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  • 1
    Electronic Resource
    Electronic Resource
    Er–Yb codoped CaF2 thin films grown by molecular beam epitaxy (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 679-684 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Yb:Er: codoped CaF2 monocrystalline films have been grown by molecular beam epitaxy (MBE) using YbF3, ErF3, and CaF2 evaporation on CaF2 substrates. Luminescence and excitation of luminescence at 25 K are measured in order to investigate the role of Yb3+ codoping and the effect of the growth conditions during the MBE process on the incorporation of active rare-earth species in CaF2. It is found, from a comparison with earlier work on singly doped thin films, that the energies of the levels of Er3+ ions are not modified by the double doping, whereas mixed complex centers are formed. Growth conditions are found to be important controlling factors for the incorporation of Yb3+ as a sensitizer, and, consequently, for the transfer efficiency. From excitation and absorption spectra it is shown that the lowest component of the Er:4I11/2 manifold has an energy higher than that of Yb:2F5/2 and the consequences are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364230
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of growth temperature and doping concentration on the distribution of the emitting centers in CaF2:Er molecular beam epitaxial layers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2749-2752 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular beam epitaxy of Er-doped CaF2 layers on (100)oriented CaF2 substrates was performed using CaF2 and ErF3 evaporation cells. The effect of growth temperature and Er concentration on the distribution of the different emission centers observed in these epitaxial Er-doped layers was investigated. Photoluminescence analyses were performed in the 830–860 nm wavelength range in which the 4S3/2→4I13/2 transitions of the Er3+ ions take place. The evolution of the relative emission intensity between single and aggregate Er3+ centers as a function of growth temperature shows that the emission from isolated Er3+ ions is favored in a growth temperature range of 500–520 °C. Emission lines from complex Er3+ centers are found to rise relative to those of isolated sites as Er concentration increases. Finally, no quenching of the integrated luminescence intensity occurs in the concentration range investigated, 0.05–6 mol % (0.1–16 wt%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356211
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  • 3
    Electronic Resource
    Electronic Resource
    1.54 μm wavelength emission of highly Er-doped CaF2 layers grown by molecular-beam epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 270-273 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CaF2:Er layers have been grown by molecular-beam epitaxy on (100)-oriented CaF2 substrates; the Er concentration ranges from 1% to 50% (mole fraction). The 1.54 μm emission observed under excitation around 800 nm was studied by photoluminescence. Up to 35% Er concentration the integrated emission increases monotonously, quenching appearing for higher doping levels. Photoluminescence results are discussed within the framework of previous studies of Er3+ emission in the near-infrared range (830–860 nm) in order to gain insight into the Er centers involved in the 1.54 μm emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357140
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature dependence of the fundamental absorption edge of mercury cadmium telluride (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6454-6460 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the temperature dependence of the fundamental absorption edge of a series of Hg1−xCdxTe alloys (with composition x ranging from 0.5 to 1). Analyzing our data in the light of the three-dimensional theory of direct-allowed excitons, we find precise values for the fundamental Γ8-Γ6 interband transition energy in a temperature range extending from 0 to 300 K. All experimental results, including previous data for HgTe and mercury-rich Hg1−xCdxTe alloys, are well accounted for using a simple empirical formula: Eg (eV)=−0.303(1−x)+1.606x−0.132x(1−x)+[6.3(1−x) −3.25x −5.92x(1−x)]10−4T2/[11(1−x)+78.7x+T]. This expression, which is valid for all compositions 0≤x≤1 and temperatures 0≤T≤500 K, predicts an alloy composition such that the band-gap energy is temperature independent: We find x=0.505. Finally, it can be used for technological application purpose (far-infrared detection as well as optical-fiber communications performed at realistic values of the temperature) and gives accurate values for the temperature and composition dependence of the effective mass in the semiconducting range of alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345119
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  • 5
    Electronic Resource
    Electronic Resource
    Cathodoluminescence mapping, deep-level transient spectroscopy, and electron-beam-induced current measurements on GaAs layers grown on Si substrates by metalorganic chemical vapor deposition (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3831-3838 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaAs layers grown by organometallic chemical vapor deposition (OMCVD) on Si substrates oriented 2° off (100) toward [011] have been studied by 10-K filtered cathodoluminescence, deep-level transient spectroscopy (DLTS), electron-beam-induced current (EBIC), and secondary ion mass spectrometry (SIMS) measurements. The mapping of the near-band-edge emission intensity shows the existence of zones of lower defect density, whose relative volume increases with the layer thickness. Four deep-level energy peaks have been characterized at 1.33, 1.20, 1.15, and 1.02 eV. The 1.33 and 1.20 eV energy peaks are attributed to Si in GaAs. Strong inhomogeneities in the intensity of these two emissions have been observed with depth of the layers, and this behavior has been related to the silicon distribution. From measurements on structures grown with different buffer layers, we show that a GaAs/AlAs supperlattice located at 1 μm from the Si substrate is efficient in decreasing the width of a highly Si-doped interface region. DLTS measurements confirm the decrease in the deep-level concentration with increasing thickness. Furthermore, by EBIC characterization, we measure a minority-carrier diffusion length of 2.7–3 μm on a 5-μm-thick layer. This corresponds to a dislocation density of 8×106 cm−2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344047
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  • 6
    Electronic Resource
    Electronic Resource
    Photoluminescence and electrical properties of close space vapor transport GaAs epitaxial layers (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 3652-3654 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Close spaced vapor transport (CSVT) epitaxial layers have been grown under water vapor partial pressure p ranging from 5×10−2 to 5 mm Hg for source temperatures of 800 and 850 °C and a substrate temperature of 730 °C, using undoped high-purity GaAs as source material and 〈100〉 chromium doped high-resistivity GaAs as substrate. From Hall measurements, all layers were found to be n-type with a majority carrier concentration in the range of (2–3) ×1017 cm−3 and a mobility 3100–3600 cm2 V−1 s−1 as p varies from 5.0 to 5×10−2 mm Hg. Photoluminescence measurements show the following dominant recombination processes: an exitonic peak at 1.514 eV, a free band acceptor at 1.498 eV, a donor acceptor at 1.490 eV, and two peaks involving complexes at 1.47 and 1.42 eV. These peaks depend on the water vapor pressure: for low values of p only the exitonic peaks exist; as p increases the photoluminescence becomes less efficient until it disappears for p=5.0 mm Hg. This study shows that CSVT-GaAs epilayers grown under proper conditions have high quality and could be used for producing some electronic devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335749
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  • 7
    Electronic Resource
    Electronic Resource
    Aging study of nickel-copper-manganite negative temperature coefficient thermistors by thermopower measurements (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4705-4709 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ceramic nickel-copper-manganite based negative temperature coefficient thermistors are unstable under thermal constraint, which increases the resistivity of these devices. This unstability can be reduced by the addition of a small amount of barium. These ceramics have a spinel structure, and the conduction takes place by a hopping process involving [Mn3+]/[Mn4+] octahedral ions. This study by the use of thermopower measurements points out that the resistivity change under thermal constraint is principally due to the disproportionation of [Mn3+]/[Mn4+] ions in the octahedral sites. Furthermore, it seems that some nickel ions migrate from octahedral to tetrahedral sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352076
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of Nd3+ concentration on the emission spectra of CaF2:Nd layers grown by molecular-beam epitaxy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4485-4489 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nd3+-doped CaF2 monocrystalline films have been grown by molecular-beam epitaxy using CaF2 and NdF3 evaporation on CaF2 (100) substrates. Auger electron spectrometry and high-energy electron diffraction have been used as in situ techniques to characterize the grown layers. No degradation of crystallinity was observed even for the highest levels of doping considered. The effect of Nd3+ concentration is studied by means of the photoluminescence signal of Nd3+ ions. The results can be compared favorably with those of bulk CaF2:Nd crystals. For a given Nd3+ concentration a lower quantity of Nd3+ aggregate centers is observed. Nd3+ ions can, therefore, be efficiently incorporated in isolated Nd3+-F− centers up to concentrations of 3.7 wt % Nd3+ without emission quenching of the associated line at 1.0457 μm. The results are related to the thermodynamic conditions imposed by the molecular-beam epitaxy technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349082
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  • 9
    Electronic Resource
    Electronic Resource
    Precision Bragg reflectors obtained by molecular beam epitaxy under in situ tunable dynamic reflectometry control (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3390-3392 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Highly accurate layer thicknesses are required for multilayers involved in photonic devices, such as Bragg reflectors. In this letter, we demonstrate that precise, real-time monitoring of molecular beam epitaxy growing layers can be achieved by near-normal incidence dynamic reflectometry with a tunable sapphire–titanium laser used as a source. The advantage of this new technique lies in the possibility of synchronizing the material changes and the reflectivity extrema by selecting adequate analysis wavelengths. This technique is shown to provide 885 nm GaAs–AlAs Bragg reflectors with a layer thickness accuracy in excess of 1%. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114903
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  • 10
    Electronic Resource
    Electronic Resource
    In situ measurement of AlAs and GaAs refractive index dispersion at epitaxial growth temperature (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 244-246 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ molecular beam epitaxy control of III–V optoelectronic device growth has been achieved by dynamic optical reflectometry with tunable excitation wavelength, through the use of a titanium:sapphire laser light source. This new multiwavelength reflectometry method was used to determine the values of the AlAs and GaAs refractive indices at growth temperature (600 °C). Index dispersion between 760 and 960 nm is presented and found to be in good agreement with the existing models. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114681
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