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  • Articles  (23)
  • MOVPE  (12)
  • YBCO  (11)
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  • Electrical Engineering, Measurement and Control Technology  (23)
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  • 1
    Electronic Resource
    Electronic Resource
    Angular dependence of transport current near critical at fields to 4 T in metalorganic thin films (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 303-308 
    Details
    ISSN: 1572-9605
    Keywords: Critical current ; high temperature superconductor ; thin film ; angular dependence ; magnetic field dependence ; YBCO ; metalorganic preparation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Values of the transport current have been obtained as a function of angle of the magnetic field to the plane of the thin film YBa2Cu3O7−d (YBCO) prepared by metalorganic deposition. Current flowed in thea, b planes at various angles to the applied magnetic fields to 4.2 T. Films with thicknesses near 350 nm were studied. For these thin films andH∥c a secondary maximum is observed whenJ c〉 1 MA/cm2. NearH∥a, b a large increase inI c is observed, and the sharpness, field dependence, and field directional dependence is discussed. The response to currents aboveI c is determined and the fit to a power lawV∼I n shows a strong correlation betweenI c andn.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724558
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  • 2
    Electronic Resource
    Electronic Resource
    Low-temperature critical field of YBCO (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 269-270 
    Details
    ISSN: 1572-9605
    Keywords: YBCO ; high field ; critical field ; resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have measured the upper critical fieldH C2(T) of YBa2Cu3O7 (YBCO) thin films in magnetic fields up to 140 T forH applied parallel to thec-axis of the film. The critical field in the zero-temperature limit is 138 T, and the temperature dependence does not fit any simple model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724550
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructures of high-J c melt-textured YBa2Cu3O7−x /Ag superconductors (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 947-950 
    Details
    ISSN: 1572-9605
    Keywords: Critical current density ; Ag addition ; grain alignment ; flux pinning ; defect structure ; YBCO ; melt-texturing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Silver has been previously added to the melt-textured YBa2Cu3O7−x in order to increase the critical current density (J c ) of these materials. However, the effect of this addition on theJ c is presently unclear. The purpose of this study is to investigate the effect of silver on both critical current density and the microstructure of the melt-textured YBa2Cu3O7−x superconductors by means of X-ray diffraction, optical polarized microscopy, and transmission electron microscopy (TEM). TheJ c of the MTG YBCO/Ag samples is more than 104A/cm2 under the 5 kOe magnetic field. It has been shown that as the concentration of silver increases, the fraction of the 211 phase dispersed within the 123 matrix decreases. Therefore, theJ c slightly decreases. These results, together with the effect of the 211 phase, dislocations, and other structure defects on flux pinning, are described in this paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00732277
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  • 4
    Electronic Resource
    Electronic Resource
    Specific heat of YBa2Cu3O7 (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 251-255 
    Details
    ISSN: 1572-9605
    Keywords: Specific heat ; impurity ; defects ; YBCO ; superconducting volume fraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Specific heat measurements, including measurements in magnetic fields and at both low temperatures and nearT c , on a number of YBa2Cu3O7 samples have revealed several correlations among strongly sample-dependent parameters. These correlations suggest that the sample dependence of the parameters reflects a sample dependence of the volume fraction of superconductivity, which is in turn correlated with a low concentration of Cu2+ moments. The correlations give a criterion for recognizing the values of the parameters characteristic of the fully superconducting material. Preliminary results on the effects of sample heat treatment are reported. New data on the “linear term” is presented and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730406
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  • 5
    Electronic Resource
    Electronic Resource
    Absorption and emission spectra of the YBCO laser plume (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 823-828 
    Details
    ISSN: 1572-9605
    Keywords: YBCO ; laser plume ; emission spectroscopy ; absorption spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The plasma produced during laser ablation deposition of thin film YBCO has been studied by optical emission spectroscopy. There is evidence of increased YO band emission in the range 590–625 nm as the ambient oxygen gas pressure confining the plume is increased in the range 30–200 m Torr. Temporal profiles show that close to the target the plume is insensitive to ambient oxygen pressure. It is deduced that the optical emission here is excited by electron impact excitation. Further away from the target there is evidence that two distinct processes are at work. One is again electron excitation; the emission from this process decreases with distance because the expanding plume cools and collisions become less frequent in the expanding gas. The second is driven by oxidation of atomic species expelled at high speeds from the target. The main region of this activity is in the plume sheath where a shock front ensures heating of ambient O2 and reaction of monatomic plasma species to form oxide in an exothermic reaction. Spatial mapping of the emission demonstrates clearly how increasing oxygen gas pressure confines the plasma and enhances the emission intensity from the molecular YO species ejected from the target in a smaller region close to the target. Ba+ is observed as a dominant species only very close to (within 1 mm of) the target. Absorption spectra have been taken in an attempt to examine ground state and cool species in the plume. They reveal the quite surprising result that YO persists in the chamber for periods up to 1 msec. This suggests an explanation for the recent report of off-axis laser deposition in terms of simple condensation. Previously, quasi-ballistic transfer of material from target to substrate has been considered the only significant process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320877
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  • 6
    Electronic Resource
    Electronic Resource
    Symmetry of the pairing state in the high-T c oxides (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 865-869 
    Details
    ISSN: 1572-9605
    Keywords: Symmetry of the pairing ; gaplessness ; YBCO ; cuprates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract There are conflicting experimental data related to the symmetry of the order parameter in cuprate superconductors. Our previously developed concept, which contains unusuals-wave pairing with a two-gap spectrum, energy gap anisotropy, and gaplessness for a nonstoichiometric state, provides a unified and consistent description of experimental data related to the symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320884
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  • 7
    Electronic Resource
    Electronic Resource
    Anisotropy of optical constants of YBCO (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 943-946 
    Details
    ISSN: 1572-9605
    Keywords: YBCO ; optical constants ; attenuated total reflection ; ellipsometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Otto configuration attenuated total reflection (ATR) measurements of the excitation of surface plasmons in the infrared have been carried out on YBCO films deposited on MgO (100) substrates. The dielectric constants for YBCO at 3.392μm are determined to be −10+15i forc-axis material. The anisotropic nature of the cuprate is seen from films with other orientations: nearlya-axis material has constants of 4.0+7.0i. It is thus not metallic in its optical response along thec-axis which lies parallel to the substrate plane. Ellipsometric measurements in the visible onc-axis material point to a maximum surface plasmon energy of 1 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00732276
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  • 8
    Electronic Resource
    Electronic Resource
    p-Doping of GaAs and AlGaAs using the triethylamine adduct of dimethylzinc (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 4 (1994), S. 343-347 
    Details
    ISSN: 1057-9257
    Keywords: Dimethyzinc ; Adduct ; MOVPE ; GaAs (p-doping) ; AlGaAs (p-doping) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The adduct between dimethylzinc and triethylamine has been used as a p-dopant source in the growth of GaAs and Al0.3Ga0.7As alloys by metalorganic vapour phase epitaxy (MOVPE). The dopling efficiency of this adduct in these alloys and in InP is lower than that of dimethyl zinc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860040505
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  • 9
    Electronic Resource
    Electronic Resource
    In situ optical monitoring of the movpe growth of ZnSe on GaAs (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 4 (1994), S. 401-405 
    Details
    ISSN: 1057-9257
    Keywords: MOVPE ; ZnSe ; Growth mechanism ; Surface chemistry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In situ optical reflection measurement was employed to study surface processes during the MOVPE growth of ZnSe films under an alternate supply of diethylzinc (DEZn) and dimethylselenide (DMSe) using H2 and/or N2 as carrier gases. We have found that the time-dependent reflection signal exhibits a unique saw-toothed pattern during the DEZn supply, which is attributed to the adsorption and structural change of the DEZn. In contrast, the influence of DMSe on the time-dependent signal appears to be rather marginal. A growth mechanism is proposed based on these experimental results, through which the important role of ambient hydrogen is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860040603
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  • 10
    Electronic Resource
    Electronic Resource
    Identification of the volatile decomposition products produced in the deposition of (Hg,Cd)Te by MOVPE (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 151-161 
    Details
    ISSN: 1057-9257
    Keywords: MOVPE ; (Hg, Cd)Te ; Decomposition products ; GC-MS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The pyrolysis reactions of di-isopropyl telluride and dimethyl cadmium, both alone and in combination and with and without mercury, have been studied using the technique of gas chromatography-mass spectrometry (GC-MS). For example, when mercury and dimethyl cadmium are mixed in hydrogen at the growth temperature (370°C), the volatile products observed are methane, ethane and dimethyl mercury. In contrast, when di-isopropyl tellurideis substituted for the cadmium precursor in this reaction, the products observed are propane, propene and 2,3-dimethylbutane with no volatile mercury-containing compounds. Heating the two organometallic precursors together at the growth temperature in the absence of mercury gives products expected from the pyrolysis of each one alone plus a number of interaction products such as 2-methylpropane. The results of these studies will be presented, a mechanism for the reactions proposed and the implications for MOVPE growth discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030122
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  • 11
    Electronic Resource
    Electronic Resource
    MOVPE growth and characterization of ZnSxSe1 - x/ZnSe quantum wells (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 191-198 
    Details
    ISSN: 1057-9257
    Keywords: ZnSe ; ZnSSe ; GaAs substrate ; MOVPE ; Photoluminescence ; Quantum well ; Interface properties ; Growth interruption ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this work we report on ZnSxSe1 - x/ZnSe quantum wells grown by atmospheric pressure MOVPE on GaAs substrates. Diethylznc (DEZn), diethylselenium (DESe), diethylsulphur (DES) and H2S were used as source materials. Binary quantum wells with ZnSe or ZnS as barrier were usually grown in sets of 10 pairs on a 0.5 μm ZnSe or ZnS buffer, respectively. QWs with different well thicknesses (1-4 nm) show a typical shift to higher energies with decreasing well thickness and also a large decrease in PL intensity with increasing well thickness. Owing to the onset of relaxation above 5 nm well thickness, no PL emission could be observed. QWs of the same thickness but grown at different temperatures (420-520°C) show a broadened line shape with decreasing growth temperature. Growth interruption (3-50 s) also causes a broadening of the PL emission with decreasing interruption time. This is caused by interface reconstruction at higher growth temperatures and longer growth interruption. A ZnS buffer of 0.5 μm improves the PL line shape compared with a ZnSe buffer.ZnSxSe1 - x/ZnSe single and multiple QWs (Lz = 1-4 nm) were grown to reduce the strain in the structures. A typical quantum confinement energy shift of 160 meV for the 1 nm well can be observed in ZnS0.68Se0.32/ZnSe QWs. In comparison with the binary QWs, the FWHM could be reduced by about a factor of two to 34 meV. This improvement was obtained by an optimisation of the switching process to prevent the desorption of sulphur from the ZnSSe during the growth interruption.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030127
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  • 12
    Electronic Resource
    Electronic Resource
    Stimulated emission in ZnSxSe1 - x/ZnSe heterostructures grown by MOVPE (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 73-80 
    Details
    ISSN: 1057-9257
    Keywords: MOVPE ; ZnSxSe1 - x ; MQW ; Optical properties ; Lasing Exciton ; Electron-hole plasma ; Dynamics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Non-linear and stimulated emission of ZnSxSe1 - x/ZnSe multilayer structures grown by MOVPE on GaAs is investigated by means of high-density excitation spectroscopy using a high-resolution pulsed excimer-dye laser system as well as a picosecond titanium-sapphire laser for time-resolved measurements. Heterostructures with ZnSe layers or single and multiple quantum wells were grown in which the ZnSe layer widths were varied between 1 nm (strong quantum confinement) and 500 nm (quasi-bulk situation). The sulphur concentration in the ZnSxSe1 - x buffer, barrier and cap layers was chosen between x = 0.045 and x = 0.74 in order to find the most promising compromise with regard to maximum band offset to ZnSe for most efficient carrier confinement and suitable waveguiding properties depending on variation in the refractive index, and to highest structural quality of the actively emitting ZnSe layers. Stimulated emission is found to occur in all samples, being brightest in the sample with the lowest sulphur concentration in the cap and barrier layers. Its dynamical properties point to a probable interpretation in terms of electron-hole plasma creation, which, however, may not be the basic process in narrow-quantum wells or strongly structurally disturbed samples.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030111
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  • 13
    Electronic Resource
    Electronic Resource
    High-resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) of ZnSxSe1 - x/ZnSe Quantum Wells (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 183-190 
    Details
    ISSN: 1057-9257
    Keywords: Scanning transmission electron microscopy (STEM) ; High-resolution ; Z-contrast ; ADF ; HAADF ; Electron energy loss spectroscopy (EELS) ; ZnSxSe1 - x/ZnSe quantum wells ; MOVPE ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Epitaxial growth techniques for ZnSxSe1 - x/ZnSe heterostructures have already achieved a high degree of development. Further improvements strongly require characterisation techniques with high compositional sensitivity and high spatial resolution. Therefore in this work high-resolution Z-contrast, which provides compositional information down to the atomic scale, has been used for the first time to characterise ZnSxSe1 - x/ZnSe quantum well structures. The influence of structural defects on Z-contrast is demonstrated by comparison of scanning transmission electron microscopy (STEM) bright field images and STEM Z-contrast micrographs of planar defects and dislocations. The compositional abruptness of ZnSxSe1 - x/ZnSe interfaces in MOVPE-grown quantum well (QW) structures is judged from high-resolution Z-contrast micrographs. Electron energy loss spectroscopy (EELS) measurements were performed for the first time in ZnSxSe1 - x/ZnSe QW structures in order to obtain quantitative compositional information with nanometre spatial resolution. From EELS line scans, which monitor the selenium concentration across ZnSe QWs, the obtainable spatial resolution is estimated to be about 1-2 nm. The problems that have prevented quantitative analysis of the selenium concentration up to now are discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030126
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  • 14
    Electronic Resource
    Electronic Resource
    Plasma-enhanced MOVPE and nitrogen doping of ZnSe (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 203-208 
    Details
    ISSN: 1057-9257
    Keywords: ZnSe ; Diallylselende ; Plasma ; MOVPE ; Nitrogen doping ; Raman spectroscopy ; Photoluminescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In order to obtain high quality Znse epilayers on GaAs which can be intentionally P- and n-type doped growth at a reduced temperature is highly desirable. Therefore in this work the suitability of diallylselenide and the influrnce of plasma precracking have ben investigated. Photoluminesscence, Raman spectroscopy, scanning electron microscopy, X-ray, SIMS and Hall measurements were used to anaylse the samples. The selenium precursor was fully decomposed at temperatures above 360°C if it was precracked by a plasma. Bound excitions could be resolved with negligible donor-acceptor pair (DAP) and copper green emission in the PL spectra form films which were grown with a plasma at temperatures beyond 530°C. Clearly the hpe for reduction in the deposition temperature was not achieved. Raman spectra also revealed strong crystalline quality variations. For the doping experiments nitrogen was used as the carrier gasa instead of hydrogen. Plasma cracking of the selenium precursor was still necessary. Thye substitution of the H2 carrier gas by nitrogen reduced the growth rate by a factor of 2.6 but enhanced the crystalline properties of the samples as shown by the Raman measurements. Strong DAP emission at 2.7eV in the (PL) spectra was observed. SIMS measurements showed a nitrogend concertration of about 3 × 1017 cm-3. An additional nirtogen plasama (0-7W) had a begligible effect on the nitrogen concentration in the sample. The samples were semi-insulating, whichmight be a conswquence of the crystalline quality of ZnSe grown with DASe as selenium precursor.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030129
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  • 15
    Electronic Resource
    Electronic Resource
    GaAs substrates for the MOVPE growth of (Hg,Cd)Te layers (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 239-245 
    Details
    ISSN: 1057-9257
    Keywords: Substrates ; MOVPE ; MCT ; Surface morphology ; Structural properties ; Photoconductors ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: After a review of the structural properties of (Hg,Cd)Te layers grown by MOVPE on GaAs substrates, topical questions such as out-diffusion of Ga and As from the substrate into the layers, monolithic integration of signal procesing into the substrate and the presence of pyramidal defects in (100) layers will be discussed. In order to solve the last problem, a systematic study of the influence of the (h11) GaAs substrate orientation and polarity on the structrual properties and surface morphology of CdTe layers grown by MOVPE has ben carried out. Twin-free layers are obtained on (211)A, (311)B and (511)B GaAs surface orientations as ezplained by a model taking into accountthe type of dangling bonds at the interface. The performance of photoconductors fabricated on(Hg,Cd)Te layers of various orientations confirms these results. Particularly good results have been obtained for the (311)B orientation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030134
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  • 16
    Electronic Resource
    Electronic Resource
    Photoluminescence spectroscopy as a tool to assess extrinsic impurities and quality of ZnSe and ZnSxSeI - x grown by MOVPE (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 261-267 
    Details
    ISSN: 1057-9257
    Keywords: ZnSe ; ZnSxSe1 - x ; MOVPE ; Photoluminescence ; Mapping ; Purified ; DESe source ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this paper we report new results concerning the cause of impurities responsible for the Ix, and I2-peaks in photoluminescence (PL) spectra of ZnSe grown by MOVPE. An improvement in ZnSe epilayer quality is obtained by using a metal organic selenium precursor with reduced chlorine concentration. The PL spectrum of such a layer shows typical excitonic transitions, but compared with samples grown with a more contaminated source, the intensity of the Ix, and the I2 peaks decreases relative to the free exciton transition. A Gaussian fitting of the donor-bound exciton peaks taking the background of other structures into account shows that the ratio between the Ix and I2 peaks does not differ significantly between two samples. Both the decrease in donor-bound exciton transitions and the unchangeability of the ratio Ix/I2lead to the conclusion that only chlorine impurities are responsible for Ixand Ix. In order to verify the homogeneity of impurity uptake across a 2 inch wafer, we performed PL mapping of ZnSxSe1 - x layers. Mapping of a 2 inch ZnSe wafer shows that the FWHM of Ix across a wafer does not vary significantly (1.55 ± 0.21 meV). On mapping a 2 inch ZnS0.3Se0.7 wafer fabricated with H2S as the sulphur source at TD = 480°C, we found a rotational symmetric dstribution of sulphur in the layer. The sulphur content x at the centre is nearly constant. The difference in x between the centre and the boundary of a bad surface region at the edge of the wafer is less than Δx = 0.045. The FWHM of the band edge luminescence follows the same tendency across the wafer. The dependence of homogeneity on the reactor design as well as the uptake of unintentional impurities from the precursor is discussed in detail.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030137
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  • 17
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    Electronic Resource
    Gain and dynamics of excitons in MOVPE-grown ZnSe/ZnSxSe1 - x heterostructures (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 51-55 
    Details
    ISSN: 1057-9257
    Keywords: MOVPE ; Quantum wells ; ZnSe/ZnSxSe1 - x heterostructures ; Gain ; Excitons ; Luminescence dynamics ; Transfer processes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Optically pumped stimulated emission in ZnSe/ZnSxSe1 - x heterostructures grown by MOVPE has been observed up to 170 K. Gain measurements have been performed using the variable stripe length method. The underlying gain mechanism at 25 K is atributed to an excitonexciton scattering process. Photoluminescence excitation spectra and the temporal evolution of the luminescence indicate a transfer process from the ZnSxSe1 - x barrier into the ZnSe active layer.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030108
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  • 18
    Electronic Resource
    Electronic Resource
    Far-infrared and Raman spectroscopy of Zn(Se,S) layers (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 275-282 
    Details
    ISSN: 1057-9257
    Keywords: Far-infrared spectroscopy ; Raman spectroscopy ; MOVPE ; ZnSe ; Implantation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We discuss the optical analysis of Zn(Se,S) layers by the application of far-infrared (FIR) and Raman spectroscopy. First a summary is presented of the principles of FIR and Raman Spectroscopy with regard to the relevant epilayer properties which can be investigated by these methods. Subsequently we treat some selected results of FIR and Raman analysis of epilayers grown on GaAs(100) by metal organic vapour phase epitaxy (MOVPE). The main points of interest are crystalline quality, free carrier concentration and interface sharpness. It is shown that n-type conductivty is achieved by Ga implantation in ZnSe but the annealing process (870°C, 30 s) leads to a p-type interface layer in the GaAs due to Zn diffusion. Furthermore, the beneficial effect of growth interruptions to the sharpness of ZnS/ZnSe multiquantum-well interfaces is demonstrated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860030139
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  • 19
    Electronic Resource
    Electronic Resource
    DC SQUIDs based on YBCO step edge junctions (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 391-395 
    Details
    ISSN: 1572-9605
    Keywords: YBCO ; dc SQUID ; high-T- c junction ; step edge junction ; Josephson effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We describe the fabrication and testing of dc SQUIDs (Superconducting QUantum Interference Devices) obtained by photolithographic patterning of YBa2Cu3O7−x thin films deposited both on SrTiO3 and MgO substrates. The Josephson junctions in the superconducting loop are of the “step-edge” type, where the weak link is obtained through the growth of grains with different orientations across suitably prepared steps previously etched on the substrate surface. TheI−V characteristics of the devices tested show multiple branches and instabilities having a weak dependence on the external magnetic field, probably due to formation of junction clusters on the substrate step. The SQUID devices showed quantum interference behavior and an easily detectable voltage modulation with the applied magnetic field at a temperature of 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617977
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    Investigation of the dominant point defects in tetragonal YBa2Cu3Ox at elevated temperatures (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 313-316 
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    ISSN: 1572-9605
    Keywords: YBCO ; oxygen defects ; point defects ; superconductors ; tetragonal phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The manner in which oxygen is incorporated into YBa2Cu3O x (YBCO) at ∼800°C for values ofx close to 6 is shown to be in the form of neutral oxygen interstitials, O i x . The experimental data on which this conclusion is based are obtained from measurements of oxygen partial pressure,P(O2), as a function of compositionx and temperatureT (5.99≤x≤ 6.35, 825≤T≤1120 K). The data are obtained by a solid-state electrochemical method. Other conclusions of this study include: (a) O i x are noninteracting forx ≃ 6. (b) The stoichiometric composition of YBCO isx ≃ 6.0. (c) The reaction enthalpy of oxidation is 179 kJ/mol O2. (d) The Fermi level changes by ≃ −0.2 eV asx increases from 6.05 to 6.35.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617477
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  • 21
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    Vapor pressures of Y, Ba, Cu precursors for the growth of YBa2Cu3O7 by MOVPE (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 119-125 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; MOVPE ; vapor pressures ; β-diketonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The vapor pressures of theβ-diketonates Y(THD), Ba(THD), and Cu(THD), commonly used as precursors for MOVPE of YBa2Cu3O7, and Y(MCP) were measured at different temperatures. A time-resolved static method recording the pressure vs. time at constant temperature was used, permitting us to deduce the vapor pressure even if the materials tend to decompose. The values of the constants of the Clausius-Clapeyron equation log10p(T)/p 0=A-B/T are,A=11.7, 8.7, 8.27, 16.6 andB=4359, 2654, 3602, and 6453 K for Y(THD), Y(MCP), Ba(THD), and Cu(THD), respectively withp 0= 1 Pa and temperatureT in K. The thermal stability of the sources was measured and are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618055
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  • 22
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    Effect of Ho addition on the properties of Y-system superconductors (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 95-99 
    Details
    ISSN: 1572-9605
    Keywords: YBCO ; Ho addition ; critical current density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract (YHo)Ba2Cu3O7−y is prepared by the powder melting process and its properties are investigated. It is found that Ho addition can change the melting temperature of a Y-system superconductor. TheJ c values of YBCO can be improved by Ho substitution, which is due to the effect of Ho addition on the number and quality of grain boundaries and the size and distribution of 211 particles. The highestJ c value was found to be 50,000 A/cm2 (77 K, 1T,H⊥I) in Y0.8Ho0.2Ba2Cu3O7−y. Our results indicate that the number and quality of grain boundaries have a great influence on the superconducting properties. A discussion is given on the relationship betweenJ c and the size and phase proportion of 211 particles. There are a lot of dense twins in the sample, and many crystal defects exist around the 211 phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618051
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  • 23
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    Electronic Resource
    Lithographic patterning of superconducting YBCO films (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 445-449 
    Details
    ISSN: 1572-9605
    Keywords: YBCO ; microbridge ; lithography ; etching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Microbridges of YBa2Cu3O7 thin films have been fabricated by conventional photolithography and wet chemical etching using EDTA, and by the lift-off lithography technique. The variation of etch rate with etch time, etchant temperature, and post-deposition sintering temperature has been studied. It has been shown that both techniques are useful for film patterning. However, an additional sintering step is necessary for the chemically etched sample to regain the original film properties. An order of increase in critical current density is observed for the patterned film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00620502
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