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6 Apr 2009

Volume 94, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 94, 141901 (2009); http://dx.doi.org/10.1063/1.3111813 (3 pages)

G. S. Huang (黄高山), S. Kiravittaya, V. A. Bolaños Quiñones, F. Ding (丁飞), M. Benyoucef, A. Rastelli, Y. F. Mei (梅永丰), and O. G. Schmidt
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Spin splitting of upper electron subbands in a SiO2/Si(100)/SiO2 quantum well with in-plane magnetic field

Y. Niida, K. Takashina, A. Fujiwara, T. Fujisawa, and Y. Hirayama

Appl. Phys. Lett. 94, 142101 (2009); http://dx.doi.org/10.1063/1.3105987 (3 pages)

Online Publication Date: 6 April 2009

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We observe a lifting of the twofold spin degeneracy of conduction-band electrons in an upper-valley subband with in-plane magnetic field in a SiO2/Si(100)/SiO2 quantum well, which is manifest in a splitting of a feature in the conductivity accompanying the occupation of the upper-valley subband. The splitting increases in proportion to the in-plane magnetic field, allowing the product of the effective g-factor and effective mass g∗m∗ to be obtained. The value remains constant over wide ranges of valley splitting, total electron density, and potential bias.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds

Size-dependent impurity activation energy in GaN nanowires

J. Yoon, A. M. Girgis, I. Shalish, L. R. Ram-Mohan, and V. Narayanamurti

Appl. Phys. Lett. 94, 142102 (2009); http://dx.doi.org/10.1063/1.3115769 (3 pages) | Cited 12 times

Online Publication Date: 6 April 2009

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The effect of the surrounding dielectric on the conductivity of GaN nanowires is measured experimentally. The two following configurations are considered: bare suspended and SiO2-coated nanowires. The measured conductivity is consistently fitted by two exponential terms with different activation energies, indicating multichannel conduction. The larger energy, attributed to activation of impurities into the conduction subband, shows essentially inverse dependence on nanowire radius, consistent with the dielectric confinement effect. This agrees with calculated values from finite element analysis. The smaller energy is independent of the nanowire radius, suggesting a surface conduction channel.
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73.22.-f Electronic structure of nanoscale materials and related systems
71.20.Nr Semiconductor compounds

Anisotropy of In incorporation in GaN/InGaN multiquantum wells prepared by epitaxial lateral overgrowth

A. Y. Polyakov, A. V. Govorkov, N. B. Smirnov, A. V. Markov, In-Hwan Lee, Jin-Woo Ju, and S. J. Pearton

Appl. Phys. Lett. 94, 142103 (2009); http://dx.doi.org/10.1063/1.3115807 (3 pages) | Cited 5 times

Online Publication Date: 6 April 2009

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Microcathodoluminescence (MCL) spectra and monochromatic MCL images were measured for GaN/InGaN multiquantum well (MQW) structures prepared by epitaxial lateral overgrowth (ELOG). The MQW related peak is redshifted from 462 nm in the normally grown ELOG window region to 482 nm in the laterally overgrown ELOG wing region. Correspondingly, the former appears as dark contrast stripes for long wavelength MCL images and as bright stripes for the short wavelength MCL images. The redshift is consistent with a higher indium incorporation efficiency for growth in the [11math0] direction compared to the [0001] direction.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electrons and holes in a 40 nm thick silicon slab at cryogenic temperatures

K. Takashina, K. Nishiguchi, Y. Ono, A. Fujiwara, T. Fujisawa, Y. Hirayama, and K. Muraki

Appl. Phys. Lett. 94, 142104 (2009); http://dx.doi.org/10.1063/1.3112602 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2009

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We demonstrate low temperature operation of an electron-hole bilayer device based on a 40 nm thick layer of silicon in which electrons and holes can be simultaneously induced and contacted independently. The device allows the application of bias between the electrons and holes enhancing controllability over density and confining potential. We confirm that drag measurements are possible with the structure.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)

Temperature dependence of Ohmic contact characteristics in AlGaN/GaN high electron mobility transistors from −50 to 200 °C

Z. H. Liu, S. Arulkumaran, and G. I. Ng

Appl. Phys. Lett. 94, 142105 (2009); http://dx.doi.org/10.1063/1.3114422 (3 pages) | Cited 10 times

Online Publication Date: 8 April 2009

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The temperature dependent characteristics of Ti/Al/Ni/Au Ohmic contact for AlGaN/GaN high electron mobility transistors (HEMTs) on high-resistivity Si and sapphire substrates were investigated over the temperature range from −50 to 200 °C. The sheet resistances (Rsh) of AlGaN/GaN HEMTs on Si and sapphire substrates were found to increase with the temperature according to the power-law equation with power indices of −2.7 and −2.3, respectively. The specific contact resistivity (ρC) decreased with the temperature, and it was observed to be determined by the electron thermionic field emission (TFE) from the lowered conduction band edge in the modified AlGaN region with high-density N-vacancies to the quantum well at the AlGaN/GaN heterojunction with two dimensional electron gas (2DEG). Three important parameters in the TFE are extracted, that is, the barrier height (ϕB) of around 0.5 eV, the energy difference between the effective conductive-band edge and the Fermi level in 2DEG (En) of around 0.1 eV, and the 2DEG electron density (ND) with the order of magnitude of 1019 cm−3.
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73.40.Ns Metal-nonmetal contacts
85.30.Tv Field effect devices
79.70.+q Field emission, ionization, evaporation, and desorption
73.40.Cg Contact resistance, contact potential
73.21.Fg Quantum wells
79.40.+z Thermionic emission
61.72.jd Vacancies

Leakage current by Frenkel–Poole emission in Ni/Au Schottky contacts on Al0.83In0.17N/AlN/GaN heterostructures

Engin Arslan, Serkan Bütün, and Ekmel Ozbay

Appl. Phys. Lett. 94, 142106 (2009); http://dx.doi.org/10.1063/1.3115805 (3 pages) | Cited 26 times

Online Publication Date: 8 April 2009

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In order to determine the reverse-bias leakage current mechanisms in Schottky diodes on Al0.83In0.17N/AlN/GaN heterostructures, the temperature-dependent current-voltage measurements were performed in the temperature range of 250–375 K. In this temperature range, the leakage current was found to be in agreement with the predicted characteristics, which is based on the Frenkel–Poole emission model. The analysis of the reverse current-voltage characteristics dictates that the main process in leakage current flow is the emission of electrons from a trapped state near the metal-semiconductor interface into a continuum of states which associated with each conductive dislocation.
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73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.Ht High-field and nonlinear effects
73.40.Ns Metal-nonmetal contacts
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Low-voltage InGaZnO thin-film transistors with Al2O3 gate insulator grown by atomic layer deposition

J. B. Kim, C. Fuentes-Hernandez, W. J. Potscavage, Jr., X.-H. Zhang, and B. Kippelen

Appl. Phys. Lett. 94, 142107 (2009); http://dx.doi.org/10.1063/1.3118575 (3 pages) | Cited 23 times

Online Publication Date: 9 April 2009

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We report on low-voltage, high-performance amorphous indium gallium zinc oxide n-channel thin-film transistors fabricated using 100-nm-thick Al2O3 grown by atomic layer deposition as the gate dielectric layer. The Al2O3 gate dielectric shows very small current densities and has a capacitance density of 81±1 nF/cm2. Due to a very small contact resistance, transistors with channel lengths ranging from 100 μm down to 5 μm yield a channel-independent, field-effect mobility of 8±1 cm2/V s, subthreshold slopes of 0.1±0.01 V/decade, low threshold voltages of 0.4±0.1 V, and high on-off current ratios up to 6×107 (W/L = 400/5 μm) at 5 V.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors

Superconductivity in heavily compensated Mg-doped InN

E. Tiras, M. Gunes, N. Balkan, R. Airey, and W. J. Schaff

Appl. Phys. Lett. 94, 142108 (2009); http://dx.doi.org/10.1063/1.3116120 (3 pages) | Cited 1 time

Online Publication Date: 10 April 2009

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We report superconductivity in Mg-doped InN grown by molecular beam epitaxy. Superconductivity phase transition temperature occurs Tc = 3.97 K as determined by magnetoresistance and Hall resistance measurements. The two-dimensional (2D) carrier density of the measured sample is n2D = 9×1014 cm−2 corresponding to a three-dimensional (3D) electron density of n3D = 1.8×1019 cm−3 which is within the range of values between Mott transition and the superconductivity to metal transition. We propose a plausible mechanism to explain the existence of the superconductivity in terms of a uniform distribution of superconducting InN nanoparticles or nanosized indium dots forming microscopic Josephson junctions in the heavily compensated insulating bulk InN matrix.
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74.25.F- Transport properties
74.50.+r Tunneling phenomena; Josephson effects
74.78.Na Mesoscopic and nanoscale systems

Spin relaxation and dephasing mechanism in (Ga,Mn)As studied by time-resolved Kerr rotation

Yonggang Zhu, Xinhui Zhang, Tao Li, Lin Chen, Jun Lu, and Jianhua Zhao

Appl. Phys. Lett. 94, 142109 (2009); http://dx.doi.org/10.1063/1.3116716 (3 pages) | Cited 6 times

Online Publication Date: 10 April 2009

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Spin dynamics in (Ga,Mn)As films grown on GaAs(001) was investigated by Time-resolved magneto-optical Kerr effect. The Kerr signal decay time of (Ga,Mn)As without external magnetic field applied was found to be several hundreds picoseconds, which suggested that photogenerated polarized holes and magnetic ions are coupled as a ferromagnetic system. Nonmonotonic temperature dependence of relaxation and dephasing (R&D) time and Larmor frequency manifests that Bir–Aronov–Pikus mechanism dominates the spin R&D time at low temperature, while D’yakonov–Perel mechanism dominates the spin R&D time at high temperature, and the crossover between the two regimes is Curie temperature.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.20.Ls Magneto-optical effects
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
78.66.Fd III-V semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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