Showing papers on "Cathodoluminescence published in 2003"
TL;DR: Secondary ion mass spectrometry (SIMS) is a versatile technique for measuring the chemical and isotopic composition of solid materials on a scale of a few microns as mentioned in this paper.
Abstract: Secondary ion mass spectrometry (SIMS) is a versatile technique for measuring the chemical and isotopic composition of solid materials on a scale of a few microns. A beam of high-energy primary ions is focused onto the polished target surface, sputtering (ablating) atoms and molecules, and in the process ionizing a small fraction. These secondary ions, which reflect the target composition, are analyzed by mass spectrometry. The SIMS instrument most common in geoscience is the ion microprobe, which uses a focused primary ion beam in either static or scanning mode to sample target areas usually 10- to 50-μm diameter. Total sampling depth is typically less than 5 μm and the sampled mass only a few nanograms, making the analysis for most samples effectively non-destructive. Coupled with surface imaging techniques such as backscattered electron (BSE) and cathodoluminescence (CL), SIMS enables finely targeted chemical and isotopic analysis of specific domains exposed on a crystal surface.
Zircon is particularly suitable for SIMS U–Th–Pb geochronology. It is a physically and chemically robust mineral that crystallizes under a range of geological conditions, incorporating trace U and Th, but little or no Pb. Zircon grains are commonly composite, having survived and grown during several geological events. This growth record is sometimes visible under an optical microscope, but is best revealed by CL and BSE imaging of polished sectioned grains (Fig. 1⇓). The U–Th–Pb closure temperature of unaltered zircon is very high (>900°C), and the growth domains commonly can preserve an isotopic record of thermal events spanning tens to thousands of millions of years. This record of provenance, and igneous and metamorphic history, is accessible only to microanalytical techniques such as SIMS.
Figure 1.
Both zircon crystals appear homogeneous in transmitted light but cathodoluminescence images show the true growth structures: (a) an igneous zircon with simple euhedral oscillatory zoning, …
446 citations
TL;DR: In this article, a two-dimensional micrometer-sized single-crystalline ZnO thin nanosheets were achieved on a large scale, in which Zn thin pre-precursor were first grown via a thermal decomposition and reduction of the starting ZnS powder, and then converted to the ZnOs via a simple oxidation process.
Abstract: Two-dimensional micrometer-sized single-crystalline ZnO thin nanosheets were achieved on a large scale, in which Zn thin nanosheets (precursor) were first grown via a thermal decomposition and reduction of the starting ZnS powder, and then converted to the ZnO nanosheets via a simple oxidation process. The ZnO nanosheets, growing along [100] or [010] direction and enclosed by ± (001) facets, have lateral dimensions up to several hundreds of microns, and thicknesses of 30–70 nm. Both room-temperature cathodoluminescence and photoluminescence measurements reveal that the present ZnO nanosheets have visible emission bands ranging from the green to red.
193 citations
TL;DR: In this article, structural and optical properties of Zn1−xCdxO layers grown by metalorganic vapor phase epitaxy were analyzed, and a narrowing of the fundamental band gap of up to 300 meV was observed.
Abstract: The development of ZnO-based semiconductor devices requires band gap engineering. Ternary Zn1−xCdxO allows reduction of the band gap relative to ZnO, which would be necessary for devices emitting visible light. We have analyzed the structural and optical properties of Zn1−xCdxO layers grown by metalorganic vapor-phase epitaxy. A narrowing of the fundamental band gap of up to 300 meV has been observed, while introducing a lattice mismatch of only 0.5% with respect to binary ZnO. Photoluminescence, high-resolution x-ray diffraction, and spatially resolved cathodoluminescence measurements revealed a lateral distribution of two different cadmium concentrations within the Zn1−xCdxO layers.
174 citations
TL;DR: In this paper, a polycrystalline hexagonal wurtzite type structure of undoped and tin (Sn)-doped ZnO films was studied for cathodoluminescence spectroscopy, X-ray diffraction and spectrophotometery.
155 citations
TL;DR: In this article, defects in hydrothermal grown ZnO single crystals are studied as a function of annealing temperature using positron annihilation, x-ray diffraction, Rutherford backscattering, Hall, and cathodoluminescence measurements.
Abstract: Defects in hydrothermal grown ZnO single crystals are studied as a function of annealing temperature using positron annihilation, x-ray diffraction, Rutherford backscattering, Hall, and cathodoluminescence measurements. Positron lifetime measurements reveal the existence of Zn vacancy related defects in the as-grown state. The positron lifetime decreases upon annealing above 600 °C, which implies the disappearance of Zn vacancy related defects, and then remains constant up to 900 °C. The Rutherford backscattering and x-ray rocking curve measurements show the improvement of crystal quality due to annealing above 600 °C. Although the crystal quality monitored by x-ray diffraction measurements is further improved after annealing at above 1000 °C, the positron lifetime starts to increase. This is due to either the formation of Zn vacancy related defects, or the change of the Zn vacancy charge state occupancy as a result of the Fermi level movement. The electron concentration increases continuously with increasing annealing temperature up to 1200 °C, indicating the formation of excess donors, such as oxygen vacancies or zinc interstitials. The cathodoluminescence measurements reveal that the ultraviolet emission is greatly enhanced in the same temperature range. The experimental results show that the ZnO crystal quality, electrical and optical characteristics are improved by postgrowth annealing from 600 to 1200 °C. The disappearance of Zn vacancy related defects contributes to the initial stage of improved crystal quality.
151 citations
TL;DR: In this article, an overview of the properties of In x Ga 1-x N epilayers based on a systematic study of thick layers and of quantum well structures is presented.
Abstract: The In x Ga 1-x N system has electronic band gaps extending from under 1eV to 3.4 eV, and as such they are used as the active layer in commercially available visible-light emitting devices. There are many interesting features that make these nitride semiconductor alloys especially useful for efficient light emitters. It has been conjectured that the combination of piezoelectric fields and local composition inhomogeneities may be responsible for the observed high emission efficiencies, in spite of their characteristic high dislocation densities. But it is very difficult to grow In x Ga 1-x N layers with high indium composition. This paper presents an overview of the properties of In x Ga 1-x N epilayers based on a systematic study of thick layers and of quantum well structures. We find that the microstructure of thick films varies significantly with indium composition. For x 0.20, spontaneous phase separation occurs resulting in a polycrystalline, inhomogeneous layer. A correlation between optical properties and microstructure is presented. It is observed that the misfit strain is affected by threading dislocations. Mechanisms of misfit strain relaxation are presented for In x Ga 1-x N layers grown on standard GaN on sapphire and on epitaxial-lateral-overgrowth GaN layers. In addition, we have studied the properties of quantum well structures using several novel techniques. The electrostatic fields across the wells have been profiled using electron holography in the TEM. The effect of well thickness on the strength of the fields is reported. The effects of localization by compositional fluctuations and of internal field screening have been studied using time-resolved cathodoluminescence spectroscopy. In spite of significant progress that has been made in the last ten years, much work remains ahead in order to master the science and technology of these alloys.
144 citations
TL;DR: The only dopant available for bulk diamond with good controllability is boron, which acts as an acceptor and can be incorporated in relatively high concentrations, allowing the design of devices for electronic applications.
Abstract: To date, the only dopant available for bulk diamond with good controllability is boron, which acts as an acceptor and can be incorporated in relatively high concentrations, allowing the design of devices for electronic applications. This paper summarizes data on doping procedures and on optical and electrical properties.
141 citations
TL;DR: In this article, a Pechini sol-gel process combined with a soft lithography was used to obtain homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths.
135 citations
TL;DR: In this paper, three different ZnO nanomaterials (nanobelts, nanorods, and nanowires) were synthesized at three different substrate temperatures from the thermal evaporation of ball-milled znO powders at 1380°C.
120 citations
TL;DR: In this article, GaN quantum discs embedded in AlGaN nanocolumns with outstanding crystal quality and very high luminescence efficiency were grown on Si(111) substrates by plasma-assisted molecular beam epitaxy under highly N-rich conditions.
Abstract: GaN quantum discs embedded in AlGaN nanocolumns with outstanding crystal quality and very high luminescence efficiency were grown on Si(111) substrates by plasma-assisted molecular beam epitaxy under highly N-rich conditions. Nanocolumns with diameters in the range of 30--150 nm, with no traces of any extended defects, as confirmed by transmission electron microscopy, were obtained. GaN quantum discs, 2 and 4 nm thick, were grown embedded in AlGaN nanocolumns by switching on and off the Al flux during variable time spans. Strong optical emissions from GaN quantum discs, observed by photoluminescence and cathodoluminescence measurements, reveal quantum confinement effects. While Raman data indicate that the nanocolumns are fully relaxed, the quantum discs appear to be fully strained. These nanostructures have a high potential for application in efficient vertical cavity emitters.
119 citations
TL;DR: In this article, the growth mechanism, structure, and luminescence properties of ZnO hexagonal columns grown from Zn vapor and air plasma were reported, and convergent beam electron diffraction showed that the columns grow with Zn polarity in the [0001] direction.
Abstract: We report on the growth mechanism, structure, and luminescence properties of ZnO hexagonal columns grown from Zn vapor and air plasma. Single-crystal ZnO columns grow in the [0001] direction through repeated nucleation and growth of epitaxial hexagonal pyramids on the c-planes. Homoepitaxial nucleation of three-dimensional ZnO pyramids is most likely due to the Ehrlich–Schwoebel effect. This mechanism produces columns that are a few hundred nanometers in diameter and up to 2 μm in length. Convergent beam electron diffraction shows that the columns grow with Zn polarity in the [0001] direction. Cathodoluminescence and photoluminescence measurements show near-bandedge emission (3.29 eV) with no emission associated with oxygen vacancies at 2.5 eV.
TL;DR: In this paper, Gd-implanted aluminum nitride was studied with cathodoluminescence (CL) as well as time-resolved CL in the temperature range 12-300 K.
Abstract: We present investigations of Gd-implanted aluminum nitride, studied with cathodoluminescence (CL) as well as time-resolved CL in the temperature range 12–300 K. Luminescence due to intra-4f electron transitions of Gd3+ is dominated by the 6P7/2→8S7/2 transition between the first excited state and the ground state of Gd3+ detected at around 318 nm. Time-resolved CL of the 6P7/2 level monitoring the 6P7/2→8S7/2 transition shows a temperature-dependent lifetime which decreases from 0.76 ms at 12 K to 0.69 ms at 300 K, in contrast to an increasing intensity of the 6P7/2→8S7/2 transition by a factor of more than 3.5 in the same temperature range. The decay is of the Inokuti–Hirayama-type indicating energy transfer between Gd3+ ions. Due to the overall weak splitting of the 6P7/2 and 8S7/2 multiplets phonon replica with energies of 100 and 588 cm−1 can be assigned.
TL;DR: In this article, it was shown that Mn substitutionally replaces Zn in Zn1−xMnxO(x < 0.22) films and the luminescence peaks corresponding to the intra-d-shell transitions of Mn2+ were observed.
Abstract: Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial Zn1−xMnxO thin films in a high throughput fashion. Local structures around Mn were investigated for these c-axis-oriented epitaxial films by fluorescence x-ray absorption fine structure measurements. It was shown that Mn substitutionally replaces Zn in Zn1−xMnxO (x<0.22) films. Well-structured blue and ultraviolet cathodoluminescence peaks corresponding to the intra-d-shell transitions of Mn2+ were observed, especially for smaller x. The luminescence is quenched rapidly as x is increased. By comparing the relative absorption strength per mole Mn2+ with the statistical probability of isolated Mn2+, it was concluded that the quick decrement of isolated Mn2+ with increasing x is responsible for the severe suppression of the blue and ultraviolet luminescence.
TL;DR: In this article, single-crystalline ZnSe nanowires and nanoribbons were grown on (001) silicon substrates by metal-organic chemical vapor deposition.
Abstract: Zinc-blende-structured single-crystalline ZnSe nanowires and nanoribbons were grown on (001) silicon substrates by metal-organic chemical vapor deposition. The as-synthesized nanowires were characterized by x-ray powder diffraction and scanning electron microscopy. The diameters of the nanowires range from a few tens to 100 nm and the typical length is in the tens of micrometers. Individual strands of the nanowires were examined by transmission electron microscopy and cathodoluminescence spectroscopy. They were found to be single crystals elongated along the 〈112〉 crystallographic direction. Strong and narrow room-temperature band-gap light emissions indicate that their optical and electronic properties rival those of the epitaxial layers employed in diode lasers. A possible growth mechanism of the ZnSe nanowires is also discussed.
TL;DR: In this article, the lowvoltage efficiency of the blue-emitting phosphor, cerium activated yttrium silicate (Y1−mCem)2SiO5, has been improved by co-activating with gadolinium, (Y 1−m−nCemGdn)2 SiO5.
TL;DR: In this paper, the optical properties of excitonic recombinations in bulk ZnO are investigated by photoluminescence (PL) measurements, where the neutral donor bound excitons are positioned at 3.364, 3.362 and 3.361 eV.
TL;DR: In this paper, the authors examined the nature of V-defects and inclusions embedded within these defects by atomic force microscopy and high-resolution scanning electron microscopy (SEM)/cathodoluminescence (CL) in InGaN/GaN multiple quantum wells (MQWs).
Abstract: We have examined the nature of V-defects and inclusions embedded within these defects by atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM)/cathodoluminescence (CL) in InGaN/GaN multiple quantum wells (MQWs). To date, indium distribution nonuniformity in the well or GaN barrier growth temperature have been identified as the main factors responsible for the V-defect occurrence and propagation. Further complicating the matter, inclusions embedded within V-defects originating at the first InGaN-to-GaN interface have been observed under certain growth conditions. Our AFM and high-resolution SEM/CL findings provide evidence that some V-defects occur merely as direct results of barrier temperature growth, and that there are additional V-defects associated with In-rich regions, which act as sinks for further indium segregation during the MQW growth. Both types of V-defects have a tendency of promoting inclusions at low-temperature (800 °C) GaN barrier growth in an H2-free enviro...
TL;DR: In this paper, a nonuniform spatial distribution for the photon energy at grain boundaries is found, and the shift by decade of the emission spectrum is also found to depend systematically on the location of excitation.
Abstract: Cathodoluminescence spectroscopy and spectrum imaging are employed to investigate Cu(In,Ga)Se2 (CIGS) thin films used in high-efficiency solar cells. We have found a nonuniform spatial distribution for the photon energy. The shift by decade of the emission spectrum is also found to depend systematically on the location of excitation. In addition, the photon energy at grain boundaries is not affected by the external excitation. A model for radiative recombination to be applied to these chalcopyrite compounds should explain these results, and some suggestions are considered.
TL;DR: In this paper, Nanocrystalline Y2O3:Eu3+ phosphor films and their patterning were fabricated by a Pechini sol-gel process combined with a soft lithography, and the results of XRD indicated that the films began to crystallize at 500 degreesC and the crystallinity increased with the elevation of annealing temperatures.
Abstract: Nanocrystalline Y2O3:Eu3+ phosphor films and their patterning were fabricated by a Pechini sol-gel process combined with a soft lithography. X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM), optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 degreesC and the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained, which mainly consisted of grains with an average size of 70 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 mum). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped Eu3+ showed its characteristic emission in crystalline Y2O3 phosphor films due to an efficient energy transfer from Y2O3 host to them. Both the lifetimes and PL intensity of the Eu3+ increased with increasing the annealing temperature from 500 to 900 degreesC, and the optimum concentrations for Eu3+ were determined to be 5 mol%.
TL;DR: In this article, the authors investigated the photoluminescence and low-voltage cathodoluminecence characteristics of the [ x SrTiO 3 +(1− x )Li 2 TiO 3 ]:Pr 3+ system.
TL;DR: In this article, the effects of remote hydrogen plasma treatment on defect characteristics in single crystal ZnO were studied and the effect of H-plasma exposure on the defect characteristics was shown to suppress free exciton transition and redistribute intensities in the bound-exciton line set and two-electron satellites.
Abstract: We have studied the effects of remote hydrogen plasma treatment on the defect characteristics in single crystal ZnO. Temperature-dependent (9–300 K) and excitation intensity-dependent photoluminescence spectra reveal that H-plasma exposure of ZnO effectively suppresses the free-exciton transition and redistributes intensities in the bound-exciton line set and two-electron satellites with their phonon replicas. The resultant spectra after hydrogenation exhibit a relative increase in intensity of the I4 (3.363 eV) peak, thought to be related to a neutral donor bound exciton, and a peak feature at 3.366 eV with a distinctly small thermal activation energy. Hydrogenation also produces a violet 100 meV wide peak centered at ∼3.15 eV. Remote plasma hydrogenation yields similar changes in room-temperature depth-dependent cathodoluminescence spectra: the emission intensity increases with hydrogenation mostly in the violet and near-ultraviolet range. Subsequent annealing at 450 °C within the same plasma environmen...
TL;DR: In this paper, the fabrication and luminescent properties of phosphor powders and thin films of Eu3+ doped alumina Al2O3 were reported and the powders were fabricated by combustion synthesis process at a low temperature, 280°C and showed strong photoluminescent and cathodolumine emissions.
Abstract: In this letter, we report on fabrication and luminescent properties of phosphor powders and thin films of Eu3+ doped alumina Al2O3. The powders were fabricated by combustion synthesis process at a low temperature, 280 °C and showed strong photoluminescent and cathodoluminescent emissions. Powders of Eu3+ doped Al2O3 of concentration 1.0 mol % were deposited on quartz-glass substrates to form thin films by means of laser ablation. Under ultraviolet excitation and electron beam excitation, these samples containing microcrystalline structures showed strong luminescence due to f–f transitions, and the dominant transition was the hypersensitive 5D0→7F2 red emission of Eu3+.
TL;DR: In this paper, a red thin-film phosphors were fabricated based on a ZnO:La,Eu)OF nanocomposite structure where (La, Eu) OF nanoparticles were dispersed in a znO film matrix using trifluoroacetic acid as a fluorine source.
Abstract: Red thin-film phosphors were fabricated based on a ZnO:(La,Eu)OF nanocomposite structure where (La,Eu)OF nanoparticles were dispersed in a ZnO film matrix. The films were deposited on glass substrates by a sol-gel method at a low temperature of 600 °C using trifluoroacetic acid as a fluorine source. Doping gallium into the films suppressed the grain growth of ZnO, increased the optical band gap, and decreased electrical resistivity, which indicates that Ga3+ was selectively incorporated into the ZnO lattice. Eu3+ was practically doped in the LaOF lattice. As a result, strong red emissions due to the 5D0→7F2 transition of Eu3+ were observed in both photo- (PL) and cathodoluminescence (CL) measurements. The efficiency of ultraviolet light excitation at 274 nm was promoted by the charge transfer from O2− to Eu3+ in PL. Ga doping was found to increase the CL intensity of the film, which was attributed to suppression of charge accumulation on the films.
TL;DR: In this article, Mg-doped Al0.03Ga0.97N was grown on a patterned sapphire substrate and the epilayer has two distinct regions: one growing directly onto the mesa and the other an epitaxial lateral overgrowth region that overhangs the trench.
Abstract: Distinct crystalline and optical properties have been observed in Mg-doped Al0.03Ga0.97N grown on a patterned sapphire substrate; the pattern consisting of etched trenches along the sapphire 〈1120〉 direction. The epilayer has two distinct regions: one grown directly onto the sapphire mesa and the other an epitaxial lateral overgrowth (ELO) region that overhangs the trench. Transmission electron microscopy shows the presence of pyramidal defects as well as large dislocation densities in the region grown directly on sapphire. In contrast, the ELO region is defect free and contains no Mg-related pyramidal defects. Cathodoluminescence measurements show superior near-band-edge emission in the ELO region, suggesting that the emission is susceptible to nonradiative centers caused by the high defect density in the rest of the sample. The Mg-related donor–acceptor-pair emission is fairly uniform throughout the film, indicating that it is not affected by the nonradiative centers. These optical and structural prope...
TL;DR: In this paper, a complete coalesced epitaxial lateral overgrowth (ELO) of GaN on silicon was presented for ELO layer thicknesses below 3 μm.
Abstract: Completely coalesced epitaxial lateral overgrowth (ELO) of GaN on silicon (111) is presented for ELO layer thicknesses below 3 μm. Fast lateral expansion of the ELO-GaN was achieved by metalorganic vapor phase epitaxy at high growth temperature (1120 °C), low pressure (100 mbar), and a high V/III ratio of 8000. Thus full coalescence and a smooth surface (roughness of 5 nm across 100 μm2) are accomplished for wide SixNy masks along 〈11_00〉GaN with a 10 μm period and 3 μm openings. Atomic force microscopy and transmission electron microscopy are used to assess the quality of the layers. The density of dislocations is reduced from 8×109 cm−2 in the GaN template down to 8×108 cm−2 above the mask openings, and finally to 5×107 cm−2 in the laterally overgrown regions. The corresponding strong improvement of the optical properties and the stress present within the epilayer are evidenced by scanning cathodoluminescence microscopy.
TL;DR: In this article, the surface diffusion and step incorporation kinetics during the growth of AlN films were investigated and it was found that changing the vicinal angles of sapphire substrates can easily control the surface morphologies of alN films.
Abstract: AlN films grown by plasma-assisted molecular beam epitaxy on vicinal sapphire (0001) substrates were investigated. High structural and optical qualities were confirmed by high-resolution X-ray diffraction and 77 K cathodoluminescence measurements. It was found that changing the vicinal angles of sapphire substrates can easily control the surface morphologies of AlN films. Spiral-growth features were greatly suppressed. Furthermore, well-ordered straight monatomic-layer steps and multi-atomic-layer macro-steps were clearly observed by atomic force microscopy. Surface diffusion and step incorporation kinetics during the growth are the key-factors in determining the surface morphologies.
TL;DR: In this paper, thin films of M2B5O9Cl:Eu (M=Ca, Sr, Ba) were prepared on glass substrates using spray pyrolysis.
Abstract: Thin films of M2B5O9Cl:Eu (M=Ca, Sr, Ba) were prepared on glass substrates using spray pyrolysis Blue cathodoluminescence due to the abnormal reduction of Eu3+→Eu2+ was obtained by annealing films in air The cation of the host lattice was found to affect the effectiveness of the reduction process, which could result in influencing the emission band By selecting types and composition of alkaline cation, it was possible to tune the dominant emitting wavelength between 435 to 465 nm Activation of the films occurred at temperatures suitable for the use of glass substrates
TL;DR: In this article, the effect of mechanical milling on the luminescence properties of ZnO microcrystalline samples has been studied by means of cathodoluminescence in a scanning electron microscope.
Abstract: The effect of mechanical milling on the luminescence properties of ZnO microcrystalline samples has been studied by means of cathodoluminescence in a scanning electron microscope. The samples consisted of pressed pellets of commercially available ZnO powder which were ball milled to investigate the possibility of nanocrystalline ZnO formation. Changes observed in the relative intensities of the characteristic ultraviolet and green band of ZnO are discussed in terms of defects generated during milling. The effect of nano- and picosecond pulsed laser irradiation on the particle size and luminescence of the milled samples has been also investigated.
TL;DR: In this article, the authors combined with transmission electron microscopy (TEM-CL) has been used to characterize optical properties of dislocations in GaN epilayers, which act as nonradiative centers with different recombination rates.
Abstract: Cathodoluminescence technique combined with transmission electron microscopy (TEM-CL) has been used to characterize optical properties of dislocations in GaN epilayers. The dislocations act as nonradiative centers with different recombination rates. TEM-CL observation showed that even for the same Burgers vector of a, the dislocations show different electrical activity depending on the direction of dislocation line, i.e., the edge-type dislocation parallel to the c plane is very active, while the screw-type one is less active. The simulation of the CL images gives us the information of parameters such as carrier lifetime and diffusion length.
TL;DR: In this article, the main luminescent centres such as F, F + or Cr 3+ activated during the irradiation of crystals by electrons of 4-keV energy were detected and discussed.