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6 Jul 2009

Volume 95, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 95, 013107 (2009); http://dx.doi.org/10.1063/1.3167775 (3 pages)

T. Y. Tsai, C. Y. Lee, N. H. Tai, and W. H. Tuan
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Electron transport in electrospun TiO2 nanofiber dye-sensitized solar cells

Kunal Mukherjee, Tai-Hou Teng, Rajan Jose, and Seeram Ramakrishna

Appl. Phys. Lett. 95, 012101 (2009); http://dx.doi.org/10.1063/1.3167298 (3 pages) | Cited 33 times

Online Publication Date: 6 July 2009

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In this study dye-sensitized solar cells (DSCs) were fabricated using electrospun TiO2 nanofibers. Electrochemical impedance spectroscopy and open-circuit voltage decay were used to analyze electron transport in electrospun nanofibers and determine their applicability in DSCs. The polycrystalline nature and random web structure of the nanofibers exhibit effective electron diffusion coefficients close to that of high efficiency nanoparticle cells. The electron lifetime was, however, low due to the presence of a large number of surface traps despite the presence of a space-charge recombination barrier.
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84.60.Jt Photoelectric conversion
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.63.Bd Nanocrystalline materials
66.30.Pa Diffusion in nanoscale solids
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.16.-c Methods of micro- and nanofabrication and processing

Phase change behavior in oxygen-incorporated Ge2Sb2Te5 films

M. H. Jang, S. J. Park, D. H. Lim, M.-H. Cho, K. H. Do, D.-H. Ko, and H. C. Sohn

Appl. Phys. Lett. 95, 012102 (2009); http://dx.doi.org/10.1063/1.3168551 (3 pages) | Cited 6 times

Online Publication Date: 6 July 2009

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Oxygen-incorporated Ge2Sb2Te5 (GST) films were deposited using ion beam sputtering deposition. Sheet resistance in films with 16.7% oxygen content decreased at a higher annealing temperature than that of undoped GST films, while resistance in films with an oxygen content of over 21.7% decreased dramatically at lower temperatures. X-ray diffraction patterns showed crystallization to face-centered cubic phase was suppressed. However, phase separation to a hexagonal structure was observed in films with an oxygen content of over 21.7%. Extended x-ray absorption fine structure data of Ge K edge showed Ge was bonded to O as well as Te. Moreover, a stoichiometric GeO2 phase was not observed, while phase separation into Sb2O3 and Sb2Te3 occurred. The results indicate Ge–Te bonds with oxygen are related to structural stability.
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68.55.ag Semiconductors
73.61.Le Other inorganic semiconductors
64.75.St Phase separation and segregation in thin films
64.75.Qr Phase separation and segregation in semiconductors
78.70.Dm X-ray absorption spectra
81.15.Cd Deposition by sputtering

Current conduction of 0.72 nm equivalent-oxide-thickness LaO/HfO2 stacked gate dielectrics

Chuan-Hsi Liu, Hung-Wen Chen, Shung-Yuan Chen, Heng-Sheng Huang, and Li-Wei Cheng

Appl. Phys. Lett. 95, 012103 (2009); http://dx.doi.org/10.1063/1.3170235 (3 pages) | Cited 7 times

Online Publication Date: 7 July 2009

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Metal-oxide-semiconductor capacitors (MOSCs) incorporating atomic layer deposited (ALD) LaO/HfO2 stacked gate dielectrics were fabricated, where the equivalent oxide thickness (EOT) of the high-k dielectrics is only 0.72 nm and the gate leakage (Jg) is as low as 6.8×10−2 A/cm2. Based on the analysis of the temperature dependence of the gate leakage current from 300 to 500 K, the main current conduction is found to be Schottky emission or Poole–Frankel emission. Moreover, the barrier height (ΦB) at TaC and HfLaO interface is estimated to be about 1.21 eV, and the trap energy level (Φt) is about 0.51 eV.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Charging effect and capacitance modulation of Ni-rich NiO thin film

R. Ang, T. P. Chen, Z. Liu, J. I. Wong, M. D. Yi, M. Yang, Z. H. Cen, S. Zhu, W. Zhu, and E. S. M. Goh

Appl. Phys. Lett. 95, 012104 (2009); http://dx.doi.org/10.1063/1.3170353 (3 pages) | Cited 3 times

Online Publication Date: 7 July 2009

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In this letter, Ni-rich NiO thin film is deposited on p-type Si substrate by dc magnetron sputtering to form a metal-insulator-semiconductor structure. The charge trapping in the Ni nanocrystals (nc-Ni) embedded in NiO matrix induces a flatband voltage shift and capacitance modulation, which could be used for memory applications. The charging of nc-Ni depends on the voltage polarity, as well as the charging time and magnitude of gate voltage. The capacitance modulation can be described by an equivalent circuit model.
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73.63.-b Electronic transport in nanoscale materials and structures
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.15.Cd Deposition by sputtering
68.55.at Other materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Multiferroic oxides-based flash memory and spin-field-effect transistor

Chenglong Jia and Jamal Berakdar

Appl. Phys. Lett. 95, 012105 (2009); http://dx.doi.org/10.1063/1.3173203 (3 pages) | Cited 13 times

Online Publication Date: 7 July 2009

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We propose a modified spin-field-effect transistor fabricated in a two dimensional electron gas (2DEG) formed at the surface of multiferroic oxides with a transverse helical magnetic order. The topology of the oxide local magnetic moments induces a resonant momentum-dependent effective spin-orbit interaction acting on 2DEG. We show that spin polarization dephasing is strongly suppressed, which is crucial for functionality. The carrier spin precession phase depends linearly on the magnetic spiral helicity. The latter is electrically controllable by virtue of the magneto-electric effect. We also suggest a flash-memory device based on this structure.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits
85.50.Gk Non-volatile ferroelectric memories

A passivated codoping approach to tailor the band edges of TiO2 for efficient photocatalytic degradation of organic pollutants

Dan Wang, Yanhong Zou, Shuangchun Wen, and Dianyuan Fan

Appl. Phys. Lett. 95, 012106 (2009); http://dx.doi.org/10.1063/1.3174917 (3 pages) | Cited 10 times

Online Publication Date: 8 July 2009

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We propose an effective passivated codoping approach to tailor the band edges of TiO2 by doping the host with group IVA and group VIB impurities to passive donor-acceptor complexes. A way of achieving p-type TiO2 is found, which can outspread the application range of TiO2 semiconductor. It is demonstrated that the carbon (C)/tungsten (W) codoped TiO2 has a substantial increase in the valence band edge, while leaving the conduction band edge almost unchanged, thus improving the efficiency of photocatalytic degradation of organic pollutants. In principle, the suggested approach for overcoming the p-type doping bottleneck can be applied to other wide-band-gap semiconductors.
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71.20.Nr Semiconductor compounds
61.72.up Other materials
82.50.-m Photochemistry
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Abnormal magnetic-field dependence of Hall coefficient in InN epilayers

T. A. Komissarova, M. A. Shakhov, V. N. Jmerik, T. V. Shubina, R. V. Parfeniev, S. V. Ivanov, X. Wang, and A. Yoshikawa

Appl. Phys. Lett. 95, 012107 (2009); http://dx.doi.org/10.1063/1.3167823 (3 pages) | Cited 5 times

Online Publication Date: 9 July 2009

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We report on magnetic-field dependences of Hall coefficient and resistivity for InN films grown by plasma-assisted molecular beam epitaxy. The Hall coefficient rises with the magnetic field. This anomalous behavior is discussed in terms of the presence of highly conducting inhomogeneities in the films. According to the magnetic field and temperature dependences of the film resistivity, the inhomogeneities are attributed to metallic indium nanoparticles formed presumably around extended defects within the InN epilayers, at their surface and the InN/GaN interface. Good correlation is observed between the growth conditions of the InN films and their electrical properties recalculated using the model.
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73.61.Ey III-V semiconductors
68.55.ag Semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
72.20.My Galvanomagnetic and other magnetotransport effects
71.55.Eq III-V semiconductors
61.72.Nn Stacking faults and other planar or extended defects

Solution-processed InGaZnO-based thin film transistors for printed electronics applications

Jun Hyung Lim, Jong Hyun Shim, Jun Hyuk Choi, Jinho Joo, Kyung Park, Haseok Jeon, Mi Ran Moon, Donggeun Jung, Hyoungsub Kim, and Hoo-Jeong Lee

Appl. Phys. Lett. 95, 012108 (2009); http://dx.doi.org/10.1063/1.3157265 (3 pages) | Cited 26 times

Online Publication Date: 9 July 2009

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This letter reports the utility of using the sol-gel process for exploring the library of multicomponent ZnO-based oxides as an active layer of thin film transistors. We chose InGaZnO as a starting material and modulated the Ga content to examine the potential of this material. Increasing the Ga ratio from 0.1 to 1 brought about a dynamic shift in the electrical behavior from conductor to semiconductor. This exploratory work critically helped us fabricate a device with robust device performance (a mobility of 1 ∼ 2 cm2 V−1 s−1 for the 400 °C-sintered samples and 0.2 cm2 V−1 s−1 for the 300 °C-sintered samples).
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85.30.Tv Field effect devices
81.05.Dz II-VI semiconductors

Resistance switching in a single-crystalline NiO thin film grown on a Pt0.8Ir0.2 electrode

Masanori Kawai, Kimihiko Ito, and Yuichi Shimakawa

Appl. Phys. Lett. 95, 012109 (2009); http://dx.doi.org/10.1063/1.3179169 (3 pages) | Cited 8 times

Online Publication Date: 10 July 2009

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A single-crystalline NiO thin film was grown epitaxially on an atomically flat Pt0.8Ir0.2 bottom electrode layer grown epitaxially on a SrTiO3(100) substrate. The memory cells of the single-crystalline NiO thin film with Pt top electrodes showed unipolar resistance switching behaviors. The result demonstrates that a unipolar resistance switching is not a characteristic phenomenon in the polycrystalline NiO but it can also occur in the single-crystalline NiO.
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73.61.-r Electrical properties of specific thin films
68.55.A- Nucleation and growth

Inhomogeneous chemical states in resistance-switching devices with a planar-type Pt/CuO/Pt structure

R. Yasuhara, K. Fujiwara, K. Horiba, H. Kumigashira, M. Kotsugi, M. Oshima, and H. Takagi

Appl. Phys. Lett. 95, 012110 (2009); http://dx.doi.org/10.1063/1.3175720 (3 pages) | Cited 21 times

Online Publication Date: 10 July 2009

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The spatial distribution of chemical states in resistance-switching devices with a planar-type Pt/CuO/Pt structure has been studied by photoemission electron microscopy. It has been found that the change in resistance that occurs with the application of the first voltage is caused by the formation of a reduction path through the CuO channel between the Pt electrodes. A detailed analysis suggests that Joule-heat-assisted reduction induced by the current flowing through the device may play an important role in the formation of the conductive reduction path.
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84.30.Sk Pulse and digital circuits
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Sx Metal-semiconductor-metal structures

Interfacial structure of InAs/Ga1−xInxSb superlattices

Maohua Quan, Lihua Wang, Ke Wang, Fengyun Guo, Xiaodong Han, and Liancheng Zhao

Appl. Phys. Lett. 95, 012111 (2009); http://dx.doi.org/10.1063/1.3175722 (3 pages) | Cited 2 times

Online Publication Date: 10 July 2009

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The interfacial structure of InAs/Ga1−xInxSb superlattices is investigated by high-resolution transmission electron microscopy imaging. We have shown that high-resolution electron microscopy with quantitative image matching can enable the relative orientation of the closely separated atomic species in InAs and Ga1−xInxSb to be resolved. We have then used this capability to determine interfacial bonds. The shift in the atomic positions associated with this modulation may lead to distortions of the interfacial structure of Ga1−xInxAs-like. The misfit dislocations in InSb-like interface are the primary mechanism for accommodating the lattice mismatch.
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73.21.Cd Superlattices
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
71.20.Nr Semiconductor compounds

Observation of hole accumulation at the interface of an undoped InGaN/GaN heterostructure

D. J. Chen, J. J. Xue, B. Liu, H. Lu, Z. L. Xie, P. Han, R. Zhang, Y. D. Zheng, Y. C. Kong, and J. J. Zhou

Appl. Phys. Lett. 95, 012112 (2009); http://dx.doi.org/10.1063/1.3176443 (3 pages) | Cited 2 times

Online Publication Date: 10 July 2009

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A pronounced hump structure at about −5 V in the high-frequency capacitance-voltage (C-V) curve of an undoped InGaN/GaN heterostructure is observed and this hump weakens gradually with decreasing measurement frequency, indicating the occurrence of an inversion behavior in the InGaN/GaN heterostructure. The inversion behavior in the C-V curve is attributed to hole accumulation at the heterointerface where a hole well is formed due to the strong piezoelectric polarization effect in the InGaN/GaN heterostructure. The acceptor traps related to Ga vacancies in the InGaN layer are thought to be the source of the minority carriers. The theoretical calculation of band diagram of the InGaN/GaN heterostructure confirms the formation of the hole well at the heterointerface and supports the behavior of hole accumulation under negative bias voltage.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Mx High-frequency effects; plasma effects
61.72.jd Vacancies
77.65.-j Piezoelectricity and electromechanical effects

Dimensional crossover and weak localization in a 90 nm n-GaAs thin film

A. M. Gilbertson, A. K. M. Newaz, Woo-Jin Chang, R. Bashir, S. A. Solin, and L. F. Cohen

Appl. Phys. Lett. 95, 012113 (2009); http://dx.doi.org/10.1063/1.3176968 (3 pages) | Cited 1 time

Online Publication Date: 10 July 2009

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We report on the magnetotransport in a 90 nm thick n-type GaAs epitaxial thin film in the weak localization (WL) regime. Low temperature (T ≤ 50 K) magnetotransport data are fit with WL theory, from which the phase coherence time, τϕ∝T−p (p = 1.22±0.01), are extracted. We conclude that the dominant dephasing mechanism at these temperatures is electron-electron (e-e) scattering in the Nyquist limit. Evidence of a crossover from two-dimensional to three-dimensional behavior with respect to both coherent transport (WL) and e-e interactions is observed in the temperature dependence of the zero-field conductivity and τϕ, respectively.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey III-V semiconductors
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