Showing papers on "Cathodoluminescence published in 1975"

Investigation of the deformation mechanism of MgO crystals affected by concentrated load

Abstract: The mechanism of deformation under the indentation of MgO crystals has been studied by transmission and scanning electron microscopy. The dislocation structure and Burgers vectors of rosette dislocations are determined. The nature and geometry of cathodoluminescence around indentation have been also investigated. The luminescence radiation is shown to be caused by interstitial point defects built up under indentation. [Russian text ignoreed].

Scanning electron microscopy studies of GaN

Abstract: The surface of vapor−deposited GaN and the cross section of GaN light−emitting diodes were examined using secondary electron emission, cathodoluminescence, beam−induced conductivity, and beam−induced voltage. The GaN layer is an assemblage of identically oriented microcrystals. The Zn distribution in the insulating layer is usually not uniform. High built−in fields occur at the two edges of the insulating layer.

Electrical and cathodoluminescence measurements on ion implanted donor layers in GaAs

Abstract: GaAs has been doped by the ion implantation of silicon, sulphur, selenium and tin. After annealing at 700°C, the layers were n-type in all cases but with the heavier ions, selenium and tin, it was necessary to implant above room temperature. Van der Pauw measurements showed that for all the impurities the surface concentration of free electrons as a function of ion dose reached a maximum of approximately 1013 electron/cm2 with an average Hall mobility of 2000 cm2/V sec. The spatial distributions of active donors were obtained from both differential Hall measurements and capacitance measurements on reverse biased Schottky barriers. The maximum carrier density measured was 1018/cm3 at the peak of the distribution of tin ions implanted at 200°C. With selenium and tin implants the concentration and mobility of free electrons and the depth of the donor distribution were dose dependent. The cathodoluminescence spectra from implanted layers were dominated by broad low energy bands due to recombination at defects. A VGa-Si complex was thought to be responsible for one of the most intense bands at 1·18 eV. The results indicate that under certain conditions both defects and impurities migrate into the substrate.

The luminescence of SnO2-Eu3

Abstract: SnO2 single crystals have been doped with varying amounts of Eu. The cathodoluminescence and photoluminescence spectra have been measured Thermoluminescence has been investigated in as-grown and doped crystals over the temperature range 100-400K. New traps appear, which are associated with the addition of Eu. When Li is added as well, these traps are not created to any significant extent because charge compensation by interstitial Li+ ions occurs preferentially.

Localisation of caps on mouse B lymphocytes by scanning electron microscopy

Abstract: WE have used cathodoluminescence (CL) to detect fluorescein-labelled anti-IgG-induced caps on mouse B lymphocytes by means of the scanning electron microscope (SEM). This approach, which has as yet been little explored, depends critically on efficient collection of a weak CL signal1,2. It provides a means of identifying antigenic markers in the SEM.

Cathodoluminescence of biological molecules, macromolecules and cells.

Abstract: SUMMARY Cathodoluminescence observations on biological compounds are compared with previously established data from ultra violet and visible light excitation studies. The comparison demonstrates that the same molecules are responsible for the luminescence properties of macromolecules independent of the type of exciting radiation. Natural cathodoluminescence was also observed from cells. Moreover, advantages gained by the absorption of strongly cathodoluminiscent dyes into cells are demonstrated.

Microcharacterization of electroluminescent diodes with the scanning electron microscope (SEM)

Abstract: A complete material characterization of electroluminescent diodes necessarily requires a high spatial resolution because of the micron-sized thickness of the different epitaxial layers. A modified arrangement of a scanning electron microscope (SEM) has proven to be an extremely useful tool for obtaining information on the various parameters of each of these layers. It will be shown that the analysis of the electron beam induced voltages (EBIV) and currents (EBIC) allows not only the location of the junction itself, but also the detection of all other built-in barriers. Measurements of the EBIC permit separation of barriers less than 1 µm apart; even barriers in a direction oposite to that of the junction are detected in this manner. The peak value of EBIC is largely independent of the barrier height, but it is sensitive to variations in the concentration of the components of the lattice. Because of the exponential decrease of EBIC with the distance between primary electron beam and barrier, the minority carrier diffusion length can be obtained for all different barriers. The height of barriers, 2.5 µm separated and with the same direction as the p-n junction, can be determined quantitatively by the maximum of EBIV. By measurement of the cathodoluminescence (CL) signal regions of different recombination probabilities for radiative transitions (and therefore different luminescence yields) can be distinguished. Thus inhomogeneities of the structure can be detected. By spectral CL analysis the spatial variation of the width of the bandgap will be shown.

Cathodoluminescence of compositionally graded layers of GaAs1−xPx

Abstract: Compositionally graded layers of GaAs1−xPx grown on (100) planes of GaAs substrates were investigated as a function of the distance t from the substrate, using a 77 °K cathodoluminescence technique. It was found that luminescence intensity L of these layers was strongly dependent on the profile of the compositional gradient, dx/dt. A number of the nonradiative recombination centers are three−dimensionally distributed in the shape of a cross−grid. This is related to misfit dislocations associated with impurities in the graded layers. The gradient dependence of L demonstrates that the density of these nonradiative recombination centers, N, is proportional to (dx/dt)2. This quadratic relation shows that only grading profiles which satisfy the condition d2x/dt2<0 can successfully decrease N continuously with increasing t. Discontinuous variations of x and/or dx/dt cause a significant degradation in the subsequent layers. From the spatial variation in the ratio of the intensity of the 1.35−eV band to the near−...

Contrast Mechanisms of Special Interest in Materials Science

Abstract: The versatility of the scanning electron microscope is due in great measure to the rich variety of mechanisms of electron interaction with solids. These interaction mechanisms can be employed to produce contrast in SEM images, revealing differences in the physical nature of the specimen from point to point. This chapter will discuss six contrast formation mechanisms of particular interest: (1) electron channeling contrast, which is related to the crystallographic nature of a specimen; (2) type I and (3) type II magnetic contrast, which can reveal magnetic domains in both crystalline and artificial magnetic structures; (4) voltage contrast, which arises from differences in the electrostatic potential of the specimen; (5) electronbeam- induced current contrast, a phenomenon of electron-hole pair production in semiconductor devices; and (6) cathodoluminescence, which arises from the emission of long-wavelength electromagnetic radiation in the ultraviolet, visible, and/or infrared regions. Of these mechanisms, 1–5 are confined to applications in the physical sciences, while mechanism 6, cathodoluminescence, finds application in physical, mineralogical, and biological sciences.

Luminescence and charge compensation in SnO2-Tb3+

Abstract: The photoluminescence, cathodoluminescence and thermoluminescence of SnO2 crystals doped with Tb and charge compensators such as Li or H or P have been investigated. The characteristic Tb3+ lines appear in all cases under electron bombardment. Only SnO2-Tb-P crystals produce the characteristic Tb3+ emission under 365 nm excitation. Otherwise a broad orange band appears, due to the presence of tin vacancies. The traps which appear on adding Tb3+ are discussed in terms of a simple model which is used to show that the charge compensation mechanism results in the creation of traps rather than defect luminescence centres.

Cathodoluminescence of ytterbium-implanted zinc telluride

Abstract: The cathodoluminescence emission of Yb3+ ions in zinc telluride produced by implantation of ytterbium ions in samples of differing degrees of non-stoichiometry has been studied as a function of implantation and annealing parameters. Successful implantation of ytterbium in zinc telluride was found to be strongly dependent on the non-stoichiometry present in the lattice. Because the ytterbium ions can occupy interstitial sites or zinc substitutional sites the relative intensities of emission lines in the characteristic ytterbium spectrum (980–1100 nm) can be changed by controlling the annealing treatment in the temperature range 250°–500°C. Annealing at higher temperatures was found to reduce the total ytterbium emission intensity. To produce the most intense, well-structured ytterbium emission lines it is essential to implant tellurium rich material at as low a temperature as possible.

Cathodoluminescence of GaAs1−xPx alloys

Abstract: Temperature dependence of cathodoluminescence was studied for GaAs, GaP, and GaAs1−xPx alloys Specimens were investigated at temperatures from 30 to 300 °K using a beam voltage of 50 kV and a spot size of 10–15 μm The change in the band gap, from direct to indirect, was observed by the variation of the wavelength of the maximum cathodoluminescence intensity and a crossover composition of ∼051 mole% GaP was obtained for both 30 and 300 °K The relative peak intensities and half‐widths of the recombination radiation was also studied for compositions on both sides of this crossover point

Luminescence from Diffused In1-xGaxP p-n Junctions

Abstract: Electroluminescence spectra from In1-xGaxP p-n junctions have been measured at 77 K and at higher temperatures for a number of diodese with x=05 to 09, in particular, near the crossover composition Various peaks appear in the spectra as the forward current increases from 10-3 A/cm2 to 30 A/cm2 The current dependence of the spectra is studied in detail The spectra and their temperature dependences in the direct-band-gap region are found to be greatly different from those in the indirect-band-gap region In the direct-band-gap region, four peaks P1, P2, P3 and P4 are usually observed at 77 K The highest-energy peak P1 is 0 to 20 meV below the Γ conduction band which has been estimated from the 300 K cathodoluminescence The energy separation between P1 and P3 is 70–75 meV In the indirect-band-gap region, two weak bands A1 and A2 are observed on the higher energy side of the dominant band P1 due to the donor-acceptor transition at 77 K The energy position of the highest energy peak A1 is very near the expected energy position of the free exciton of excitons trapped by some shallow impurities At 177 K, A1 and A2 become dominant compared to P1 The cross-over composition of direct- and indirect-band-gaps is estimated to be close to 072

Terbium doped glasses: their optical properties and potential applications

Abstract: The optical properties of inorganic glasses doped with terbium have been investigated with particular emphasis on silicate glass systems. The effect of increasing terbium concentration on the refractive index of silicate glasses has been investigated and the optical absorption from 0.2 to 40 microns has also been studied. The energy levels of the trivalent terbium ions involved in the various optical processes have been identified by reference to theoretical predictions and spectra in other media. Glasses doped with terbium show intense series of blue and green luminescence emissions when excited by ultra-violet or X-ray radiation. Emissions from the (^5) D (_3) level of the Tb (^3+) ions produce the blue luminescence while the green emission results from transitions from the (^5) D (_4) level. At terbium concentrations above 0.3 mole % the blue emissions are quenched by multipolar transitions from the (^5) D (_3) level to the (^5) d (_4) level. The green emissions are quenched at concentrations above 6 mole % by an exchange-dipole mechanism. The effect of temperature on the emission characteristics has been determined. Intense luminescence persists to temperatures above 500 C in silicate glasses. The reduction in temperature does not greatly change the emission intensity. Inhomogeneous broadening, due to the random nature of the glass matrix, persists even at liquid helium temperatures. Decay rates have been measured at various temperatures with both ultra-violet and X-ray excitation. The effect of other rare earths on the photoluminescence has also been investigated, and a model for the lanthanide ion site is proposed. The thermoluminescence characteristics of terbium doped silicate glasses have also been measured. Increased terbium concentration reduces the glow peak intensity. A model of the mechanism producing thermoluminescence is proposed. Differences between binary (sodium silicate) and ternary (lithium aluminosilicate) glasses, observed in both photo- and thermoluminescence, are discussed. Other optical properties, such as the Faraday Effect and cathodoluminescence, are reviewed in a survey of the literature.

Direct Measurement of Impurity and Damage Distribution in Ion Implanted ZnTe by Cathodo and Photoluminescence

Abstract: In this paper, we present the luminescence properties of Boron and Aluminium implanted ZnTe. Once implanted and eventually annealed, ZnTe is deepened by Argon ionic sputtering to different depths (down to 2.2 μ). Then cathodoluminescence at 77°K and photoluminescence at 4.2°K are performed on each step. From the spectral distribution and the quantum efficiency measurements, it appears clearly that the effect of implantation is significant far beyond the penetration depth of impurities. On the other hand, annealing at 550oC during 30 minutes is not sufficient to eliminate the created damage. On the contrary, far from the surface, the annealing reduces the quantum efficiency. A model, based on the interaction between damage and luminescent centers associated with implantation, is proposed to explain the behaviour of implanted impurities in II–VI semiconductors.Important conclusions are also inferred in order to improve the external quantum efficiency of ZnTe implanted electroluminescent diodes.

Luminescence of ZnS and ZnSe Window and Filter Materials

Abstract: The visible and infrared cathodoluminescence spectra of undoped polycrystalline and single-crystal ZnSe and ZnS have been measured at 295, 78, and 10 K. Infrared luminescence bands were detected at 1.8, 2.4, 3.2, and 3.8 pm in IRTRAN 4 (ZnSe) and single-crystal ZnSe, but not in Raytran ZnSe. Similarly, bands at 1.4, 1.6, and 1.9 am were detected in IRTRAN 2 (ZnS) and single-crystal ZnS, but not in Raytran ZnS. The infrared luminescence in ZnSe materials is accompanied by edge emission and the copper red band, in addition to the copper green band appearing in IRTRAN 4. Self-activated luminescence was observed in Raytran ZnSe. The power law decay of the 1.8 and 3.8 pm bands in IRTRAN 4 suggests a bimolecular kinetic reaction. A model is proposed to account for the transitions involved.

Ultraviolet Cathodoluminescence and Photoluminescence of Zinc Sulfide

Abstract: An investigation was made of the properties and nature of the edge and other ultraviolet luminescence bands of zinc sulfide. The excitation conditions (nature of the excitation, its intensity, temperature of a crystal, intensity of infrared background illumination, etc.), conditions during synthesis, and composition (stoichiometry, quenching, crystal phase, impurity content) were varied in a wide range. The results were used to determine the energy and spectral characteristics. The radiative transitions explaining the results were identified. The explanation of the edge luminescence was based on a donor-acceptor model of radiative transitions at local levels associated with intrinsic lattice defects.

Enhancement of UV luminescence from single crystals of zinc oxide

Abstract: Crystals of the red oxide of zinc are normally heat treated in various media to produce enhanced UV luminescence. Studies have been carried out on the reflection, photoluminescence, and cathodoluminescence spectra of these crystals in order to understand the changes in the intensity of the luminescence. It has been established that with heat treatment of single crystals of zinc oxide in a vacuum or water vapor, or with diffusion of an impurity which replaces the zinc in the crystal and has atoms larger than the Zn atoms, there is an enhancement of the intensity of UV luminescence by more than two orders of magnitude.

Cathodoluminescence of ZnS single crystals subjected to thermal annealing in vapors of the constituents

Abstract: The 77°K cathodoluminescence spectra of ZnS single crystals grown from the melt and annealed in vapors of the constituents were studied in the spectral region 360 to 550 nm The single crystals contained oxygen whose phase state could be changed by thermal annealing The effect of oxygen in the ZnS lattice on the appearance and intensities of various bands in the zinc sulfide spectrum was investigated It turned out that the bands at 390–400 nm, 410–430 nm, and 500–525 nm are associated with the luminescence of a solid solution of ZnS· O in the lattice The intensity of the green luminescence was a function of oxygen concentration in precipitates of the solid solution on dislocations The luminescence in the 363 to 370 nm region is associated with zinc oxide which separates from ZnS containing various amounts of sulfur

Sensitized UV luminescence from single crystals of zinc oxide

Abstract: The reflection, absorption, excitation, photoluminescence, and cathodoluminescence spectra have been studied for indium-doped single crystals of ZnO. The temperature quenching of the UV-radiation bands has also been studied. These studies have made it possible to establish that the UV-radiation bands are excited during quantum absorption corresponding to “band-band” transitions and also by exciton absorption. The studies have also made it possible to calculate the activation energy of the temperature quenching. In the photoluminescence spectrum of ZnO crystals there is a wide radiation band in the 3950–4050-A region which could be described by transitions in donor-acceptor pairs. It is shown that the band of the equidistant series at 3834 A is complex in character.