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15 Oct 1990

Volume 57, Issue 16, pp. 1595-1698

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Transport properties of excitons in GaAs quantum wells−time‐resolved Raman probe

K. T. Tsen, O. F. Sankey, and H. Morkoç

Appl. Phys. Lett. 57, 1666 (1990); http://dx.doi.org/10.1063/1.104080 (3 pages) | Cited 9 times

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Time‐resolved, space‐imaged Raman spectroscopy has been employed to study the transport properties of excitons in GaAs quantum wells. For an injected exciton density of nex ≂1.5×1011 cm−2, the experimental results show that exciton transport can be well described by a simple diffusion model. Based on the temperature and well‐width dependence of the deduced diffusion constant, we demonstrate that at low temperatures, i.e., T ≤60 K, the transport of excitons in GaAs quantum wells is primarily governed by two dominant mechanisms: acoustic phonon scattering and interface roughness scattering.
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71.35.-y Excitons and related phenomena
78.30.Fs III-V and II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations

Electronic surface states confined to the boundary of periodic multiple quantum wells

F. Y. Huang

Appl. Phys. Lett. 57, 1669 (1990); http://dx.doi.org/10.1063/1.104081 (3 pages) | Cited 20 times

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A semi‐infinite stratified multiquantum well structure with the boundary connected to a homogeneous medium is suggested. Electronic surface states are found to exist under certain conditions. These surface states have an interesting feature that the eigenenergy may even exceed the confinement potential of the periodic substrate. Possible application of this structure in optoelectronic devices is discussed.
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73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.60.-q Optoelectronic devices

Vacuum lithography for in situ fabrication of buried semiconductor microstructures

Y. L. Wang, H. Temkin, L. R. Harriott, R. A. Hamm, and J. S. Weiner

Appl. Phys. Lett. 57, 1672 (1990); http://dx.doi.org/10.1063/1.104082 (3 pages) | Cited 18 times

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We have developed a complete lithographic process combining focused ion beam writing, dry etching, and molecular beam epitaxy for in situ preparation of buried InP‐based microstructures. A focused ion beam is used to locally remove an ultrathin oxide imaging layer grown in situ on the surface of InP. The pattern is transferred into the underlying semiconductor by free Cl2 etching with the patterned oxide layer acting as an etch mask. After removal of the oxide mask, GaInAs/InP heterostructures with excellent morphology and high luminescence efficiency can be grown on the patterned substrate. The entire process of mask formation, lithography, and regrowth can be carried out in situ repeatedly, and used for creating fully buried microstructures.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Study of electrical characteristics of polyoxides grown by rapid thermal oxdidation

G. Q. Lo, A. W. Cheung, D. L. Kwong, and N. S. Alvi

Appl. Phys. Lett. 57, 1675 (1990); http://dx.doi.org/10.1063/1.104135 (3 pages) | Cited 2 times

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Thin (∼18 nm) polyoxide films have been grown on phosphorus‐implanted polycrystalline silicon (poly‐Si) by rapid thermal oxdiation (RTO). With an emphasis on the bias polarity dependence, we have studied the electrical characteristics of polyoxides, such as leakage current, breakdown field, and charge trapping. In comparison with polyoxides grown in conventional furnace, RTO polyoxides exhibit a significantly reduced leakage current. In addition, the dielectric breakdown strength and breakdown field distribution have been improved. When electrons were injected from the top poly‐Si/SiO2 interface, RTO polyoxide shows a reduced trapping rate. However, when electrons were injected from the SiO2/bottom poly‐Si interface, RTO polyoxide shows an increased trapping rate.
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73.40.Ty Semiconductor-insulator-semiconductor structures
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
84.32.Tt Capacitors

Ballistic current vortex excitations in electron waveguide structures

Craig S. Lent

Appl. Phys. Lett. 57, 1678 (1990); http://dx.doi.org/10.1063/1.104083 (3 pages) | Cited 32 times

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Coherent ballistic transport through a cavity in a quantum electron waveguide is examined. Electrons passing through the cavity excite vortices in the current density in the cavity. The circulating currents may be larger than the current in the waveguide leads. Vortex excitations are possible even when the incoming current is totally reflected and no net current passes through the cavity.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

N+ doping of gallium arsenide by rapid thermal oxidation of a silicon cap

D. K. Sadana, J. P. de Souza, and F. Cardone

Appl. Phys. Lett. 57, 1681 (1990); http://dx.doi.org/10.1063/1.104084 (3 pages) | Cited 5 times

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Shallow (<200 nm) Si profiles with doping levels in excess of 2×1018 cm−3 were reproducively obtained in GaAs by rapid thermal oxidation (RTO) of Si caps (50 or 160 nm) in 0.1% O2/Ar ambient at 850–1050 °C. The doping level as well as distribution of the diffused Si can be controlled by the thickness of the Si cap, RTO temperature, RTO time, and oxygen level in the annealing ambient. It appears that the generation of Si interstitials at the oxidizing surface of the Si cap during RTO is responsible for the Si diffusion into the underlying GaAs substrate.
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68.35.Fx Diffusion; interface formation
81.65.-b Surface treatments
61.72.U- Doping and impurity implantation

Growth of InGaAs structures using in situ electrochemically generated arsine

D. N. Buckley, C. W. Seabury, J. L. Valdes, G. Cadet, J. W. Mitchell, M. A. DiGiuseppe, R. C. Smith, J. R. C. Filipe, R. B. Bylsma, U. K. Chakrabarti, and K‐W. Wang

Appl. Phys. Lett. 57, 1684 (1990); http://dx.doi.org/10.1063/1.104136 (3 pages) | Cited 2 times

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The use, transportation, and storage of the hazardous gas, arsine, raise serious safety issues. Consequently, there is considerable interest in the generation of arsine on demand from less hazardous substances. We report the first use of in situ generated arsine for III‐V epitaxy. The gas has been generated electrochemically at an arsenic cathode in an aqueous electrolyte and used to supply a hydride vapor phase epitaxy reactor. InGaAs/InP test structures were grown on InP substrates and were similar to comparison structures grown using tank arsine. Recessed‐gate enhanced Schottky metal‐semiconductor field‐effect transistors were fabricated and exhibited well‐behaved current‐voltage characteristics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.45.-h Electrochemistry and electrophoresis
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.Tv Field effect devices

Growth of YBa2Cu3O7 thin films on MgO: The effect of substrate preparation

B. H. Moeckly, S. E. Russek, D. K. Lathrop, R. A. Buhrman, Jian Li, and J. W. Mayer

Appl. Phys. Lett. 57, 1687 (1990); http://dx.doi.org/10.1063/1.104137 (3 pages) | Cited 88 times

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We discuss the results of a study of the effect of substrate preparation on the microstructure and superconductive properties of YBa2Cu3O7 thin films formed by laser ablation on (001) MgO substrates. Thermal annealing of the substrates is found to be highly effective in producing at fairly low growth temperatures (670 °C), epitaxial, c‐axis normal films with good superconductive properties. Alternative surface treatments result in the formation of large angle tilt boundaries and inferior superconductive properties.
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74.78.-w Superconducting films and low-dimensional structures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Application of a near coincidence site lattice theory to the orientations of YBa2Cu3O7−x grains on (001) MgO substrates

D. M. Hwang, T. S. Ravi, R. Ramesh, Siu‐Wai Chan, C. Y. Chen, L. Nazar, X. D. Wu, A. Inam, and T. Venkatesan

Appl. Phys. Lett. 57, 1690 (1990); http://dx.doi.org/10.1063/1.104138 (3 pages) | Cited 73 times

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Various orientations of YBa2Cu3O7−x grains in polycrystalline films prepared on (001)MgO substrates by in situ laser deposition were determined using electron diffraction. Eight different types of in‐plane orientations have been observed. These orientations agree well with the prediction of a simplified theory of near coincidence site lattice between YBa2Cu3O7−x and MgO. The YBa2Cu3O7−x grains were found to have a high probability of forming low angle or low Σ boundaries among themselves. These grain boundaries are of low energy and should exhibit a high connectivity of Cu‐O‐Cu chains. Therefore, YBa2Cu3O7−x thin films on MgO can attain a Tc of ∼90 K and a Jc of ∼106 A/cm2 at 77 K.
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74.70.-b Superconducting materials other than cuprates
61.72.Mm Grain and twin boundaries
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Effect of annealing on superconductivity of Pb‐doped Bi‐Sr‐Ca‐Cu‐O single‐crystal superconductors

Y. Gao, Y. Li, K. L. Merkle, P. Z. Jiang, Y. C. Chang, H. Shi, and D. J. Lam

Appl. Phys. Lett. 57, 1693 (1990); http://dx.doi.org/10.1063/1.104139 (3 pages) | Cited 12 times

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The microstructure of high quality Pb‐doped Bi2Sr2CaCu2Ox single crystals grown by the flux technique has been studied by transmission electron microscopy (TEM). The single crystals have a superconducting transition temperature (Tc) of about 90 K as grown; Tc drops to about 83 K after annealing in air at 600 °C. TEM results show that the as‐grown crystals exhibit twinning. The twin boundaries were found to be parallel to the (100) and (010) lattice planes. However, upon annealing the twin structure disappeared. This microstructure change is discussed in terms of a possible cause for the Tc decrease in the annealed crystals.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.40.Rs Electrical and magnetic properties related to treatment conditions

Femtosecond optical absorption studies of nonequilibrium electronic processes in high Tc superconductors

J. M. Chwalek, C. Uher, J. F. Whitaker, G. A. Mourou, J. Agostinelli, and M. Lelental

Appl. Phys. Lett. 57, 1696 (1990); http://dx.doi.org/10.1063/1.104140 (3 pages) | Cited 69 times

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We report the results of femtosecond optical transient absorption experiments performed on <m1;&1p>the superconducting compounds YBa2Cu3O7−x(x ∼ 0) and Bi2Sr2Ca2Cu3O10+δ(δ ∼ 0) and nonsuperconducting YBa2Cu3O6+y(y<0.4) for sample temperatures ranging from ∼7 K to room temperature. Nonequilibrium heating was found to occur on a subpicosecond time scale. A distinct, dramatic increase in the relaxation time was observed for the superconducting samples as the sample temperature was lowered below the critical temperatures of the respective films. Accompanying the increase in relaxation time was an increase in the peak fractional transmissivity change. No such changes were observed for the nonsuperconducting YBCO sample. We believe the above described behavior is electronic in origin and intimately related to the superconductivity of the compounds.
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78.47.-p Spectroscopy of solid state dynamics
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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