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25 Jan 1993

Volume 62, Issue 4, pp. 325-431

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Nonresonant tunneling in InGaP/InAlP asymmetric double quantum wells

O. Buccafusca, J. L. A. Chilla, C. S. Menoni, J. J. Rocca, M. J. Hafich, L. M. Woods, and G. Y. Robinson

Appl. Phys. Lett. 62, 399 (1993); http://dx.doi.org/10.1063/1.108942 (3 pages) | Cited 4 times

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Nonresonant tunneling rates have been measured in InGaP/InAlP asymmetric double quantum‐well structures for which optical phonon assisted tunneling is energetically forbidden. For an initial photoexcited carrier density of 2.4×1011 cm−2, tunneling times of 220, 60, and less than 9 ps have been measured in samples with barrier thickness 4.5, 3.0, and 1.5 nm, respectively. The tunneling times were found to be strongly dependent on carrier density. The measured tunneling times and their dependence on carrier density are compatible with impurity scattering being the dominant mechanism assisting the tunneling.
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73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Hot‐electron electroluminescence in AlGaAs/GaAs heterojunction bipolar transistors

Enrico Zanoni, Loris Vendrame, Paolo Pavan, Manfredo Manfredi, Stefano Bigliardi, Roger Malik, and Claudio Canali

Appl. Phys. Lett. 62, 402 (1993); http://dx.doi.org/10.1063/1.108943 (3 pages) | Cited 7 times

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When biased in the active region at high collector voltages, AlGaAs/GaAs single heterojunction bipolar transistors have been observed to emit light in the 1.1–2.5 eV energy range. The spectral distribution of the emitted radiation results from the superimposition of (i) two peaks at about 1.4 and 2.1 eV, due to band‐to‐band recombination of cold electrons and holes, and (ii) a nearly exponential tail due to hot‐electron‐induced electroluminescence, whose intensity depends on reverse collector‐base voltage. Moreover, a linear correlation has been found between the intensity of the hot‐electron‐induced electroluminescence and the current generated by impact ionization.  
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78.60.Fi Electroluminescence
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Pq Bipolar transistors

Influence of silicon wafer surface orientation on very thin oxide quality

T. Ohmi, K. Matsumoto, K. Nakamura, K. Makihara, J. Takano, and K. Yamamoto

Appl. Phys. Lett. 62, 405 (1993); http://dx.doi.org/10.1063/1.108944 (3 pages) | Cited 9 times

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We studied effects of silicon wafer surface orientation on very thin oxide quality, testing Si(100) and (111) wafers. It has been found that the very thin oxide structure is dominating by the silicon wafer surface orientation, and that when Si(111) is oxidized, SiO2/Si(111) interface microroughness increases as oxide gets thicker than 10 nm, resulting in a degradation of oxide films quality on Si(111). When oxide thickness is decreased to less than 10 nm, SiO2/Si interface smoothness is maintained similar to Si(100) and (111) but the SiO2/Si interface exhibits larger interface charges and larger flatband voltage shift for Si(111) than for Si(100).
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81.65.-b Surface treatments
68.55.-a Thin film structure and morphology

Extremely smooth YBa2Cu3Oy thin films grown using the reactive coevaporation technique in radical oxygen at an ultralow growth rate

Yasuo Tazoh and Shintaro Miyazawa

Appl. Phys. Lett. 62, 408 (1993); http://dx.doi.org/10.1063/1.108917 (3 pages) | Cited 10 times

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The effect of using drastically reduced growth rates on the surface morphology of YBa2Cu3Oy (YBCO) thin films grown on lattice‐matched (110) NdGaO3 substrates using the reactive coevaporation technique in a radical oxygen atmosphere is reported. The surface of films grown at an ultralow growth rate (∼0.0065 nm/s) appears to be very smooth without any precipitates, holes, crevasses, or pits. The film surface roughness is on the order of the unit‐cell constant of superconducting YBCO, about 1.2 nm. This shows that decreasing the growth rate enhances the lateral spreading of nucleated islands, with a height of one unit cell, in the Stranski–Krastanov growth mode [Ber. Akad. Wiss, Wien 146, 797 (1938)].
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68.55.-a Thin film structure and morphology
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Transport characteristics of Tl2Ba2CaCu2O8 bicrystal grain boundary junctions at 77 K

A. H. Cardona, H. Suzuki, T. Yamashita, and K. H. Young

Appl. Phys. Lett. 62, 411 (1993); http://dx.doi.org/10.1063/1.108918 (3 pages) | Cited 34 times

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We report the fabrication and characterization of thin‐film grain boundary junctions in Tl‐based superconductors on bicrystal substrates. Post‐deposition processed Tl2Ba2CaCu2O8 films were grown on bicrystal SrTiO3 substrates, with varying degrees of misorientation angle θ. Critical current densities and current‐voltage curves had a strong dependence on θ. For θ≥10°, there was a two‐to‐three order of magnitude reduction in critical current density, and for θ≥20°, the current‐voltage curves displayed resistively shunted junction behavior. These high angle grain boundary junctions have features at 77 K that are attractive for device applications, including sharp voltage onsets, well‐behaved dc magnetic and rf field dependence, IcRn products as large as 300 μV, and low 1/f noise. Simple dc superconducting quantum interference devices fabricated with these junctions exhibited transfer functions of up to 30 μV/Φ0 at 77 K.
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74.50.+r Tunneling phenomena; Josephson effects
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.72.-h Cuprate superconductors

Epitaxial growth of Ba1−xKxBiO3 thin films by pulsed‐laser deposition

D. P. Norton, J. D. Budai, B. C. Chakoumakos, and R. Feenstra

Appl. Phys. Lett. 62, 414 (1993); http://dx.doi.org/10.1063/1.108919 (3 pages) | Cited 4 times

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Epitaxial Ba1−xKxBiO3 thin films have been grown by pulsed‐laser deposition at temperatures as low as 400 °C. Films have been grown on (100) MgO and SrTiO3 with Tc(R=0)=19.5 K and transition widths less than 1 K. Four circle x‐ray diffraction shows that these epitaxial films are mostly (00l) oriented with good in‐plane epitaxy. We find that, especially for growth on (100) MgO, an initial epitaxial layer of BaBiO3 grown at 600 °C significantly improves the properties of the Ba1−xKxBiO3 films.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.78.-w Superconducting films and low-dimensional structures
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Weak link behavior of grain boundaries in Nd‐, Bi‐, and Tl‐based cuprate superconductors

M. Kawasaki, E. Sarnelli, P. Chaudhari, A. Gupta, A. Kussmaul, J. Lacey, and W. Lee

Appl. Phys. Lett. 62, 417 (1993); http://dx.doi.org/10.1063/1.108920 (3 pages) | Cited 51 times

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We have studied single‐grain‐boundary junctions in the neodymium‐, bismuth‐, and thallium‐based cuprate superconductors and find that they behave as weak links, qualitatively similar to the YBa2Cu3O7−δ superconductor. In general, the grain boundary critical current is determined by flux flow for small misorientation angles and by Josephson junctionlike coupling for large angles. The latter is verified by the observation of voltage oscillations with an external magnetic field in superconducting quantum interference devices built using single‐grain‐boundary junctions of these materials. The commonality of behavior of grain boundaries in all of the high temperature cuprate superconductors suggests that the weak link is most likely associated with the structure of the grain boundary and the evidence points increasingly to dislocations, which describe the topology of the boundary.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors

Giant magnetoresistance and its evolution in the granular FexAg100−x system (0≤x≤100)

Gang Xiao, Jian Qing Wang, and Peng Xiong

Appl. Phys. Lett. 62, 420 (1993); http://dx.doi.org/10.1063/1.108921 (3 pages) | Cited 45 times

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We have studied the magnetotransport and magnetic properties of a metallic granular FexAg100−x system, fabricated by using a magnetron cosputtering technique. Giant magnetoresistance was observed in a narrow range between x=10 and 25 vol %. Both the Fe volume fraction and the sample orientation significantly influence the magnetoresistance. This granular system also demonstrates some unique features as compared to multilayer systems.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.-y Studies of specific magnetic materials

Effect of self‐implantation on structure and oxidation behavior of single crystal β‐SiC

Honghua Du, Matthew Libera, Zunde Yang, Po‐Jen Lai, Dale C. Jacobson, Yu. C. Wang, and Robert F. Davis

Appl. Phys. Lett. 62, 423 (1993); http://dx.doi.org/10.1063/1.108922 (3 pages) | Cited 7 times

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Single crystal β‐SiC was self‐implanted with high‐dose Si and C at 773 K. In situ lattice recovery occurred and SiC remained single crystalline during implantation. Notable structural damage resulted in the implanted region. The residual damage significantly accelerated the oxidation rate of SiC at 1373 K but caused no appreciable rate increase at 1573 K. The diminishing of the effect of the damages on oxidation can be attributed to enhanced damage annealing with temperature.
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81.65.-b Surface treatments
61.80.Jh Ion radiation effects

High current density produced by femtosecond nonlinear single‐photon photoelectric emission from gold

J. P. Girardeau‐Montaut, C. Girardeau‐Montaut, S. D. Moustaizis, and C. Fotakis

Appl. Phys. Lett. 62, 426 (1993); http://dx.doi.org/10.1063/1.108923 (3 pages) | Cited 16 times

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The sensitivity of single‐photon photoelectric emission of pure‐polycrystalline Au induced by a KrF excimer laser emitting at 248 nm pulses of 450 fs duration, has been measured. A nonlinear increase of photoelectric efficiency as a function of the laser peak intensity has been observed. The threshold of this nonlinearity is estimated from the experimental data to be slightly less than 0.1 GW/cm2. This value is in good agreement with earlier observations for W and Zr. We demonstrate that this is the direct consequence of nonequilibrium electron and lattice temperatures produced at the surface by the subpicosecond laser pulses.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Ds Laser-beam impact phenomena
41.75.Fr Electron and positron beams

Nonequilibrium phase transformations of the Nb‐Au alloy system by ball milling

L. M. Di and H. Bakker

Appl. Phys. Lett. 62, 429 (1993); http://dx.doi.org/10.1063/1.108924 (3 pages)

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Various compositions of Nb‐Au alloys (intermetallic compounds and mixtures of intermetallic compounds) were subjected to heavy mechanical impact in a high‐energy ball mill for 40 h. Nb‐rich compounds transformed to the bcc solid solution of Au in Nb (down to about 60 at. % Nb), whereas compounds containing 50 at. % Nb or less transformed to the fcc solid solution of Nb in Au. Around 58 at. % of Nb a two‐phase bcc/fcc region was found.
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81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
64.70.K- Solid-solid transitions
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