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4 Apr 2011

Volume 98, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 98, 141903 (2011); http://dx.doi.org/10.1063/1.3548546 (3 pages)

H. Hattab, A. T. N’Diaye, D. Wall, G. Jnawali, J. Coraux, C. Busse, R. van Gastel, B. Poelsema, T. Michely, F.-J. Meyer zu Heringdorf, and M. Horn-von Hoegen
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Giant mesoscopic photoconductance fluctuations in Ge/Si quantum dot system

N. P. Stepina, E. S. Koptev, A. V. Dvurechenskii, A. I. Nikiforov, J. Gerharz, J. Moers, and D. Gruetzmacher

Appl. Phys. Lett. 98, 142101 (2011); http://dx.doi.org/10.1063/1.3574022 (3 pages) | Cited 2 times

Online Publication Date: 4 April 2011

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We studied the impact of weak photon flux on the electron transport in strongly localized quantum dot system. Exploring devices with narrow transport channels lead to the observation of giant fluctuations of the photoconductance, which is attributed to the strong dependence of hopping current on the filling of dots by holes. This phenomenon has the potential to detect a single photoexcited carrier for a wide range of wavelength. In our experiments, single-photon mode operation is indicated by the linear dependence of the frequency of photoinduced fluctuations on the light intensity and the steplike response of conductance on the pulse excitation.
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72.40.+w Photoconduction and photovoltaic effects
72.20.-i Conductivity phenomena in semiconductors and insulators
72.20.Ee Mobility edges; hopping transport
73.50.Dn Low-field transport and mobility; piezoresistance
81.07.Ta Quantum dots

High-temperature thermoelectric properties of nanostructured Ca3Co4O9 thin films

Min-Gyu Kang, Kwang-Hwan Cho, Seung-Min Oh, Jin-Sang Kim, Chong-Yun Kang, Sahn Nahm, and Seok-Jin Yoon

Appl. Phys. Lett. 98, 142102 (2011); http://dx.doi.org/10.1063/1.3574530 (3 pages) | Cited 5 times

Online Publication Date: 4 April 2011

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We prepared nanostructured Ca3Co4O9 (CCO) thin films by promoting localized epitaxial growth on polycrystalline Al2O3 substrates. The thermoelectric properties of the CCO films were studied in the temperature range 300 to 1023 K. We confirmed that localized epitaxial growth occurred on the seed grains that dominate the (006) plane. The nanostructured CCO thin films were found to have a maximum Seebeck coefficient of 206 μV/K and a power factor (at 920 K) of 0.514 mW/mK2. Moreover, the presence of nanostructure was found to reduce the thermal conductivity, and thus, should enhance the overall performance of CCO films in thermoelectric devices.
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73.50.Lw Thermoelectric effects
81.15.Cd Deposition by sputtering
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.55.ag Semiconductors
73.61.Le Other inorganic semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization

Electronic structure of cation-codoped TiO2 for visible-light photocatalyst applications from hybrid density functional theory calculations

Run Long and Niall J. English

Appl. Phys. Lett. 98, 142103 (2011); http://dx.doi.org/10.1063/1.3574773 (3 pages) | Cited 3 times

Online Publication Date: 4 April 2011

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The electronic structures of Mg/Ca- and/or Mo/W- (mono- and co-) doped anatase TiO2 have been investigated via generalized Kohn–Sham theory with the Heyd–Scuseria–Ernzerhof hybrid functional for exchange-correlation { J. Heyd et al., [J. Chem. Phys. 118, 8207 (2003)] , J. Heyd et al., [J. Chem. Phys. 124, 219906 (2006)] , and J. Paier et al., [J. Chem. Phys. 125, 249901 (2006)] }, in the context of density functional theory. Gap narrowing is small for monodoping, which also creates impuritiy bands in the “forbidden gap,” either as acceptor or donor states, limiting possible utility as visible-light photocatalysts. However, codoping of Mg/Ca and Mo/W not only induces appreciable gap narrowing, but also serves to passivate the impurity bands, which can harvest visible-light to a greater extent. Considering ionic radii, Mg and Mo should constitute the best cation-pair.
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71.20.Nr Semiconductor compounds
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.Hp Processes caused by visible and UV light
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.40.Fy Semiconductors
61.72.up Other materials

Si/SiGe quantum dot with superconducting single-electron transistor charge sensor

Mingyun Yuan, Feng Pan, Zhen Yang, T. J. Gilheart, Fei Chen, D. E. Savage, M. G. Lagally, M. A. Eriksson, and A. J. Rimberg

Appl. Phys. Lett. 98, 142104 (2011); http://dx.doi.org/10.1063/1.3572033 (3 pages) | Cited 3 times

Online Publication Date: 4 April 2011

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We report a robust process for fabrication of surface-gated Si/SiGe quantum dots (QDs) with an integrated superconducting single-electron transistor (SSET) charge sensor. A combination of a deep mesa etch and AlOx backfill is used to reduce gate leakage. After the leakage current is suppressed, Coulomb oscillations of the QD and the current-voltage characteristics of the SSET are observed at a temperature of 0.3 K. Coupling of the SSET to the QD is confirmed by using the SSET to perform sensing of the QD charge state.
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81.07.Ta Quantum dots
85.35.Gv Single electron devices

Heteromaterial gate tunnel field effect transistor with lateral energy band profile modulation

Ning Cui, Renrong Liang, and Jun Xu

Appl. Phys. Lett. 98, 142105 (2011); http://dx.doi.org/10.1063/1.3574363 (3 pages) | Cited 2 times

Online Publication Date: 5 April 2011

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A tunnel field effect transistor (TFET) device with a heteromaterial gate structure was introduced, and the influence of the lateral energy band profile modulation effect on the performance of TFET devices has been investigated. The two-dimensional numerical simulations demonstrated that a local minimum of the conduction band in the channel was formed by work function mismatch, which resulted in the abrupt transition between the on- and off-states and significant drive current enhancement. In particular, these unique features could be manipulated by engineering the heteromaterial and the gate length. This work reveals an effective method to improve the performance of nanoscale TFETs.
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85.30.Tv Field effect devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Correlation of thermoelectric and microstructural properties of p-type CeFe4Sb12 melt-spun ribbons using a rapid screening method

Y. G. Yan, W. Wong-Ng, J. A. Kaduk, G. J. Tan, W. J. Xie, and X. F. Tang

Appl. Phys. Lett. 98, 142106 (2011); http://dx.doi.org/10.1063/1.3570690 (3 pages) | Cited 1 time

Online Publication Date: 6 April 2011

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We have demonstrated the effect of gradients in phase composition and microstructure of p-type CeFe4Sb12 melt-spun ribbons on Seebeck coefficient by using a thermoelectric (TE) screening tool in conjunction with x-ray diffraction. The spatial Seebeck coefficient variation was found to correlate with the changes in the phase composition and microstructure. The observed gradient was the result of a postannealing effect caused by the thermal lag between the contact surface with the roller and the free surface. Our results illustrate the application of our screening tool to the three-dimensional variation in Seebeck coefficient in a model TE material.
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72.15.Jf Thermoelectric and thermomagnetic effects
81.40.Gh Other heat and thermomechanical treatments
81.20.-n Methods of materials synthesis and materials processing

Direct determination of the band alignment at the (Zn,Mg)O/CISSe interface

F. Erfurth, A. Grimm, J. Palm, T. P. Niesen, F. Reinert, L. Weinhardt, and E. Umbach

Appl. Phys. Lett. 98, 142107 (2011); http://dx.doi.org/10.1063/1.3565972 (3 pages) | Cited 1 time

Online Publication Date: 6 April 2011

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The electronic and chemical properties of the (Zn1−x,Mgx)O/CuIn(S,Se)2 interface, prepared by sputtering of thin (Zn,Mg)O layers, were investigated with direct and inverse photoelectron spectroscopy on in situ prepared samples. With the combination of both techniques we have determined the band alignment at this interface as a function of Mg-content in the range 0 ≤ x ≤ 0.30. We find that the band alignment at the interface can be tailored between a “cliff” (downward step) in the conduction band for pure ZnO and a “spike” (upward step) for high Mg-contents. A direct influence of the band alignment modifications on the solar cell parameters is found.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Cd Deposition by sputtering
79.60.Jv Interfaces; heterostructures; nanostructures

Ohmic contact between ZnO and Pt by InSb layer in a ZnO Schottky diode

Seung Hyun Jee, Nitul Kakati, Seok Hee Lee, Hyon Hee Yoon, and Young Soo Yoon

Appl. Phys. Lett. 98, 142108 (2011); http://dx.doi.org/10.1063/1.3574933 (3 pages) | Cited 1 time

Online Publication Date: 6 April 2011

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The surface of the ZnO thin films was modified by a thin InSb layer by using a thermal evaporator to increase the work function without altering the physical properties of the film. We expected that the InSb thin layer with a high work function could achieve the Ohmic contact between the ZnO and Pt electrodes by reducing an energy barrier due to increase in the ZnO thin film. The Ohmic contact was achieved in the interface between the ZnO and Pt electrodes by the InSb thin layer.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices

Resistively detected nuclear magnetic resonance via a single InSb two-dimensional electron gas at high temperature

K. F. Yang, H. W. Liu, K. Nagase, T. D. Mishima, M. B. Santos, and Y. Hirayama

Appl. Phys. Lett. 98, 142109 (2011); http://dx.doi.org/10.1063/1.3579257 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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We report on the demonstration of the resistively detected nuclear magnetic resonance (RDNMR) of a single InSb two-dimensional electron gas (2DEG) at elevated temperatures up to 4 K. The RDNMR signal of 115In in the simplest pseudospin quantum Hall ferromagnet triggered by a large direct current shows a peak-dip line shape, where the nuclear relaxation time T1 at the peak and the dip is different but almost temperature independent. The large Zeeman, cyclotron, and exchange energy scales of the InSb 2DEG contribute to the persistence of the RDNMR signal at high temperatures.
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76.60.Es Relaxation effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.43.-f Quantum Hall effects
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions

Magnetotransport properties of (In,Zn)As/InAs p-n junctions

K. H. Gao, Q. W. Wang, G. Yu, T. Lin, H. Y. Deng, N. Dai, and J. H. Chu

Appl. Phys. Lett. 98, 142110 (2011); http://dx.doi.org/10.1063/1.3576922 (3 pages)

Online Publication Date: 7 April 2011

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We study the magnetotransport properties of nonmagnetic (In,Zn)As/InAs p-n junctions prepared by liquid phase epitaxy. The junctions show a clear rectifying behavior. A relatively large positive magnetoresistance is observed and its maximum value is greater than 140% at 12 K and gets to 38% at 292 K when a small magnetic field of 1.38 T is applied, which is not related to the series resistance. We attribute the observed magnetoresistance to the impurity-assisted tunneling mechanism.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification
81.05.Ea III-V semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
72.20.My Galvanomagnetic and other magnetotransport effects

Band gap shift in Al1−xInxN/AlN/GaN heterostructures studied by surface photovoltage spectroscopy

Daniela Cavalcoli, Saurabh Pandey, Beatrice Fraboni, and Anna Cavallini

Appl. Phys. Lett. 98, 142111 (2011); http://dx.doi.org/10.1063/1.3576938 (3 pages) | Cited 6 times

Online Publication Date: 7 April 2011

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GaN based heterostructures have recently gained increased interest due to their applications for high electron mobility transistors. In this letter AlInN/AlN/GaN heterojunctions grown by metal-organic chemical-vapor deposition with different AlN thicknesses have been investigated by surface photovoltage spectroscopy. The density of the two-dimensional electron gas (2DEG) forming at the interface has been measured by Hall effect. A band gap shift has been detected and its dependence on the 2DEG electron density at the AlN/GaN interface has been analyzed on the basis of the Moss–Burstein and renormalization effects.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
73.21.Cd Superlattices
72.40.+w Photoconduction and photovoltaic effects

Effects of hydrostatic pressure on the electrical properties of hexagonal Ge2Sb2Te5: Experimental and theoretical approaches

B. Xu, Y. Su, Z. G. Liu, C. H. Zhang, Y. D. Xia, J. Yin, Z. Xu, W. C. Ren, and Y. H. Xiang

Appl. Phys. Lett. 98, 142112 (2011); http://dx.doi.org/10.1063/1.3577606 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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A combination of experiments and first-principles method calculations has been applied to investigate the influence of the hydrostatic pressure on the electrical properties of the phase-change material hexagonal Ge2Sb2Te5 (h-GST). Experimentally, it is found that the resistance of h-GST declines monotonically with increasing hydrostatic pressure up to 0.7 GPa. Theoretically, the band-structure calculations revealed that the electronic band gap also decreases with the pressure. The hydrostatic pressure increases the conductivity of h-GST by reducing the electronic band gap. The dEg/dP obtained from theoretical calculations and the d ln ρ/dP by experimental result are in the same order of magnitude.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ng Disordered solids
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
62.50.-p High-pressure effects in solids and liquids

Atomic layer deposition ZnO:N flexible thin film transistors and the effects of bending on device properties

Jae-Min Kim, Taewook Nam, S. J. Lim, Y. G. Seol, N.-E. Lee, Doyoung Kim, and Hyungjun Kim

Appl. Phys. Lett. 98, 142113 (2011); http://dx.doi.org/10.1063/1.3577607 (3 pages) | Cited 5 times

Online Publication Date: 7 April 2011

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ZnO:N flexible thin film transistors were fabricated by atomic layer deposition on polyethylene naphthalate substrates and the effects of bending on the device properties investigated. The threshold voltage and saturation mobility were observed to change with respect to the amount of substrate bending. These modulations can be explained in terms of piezoelectric nature of in ZnO. In comparison with the previously reported single crystal nanowires ZnO field effect transistors, the amount of the electrical property modulation under bent condition is significantly reduced and our report shows a much improved stability for ZnO:N as a flexible device material.
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85.30.Tv Field effect devices

Quasi one-dimensional transport in single GaAs/AlGaAs core-shell nanowires

D. Lucot, F. Jabeen, J.-C. Harmand, G. Patriarche, R. Giraud, G. Faini, and D. Mailly

Appl. Phys. Lett. 98, 142114 (2011); http://dx.doi.org/10.1063/1.3574026 (3 pages) | Cited 10 times

Online Publication Date: 7 April 2011

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We present an original approach to fabricate single GaAs/AlGaAs core-shell nanowire with robust and reproducible transport properties. The core-shell structure is buried in an insulating GaAs overlayer and connected as grown in a two-probe setup using the highly doped growth substrate and a top diffused contact. The measured conductance shows a non-Ohmic behavior with temperature and voltage-bias dependences following power laws, as expected for a quasi one- dimensional system.
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81.07.Gf Nanowires
81.05.Ea III-V semiconductors
81.07.Vb Quantum wires
81.16.Nd Micro- and nanolithography
73.63.Nm Quantum wires

Ballistic transport and electrical spin signal enhancement in a nanoscale three-terminal spintronic device

Lei Zhu and Edward T. Yu

Appl. Phys. Lett. 98, 142115 (2011); http://dx.doi.org/10.1063/1.3567922 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2011

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Ballistic electron transport at nanoscale dimensions is investigated and exploited in a nanoscale three-terminal, all-electrical spintronic semiconductor device. Charge current cancellation under appropriate device biasing yields a large, spin-dependent current signal even with modest spin injection efficiency into the semiconductor, while reliance on ballistic, rather than diffusive, carrier transport is expected to enable robust scalability to smaller dimensions. Magnetocurrent in excess of 200% is measured with spin injection efficiency of 5%, and a spin-dependent ballistic carrier transport model is shown to yield accurate, quantitative predictions of current-voltage behavior.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.30.De Semiconductor-device characterization, design, and modeling
85.35.-p Nanoelectronic devices

Atomically resolved silicon donor states of β-Ga2O3

K. Iwaya, R. Shimizu, H. Aida, T. Hashizume, and T. Hitosugi

Appl. Phys. Lett. 98, 142116 (2011); http://dx.doi.org/10.1063/1.3578195 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2011

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The electronic states of silicon donors in a wide gap semiconductor, β-Ga2O3(100), have been studied using low-temperature scanning tunneling microscopy. We observe one-dimensional rows along [010], as expected from the crystal structure. In addition, substitutional Si donors are identified up to the fourth subsurface layer with clear spectroscopic features at the bottom of the conduction band. The decay length of each subsurface Si donor is systematically measured, and reasonably agrees with a picture of the Si donor in bulk β-Ga2O3. These results strongly suggest that Si impurities are shallow donors and responsible for the high electrical conductivity of β-Ga2O3.
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71.55.Ht Other nonmetals
72.80.Jc Other crystalline inorganic semiconductors
73.20.At Surface states, band structure, electron density of states
61.66.Fn Inorganic compounds
72.20.Fr Low-field transport and mobility; piezoresistance

Al0.44Ga0.56N spacer layer to prevent electron accumulation inside barriers in lattice-matched InAlN/AlGaN/AlN/GaN heterostructures

M. Akazawa, B. Gao, T. Hashizume, M. Hiroki, S. Yamahata, and N. Shigekawa

Appl. Phys. Lett. 98, 142117 (2011); http://dx.doi.org/10.1063/1.3578449 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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The barrier structure in lattice-matched InAlN/GaN heterostructures with AlGaN-based spacer layers grown by metal organic vapor phase epitaxy was studied by the capacitance-voltage (C-V) method. To investigate the characteristics under positive bias, an Al2O3 overlayer was added. The C-V characteristic of a sample with an Al0.38Ga0.62N (5 nm)/AlN (0.75 nm) double spacer layer exhibited an anomalous saturation at a value far below the insulator capacitance under positive bias, which indicated electron accumulation at the InAlN/AlGaN interface. The C-V characteristic of an alternative sample with a single Al0.44Ga0.56N (1.5 nm) spacer layer did not exhibit the anomalous saturation.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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