Showing papers on "Cathodoluminescence published in 1991"
TL;DR: In this article, the bulk properties of cubic GaN/GaAs were investigated by cathodoluminescence, which revealed a broad midgap peak as well as several sharp emission peaks just below the expected band gap.
Abstract: We present the first comprehensive investigation of the bulk properties, both optical and structural, of cubic GaN as grown by plasma‐assisted molecular‐beam epitaxy on vicinal (100) GaAs substrates. X‐ray measurements determined the crystal structure of GaN/GaAs to be cubic with a lattice constant of 4.5 A. High resolution transmission electron microscopy revealed a high density of planar defects propagating along the GaN {111} planes. The majority of the defects originated from disordered regions at the GaN/GaAs interface. The optical properties of the films were investigated by cathodoluminescence which revealed a broad midgap peak as well as several sharp emission peaks just below the expected band gap. The data imply that the room temperature band gap of cubic GaN is approximately 3.45 eV.
276 citations
TL;DR: In this article, a tetrahedral quantum dot (TQD) was proposed to make a zero-dimensional electron-hole system, where the TQDs are surrounded by crystallographic facets fabricated using selective area metalorganic chemical vapor deposition (MOCVD) on (111)B GaAs substrates.
Abstract: New GaAs quantum dot structures, called tetrahedral quantum dots (TQDs), are proposed to make a zero‐dimensional electron‐hole system. The TQDs are surrounded by crystallographic facets fabricated using selective area metalorganic chemical vapor deposition (MOCVD) on (111)B GaAs substrates. The calculated energy sublevel structures of zero‐dimensional electrons in a GaAs TQD show large quantum size effects, because electrons are confined three dimensionally. GaAs and AlGaAs tetrahedral facet structures on (111)B GaAs substrates partially etched into a triangular shape were grown using MOCVD. Tetrahedral growth with {110} facets occurs in the triangular areas. The cathodoluminescence intensity map for GaAs tetrahedrons buried in AlGaAs shows the tetrahedral dot array.
212 citations
TL;DR: In this article, it was found that cubic GaN grows on GaAs (001) surfaces epitaxially, while hexagonal GaN growing on GaA (111) surfaces, from the analyses of x-ray diffraction and reflection high-energy electron diffraction patterns.
Abstract: GaN epilayers were grown on GaAs substrates by gas‐source molecular‐beam‐epitaxy technique using dimethylhydrazine as a nitrogen source. It was found that cubic GaN grows on GaAs (001) surfaces epitaxially, while hexagonal GaN grows on GaAs (111) surfaces, from the analyses of x‐ray diffraction and reflection high‐energy electron diffraction patterns. Cathodoluminescence measurements suggested that the band‐gap energy of cubic GaN is around 0.37 eV larger than that of hexagonal GaN.
198 citations
01 Jan 1991
TL;DR: In this paper, the authors used luminance spectra for activator identification in calcite and dolomite, and found that 10-20 ppm Mn2* in solid solution is sufficient to produce visually detectable luminescence, if total Fe contents are below about 150 ppm.
Abstract: Luminescence in calcite and dolomite is governed by physical phenomena that are common to all oxygen-dominated crystalline substances, including other carbonates and silicates. Absorption of excitation energy, energy transfer, and emission involve predictable transitions between electronic energy levels. Strong emission in various colors is always caused by impurities which function as activators of luminescence. Visible luminescence is not expected from pure, undistorted insulators, including carbonates. However, a faint blue 'intrinsic' luminescence, with a broad emission peak (band) around 400 nm, presumably caused by lattice defects, occurs in pure calcite and dolomite, and even in some samples containing impurities. The most important activators in carbonates are transition elements and rare earth elements. Luminescence spectra can be used for activator identification. These spectra are largely independent of the type of excitation, e. g., electron beam (cathodoluminescence = CL), photon (photoluminescence = PL), X-Ray (radioluminescence = RL) excitation, and others. Emission intensities depend on activator, sensitizer, and quencher concentrations, and on the method of excitation. At a given activator concentration, the luminescence intensity generally increases with an increase in excitation energy from PL (relatively weak) to CL (strong). Changes in visual luminescence color between different excitation methods are caused by relative changes in emission peak heights. Mn2* appears to be the most abundant and important activator in natural calcite and dolomite. Substituting for calcium in both minerals, its emission is orange-red to orange-yellow, with a fairly broad band between 570-640 nm (maximum between 590-620 nm). The emission band maximum of Mn2* substituting for Mg2* (in dolomite) is located around 640-680 nm. As little as 10-20 ppm Mn2* in solid solution are sufficient to produce visually detectable luminescence, if total Fe contents are below about 150 ppm. Sm3* activated luminescence can be visually indistinguishable from that activated by Mn2*. The spectrum of Sm3* emission, however, is quite distinct from that of Mn2* and consists of three narrow bands at 562 nm, 604 nm, and 652 nm. Tb3+ and Dy3+ activate green and cream-white luminescence, respectively. The main emission of Tb3* is at 546 nm. The emission of Dy3t consists of three bands, located at 484 nm, 578 nm, and 670 nm. Emission from Eu-containing calcite is red or blue. Narrow spectral bands of 590 nm, 614 nm, and 656 nm are caused by Eu3* and correspond to the red emission. A broad emission spanning a large range of shorter wavelengths is caused by Eu2* and corresponds to the blue emission. As in the case of Sm3*-activated luminescence, the red Eu3* luminescence can be mistaken visually for Mn2*-activated luminescence. Visual luminescence detection limits for rare earths are on the order of 10 ppm. Pb2* is an activator, with an emission band around 480 nm, but it also is a sensitizer of Mn2*-activated luminescence in carbonates. Another recognized sensitizer for Mn2* in carbonates is Ce3*. Sensitizers appear to be effective at concentrations as low as 10 ppm in calcite. Quenchers of Mn2*-activated luminescence in carbonates are Fe2*, Co2*, Ni2*, and Fe3*. The concentrations at which quenchers appear to be effective may vary from element to element and with host mineralogy. Effective minimum concentrations as low as 30-35 ppm have been reported for calcite. The interplay of Mn2* and Fe2*, commonly regarded to be the most important activator and quencher, respectively, in determining the luminescence characteristics of natural carbonates is not well understood because the available data are partially inconsistent. The Mn/Fe ratio may exert a control on luminescence intensity. Mn and Fe concentrations at which 'bright' CL changes to 'dull' can be determined only semi-quantitatively. The available data on the concentration of Mn2* at which quenching starts are partially inconsistent Consequently, the Mn2* concentration at which concentration extinction occurs has not been determined unequivocally. The data presented and summarized in this paper can be used as a basis for the interpretation of luminescence of geological materials. Li particular, knowledge of the possibilities and complexities of activation, sensitization, and quenching has great potential for the interpretation of diagenetic carbonate cements.
187 citations
TL;DR: In this paper, the ZnCa{sub 2}O{sub 4} phosphor was investigated for its application to vacuum fluorescent displays (VFDs) utilizing lowvoltage cathodoluminescence.
Abstract: This paper reports on the ZnCa{sub 2}O{sub 4} phosphor investigated for its application to vacuum fluorescent displays (VFDs) utilizing low-voltage cathodoluminescence. It is expected that this oxide phosphor does not cause damage to filaments in VFD's, while it is a serious problem for conventional sulfide phosphors. This phosphor shows blue luminescence with a spectral peak at with 470 nm and a chromaticity at X = 0.170 and Y = 0.130. A luminous efficiency of 0.7 lm/W has been obtained, when the VFD with this phosphor is operated at 30 V dc. The results of high-temperature operating life test have proven the excellent stability of VFDs utilizing this phosphor.
186 citations
TL;DR: In this paper, the growth of GaN films on Si (111) substrates has been studied and 3C-SiC is found to be an effective intermediate layer for growth of single crystalline GaN film with flat surfaces.
185 citations
TL;DR: The environmental scanning electron microscope (ESEM) as mentioned in this paper allows the examination of specimens in a gaseous environment, which is based on an integration of efficient differential pumping with a new design of electron optics and detection systems.
Abstract: SUMMARY
The environmental scanning electron microscope (ESEM) allows the examination of specimens in a gaseous environment. It is based on an integration of efficient differential pumping with a new design of electron optics and detection systems. Backscattered, cathodoluminescence and X-ray detectors can be designed to fit and to perform optimally in the ESEM. The secondary electron signal can be detected with the gaseous detector device, which is a new multipurpose detector. Insulating, uncoated, wet and generally both treated or untreated specimens can be studied.
166 citations
TL;DR: The cathodoluminescence wavelength imaging (CLWI) method as discussed by the authors uses a focused focused electron beam across the area under investigation to obtain a 3D image of the atomic-scale morphology of QW interfaces.
Abstract: Luminescence experiments provide a powerful and nondestructive approach to the e x s i t u investigation of semiconductorheterointerfaces which might be buried up to several μm below the surface in a given complex sample structure. Combined with the ability of taking images simply by scanning the exciting focused electron beam across the area under investigation, lateral fluctuations of electronic properties like the variation of the fundamental band gapE g (x,y) can be directly visualized by scanning cathodoluminescence(CL). The novel experimental approach, cathodoluminescence wavelength imaging (CLWI), which involves recording of a complete CLspectrum at every scanning position (x,y), yields direct 3D images of the atomic‐scale morphology of quantum wells(QWs) as sensed by the QWexciton: similar to the tip of a scanning tunneling microscope, the exciton samples the local fluctuations of QW thickness L z and transforms this structural information L z (x,y) into a spectral one, the lateral variation of band gapE g (x,y) and thus the CL emission wavelength λ(x,y). Topological maps of QW interfaces can thus be recorded at various positions and at various magnifications. The interface roughness can be investigated statistically at lateral resolution starting with the diameter of the QWexciton up to the mm regime. The same experimental principle for recording λ(x,y) and E g (x,y) maps is successfully applied for the analysis of patterned structures. In the nonlattice‐matched system GaAs on Si, the lateral strain variation causes E g (x,y) fluctuations and can thus be directly imaged by CLWI. Metalorganic chemical vapor deposition grown GaAs layers on micropatterned Si(001) substrates show strongly inhomogeneous doping with Si impurities. By means of CLWI the strong increase of this Si incorporation in the vicinity of free {111} surfaces is measured and Si concentration maps are recorded across the complete sample pattern.
139 citations
TL;DR: In this article, a method for the natural reduction of threading dislocations in GaAs on Si by growing on patterned Si substrates was reported. But the GaAs were grown on the 40μ-wide Si mesas and showed a 1.6 increase in luminescence intensity over the luminecence intensity from the unpatterned control area.
Abstract: We report a new method for the natural reduction of threading dislocations in GaAs on Si by growing on patterned Si substrates. We also explore other effects of patterning on dislocation formation during growth: stress relief near the mesa edges at high aspect ratios, and limited dislocation nucleation and propagation. Prior to growth, the Si substrates were processed to produce a plurality of mesas varying in width (5-170 μm) and geometry (circular, rectangular, and square mesas). After growth of the GaAs, the material was characterized with cathodoluminescence (CL) and secondary electron microscopy. For a GaAs growth temperature of 570° C and a thickness of 10 μm, the GaAs grown on the 40μ-wide Si mesas show a factor of 1.6 increase in luminescence intensity over the luminescence intensity from the unpatterned control area. Also, the emission wavelength from the smaller mesas is shifted to shorter wavelengths as compared to GaAs/GaAs and the unpatterned control area. The emission wavelength and CL intensity varies across the mesas; for 40 μm wide mesas, the emission wavelength is fairly constant across the mesa and the CL intensity decreases near the edges, whereas for larger mesas the emission wavelength decreases and the CL intensity increases at the mesa edges. For the 40 μm wide mesas, the integrated CL intensity is equal to that of a control GaAs/GaAs grown with the same doping level. No cracks were observed in the GaAs grown on the Si mesas, even though the thickness of the GaAs was 10 μ,m.
83 citations
TL;DR: In this paper, defects and impurities in diamond films grown by chemical vapor deposition (CVD) were analyzed by high-resolution cathodoluminescence spectroscopy and imaging in transmission electron microscopy (TEM).
Abstract: Defects and impurities in diamond films grown by chemical vapor deposition (CVD) were analyzed by high‐resolution cathodoluminescence (CL) spectroscopy and imaging in transmission electron microscopy (TEM). The combination of CL and TEM makes it possible to correlate the film microstructure with the electronic structure due to defects. Broad CL bands observed at 428±1 nm (2.90±0.01 eV) and 551±1 nm (2.250±0.004 eV) are attributed to closely spaced and widely separated donor‐acceptor (D‐A) pairs, respectively. A narrow peak at 738.7±0.5 nm (1.679±0.001 eV) is attributed to interstitial silicon atom impurities. An additional wide band at 365±1 nm (3.40±0.01 eV) was not identified. The material was found to be type IIb (semiconducting) and varied in quality with the growth conditions. Impurities are evidently distributed nonuniformly on a submicrometer scale, and both highly faulted and defect‐free grains were found to emit no visible CL. For the first time in CVD‐grown diamond, band‐A CL due to closely spac...
73 citations
TL;DR: In this paper, the annealing behavior of the 1.681 eV (737.4 nm) line in the CVD diamond films grown on Si substrates is compared with that of the GR1 spectral line (1.673 eV) of natural diamond.
Abstract: Cathodoluminescence (CL) and annealing studies of microwave plasma‐assisted chemical vapor deposited (CVD) diamond films were carried out. The annealing behavior of the 1.681 eV (737.4 nm) line in the CL spectra of CVD diamond films grown on Si substrates is compared with that of the GR1 spectral line (1.673 eV) of natural diamond. We determine that these two lines have different origins. The comparison of CL spectra of diamond films grown on different substrates shows that the 1.681 eV peak is due to Si impurity in CVD diamond films.
TL;DR: In this paper, the effects of Si-doping on the electrical and luminescence properties of GaN and A1 0.1 Ga 0.9 N epitaxial films have been studied.
TL;DR: In this paper, the authors measured the cathodoluminescence spectra of microwave plasma assisted chemical-vapor deposited (CVD) polycrystalline diamond films at 77 K over the spectral range of 2300-8000 A.
Abstract: We have measured the cathodoluminescence spectra of microwave plasma‐assisted chemical‐vapor deposited (CVD) polycrystalline diamond films at 77 K over the spectral range of 2300–8000 A. Annealing studies of these spectra have been carried out at 500, 800, 1000, 1200, and 1350 °C. Rich spectra are observed. Many of them are stable up to the highest annealing temperature. Two peaks at 3.188 and 2.638 eV and the 5RL lines are destroyed, while other lines at 3.57 and 3.462 eV appear, after a 1200 °C anneal. The two neighboring peaks at 2.330 and 2.320 eV are probably responsible for the broadness of the often observed peak at 2.328 eV in CVD diamond films. We also compare some of the annealing behavior of the CVD diamond films with those of natural single‐crystal diamond, and conclude that while most of the annealing characteristics of plasma‐deposited diamond films are similar with those which have been reported for single‐crystal natural diamonds, some of the annealing behaviors are different for these two...
TL;DR: Using metalorganic vapor phase epitaxy to grow GaInAs/InP layers on masked InP substrates patterned with submicron square holes, the authors fabricated in situ buried quantum dot arrays for the first time.
Abstract: Using metalorganic vapor phase epitaxy to grow GaInAs/InP layers on masked InP substrates patterned with submicron square holes, we have fabricated in situ buried quantum dot arrays for the first time. Starting with mask openings ≥150 nm × 150 nm and utilizing the natural crystal habits to form low‐index plane facetted pyramids inside the holes, highly regular GaInAs quantum dots embedded in InP are obtained in a single growth step. As verified by cathodoluminescence, the dots exhibit very high luminescence efficiencies, even at room temperature, owing to the absence of air‐exposed or etch‐damaged heterointerfaces.
TL;DR: In this paper, cathodoluminescence (CL) scanning electron microscopy and spectroscopy techniques were used to study diamond films, produced by microwave plasma assisted chemical vapor deposition.
Abstract: Diamond films, produced by microwave plasma assisted chemical vapor deposition, were studied using cathodoluminescence (CL) scanning electron microscopy and spectroscopy techniques. Luminescence intensities of the observed prominent peaks at 420, 445, and 738 nm were found to vary widely as a function of both the deposition conditions and the location in the same sample. Additional peaks and shoulders at 464, 483, 500, 514, and 532 nm were also observed in some regions of diamond films deposited using the higher (i.e., 1%) CH4/H2 concentration and the substrate temperatures below 950 °C. Strong variations in CL intensities in different regions of the same sample were observed, indicating substantial variations in the distribution of defects and impurities in these diamond films. Luminescence due to the boron in a doped sample was also observed, and it was concluded that the higher CL intensity in that sample compared to other samples was due to the reduced defect densities and not due to the boron.
TL;DR: In this paper, the compositional dependence of the peak energy of the UV band is similar to that of the band gap energy, while the VB and BG bands are somewhat smaller than that of band gap energies.
Abstract: Cathodoluminescence of undoped and Zn-doped AlxGa1-xN epitaxial layers grown by Metalorganic Vapor Phase Epitaxy (MOVPE) in the composition range of 0≤x≤0.3 has been studied at room temperature. The dominant emission of undoped AlxGa1-xN grown at 1030°C is a near-band-edge emission (UV band), while that of Zn-doped AlxGa1-xN grown at 1030°C is a violet-blue one (VB band), and that of Zn-doped AlxGa1-xN grown at 910°C is a blue-green one (BG band). Each emission band shifts toward a higher-energy side with increasing x. The compositional dependence of the peak energy of the UV band is similar to that of the band gap energy. On the other hand, the compositional dependences of the VB band and BG band are somewhat smaller than that of the band gap energy.
TL;DR: In this paper, a modified gas source molecular beam epitaxy (MBE) technique was used to grow a superlattice with layer thickness between 0.5 and 20 nm.
TL;DR: In this paper, the authors described more elaborate characterizations of the free-standing, flame-grown diamond and identified hydrogen, nitrogen and perhaps oxygen as impurities, based on IR spectroscopy and both photoluminescence and cathodoluminecence (PL and CL).
Abstract: Recently an account of the homoepitaxial growth of diamond in an oxygen-acetylene combustion flame was published (J. Cryst. Growth, 104 (1990) 752). Notwithstanding the high deposition rate (50 μm-1 h), the material had good optical quality. After removal of the natural diamond substrate from one of the samples, it was proved that the deposit was single-crystal diamond. However, most of the optical properties were measured with the layers still attached to the substrate. In this study more elaborate characterizations of the free-standing, flame-grown diamond are described. Hydrogen, nitrogen and perhaps oxygen are identified as impurities, based on IR spectroscopy and both photoluminescence and cathodoluminescence (PL and CL). The distribution of the impurities is non-uniform, as was verified by CL topography and stress birefringence microscopy. Following the standard classification rules the flame-grown diamond is neither type I nor type II.
TL;DR: In this article, cathodoluminescence (CL) images, obtained using a scanning electron microscope, of a low-temperature granitic mylonite from central Japan were used for elucidating the importance of solution-transfer processes during mylonitization.
TL;DR: In this paper, a traverse across the BI~M~ne Sr perthosite unit in the Tugtut6q Central Complex of the Gardar province, South Greenland has been examined for cathodoluminescence characteristics, microporosity and 6180 isotopic values.
Abstract: Samples from a traverse across the BI~ M~ne Sr perthosite unit in the Tugtut6q Central Complex of the Gardar province, South Greenland have been examined for cathodoluminescence characteristics, microporosity and 6180 isotopic values. Reddening of cathodoluminescence colours in alkali feldspars (normally blue) from the unit may be correlated with increased microporosity of the feldspars as determined using scanning electron microscopy. 6180 values of all samples lie within the range of values expected of juvenile fluids, independent of the level of alteration indicated by cathodoluminescence studies. Observations are consistent with previous suggestions that levels of alkali feldspar microporosity and levels of fluid alteration (as determined by cathodoluminescence of alkali feldspars) are related phenomena. Oxygen isotope ratios suggest that the fluid is largely juvenile in origin, with, perhaps, some meteoric (low 6180) component.
TL;DR: In this article, cathodoluminescence (CL) imaging and spectroscopy in a scanning electron microscope was used to measure the residual stresses in the region surrounding the indentation.
Abstract: Alumina single crystals indented with a Vickers hardness indenter were investigated by cathodoluminescence (CL) imaging and spectroscopy in a scanning electron microscope. The spatial resolution of the CL images was approximately 0·4 μm. CL spectra were measured with wavelength resolution of 1·0 nm in the wavelength range of 200 to 900 nm; in the immediate region of the ruby lines (693 nm), spectra were measured with a resolution of 0·15 nm. Stress-induced frequency shifts of the ruby lines were utilized to measure the residual stresses in the region surrounding the indentation. Both hydrostatic and non-hydrostatic stresses were measured. The magnitude of the stresses was observed to vary with distance from the center of the indent and also with crystallographic orientation. After the samples were annealed at 1600°C for 10 h, no measurable stresses remained either in the center of the indent or in the surrounding area.
TL;DR: In this article, the effect of a thin interface layer between the n-layer and the p-layer is supposed for the (000 1 )C face, but the effect disappeared by continuous electrical driving of the LEDs and the spectra became similar to those of the (0001)Si face.
15 Oct 1991
TL;DR: In this paper, the feasibility of full-color MFD displays has been demonstrated using Sulfide phosphors as potential primaries and used in 6-in full color prototypes operating in a specific addressing mode using sequential excitation of the red, green, and the phosphor stripes.
Abstract: Cathodoluminescence studies in the range from 150 to 800 V have demonstrated specificities of MFD (microtip fluorescent display) phosphor requirements as compared with CRTs (much higher acceleration voltage) and hot cathode vacuum fluorescent displays (lower acceleration voltage). Sulfide phosphors have been selected as potential primaries and used in 6-in full-color prototypes operating in a specific addressing mode using sequential excitation of the red, green, and the phosphor stripes. In this way, the feasibility of full-color MFDs has been demonstrated. Present work on phosphor materials, processing of powders, and outgassing in cells leads one to expect significant improvements in resolution, luminance, and lifetime of full-color displays. >
TL;DR: In this paper, near-infrared cathodoluminescence (CL) in the scanning electron microscope has been used to characterize GaP:S. Spectra of as-grown crystals show a broadband at about 1240 nm, probably related to PGa antisite defects.
Abstract: Near‐infrared cathodoluminescence (CL) in the scanning electron microscope has been used to characterize GaP:S. Spectra of as‐grown crystals show a broadband at about 1240 nm, probably related to PGa antisite defects. This emission has been found to be higher at dislocations giving a CL image opposite to the visible CL image.
TL;DR: In this paper, the first order phase transition at the Si surface from single to double atomic steps as a function of temperature T and off-orientation θ of the Si (001) surface along [110] is observed in a metalorganic chemical vapor deposition environment at surprisingly low temperatures.
Abstract: The first‐order phase transition at the Si (001) surface from single to double atomic steps as a function of temperature T and off‐orientation θ of the Si (001) surface along [110] is observed in a metalorganic chemical vapor deposition environment at surprisingly low temperatures. At a given temperature the surface morphology of Si is frozen in by growing InP on top of Si. The existence or the lack of antiphase domains in the InP provides the information about the presence of single or double atomic steps on the Si, respectively, in the moment of growth. Reversability and slight hysteresis of the phase transition are found. The growth parameters for obtaining antiphase domain‐free InP are optimized. Residual stress, epilayer tilt, and defect distribution are discussed. The different peaks in photoluminescence spectra are identified; the assignments are confirmed by using time‐delayed cathodoluminescence (CL) spectra. The lateral variation of quantum efficiency is imaged with scanning CL.
TL;DR: In this article, the degradation during cw operation or under electron beam bombardment of the graded index separate-confining heterostructure laser devices grown on Si and on GaAs substrates was investigated.
Abstract: The degradation during cw operation or under electron beam bombardment of the graded index separate‐confining heterostructure laser devices grown on Si and on GaAs substrates was investigated. The induced current and the cathodoluminescence modes of a scanning electron microscope were used to observe the cleaved face of these devices as a function of the stage of degradation. Our findings strongly suggest that the degradation starts owing to a mechanism of donor annihilation and complex formation within the space‐charge region of the device. Two different methods allowing the evaluation of the donor concentration within the depletion zone were developed. One method is based on the measurement of the direct bias necessary to recover the initial microscopic characteristics of a damaged device. The other one relies on a numerical calculation of the partition of nonequilibrium carriers which takes into account the detailed structure of the device. This calculation is based on a three‐dimensional analytical fu...
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