Showing papers on "Cathodoluminescence published in 1994"

Properties of group III nitrides

Abstract: Basic physical properties phase diagrams electrical properties band structure optical functions infra-red absorption and impurity energy levels photoluminescence and cathodoluminescence Raman and reflection spectra interfaces including heterojunctions.

Study of the two‐dimensional–three‐dimensional growth mode transition in metalorganic vapor phase epitaxy of GaInP/InP quantum‐sized structures

Abstract: Ga0.5In0.5P/InP quantum‐sized structures, grown by metalorganic vapor phase epitaxy, have been optically characterized by photoluminescence, cathodoluminescence, and photoluminescence excitation spectroscopy. Additional structural information has been obtained by atomic force microscopy. We find that the two‐dimensional layer‐by‐layer growth mode is limited to the growth of 1‐ML‐thick and, in part, 2‐ML‐thick quantum wells. The transition towards three‐dimensional Stranski–Krastanow island growth occurs before the second monolayer of InP is completed. To further study the dynamics of the island formation, growth interruptions were introduced between the InP deposition and the subsequent growth of the upper GaInP barrier. The two types of coherent islands show a quantum confinement in vertical direction, corresponding to about 2‐ and 3‐ML‐thick and about 9‐ and 10‐ML‐thick InP strained quantum wells.

Formation of GaAs ridge quantum wire structures by molecular beam epitaxy on patterned substrates

Abstract: A ridge quantum wire structure has been successfully fabricated on a patterned (001) GaAs substrate by first growing a (111)B facet structure with a very sharp ridge and then depositing a thin GaAs quantum well on its top. Electron microscope study has shown that a GaAs wire with the effective lateral width of 17–18 nm is formed at the ridge top. Photoluminescence and cathodoluminescence measurements indicate that one of the luminescence lines comes from the wire region at the ridge and its blue shift (∼60 meV) agrees with the quantum confined energy calculated for the observed wire structure.

Structural, optical, and electrical properties of epitaxial chalcopyrite CuIn3Se5 films

Abstract: Single crystal CuIn3Se5 epitaxial films have been synthesized on GaAs(001) by a hybrid sputtering and evaporation technique The microstructure, microchemistry, and selected electrical and optical properties of the films have been investigated by scanning electron microscopy, energy dispersive x‐ray spectroscopy, transmission electron microscopy, cathodoluminescence, optical absorption and reflection, and four‐point probe resistivity measurements The results showed that the CuIn3Se5 crystals have an ordered point defect structure, a band gap of ≥118 eV, an optical absorption coefficient of about 15 000 cm−1 at a photon energy of 135 eV, and a film resistivity of ≳105 Ω cm The results suggest the presence of band tails giving rise to subgap radiative recombination and absorption Antiphase domain boundaries, stacking faults, and nanotwins were observed in the epitaxial layers and were reduced in number by rapid thermal annealing

Correlation of the structural and optical properties of luminescent, highly oxidized porous silicon

Abstract: The light‐emitting properties of rapid thermally oxidized porous Si are studied by both photoluminescence and cathodoluminescence methods. The structure of the material is examined by transmission electron microscopy, while its oxygen content is determined by x‐ray microanalysis. These investigations show that crystalline Si nanostructures remain in the heavily oxidized porous material and account for its ∼750 nm red photo‐ and cathodoluminescence. The work demonstrates that the previously speculated possible importance of either Si‐based amorphous phases or the interesting material, siloxene, in this regard is unrealistic. Furthermore, it is shown that the luminescence properties of silicon oxides are of paramount importance in interpreting the many additional (shorter wavelength) emission bands observed.

Cathodoluminescent characteristics of ZnGa2O4 phosphor grown by radio frequency magnetron sputtering

Abstract: Low voltage cathodoluminescent characteristics of ZnGa2O4 phosphor grown by rf magnetron sputtering have been investigated from 300 to 700 nm. The effects of substrate heating and annealing treatment on the luminescent characteristics are also studied. A blue cathodoluminescent emission peaked at 470 nm is observed. Better luminescent properties are achieved on the films which have crystal structure with a standard powder x‐ray diffraction pattern of ZnGa2O4. The effect of the strength of the ligand field on the resultant energy levels for the ZnGa2O4 phosphor is investigated. Low‐voltage phosphor films with excellent cathodoluminescent characteristics have been successfully developed in this research.

Low Voltage Cathodoluminescence of Mn2+‐Activated ZnGa2 O 4

Abstract: ZnGa 2 O 4 and Zn 1-x Mn x Ga 2 O 4 were investigated as potential low voltage cathodoluminescence phosphors for use in vacuum fluorescent displays. A low-voltage cathodoluminescence spectrophotometer was developed for phosphor characterization. Brightness was measured as a function of anode voltage (10 to 300 V). The effects of activator concentration, phosphor layer thickness, deposition process, and internal pressure were examined. The stability of these oxide phosphors in high vacuum and absence of corrosive gas emission under electron bombardment, offer advantages over commonly used sulfide phosphors

Observation of near‐band‐gap luminescence from boron nitride films

Abstract: We report results from cathodoluminescence spectroscopy of boron nitride films grown on Si(100) substrates by ion‐source‐assisted magnetron sputtering of a hexagonal BN target. Three main peaks are observed in the near‐band‐gap region for hexagonal boron nitride films at energies of 4.90, 5.31, and 5.50 eV. We also report deep‐level emission spectra of predominantly cubic boron nitride films which are correlated with sample growth conditions. In particular we show that the emission intensity, position, and linewidth are strongly dependent on the substrate bias voltage used during sample growth.

Phase Characterization of Precipitated Zirconia

Abstract: The phase compositions of undoped and europium-doped zirconia samples, obtained by precipitation and thermal treatment from 350 to 1,000 C, have been investigated by powder X-ray diffractometry, infrared spectroscopy, and cathodoluminescence spectroscopy. The low-temperature stabilization of tetragonal zirconia is mainly controlled by the presence of anion additives, such as ammonium chloride. The influences of the crystallite size is less important. Cathodoluminescence spectra show a structural similarity between tetragonal and amorphous zirconia.

Growth of ZnGa2O4 phosphor by radio frequency magnetron sputtering

Abstract: ZnGa204 films have been prepared by radio frequency (RF) magnetron sputtering at various total pressure, RF power, and substrate temperatures. Microstructure and crystallographic orientation were characterized by x-ray diffraction. Surface morphologies were observed by scanning electron microscope. In addition, cathodoluminescence (CL) measurement was employed to observe the emission spectra of ZnGa204 films. The influences of various deposition parameters on the properties of grown films were studied. The optimum substrate deposition temperature for luminous characteristics was about 500~ in this investigation. A blue cathodoluminescent emission peaked at 470 nm was observed. Good luminescent properties were observed in the films which exhibit the standard ZnGa204 x-ray diffraction pattern. Field emission display (FED) is a new kind of vacuum flat cathode ray tube. Due to the attractive advantage of FED, it is a good candidate for replacing conventional cathode ray tube (CRT) in flat panel display. In FED, light emission is based on low voltage cathodoluminescence. 1'2 Usually, phosphors show a decrease in cathodoluminescent efficiency as the accelerating voltage is reduced, especially below 1 kV. Low-voltage (of the order of 50 V) CL phosphors have also attracted substantial interests for the reduction in accelerating voltage in cathode tubes. 35 The ZnGa204 phosphor has been investigated for its good cathodoluminescence characteristics at low voltage. A minous efficiency of 0.7 im/W has been obtained when this phosphor is operated at 30 V dc. The results of high temperature operating lifetime test have been proven to show the excellent stability of this phosphor. In addition, ZnGa2Q shows emission from green to red when it is doped with Cr and IV[n, and also shows blue emission even without being doped with impurity. The conventional phosphors have been prepared by powder metallurgy. In the recent development, the thin films of ZnGa204 phosphor were of interest for the applications of FED. The properties of phosphors are strongly dependent on the particle size and crystal structure, 6'7 and the growth conditions may be adjusted to achieve better luminescent characteristics. In this work, the technique of sputtering was employed to deposit ZnGa204 phosphor films. The sputtering condition were adjusted for investigating the relationship among deposition condition, deposition rate, and luminescent characteristics.

Control of ordering in GaInP and effect on bandgap energy

Abstract: GaxIn1-x P layers with x ≈ 0.5 have been grown by atmospheric pressure organometallic vapor phase epitaxy on GaAs substrates with 10 micron wide, [110]-oriented grooves produced photolithographically on the surface. The [110] steps and the misorientation produced at the edges of the grooves have been found to have important effects on the formation of the Cu-Pt ordered structure (ordering on {111} planes) in the GaInP layers during growth. In this work, the groove shape is demonstrated to be critically important. For the optimum groove shape, with a maximum angle to the (001) surface of between 10 and 16°, single domains of the (-111) and (1-11) variants of the Cu-Pt ordered structure are formed on the two sides of the groove. Shallow (≤0.25 μm deep) grooves, with maximum angles of 1 μm2 cross-sectional area and several mm long) regions of highly ordered and completely disordered material separated by no more than a few microns. This allows a direct determination of the effect of ordering on the bandgap of the material using cathodoluminescence (CL) spectroscopy. The 10K photoluminescence (PL) consists of three distinct peaks at 1.94, 1.88, and 1.84 eV. High resolution CL images reveal that the peaks come from different regions of the sample. The high energy peak comes from the disordered material and the low energy peak comes from the large ordered domains. Electron microprobe measurements of the solid composition demonstrate that the shift in emission energy is not due to changes in solid composition. This is the firstdirect verification that ordering causes a reduction in bandgap of any III/V alloy. Decreasing the Ga0.5In0.5P growth rate from the normal 2.0 to 0.5 μ/h is found to enhance ordering in layers grown on planar GaAs substrates. Transmission electron diffraction results show that the domain size also increases significantly. For material grown on exactly (001)-oriented substrates, a pronounced [001] streaking of the superlattice spots is observed. This is correlated with the presence of a dense pattern of fine lines lying in the (001) plane in the transmission electron micrographs. The PL of this highly ordered material consists of a single peak that shifts to higher energy by > 110 meV as the excitation intensity is increased by several orders of magnitude.

Atomic structure and luminescence excitation of GaAs/(AlAs) n (GaAs) m quantum wires with the scanning tunneling microscope

Abstract: We report on the imaging of a molecular beam epitaxially grown GaAs/(AlAs)n(GaAs)m quantum well‐wire array by means of cross‐sectional scanning tunneling microscopy (XSTM) and scanning tunneling‐induced luminescence (STL). XSTM provides atomically resolved cross‐sectional images of sets of quantum well wires with chemical sensitivity within the group III species and electrical sensitivity to single dopant atoms. This permits the precise observation of growth mechanisms and the identification of defects responsible for inhomogeneities in the growth morphology, as well as the determination of dopant incorporation throughout the structure. STL permits the relative quantum efficiency of individual quantum wires to be quantified.

Cathodoluminescence of brown diamonds as observed by transmission electron microscopy

Abstract: Cathodoluminescing features in brown diamonds correlate with the crystalline microstructure as observed by transmission electron microscopy. We identified distinctive emissions at 415.3, 425, 491.3 and 525 nm. The first two correlate with the so-called N3 and band-A emissions, while the last correlates with what is called a strain-broadened H3 band. The N3 emission is associated with stacking faults on {111} planes. H3 emission is correlated with straight dislocations and dislocation tangles. The 491.3 nm and H3 emissions suggest that the diamonds have undergone severe plastic deformation, which may have also contributed to the apparent high concentrations of the N3 defects.

Hydrogen effect on the optical activity of dislocations in silicon introduced at room temperature

Abstract: Dislocations were introduced into silicon crystals by mechanical scratching at room temperature. The optical property of such dislocations was investigated by means of cathodoluminescence. Neither deformation‐induced luminescence nor the exciton luminescence was detected in the scratched region, showing that a high density of nonradiative recombination centers is induced on or around dislocations. Hydrogen plasma treatment of a scratched crystal led to the appearance of the so‐called D1–D4 luminescence lines along the scratch. Deep‐level transient spectroscopy revealed that deep traps were induced by scratching and diminished drastically due to subsequent hydrogen plasma treatment. Thus, it was concluded that hydrogen passivated nonradiative recombination centers but not the luminescence centers. The characteristics in spatial distribution of D1 and D2 lines and those of D3 and D4 lines showed that these two groups of luminescence lines were of different origins. Since the specimens used were thought to b...

Homoepitaxial Growth of Cubic GaN by Hydride Vapor Phase Epitaxy on Cubic GaN/GaAs Substrates Prepared with Gas Source Molecular Beam Epitaxy.

Abstract: Thick cubic GaN (c-GaN) layers were homoepitaxially grown on c-GaN/(100)GaAs by hydride vapor phase epitaxy (HVPE). The c-GaN crystals used as substrates in this work were prepared by gas source molecular beam epitaxy (GSMBE). When the growth temperature was too low (?700? C) or too high (?1000? C), hexagonal GaN (h-GaN) was included in the grown layer, but pure c-GaN was obtained at 900? C. The growth rate of c-GaN by HVPE in this work was about 1.6 ? m/h, which was 4?10 times higher than that of GSMBE or metalorganic vapor phase epitaxy (MOVPE), and an about 5 ? m thick c-GaN film was obtained by 3-h growth. The X-ray diffraction (XRD) patterns showed only the (200) and (400) c-GaN peaks but no h-GaN one. The cathodoluminescence (CL) spectra exhibited a strong peak at about 365 nm, which corresponds to the band edge emission. No emission due to deep levels was observed.

Scanning tunneling microscope and electron beam induced luminescence in quantum wires

Abstract: Quantum wire structures of GaAs/AlGaAs have been grown by metalorganic vapor phase epitaxy in V grooves using pre‐etched corrugated substrates and have been characterized by high‐resolution transmission electron microscopy. Low‐temperature cathodoluminescence (CL) identifies luminescence peaks with the spatial distributions of the different recombinations, achieving a top view spatial resolution of ≊0.2 μm in the CL images. Principally we report how a scanning tunneling microscope (STM) induces local luminescence in the sample structure, and we spectrally resolve STM‐induced luminescence for the tip in different positions relative to the wires. We have recorded the luminescence from a single wire and observed band‐filling effects resulting from varying levels of excitation into a wire. We have demonstrated the difference between recombination of electron‐hole pairs generated in CL and the recombination of injected holes from the STM tip with a thermalized distribution of accumulated electrons in scanning tunneling luminescence.

Realization of three-dimensionally confined structures via one-step in situ molecular beam epitaxy on appropriately patterned GaAs(111)B and GaAs(001)

Abstract: The realization of three‐dimensionally confined GaAs/AlGaAs structures on GaAs (111)B and GaAs (001) substrates via one step in situ molecular beam epitaxy is reported. Growth is carried out on nonplanar patterned substrates with crystallographically equivalent mesa top edges. Equivalent side facets evolve during growth and completely surround the mesa top. Adatom migration from these facets to the mesa top result in shrinkage of the mesa top area leading to mesa pinch‐off. Scanning and transmission electron microscopy provide evidence for the realization of structures with lateral linear dimensions ≲500 A. Cathodoluminescence images from the (111)B structures attest to their high optical quality.