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13 Dec 2004

Volume 85, Issue 24, pp. 5819-6053

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 5968 (2004); http://dx.doi.org/10.1063/1.1830083 (3 pages)

A. Urbieta, P. Fernández, and J. Piqueras
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Room-temperature operations of memory devices based on self-assembled InAs quantum dot structures

C. Balocco, A. M. Song, and M. Missous

Appl. Phys. Lett. 85, 5911 (2004); http://dx.doi.org/10.1063/1.1831558 (3 pages) | Cited 28 times

Online Publication Date: 9 December 2004

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Memory devices have been fabricated in high-electron-mobility transistors with embedded InAs quantum dots (QDs). We show that memory operations can be fully controlled by gate biases at room temperature, without the need for light excitations to erase memory states. Real-time measurements indicate a charge retention time of a few minutes. Neither such retention time nor the self-consistent simulations can justify the picture that the memory effect is due to charging/discharging of intrinsic QD states. Experiments at a series of gate biases point to the presence of deep levels coexisting in the QD layer(s), which are responsible for the memory effect.
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85.30.Tv Field effect devices
73.63.Kv Quantum dots
73.21.La Quantum dots
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Spin-polarized tunneling in room-temperature mesoscopic spin valves

S. O. Valenzuela and M. Tinkham

Appl. Phys. Lett. 85, 5914 (2004); http://dx.doi.org/10.1063/1.1830685 (3 pages) | Cited 47 times

Online Publication Date: 9 December 2004

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We study optimization of spin injection and detection both at 4.2 K and at room temperature using a metallic mesoscopic spin valve structure with tunneling interfaces between the ferromagnetic electrodes (CoFe or NiFe) and the central metallic conductor (Al). We investigate the influence of the barrier transparency on the spin polarization of the tunneling electrons by varying the O2 exposure of the Al film before depositing the ferromagnetic electrodes. An increase of the polarization from ∼10% to 16% (25% at 4.2 K) is observed as the resistance of the junction is increased from 100 to 700 Ωμm2. A spin transresistance as high as 2.5 Ω is obtained at 4.2 K.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.61.At Metal and metallic alloys
85.75.Mm Spin polarized resonant tunnel junctions
68.55.-a Thin film structure and morphology

Band alignment between (100)Si and complex rare earth∕transition metal oxides

V. V. Afanas’ev, A. Stesmans, C. Zhao, M. Caymax, T. Heeg, J. Schubert, Y. Jia, D. G. Schlom, and G. Lucovsky

Appl. Phys. Lett. 85, 5917 (2004); http://dx.doi.org/10.1063/1.1829781 (3 pages) | Cited 62 times

Online Publication Date: 9 December 2004

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The electron energy band alignment between (100)Si and several complex transition∕rare earth (RE) metal oxides (LaScO3, GdScO3, DyScO3, and LaAlO3, all in amorphous form) is determined using a combination of internal photoemission and photoconductivity measurements. The band gap width is nearly the same in all the oxides (5.6–5.7 eV) yielding the conduction and valence band offsets at the Si∕oxide interface of 2.0±0.1 and 2.5±0.1 eV, respectively. However, band-tail states are observed and these are associated with Jahn-Teller relaxation of transition metal and RE cations which splits their d* states.
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71.20.Ps Other inorganic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Ht Disordered structures
72.40.+w Photoconduction and photovoltaic effects

Mechanism for ohmic contact formation of Ni∕Ag contacts on p-type GaN

Ho Won Jang and Jong-Lam Lee

Appl. Phys. Lett. 85, 5920 (2004); http://dx.doi.org/10.1063/1.1835535 (3 pages) | Cited 33 times

Online Publication Date: 9 December 2004

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The mechanism for ohmic contact formation of Ni∕Ag contacts on p-type GaN was investigated using synchrotron photoemission spectroscopy. A low contact resistivity of 6.6×10−5 Ω cm2 was obtained from Ni(50 math)∕Ag(1200 math) contact after annealing at 500°C in O2 ambient. Ni out-diffused to form a NiO and Ag in-diffused into the contact interface during the oxidation annealing. Out-diffused Ga atoms from GaN could dissolve in the Ag layer to form Ag–Ga solid solutions, leaving Ga vacancies below the contact. Ga vacancies could increase the net hole concentration and reduce the surface band bending, resulting in the ohmic contact formation.
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73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Cg Contact resistance, contact potential
81.40.Gh Other heat and thermomechanical treatments
61.72.J- Point defects and defect clusters

ZnO nanowire field-effect transistor and oxygen sensing property

Zhiyong Fan, Dawei Wang, Pai-Chun Chang, Wei-Yu Tseng, and Jia G. Lu

Appl. Phys. Lett. 85, 5923 (2004); http://dx.doi.org/10.1063/1.1836870 (3 pages) | Cited 269 times

Online Publication Date: 9 December 2004

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Single-crystal ZnO nanowires are synthesized using a vapor trapping chemical vapor deposition method and configured as field-effect transistors. Electrical transport studies show n-type semiconducting behavior with a carrier concentration of ∼107 cm−1 and an electron mobility of ∼17 cm2∕V s. The contact Schottky barrier between the Au/Ni electrode and nanowire is determined from the temperature dependence of the conductance. Thermionic emission is found to dominate the transport mechanism. The effect of oxygen adsorption on electron transport through the nanowires is investigated. The sensitivity to oxygen is demonstrated to be higher with smaller radii nanowires. Moreover, the oxygen detection sensitivity can be modulated by the gate voltage. These results indicate that ZnO holds high potential for nanoscale sensing applications.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Dn Low-field transport and mobility; piezoresistance
79.40.+z Thermionic emission
73.30.+y Surface double layers, Schottky barriers, and work functions
68.43.Mn Adsorption kinetics
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

290 fs switching time of Fe-doped quantum well saturable absorbers in a microcavity in 1.55 μm range

M. Gicquel-Guézo, S. Loualiche, J. Even, C. Labbé, O. Dehaese, A. Le Corre, H. Folliot, and Y. Pellan

Appl. Phys. Lett. 85, 5926 (2004); http://dx.doi.org/10.1063/1.1804239 (3 pages) | Cited 10 times

Online Publication Date: 9 December 2004

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Ultrafast all-optical switch has been demonstrated by inserting Fe-doped multiple quantum wells (MQWs) in asymmetric Fabry-Perot microcavities. Heavy Fe doping during the InGaAs∕InP MQW epitaxial growth is a well-controlled technique to reach subpicosecond optical time constants. An asymmetric Fabry-Perot microcavity using gold metal as a back mirror and air/InP interface as a front mirror is realized. Pump-probe experiments using a conventional scheme on such switching devices are investigated. The device reveals an ultrafast response time, as low as 290 fs, for an iron concentration of 2×1019 cm−3, a contrast ratio of 8 dB, a threshold switching fluence of 3.5 μJ∕cm−2, and a 37-nm 3-dB bandwidth in the 1.55-μm telecommunication spectral range.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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