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  • 1
    Electronic Resource
    Electronic Resource
    A comparison of the thermal and near band-gap light-induced recoveries of EL2 from its metastable state in semiinsulating GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5004-5008 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reverse transition from the EL2 metastable state to the ground state is achieved by thermal annealing above 140 K. An optical recovery of the ground state photoresponse (1–1.3 eV) can be also done exciting with near band-gap light. We present herein a photocurrent study of the photoquenching transients starting from either a thermal recovery situation or an optically recovery one. It is seen that the recovered states are not the same for both of them. While the thermal recovery restores the ground state of EL2, the optical recovery restores another state, labeled EL2r, which gives a different photoquenching transient as compared to the ground EL2 level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353820
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  • 2
    Electronic Resource
    Electronic Resource
    Adjustable nanofabricated atomic size contacts (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 108-111 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Metallic point contacts and tunnel junctions with a small and adjustable number of conduction channels have been obtained in the last few years using scanning tunneling microscope and break junction techniques. For conventional break junctions, the reported drift of the interelectrode spacing in the tunnel regime is typically of the order of 0.5 pm/min (1 pm=10−12 m). We have nanofabricated break junctions which display a drift smaller than 0.2 pm/h. The improvement results from the scaling down by two orders of magnitude of the device dimensions. We describe the nanofabrication process, which can be adapted to most metals. We have performed measurements on Al, Cu, and Nb devices. The results illustrate the ability of the technique to explore phenomenalike conductance quantization and two level fluctuations. These new adjustable atomic size contacts and tunnel junctions can be integrated in complex circuits. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146558
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  • 3
    Electronic Resource
    Electronic Resource
    Harvest management effects on alfalfa (Medicago sativaL.) production and quality in Mediterranean areas (1998)
    Oxford BSL : Blackwell Publishing Ltd
    Grass and forage science 53 (1998), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of plant harvest stage, autumn harvest dateand cultivars on alfalfa production and quality weredetermined in a 3-year field experiment established in1992. Harvesting stage influenced annual yield andquality. Late bud-first flower harvests increased harvestfrequency and forage quality in comparison with har-vestingat the full bloom stage while decreasing dry-matteryield by 18% (25·5 vs. 21·6 t ha 21 ). Harvestingstage significantly affected autumn forage productionand quality and yield at the first spring cut. Harvests atfull bloom allowed greater autumn and spring regrowththan cutting at the late bud stage, possibly because ofthe accumulation of higher root reserves. Autumn har-vestsand cultivar significantly influenced the yields atthe first spring cut in any growing season. Cuttingbefore the first frost in autumn reduced the vigour ofboth cultivars, and the subsequent yield at the first cutin any year, in comparison with harvests taken after ornear the first autumn frost. It is concluded that theeffects of the stage of harvesting alfalfa on dry-matterproduction and quality are important in theMediterranean environment of the Ebro Valley; theeffects of autumn management were observed mainlyon the yields of the subsequent first cut in spring but noton the total annual production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2494.1998.00100.x
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  • 4
    Electronic Resource
    Electronic Resource
    A Raman spectroscopic study of the Si, Be, and C incorporation in InxGa1−xAs relaxed layers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4690-4695 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The incorporation of high concentrations ((approximately-greater-than)1019 cm−3) of Si, Be, and C in InxGa1−xAs relaxed layers has been studied as a function of In content (x≤0.16) by Raman spectroscopy of local vibrational modes (LVM). The frequencies of the Raman peaks resulting from the convolution of several split modes shift to lower values as the In content is increased, the carbon acceptor (CAs) local mode frequency showing the strongest dependency on x. Features attributed exclusively to the influence of In on second-neighbor sites are identified only in the Si-doped samples. The transverse and longitudinal modes expected from the splitting of a LVM of CAs with one In first neighbor are not observed in layers with x up to 0.085. A new calibration for the BeGa, CAs, and Si-related LVM leads to the conclusion that In increases the total electrical activation of Si and favors its incorporation on group-III sublattice sites. In contrast, no influence of In on the Be or C doping activation has been detected. The analysis of the CAs LVM spectra supports the view that in InxGa1−xAs CAs is preferably surrounded by Ga instead of In atoms for x≤0.085. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359816
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of In on Si local vibrational modes in InxGa1−xAs (0≤x≤0.12) (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7797-7804 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local vibrational modes (LVM) of Si in substitutional sites have been observed by resonant Raman spectroscopy in highly doped (≥8×1018 cm−3) InxGa1−xAs layers, either relaxed or under strain, on [100] GaAs substrates. The peak frequency ωLVM of the Si on Ga site (SiGa) LVM in unstrained samples shifts to lower values with increasing In content. For x≤0.10 this shift is clearly higher than expected from a linear interpolation between the measured values in the binaries. The comparison between the SiGa peak frequency measured in both a full strained layer and a relaxed layer with similar composition provides a rough determination of the deformation potentials for the SiGaLVM in these layers: q/ω2LVM=−2.7±1 and p/ω2LVM=−2.5±1. As the In content becomes higher the width of the SiGa peak increases much more than that of the GaAs-like longitudinal optical-phonon peak, revealing the splitting due to the loss of local symmetry introduced by the In. New calibration factors for the Si-defect concentrations have been deduced, which allow estimation of the solubility limit for the Si incorporation in substitutional positions, which ranges from 2.3×1019 to 2.6×1019 cm−3 for the layers at the growth conditions used. The analysis of the integrated intensity of the LVM Raman peaks indicates that the degree of electrical compensation is clearly reduced for increasing In up to x≤0.05, due to both an increase of the solubility limit for Si in these layers and a saturation or slight reduction of the SiAs-related defect concentrations. This conclusion is also supported by Hall and plasmon measurements. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358521
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  • 6
    Electronic Resource
    Electronic Resource
    Metastable transformation of EL2 in semi-insulating GaAs: The role of the actuator level and the photoionization of EL2 (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2959-2961 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The metastable transformation of EL2 is modeled in terms of an additional acceptor level, whose role is the activation of the metastable transformation of EL2. This level, called the actuator of the metastability, enables the metastable transformation after capturing a hole. Thermal emission of this hole at 80–85 K renders the metastable transformation of EL2 quite ineffective above this temperature. The double acceptor 78/203 meV is proposed as a possible actuator. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116368
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  • 7
    Electronic Resource
    Electronic Resource
    Uniformity and physical properties of semi-insulating Fe-doped InP after wafer or ingot annealing (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3836-3845 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semi-insulating Fe-doped InP was annealed under different conditions and investigated by Hall effect, extrinsic photocurrent mapping, chemical etching, and optical microscopy. The resistivity is increased for any treatment, particularly in wafer-annealed InP. This result is probably due to strong losses of shallow donors. Remarkable differences exist between the structural properties of the wafer and ingot annealed material; wafer annealing produces a quick elimination of growth striations and decoration microdefects while ingot-annealed InP still retain these microdefects, both along dislocations and in the matrix. The photocurrent maps indicate that the thermal treatments normally improve the doping uniformity (especially the short-range fluctuations). The best uniformity is achieved for the long annealing time (≥50 h), while a slow cooling rate improves the mobility. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365748
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  • 8
    Electronic Resource
    Electronic Resource
    Photocurrent study of the influence of photogenerated carriers on the EL2*-EL2 transformation in semi-insulating GaAs (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 1253-1255 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optically induced EL2*-EL2 transformation is studied by photocurrent measurements, allowing the monitorization of the free-carrier generation during the near-band-gap (NBG) recovery excitation. The efficiency recovery spectrum is found to be anticorrelated with the NBG photocurrent spectrum. This observation rules out the possibility of a free-carrier assisted process as the main mechanism accounting for the NBG induced EL2*-EL2 reverse transformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107421
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  • 9
    Electronic Resource
    Electronic Resource
    Relaxation of InGaAs layers grown on (111)B GaAs (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 3212-3214 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The relaxation behavior of InGaAs layers grown by molecular beam epitaxy on (111)B GaAs is investigated and compared with simultaneously grown (100) reference samples. Surface morphology, defect microstructure, and optical quality of the layers during the relaxation process are studied by Nomarski interference contrast, transmission electron microscopy, low-temperature photoluminescence, and Raman spectroscopy. These techniques reveal an inhomogeneous and anisotropic relaxation in (111) samples. In (111) samples, the increase of critical thickness and the slower relaxation dependence on thickness, as compared with the (100) reference samples, is discussed © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112415
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  • 10
    Electronic Resource
    Electronic Resource
    Surface Fermi level pinning in epitaxial InSb studied by electric-field-induced Raman scattering (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 349-351 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electric-field-induced Raman scattering by longitudinal optical (LO) phonons has been used to study the surface Fermi level position in InSb layers grown by molecular beam epitaxy on (100) GaAs. From the analysis of a variety of layers it is found that the LO phonon scattering intensity, relative to that of intrinsic two-LO phonon scattering, decreases with increasing optical power density in n-type samples, but remains constant in p-type and undoped layers, which are residual p type. The power dependence of the relative LO phonon intensity for n-type doping is shown to be caused by a surface electric field, the strength of which is reduced upon increasing illumination due to screening by photogenerated carriers. As this effect is only found in n-type layers, we conclude that the surface Fermi level is pinned at the valence band thus giving rise to a sizeable surface electric field in n-type but not in p-type material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110039
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