Characterization of radiative centers in wide-band-gap materials by local cathodoluminescence by the example of europium-doped YAG

Europium-doped yttrium-aluminum garnet (YAG) samples were studied by local cathodoluminescence. The europium valence in YAG is 3+; an addition of a small amount of zirconium partially converted europium to the divalent state (2+). The local cathodoluminescence method made it possible to detect the presence of both europium valence states. Concentration dependences of the cathodoluminescence intensity and decay time for various spectral lines and bands were studied. The dependence of the cathodoluminescence intensity on the electron beam current density was studied. The results obtained were interpreted within the two-level model of the radiative center. The local cathodoluminescence method potential and the two-level model applicability were demonstrated. An analysis of the spectra allowed for the detection and identification of an unintentional impurity in one of the samples.     

SiC晶体缺陷的阴极荧光无损表征研究

由于在研究SiC晶体缺陷对器件性能的影响的过程中,表征材料缺陷的常用的方法是破坏性的,因此寻找一种无损的测试方法对缺陷进行有效的表征显得尤为重要。基于阴极荧光(CL)的工作原理对4H-SiC同质外延材料的晶体缺陷进行了无损测试研究。结果发现利用阴极荧光可以观测到晶体内部的堆垛层错、刃位错和螺位错以及基面位错,其阴极荧光图中的形貌分别为直角三角形、点状和短棒状。因此该方法成为SiC晶体缺陷的无损表征时的一种有效的测试方法。如果利用该方法对材料的衬底和外延层缺陷分别进行观测就能建立起衬底和外延层缺陷之间的某种联系,另外对器件工作前后的缺陷进行表征,建立器件工作前后缺陷之间的联系,就可以进一步地研究材料缺陷对器件性能影响的问题。     

Photo- and cathodoluminescence investigation of ZnO films

Photo- and cathodoluminescence spectra of ZnO films obtained by magnetron sputtering and annealed at different temperatures have been studied. The effect of irradiation in a scanning electron microscope on the cathodoluminescence spectra of these films is investigated. It is shown that even relatively small irradiation durations result in a noticeable change in signal intensity. Both signal enhancement and reduction can occur depending on the annealing temperature. Data obtained are explained by defect formation and rearrangement stimulated by electron irradiation.     

PPV固态类阴极射线发光动力学的研究

制备了三种结构的薄膜电致发光器件，以PPV作为发光层，SiO2作加速层，证明了固态类阴极射线发光的存在，对其发光动力学中的一些问题进行了研究，固态类阴极射线发光这一现象将为形成一类新的平板显示技术的开创成为可能。     

Changes of cathodoluminescence emission from MgO in the scanning electron microscope

The effect of electron beam on the cathodoluminescence (CL) from MgO single crystals has been studied in the scanning electron microscope. It has been found that CL intensity and spectrum vary with irradiation time. The behaviour is discussed in terms of impurities and vacancy defects.     

Influence of the thickness of CdTe and ZnTe layers on cathodoluminescence spectra of strained CdTe/ZnTe superlattices with quantum-dot layers

The influence of the thickness of ZnTe barrier layers on the cathodoluminescence spectra of strained CdTe/ZnTe superlattices containing layers of quantum dots with an average lateral size of approximately 3 nm has been investigated. In samples with thick barrier layers (30, 15 nm), the cathodoluminescence spectra of quantum dots exhibit one band with a maximum at E = 2.03 eV. It has been revealed that, at a barrier layer thickness of ∼3 nm, the luminescence band is split. However, at a ZnTe layer thickness of 1.5 nm, the luminescence spectrum also contains one band. The experimental results have been interpreted with allowance made for the influence of elastic biaxial strains on the energy states of light and heavy holes in the CdTe and ZnTe layers. For the CdTe/ZnTe heterostructure with quantum dots in which the thickness of the deposited CdTe layer is 1.5 monolayers and the thickness of the barrier layer is 100 monolayers, the cathodoluminescence spectrum contains 2LO-phonon replicas. This effect has been explained by the resonance between two-phonon LO states and the difference between the energy states in the electronic spectrum of wetting layer fragments.     

Prospects for using cathodoluminescence in SEM to study the distribution and types of breakdown in glass insulators

A method for detecting dielectric breakdown in the signal of cathodoluminescence in SEM is compared with both capacitive and secondary-emission methods. In the investigated samples of glass dielectrics, breakdowns of two types are found: surface and emission. The prospects for using cathodoluminescence to detect and localize defects in insulators that lower the breakdown voltage are discussed.     

Luminescence Quenching in Magnesium-Doped Alumina Ceramics

Physics of the Solid State - The effect of magnesium impurity on luminescent properties of alumina ceramics sintered at high temperatures under vacuum is studied by pulsed cathodoluminescence,...     

Applications of cathodoluminescence in mineralogy

Cathodoluminescence microscopy and cathodoluminescence spectrometry with the electron microprobe and the scanning electron microscope are applied to the study of some natural cassiterite, quartz and sphalerite crystals. Some examples of localization and distribution of crystalline defects revealed by cathodoluminescence microscopy are given. X-ray spectrometry and secondary ion mass analysis allow to illustrate the coincidence between the spatial variations of cathodoluminescence emission and the distribution of impurities within minerals. In order to establish a relationship between the spectral distribution of the luminescence and the nature of trace elements, comparisons are made between cathodoluminescence properties of natural and artificial zinc sulphide crystals. Particular attention is given to specimen containing copper-gallium impurities. It has been possible to distinguish between the impurities which can be responsible for the luminescence and those which are not associated with cathodoluminescence emission characteristic of the crystals. The study of cathodoluminescence intensity according to the excitation conditions led to consider the contribution of the X-ray photons generated in the specimen for the production of luminescence photons. An in-depth distribution law of generated photons similar to that used to take account of X-ray emission led to introduce an absorption function in the relation giving the measured intensity of cathodoluminescence according to the incident energy and the electron beam density.     

Chatham合成钻石紫外阴极发光谱

用自制的阴极发光分析仪在JCXA-733电子探针上分析两批美国Chatham公司合成钻石的微区紫外-可见阴极荧光,结果表明Chatham合成钻石具有峰波长为234,268 nm等的紫外阴极荧光谱。不同批次的Chatham钻石的紫外阴极荧光谱特征也有所不同。这些紫外阴极发光谱在天然钻石和人工处理后的天然钻石中都没有发现,可能是Chatham合成钻石的特征谱,因而可能具有一定鉴定价值。经进一步完善后,紫外阴极荧光谱技术有望成为鉴别天然和合成钻石、不同公司合成钻石或同一公司不同批次合成钻石的有效方法。     

Raman-in-SEM,a multimodal and multiscale analytical tool: Performance for materials and expertise

The availability of Raman spectroscopy in a powerful analytical scanning electron microscope (SEM) allows morphological, elemental, chemical, physical and electronic analysis without moving the sample between instruments. This paper documents the metrological performance of the SEMSCA commercial Raman interface operated in a low vacuum SEM. It provides multiscale and multimodal analyses as Raman/EDS, Raman/cathodoluminescence or Raman/STEM (STEM: scanning transmission electron microscopy) as well as Raman spectroscopy on nanomaterials. Since Raman spectroscopy in a SEM can be influenced by several SEM-related phenomena, this paper firstly presents a comparison of this new tool with a conventional micro-Raman spectrometer. Then, some possible artefacts are documented, which are due to the impact of electron beam-induced contamination or cathodoluminescence contribution to the Raman spectra, especially with geological samples. These effects are easily overcome by changing or adapting the Raman spectrometer and the SEM settings and methodology. The deletion of the adverse effect of cathodoluminescence is solved by using a SEM beam shutter during Raman acquisition. In contrast, this interface provides the ability to record the cathodoluminescence (CL) spectrum of a phase. In a second part, this study highlights the interest and efficiency of the coupling in characterizing micrometric phases at the same point. This multimodal approach is illustrated with various issues encountered in geosciences.     

Effect of low-energy electron irradiation on the cathodoluminescence of multiple quantum well (MQW) InGaN/GaN structures

The effect of low-energy electron-beam (e-beam) irradiation on the InGaN-related cathodoluminescence in multiple quantum well (MQW) InGaN/GaN light-emitting diode (LED) structures has been studied. It is shown that the e-beam exposure leads to an increase of emission intensity and to a formation of new blue-shifted emission bands. The changes observed were explained by the enhancement of In diffusion stimulated by excess carrier recombination.     

Memory effect and cathodoluminescent properties of YAG:Nd<Superscript>3+</Superscript> nanoceramics

The cathodoluminescent properties of nanoceramics based on neodymium-doped yttrium–aluminum garnet (YAG:Nd³⁺) are studied in a wide optical spectral range (from UV to IR). It is shown that the spectral positions of the emission bands of nanoceramics are identical to that of single crystal, but the bands of nanoceramics are broadened by no more than 15% from the half bandwidths of single crystal. The intensity of cathodoluminescence bands in nanoceramics is lower, and the lifetimes of radiative levels are shorter. It is found for the first time that electron-beam irradiation of nanoceramics increases the cathodoluminescence intensity of bands in visible and UV ranges (by two or more times). Preliminary electron beam irradiation of YAG:Nd³⁺ nanoceramics samples leads to the increase of cathodoluminescence efficiency. Such effect retains for a long time (a year and more) and can be compared to the memory effect. This effect is not observed in single crystal. We propose a model describing this effect in nanoceramics.     

Rare earth elements as activators of zinc sulfide cathodoluminophors

Luminescence spectra of zinc sulfide luminophore activated by ten rare earth elements and their relative yield of cathodoluminescence in the visible region are studied at room temperature. The effect of the conditions of synthesis is studied. Using ZnS · CdS-Ho phosphor as an example, the marked effect of a change in lattice constant and the width of the forbidden zone on luminescence of rare earth centers is shown.     

Scanning near-field cathodoluminescence microscopy of an Si+ implanted and thermally annealed SiO2 layer

A scanning near-field cathodoluminescence microscope (SNCLM) is successfully used to image the cathodoluminescence of an Si⁺ implanted and thermally annealed submicronic SiO₂ layer. Owing to the subwavelength resolution of the system a “cross-sectional” cathodoluminescence image was obtained. The intensity image profile shows that sample luminescence results from the whole SiO₂ layer confirming a preceding electroluminescence study. Sample luminescence is attributed to point defects generated into the whole SiO₂ layer during Si⁺ ion implantation and thermal annealing.     

On the choice of initial approximation in the problem of parameter identification of direct-gap semiconductors by cathodoluminescence microscopy

The problem of the choice of initial approximation has been considered to identify the parameters of direct-gap semiconductors by cathodoluminescence microscopy using the dependence of monochromatic cathodoluminescence intensity on electron beam energy for the case of a low level of signal excitation. It has been shown that the realization of the confluent analysis method can lead to the problem of multidimensional numerical minimization of a quadratic functional, the solution of which depends significantly on the choice of initial approximation. On this basis, some conditions of correct processing of the experimental data have been determined to identify the required parameters for gallium arsenide.     

Properties of n-type gallium arsenide doped with germanium when single crystals are grown from the melt

The temperature dependences of the density, mobility, and lifetime of electrons, and the photoconductivity and cathodoluminescence spectra of gallium arsenide with different electron densities doped with germanium when single crystals are grown by the Czochralski method are investigated. An analysis of the scattering mechanism is given, and the acceptor and donor densities are determined. The acceptor-type capture levels are found from the temperature dependence of the electron lifetime. The results of a study of the cathodoluminescence spectra indicate the presence in the specimens of complex radiational recombination centers similar to germanium-atom complexes with inherent lattice defects.     

Two-dimensional diffusion and cathodoluminescence of excitons generated by an electron beam in a semiconductor material: Results of mathematical modeling

Mathematical models of the two-dimensional diffusion and cathodoluminescence of excitons excited by an electron beam in a semiconductor material have been studied and are described. It is shown that the obtained models can be used to estimate the coefficients of exciton diffusion and mobility by means of the results of experimental measurements of the cathodoluminescence decay. Parameters typical of gallium nitride were used in the modeling.     

Structural study of thermal-oxide films on silicon by cathodoluminescence

A study of cathodoluminescence spectra of silicon oxide films grown thermally on silicon is reported. It has been established that the cathodoluminescence properties of thermal films are nonuniform in depth and depend on the growth conditions and characteristics of the silicon substrate. Fiz. Tverd. Tela (St. Petersburg) 40, 1984–1989 (November 1998)     

On the Influence of Electron Energy on Characteristics of the Cherenkov Radiation and Cathodoluminescence

Russian Physics Journal - A review of the results of investigations of the Cherenkov radiation (CR) and pulsed cathodoluminescence during irradiation of different crystals and...