin, das wahrend des Anlassens Vernichtung und Diffusion der Punktfehler, die KL erzeugen, stattfinden.

Study of the thermal conversion of semi-insulating GaAs:Cr with cathodoluminescence, photoluminescence, and secondary ion mass spectrometry

Abstract: Low‐temperature cathodoluminescence and photoluminescence spectra of heat‐treated GaAs:Cr are compared and differences are attributed to the difference in excitation depth. Cathodoluminescence spectra at 30 K indicate that the 1.23‐eV emission band in the as‐grown GaAs:Cr may be associated with a SiGa‐VGa complex while emission bands in the heat‐treated materials at 1.363 and 1.407 eV may correspond to acceptor levels introduced through the site transfer of silicon. The 1.363‐eV peak is strongly correlated with carrier concentration of the converted layer. Secondary ion mass spectrometry depth profiles show that this peak is not due to Cu. It may be due to recombination involving a SiAs‐VGa complex.

X-Ray imaging device for directly displaying X-ray images

Abstract: A device for directly displaying X-ray images on a phosphor screen of a cathode ray tube by means of a steady cathodoluminescence is arranged such that the excitation of the phosphor screen is controlled by the persistent polarization and depolarization of the phosphor crystals in the phosphor screen by exposure to X-rays The X-ray images formed on the phosphor screen in the cathode ray tube may be read out by synchronously detecting changes in the electric current of the collecting electrodes of the tube during the scanning of a reading electron beam on the phosphor screen displaying the X-ray images

Spectral resolution in low temperature cathodoluminescence. Application to CdTe

Abstract: Spectrally resolved cathodoluminescence (CL) studies made on Li and Cu doped CdTe are reported. The CL was performed in a scanning electron microscope (SEM), at low temperature (10 K). High resolution spectral analysis of the SEM-CL pictures revealed the inhomogeneous distribution of the impurities into the crystal. A preferential diffusion of Li and Cu along the crystal defects is observed. Some black dots in Cu diffused CdTe, have been related to Cu complexes due to a supersaturation. This work illustrates the interest of coupling SEM and photoluminescence studies for semiconductor characterization.

Luminescence of Ga‐Doped α‐Al2O3 Crystals

Abstract: The introduction of Ga3+ ions into α-Al2O3 crystals results in a new complex luminescence band at about 5 eV. The main optical excitation maximum is observed at 8.5 eV indicating the bound exciton nature of the excited state. In the cathodoluminescence spectra at 80 K three sub-bands can be detected with maxima at 4.61, 5.15, and 5.58 eV. The luminescence decay in all the three bands has two exponential components — a short one with τ = (15 ± 1) ns and a long one with τ about 1 ms. The Ga-related luminescence can be observed under the excitation of X-rays up to 600 K; a drop in intensity takes place at about 210 K corresponding to the Ga-related TSL peak. The activation energy of the release of electrons at this peak as determined by the fractional-glow method is (0.70 ± 0.02) eV and the frequency factor 1014 s−1. [Russian Text Ignored]

Luminescence study of thallium implanted silicon

Abstract: Ion‐implanted Si:Tl was characterized using photo‐ and cathodoluminescence. The same sharp line defects were found to be produced by the Tl heavy ions as were identified in previous light ion studies. The defects produced by the implantation were removed and the Tl was activated using a two‐step anneal process. A high quality annealed implant layer was produced from which the four excited states of the Tl bound exciton no‐phonon transition could be resolved. An unidentified bound exciton peak related to the Tl acceptor was observed for the first time in both ion‐implanted Si:Tl and in a comparison sample of bulk grown Si:Tl. This is the first reported study of an implanted dopant in silicon using luminescence.

Extremely rapid out diffusion of sulfur in InP

Abstract: During sealed ampoule annealing of n‐type (S,Se,Sn) InP crystals at 550 °C, an unexpected diffusion front was observed whose apparent diffusivity exceeded that of the rapidly diffusing Zn impurity by about two orders of magnitude. Using luminescence techniques, this diffusion front was correlated with changes in the ionized impurity level. In this letter, we show that for annealed InP:S (2×1018 cm−3) crystals the donor profile obtained from cathodoluminescence (CL) intensity measurements corresponds to the 34S profile obtained by secondary ion mass spectroscopy. Although dislocations are generally paths along which impurities can rapidly migrate, CL imaging shows that dislocations impede rather than enhance sulfur out diffusion. Further study is required to determine the rapid out‐diffusion mechanism.

Cathodoluminescence assessment of electron beam recrystallized silicon

Abstract: A preliminary report is given of dramatic changes observed in the cathodoluminescence (CL) properties of silicon melted under vacuum by electron beam excitation. The band edge luminescence is found to be modified and enhanced in the recrystallized material. These changes in the spectral character of the material correlate with changes in the minority carrier lifetime. In addition, deep level luminescence bands are also observed at 0.39, 0.52, and 0.58 eV. The behavior of CL transients as a function of beam excitation indicates that saturation of the bulk recombination path occurs, and this is believed to be related to the improved surface quality of the recrystallized material. Both n‐ and p‐type silicon are found to exhibit these new properties. All the work has been performed on a purposely built scanning electron microscope optimized for CL work.

Luminescence characteristics of the 1.4 eV silicon related complex in gallium arsenide

Abstract: The 1.4 eV emission which is associated with the V As -Si As complex was investigated in silicon implanted and bulk Si doped gallium arsenide through 4.2°K photoluminescence and 8°K cathodoluminescence. These two characterization techniques, with the latter using a UV laser excitation source, allowed the examination of less than 200 A thick layers, and when coupled with chemical etching, provided profiling techniques for observing the change in emissions from the surface into the crystal. Substrates were implanted with 120 keV Si ions at dosages of 1 × 10 13 - 1 × 10 15 cm -2 and, as the bulk Si doped crystals, were annealed from 650 to 950°C for 15 minutes. It is speculated that the complex, which is characterized by energy positions between 1.39 and 1.47 eV, is associated with three recombination processes instead of one. For the implanted samples the shifting nature of the emission is characterized, and it is assumed that in the near surface region ( p ) the complex is primarily due to the V As -Si As recombination process, while at greater depths (≧R p ) the Ga i -Si As complex is the main transition.

Simple collectors for cathodoluminescence in the SEM made from aluminium foil

Abstract: SUMMARY Inexpensive cathodoluminescence collectors for scanning electron microscopes can easily be made from aluminium foil fashioned as tubes which abut against the window of the photo-multiplier at one end and shroud the specimen at the other. Their use in the study of fluorescent labelled mineralized tissues is illustrated.

Characterization of ion-implanted GaAs using cathodoluminescence

Abstract: Cathodoluminescence is investigated as a method for determining the depth profiles of ion‐implanted layers in GaAs A computer simulation of the cathodoluminescence process is developed and used to study the sensitivity of the luminescence to changes in implant profile and electron beam energy The results obtained for both uniformly doped layers and ion‐implanted layers are then compared to experimental results from Mg‐implanted GaAs Clear differences are found to exist between the predicted luminescence curves for different types of layers suggesting that cathodoluminescence is a potentially useful diagnostic tool for use in profile determination

Luminescence emission and excitation spectra of benzene thin film under slow electron impact at 77 K

Abstract: Luminescence bands of thin-film benzene at 77K, excited by slow electron impact, are attributed to fluorescence of the monomer at 280 nm, and tentatively to fluorescence and phosphorescence of benzene isomers at 303 and 395 nm, respectively. The electron impact excitation spectra dL/dV/sub i/ vs. eV/sub i/ for the 280-nm band were measured, where L is the luminescence intensity and eV/sub i/ is the electron energy. Four peaks are clearly resolved which served for the calibration of electron energy, and thus for the assignment of peaks in the electron transmission spectra. 2 figures.

The identification of copper in long lived GaAlAs double heterostructure lasers by means of electron probe x-ray microanalysis

Abstract: Long lived, lifetested GaAlAs/GaAs stripe geometry, double heterostructure lasers have been examined in the scanning electron microscope using a combination of cathodoluminescence, electron beam induced conductivity, and electron probe microanalysis. The dark spot arrays, occasionally seen in the cathodoluminescence images of the active layers of these devices, have been found to be caused by the diffusion of copper into the laser chip from the heat sinks, despite the presence of a nickel barrier layer on the heat sinks.

Study of defects in optoelectronic materials using a scanning acoustic microscope

Abstract: We report a study of defects in some optoelectronic material of technological interest using a scanning acoustic microscope (SAM). Acoustic micrographs of InP, CdTe, and InGaAsP were compared with defect maps obtained by etching, cathodoluminescence (CL), or photoluminescence. Inclusions in InGaAsP were visible using the SAM. However, at low acoustic powers dislocations in InP and CdTe and dark line defects in InGaAsP were not visible. It was possible at high acoustic powers to create ‘‘acoustic etch pits’’ in CdTe which corresponded to defect areas as revealed by CL scans.

Cathodoluminescence Enhancement by Coagulation of Phosphor Particles

Abstract: The cathodoluminescence intensity of Y2O2S:Eu phosphor settled on nesa-coated glass plates was measured from both the gun side and the glass side. The packing density of the phosphor screens was varied by using coagulating agents during the sedimentation process. As the packing densities decreased, enhancement of the luminescence of up to 6%, was observed. This enhancement is explained by the capture of back-scattered electrons at the rough screen surfaces of the coagulated phosphor.