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18 Jun 2012

Volume 100, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 100, 252401 (2012); http://dx.doi.org/10.1063/1.4727909 (4 pages)

Ming Yan, Christian Andreas, Attila Kákay, Felipe García-Sánchez, and Riccardo Hertel
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Considerably long carrier lifetimes in high-quality 3C-SiC(111)

J. W. Sun (孙建武), I. G. Ivanov, R. Liljedahl, R. Yakimova, and M. Syväjärvi

Appl. Phys. Lett. 100, 252101 (2012); http://dx.doi.org/10.1063/1.4729583 (5 pages)

Online Publication Date: 18 June 2012

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As a challenge and consequence due to its metastable nature, cubic silicon carbide (3C-SiC) has only shown inferior material quality compared with the established hexagonal polytypes. We report on growth of 3C-SiC(111) having a state of the art semiconductor quality in the SiC polytype family. The x-ray diffraction and low temperature photoluminescence measurements show that the cubic structure can indeed reach a very high crystal quality. As an ultimate device property, this material demonstrates a measured carrier lifetime of 8.2 μs which is comparable with the best carrier lifetime in 4 H-SiC layers. In a 760-μm thick layer, we show that the interface recombination can be neglected since almost all excess carriers recombines before reaching the interface while the surface recombination significantly reduces the carrier lifetime. In fact, a comparison of experimental lifetimes with numerical simulations indicates that the real bulk lifetime in such high quality 3C-SiC is in the range of 10–15 μs.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
81.15.Kk Vapor phase epitaxy; growth from vapor phase
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Signatures of the semiconductor crystallographic orientation on the charge transport across non-epitaxial diodes

John J. Garramone, Joseph R. Abel, Salvador Barraza-Lopez, and Vincent P. LaBella

Appl. Phys. Lett. 100, 252102 (2012); http://dx.doi.org/10.1063/1.4729622 (4 pages) | Cited 1 time

Online Publication Date: 18 June 2012

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The hot electron attenuation length of Ag is measured utilizing ballistic electron emission microscopy on nanoscale Schottky diodes for Si(001) and Si(111) substrates. Marked differences in the attenuation length are observed at biases near the Schottky barrier depending upon the substrate orientation, increasing by an order of magnitude only for Si(001). These results provide clear evidence that the crystallographic orientation of the semiconductor substrate and parallel momentum conservation affect the charge transport across these interfaces. A theoretical model reproduces the effect that combines a free-electron description within the metal with an ab-initio description of the electronic structure of the semiconductor.
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85.30.Kk Junction diodes

Investigation of unusual mobile ion effects in thermally grown SiO2 on 4H-SiC(0001) at high temperatures

Atthawut Chanthaphan, Takuji Hosoi, Shuhei Mitani, Yuki Nakano, Takashi Nakamura, Takayoshi Shimura, and Heiji Watanabe

Appl. Phys. Lett. 100, 252103 (2012); http://dx.doi.org/10.1063/1.4729780 (4 pages) | Cited 3 times

Online Publication Date: 19 June 2012

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Generation and elimination of mobile ions in thermally grown SiO2 on 4H-SiC(0001) were systematically investigated by electrical measurements of MOS capacitors. In contrast to a SiO2/Si system, intrinsic positive mobile ions were found to exist in as-oxidized SiO2/SiC structures, leading to significant instability of SiC-MOS devices. Post-oxidation annealing in Ar ambient mostly eliminates the mobile ions, but they are generated again by subsequent high-temperature hydrogen annealing despite the improved interface quality. The density of the mobile ions was estimated to be several 1012 cm−2. Possible physical origins of the mobile ions are discussed on the basis of the experimental findings.
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84.32.Tt Capacitors

Enhanced thermoelectric properties by Ir doping of PtSb2 with pyrite structure

Yoshihiro Nishikubo, Seiya Nakano, Kazutaka Kudo, and Minoru Nohara

Appl. Phys. Lett. 100, 252104 (2012); http://dx.doi.org/10.1063/1.4729789 (3 pages) | Cited 2 times

Online Publication Date: 19 June 2012

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The effects of Ir doping on the thermoelectric properties of Pt1–xIrxSb2 (x = 0, 0.01, 0.03, and 0.1) with pyrite structure were studied. Measurements of electrical resistivity ρ, Seebeck coefficient S, and thermal conductivity κ were conducted. The results showed an abrupt change from semiconducting behavior without Ir (x = 0) to metallic behavior at x = 0.01. The sample with x = 0.01 exhibited large S and low ρ, resulting in a maximum power factor (S2/ρ) of 43 μW/cmK2 at 400 K. The peculiar “pudding mold”-type electronic band dispersion could explain the enhanced thermoelectric properties in the metallic state.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
61.72.up Other materials
61.66.Fn Inorganic compounds

Repeatable low-temperature negative-differential resistance from Al0.18Ga0.82N/GaN resonant tunneling diodes grown by molecular-beam epitaxy on free-standing GaN substrates

D. Li, L. Tang, C. Edmunds, J. Shao, G. Gardner, M. J. Manfra, and O. Malis

Appl. Phys. Lett. 100, 252105 (2012); http://dx.doi.org/10.1063/1.4729819 (4 pages) | Cited 1 time

Online Publication Date: 19 June 2012

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Low-aluminum composition AlGaN/GaN double-barrier resonant tunneling structures were grown by plasma-assisted molecular-beam-epitaxy on free-standing c-plane GaN substrates grown by hydride-vapor phase epitaxy. Clear, exactly reproducible, negative-differential resistance signatures were observed from 4 × 4 μm2 devices at 1.5 V and 1.7 V at 77 K. The relatively small value of the maximum peak-to-valley ratio (1.03) and the area dependence of the electrical characteristics suggest that charge transport is affected by leakage paths through dislocations. However, the reproducibility of the data indicates that electrical traps play no significant role in the charge transport in resonant tunneling diodes grown by molecular-beam-epitaxy under Ga-rich conditions on free-standing GaN substrates.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Kk Junction diodes

Fast electron transfer from PbSe quantum dots to TiO2

Yasuaki Masumoto, Hayato Takagi, Hikaru Umino, and Eri Suzumura

Appl. Phys. Lett. 100, 252106 (2012); http://dx.doi.org/10.1063/1.4729881 (3 pages) | Cited 2 times

Online Publication Date: 19 June 2012

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Fast electron transfer from PbSe quantum dots (QDs) to the porous anatase TiO2 film was observed in transient absorption and luminescence, when the lowest unoccupied molecular orbital level of PbSe QDs is higher than that of TiO2. In PbSe QDs 2.7 nm in diameter linked to the TiO2 film the bleaching recovery and the luminescence decay shortened to 1 ps and 4.2 ns from 650 ps and 1.3 μs observed in the non-linked PbSe QDs, respectively. The electron transfer from both the quantum state and the localized state in PbSe QDs to TiO2 takes place fast and efficiently.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
71.70.-d Level splitting and interactions
78.55.Mb Porous materials

High mobility two-dimensional hole system on hydrogen-terminated silicon (111) surfaces

Binhui Hu, Tomasz M. Kott, Robert N. McFarland, and B. E. Kane

Appl. Phys. Lett. 100, 252107 (2012); http://dx.doi.org/10.1063/1.4729584 (4 pages) | Cited 1 time

Online Publication Date: 19 June 2012

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We have realized a two-dimensional hole system (2DHS), in which the 2DHS is induced at an atomically flat hydrogen-terminated Si(111) surface by a negative gate voltage applied across a vacuum cavity. Hole densities up to 7.5 × 1011 cm−2 are obtained, and the peak hole mobility is about 104 cm2/Vs at 70 mK. The quantum Hall effect is observed. Shubnikov-de Haas oscillations show a beating pattern due to the spin-orbit effects, and the inferred zero-field spin splitting can be tuned by the gate voltage.
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73.43.-f Quantum Hall effects
73.61.Ng Insulators
72.20.My Galvanomagnetic and other magnetotransport effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Laser-assisted sol-gel growth and characteristics of ZnO thin films

Min Su Kim, Soaram Kim, and Jae-Young Leem

Appl. Phys. Lett. 100, 252108 (2012); http://dx.doi.org/10.1063/1.4729944 (3 pages) | Cited 1 time

Online Publication Date: 20 June 2012

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ZnO thin films were grown on Si(100) substrates by a sol-gel method assisted by laser beam irradiation with a 325 nm He-Cd laser. In contrast to conventional sol-gel ZnO thin films, the surface morphology of the laser-assisted sol-gel thin films was much smoother, and the residual stress in the films was relaxed by laser irradiation. The luminescent properties of the films were also enhanced by laser irradiation, especially, by irradiation during the deposition and post-heat treatment stages. The incident laser beam is thought to play several roles, such as annihilating defects by accelerating crystallization during heat treatment, enhancing the surface migration of atoms and molecules, and relaxing the ZnO matrix structure during crystallization.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.40.Gh Other heat and thermomechanical treatments
68.55.ag Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
81.05.Dz II-VI semiconductors

Electronic structure and linear magnetoresistance of the gapless topological insulator PtLuSb

Chandra Shekhar, Siham Ouardi, Gerhard H. Fecher, Ajaya Kumar Nayak, Claudia Felser, and Eiji Ikenaga

Appl. Phys. Lett. 100, 252109 (2012); http://dx.doi.org/10.1063/1.4730387 (4 pages) | Cited 9 times

Online Publication Date: 20 June 2012

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The present work reports on the experimental investigation of electronic structure and transport properties of the proposed topological insulator PtLuSb. The electronic structure was investigated by means of polarization dependent hard x-ray photoelectron spectroscopy. The valence band spectra exhibit a linear behavior close to the Fermi energy, as is typical for massless electrons. The transport properties are similar to that of a gapless semiconductor with low carrier concentration. This compound also exhibits an exceptionally high Hall mobility. At low temperatures, the magnetoresistance changes linearly with the applied magnetic field, whereas it exhibits a quadratic nature at high temperatures. A tentative relation between linear magnetoresistance and high mobility is discussed.
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71.20.Nr Semiconductor compounds
72.20.My Galvanomagnetic and other magnetotransport effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
72.80.Jc Other crystalline inorganic semiconductors

Determination of conduction band offset between strained CdSe and ZnSe layers using deep level transient spectroscopy

Victor-Tapio Rangel-Kuoppa

Appl. Phys. Lett. 100, 252110 (2012); http://dx.doi.org/10.1063/1.4729764 (4 pages)

Online Publication Date: 21 June 2012

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The conduction band offset between strained CdSe layers embedded in unintentionally n-type doped ZnSe is measured using deep level transient spectroscopy and reported. The activation energy for electrons in three monolayers thin ultra thin quantum wells (UTQWs) is obtained, with a value of 223 ± 10 meV. This corresponds to an UTQW barrier height (the conduction band offset) between 742 meV and 784 meV. These values show that the band gap misfit between strained CdSe and ZnSe is around 70% to 74% in the conduction band.
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71.20.Nr Semiconductor compounds
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.21.Fg Quantum wells
79.10.Ca Deep-level photothermal spectroscopy

Maxwell-Wagner polarization in Cu(In,Ga)(S,Se)2

U. Reislöhner and C. Ronning

Appl. Phys. Lett. 100, 252111 (2012); http://dx.doi.org/10.1063/1.4730379 (4 pages) | Cited 3 times

Online Publication Date: 22 June 2012

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We give experimental evidence of Maxwell-Wagner polarization within Cu(In,Ga)(S,Se)2 and CuInSe2, which is caused by inhomogeneity. The transport of charge carriers is quantitatively described by a percolation network of capacitive and resistive pathways, where the transmissibility of the latter depends on voltage and is strongly narrowed down with decreasing temperature. Additionally, we find that leakage currents through barrier layers with a linkage to inhomogeneous semiconductors may significantly convey a phase-shifted component that gives information on the interface. The finding of percolative charge transport strongly questions results of standard characterization methods, which assume regular charge transport in inhomogeneous semiconductors.
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77.22.Ej Polarization and depolarization
72.80.Jc Other crystalline inorganic semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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