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11 Aug 2003

Volume 83, Issue 6, pp. 1063-1275

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Appl. Phys. Lett. 83, 1163 (2003); http://dx.doi.org/10.1063/1.1599972 (3 pages)

M. C. Rogge, C. Fühner, U. F. Keyser, R. J. Haug, M. Bichler, G. Abstreiter, and W. Wegscheider
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Formation of vanadium-based ohmic contacts to n-GaN

June O Song, Sang-Ho Kim, Joon Seop Kwak, and Tae-Yeon Seong

Appl. Phys. Lett. 83, 1154 (2003); http://dx.doi.org/10.1063/1.1598284 (3 pages) | Cited 16 times

Online Publication Date: 5 August 2003

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We investigate vanadium (V)-based ohmic contacts on n-GaN (Nd = 2.0×1018 cm−3) as a function of annealing temperature. It is shown that the V (60 nm) contacts become ohmic with specific contact resistances of 10−3–10−4 Ω cm2 upon annealing at 650 and 850 °C. The V (20 nm)/Ti (60 nm)/Au (20 nm) contacts produce very low specific contact resistances of 2.2×10−5 and 4.0×10−6 Ω cm2 when annealed at 650 and 850 °C, respectively. A comparison shows that the use of the overlayers (Ti/Au) is very effective in improving ohmic property. Based on Auger electron spectroscopy and glancing-angle x-ray diffraction results, possible explanations for the annealing temperature dependence of the ohmic behavior of the V-based contacts are described and discussed. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.61.Ey III-V semiconductors
73.40.Cg Contact resistance, contact potential
79.20.Fv Electron impact: Auger emission

Determination of free carrier bipolar diffusion coefficient and surface recombination velocity of undoped GaN epilayers

R. Aleksiejūnas, M. Sūdžius, T. Malinauskas, J. Vaitkus, K. Jarašiūnas, and S. Sakai

Appl. Phys. Lett. 83, 1157 (2003); http://dx.doi.org/10.1063/1.1599036 (3 pages) | Cited 24 times

Online Publication Date: 5 August 2003

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Time-resolved nondegenerate four-wave mixing experiments were performed on 2.6-μm-thick GaN epilayers grown by metalorganic chemical-vapor deposition using picosecond pulses at 355 and 1064 nm for grating recording and probing, respectively. Measurements of free carrier grating kinetics at various grating periods Λ in range from 3 to 10 μm allowed determination of nonequilibrium carrier bipolar diffusion coefficient D = 1.7 cm2/s at 300 K. Substitution of the D value into two-dimensional carrier transport model allowed fitting of the whole set of grating kinetics at various Λ varying surface recombination velocity S and linear recombination time τR. This procedure provided us a value of S = 5×104 cm/s as well as carrier lifetime of ∼1 ns. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena

Enhanced room-temperature piezoconductance of metal–semiconductor hybrid structures

A. C. H. Rowe, D. R. Hines, and S. A. Solin

Appl. Phys. Lett. 83, 1160 (2003); http://dx.doi.org/10.1063/1.1600840 (3 pages) | Cited 13 times

Online Publication Date: 5 August 2003

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Metal–semiconductor hybrids (MSHs) are found to exhibit enhanced room-temperature piezoconductance in the presence of uniaxial tensile strain. The magnitude of the enhanced piezoconductance is more than five times greater than that of the homogeneous semiconductor alone and is strongly dependent on both the location and properties of the metal–semiconductor interface. MSHs may be useful in determining the electrical properties of low-resistance metal contacts on semiconductors. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Combined atomic force microscope and electron-beam lithography used for the fabrication of variable-coupling quantum dots

M. C. Rogge, C. Fühner, U. F. Keyser, R. J. Haug, M. Bichler, G. Abstreiter, and W. Wegscheider

Appl. Phys. Lett. 83, 1163 (2003); http://dx.doi.org/10.1063/1.1599972 (3 pages) | Cited 2 times

Online Publication Date: 5 August 2003

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We have combined direct nanofabrication by local anodic oxidation with conventional electron-beam lithography to produce a parallel double quantum dot based on a GaAs/AlGaAs heterostructure. The combination of both nanolithography methods allows fabrication of robust in-plane gates and Cr/Au top-gate electrodes on the same device for optimal controllability. This is illustrated by the tunability of the interdot coupling in our device. We describe our fabrication and alignment scheme in detail and demonstrate the tunability in low-temperature transport measurements. © 2003 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
81.16.Ta Atom manipulation
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.47.Fg Semiconductor surfaces
68.65.Hb Quantum dots (patterned in quantum wells)
85.40.Hp Lithography, masks and pattern transfer
81.65.Mq Oxidation

Isoelectronic doping of AlGaN alloys with As and estimates of AlGaN/GaN band offsets

C. T. Foxon, S. V. Novikov, L. X. Zhao, and I. Harrison

Appl. Phys. Lett. 83, 1166 (2003); http://dx.doi.org/10.1063/1.1599635 (3 pages) | Cited 7 times

Online Publication Date: 5 August 2003

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The isoelectronic doping of AlxGa1−xN alloys with arsenic in films grown by molecular-beam epitaxy has been investigated. In photoluminescence spectra of AlxGa1−xN layers, with an increase in Al mole faction, there is a progressive shift of the position of the blue band emission towards higher energies. The observed energy shift for blue band emission is less than the corresponding increase in the band gap of AlxGa1−xN. A model is presented, which can explain the observed shift in the energy of the blue band emission. This model also allows the AlxGa1−xN/GaN valence band offset to be estimated. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Composition dependence of polarization fields in GaInN/GaN quantum wells

A. Hangleiter, F. Hitzel, S. Lahmann, and U. Rossow

Appl. Phys. Lett. 83, 1169 (2003); http://dx.doi.org/10.1063/1.1601310 (3 pages) | Cited 37 times

Online Publication Date: 5 August 2003

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We report an experimental determination of the internal polarization field in GaInN/GaN quantum wells, due to piezoelectric and spontaneous polarization, utilizing the quantum confined Stark effect, with fields as large as 3.1 MV/cm at 22% In. From its dependence on quantum well composition and strain, we find that the total field in GaInN is a linear combination of polarization charges from GaN and InN. The piezoelectric constants d31 for GaN and InN derived from our data are 1.05±0.05 pm/V and 3.7±0.5 pm/V, in fair agreement with theoretical data. © 2003 American Institute of Physics.
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73.21.Fg Quantum wells
77.22.Ej Polarization and depolarization
77.65.Bn Piezoelectric and electrostrictive constants
78.67.De Quantum wells
78.20.Jq Electro-optical effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
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