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31 Mar 2008

Volume 92, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 92, 133501 (2008); http://dx.doi.org/10.1063/1.2901684 (3 pages)

Eric Akmansoy, Emmanuel Centeno, Kevin Vynck, David Cassagne, and Jean-Michel Lourtioz
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Temperature dependence of the phase-coherence length in InN nanowires

Ch. Blömers, Th. Schäpers, T. Richter, R. Calarco, H. Lüth, and M. Marso

Appl. Phys. Lett. 92, 132101 (2008); http://dx.doi.org/10.1063/1.2905268 (3 pages) | Cited 11 times

Online Publication Date: 31 March 2008

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We report on low-temperature magnetotransport measurements on InN nanowires, grown by plasma-assisted molecular beam epitaxy. The characteristic fluctuation pattern observed in the conductance was employed to obtain information on phase-coherent transport. By analyzing the root mean square and the correlation field of the conductance fluctuations at various temperatures, the phase-coherence length was determined.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.63.Nm Quantum wires

On the identity of a crucial defect contributing to leakage current in silicon particle detectors

J. H. Bleka, L. Murin, E. V. Monakhov, B. S. Avset, and B. G. Svensson

Appl. Phys. Lett. 92, 132102 (2008); http://dx.doi.org/10.1063/1.2896313 (3 pages) | Cited 5 times

Online Publication Date: 31 March 2008

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The annealing kinetics of the so-called E4/E5 center or E4a/E4b center in electron-irradiated Si particle detectors has been studied at four different temperatures from 23 to 65 °C using deep-level transient spectroscopy (DLTS). The center gives rise to two energy levels at 0.37 and 0.45 eV below the conduction-band edge, and the annealing process is found to be of dissociative nature with an energy barrier of 1.1–1.2 eV. A striking similarity of the annealing rates (and kinetics) is revealed with that obtained for the 936-cm−1 infrared absorption band, studied by Fourier-transform infrared spectroscopy using identical type of Si material as in the DLTS study but irradiated with neutrons. The result strongly suggest that the E4/E5 levels and the 936-cm−1 band originate from the same defect, and the latter has been attributed to a di-interstitial-oxygen (I2O) complex. The E4/E5 center plays a crucial role for the detrimental leakage current in irradiated Si particle detectors, and an assignment of E4/E5 to I2O implies that oxygen-lean Si material (<1014 cm−3) should be advantageous to enhance detector performance.
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61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters

Correlation between microstructure, electronic properties and flicker noise in organic thin film transistors

Oana D. Jurchescu, Behrang H. Hamadani, Hao D. Xiong, Sungkyu K. Park, Sankar Subramanian, Neil M. Zimmerman, John E. Anthony, Thomas N. Jackson, and David J. Gundlach

Appl. Phys. Lett. 92, 132103 (2008); http://dx.doi.org/10.1063/1.2903508 (3 pages) | Cited 21 times

Online Publication Date: 31 March 2008

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We report on observations of a correlation between the microstructure of organic thin films and their electronic properties when incorporated in field-effect transistors. We present a simple method to induce enhanced grain growth in solution-processed thin film transistors by chemical modification of the source-drain contacts. This leads to improved device performance and gives a unique thin film microstructure for fundamental studies concerning the effect of structural order on the charge transport. We demonstrate that the 1/f flicker noise is sensitive to organic semiconductor thin film microstructure changes in the transistor channel.
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85.30.Tv Field effect devices

Analysis of electronic memory traps in the oxide-nitride-oxide structure of a polysilicon-oxide-nitride-oxide-semiconductor flash memory

Y. J. Seo, K. C. Kim, T. G. Kim, Y. M. Sung, H. Y. Cho, M. S. Joo, and S. H. Pyi

Appl. Phys. Lett. 92, 132104 (2008); http://dx.doi.org/10.1063/1.2830000 (3 pages) | Cited 12 times

Online Publication Date: 31 March 2008

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The origin of the electron memory trap in an oxide-nitride-oxide structure deposited on n-type Si is investigated by both capacitance-voltage and deep level transient spectroscopy (DLTS). Two electron traps are observed near 0.27 and 0.54 eV, below the conduction band minimum of Si and are identified as the nitride bulk trap and the Si–SiO2 interfacial trap, respectively. The trap depth, viz., vertical distribution of the electron trap, in both nitride bulk and Si–SiO2 interface, are also estimated from the bias voltage dependent DLTS.
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84.30.Sk Pulse and digital circuits

Enhancement of upconversion luminescence of Er doped Al2O3 films by Ag island films

Takeho Aisaka, Minoru Fujii, and Shinji Hayashi

Appl. Phys. Lett. 92, 132105 (2008); http://dx.doi.org/10.1063/1.2896303 (3 pages) | Cited 32 times

Online Publication Date: 1 April 2008

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Strong enhancement of upconversion photoluminescence (PL) of Er3+ in the visible range was achieved by placing it near rough Ag island films. In order to understand the mechanism of the enhancement, PL was excited by 978 and 488 nm light and the enhancement factors were obtained in a wide spectral range (520 nm to 1.6 μm). The emission and excitation wavelength dependence of the enhancement factors revealed that both the incident electric fields and the radiative decay rate of Er3+ are enhanced due to the excitation of surface plasmons supported by Ag islands. It was found that the upconversion PL is more sensitive to the enhancement of the incident electric field than the downconversion PL because of the multiphoton absorption process. The present result indicates that the upconversion PL obtains more benefit from the metal-enhanced fluorescence technique than the downconversion PL.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics

Determination of spin polarization in InAs/GaAs self-assembled quantum dots

F. G. G. Hernandez, T. P. Mayer Alegre, and G. Medeiros-Ribeiro

Appl. Phys. Lett. 92, 132106 (2008); http://dx.doi.org/10.1063/1.2905809 (3 pages) | Cited 2 times

Online Publication Date: 1 April 2008

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The spin polarization of electrons trapped in InAs self-assembled quantum dot ensembles is investigated. A statistical approach for the population of the spin levels allows one to infer the spin polarization from the measured values of the addition energies. From the magnetocapacitance spectroscopy data, the authors found a fully polarized ensemble of electronic spins above 10 T when B∥[001] and at 2.8 K. Finally, by including the g-tensor anisotropy, the angular dependence of the spin polarization with the magnetic field B orientation and strength could be determined.
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72.25.-b Spin polarized transport
73.21.La Quantum dots
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
75.30.Gw Magnetic anisotropy

High quality anatase TiO2 film: Field-effect transistor based on anatase TiO2

Masao Katayama, Shinya Ikesaka, Jun Kuwano, Hideomi Koinuma, and Yuji Matsumoto

Appl. Phys. Lett. 92, 132107 (2008); http://dx.doi.org/10.1063/1.2906361 (3 pages) | Cited 12 times

Online Publication Date: 2 April 2008

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We proposed an oxygen modulation method for the growth of high crystalline and insulative anatase films. The cycle of deposition under low oxygen pressure and annealing under high oxygen pressure was repeated every 1 nm thick growth. The sharp reflection high-energy electron diffraction pattern and step-and-terrace surface morphology confirmed high crystallinity of the obtained anatase film; the resistivity reached as high as 1.8 MΩ cm. As a result, the present anatase film exhibited high performance in a field-effect transistor as an active channel. On-to-off current ratio and field-effect mobility exceeded 105 and 0.3 cm2/V s, respectively.
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68.55.ag Semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.35.bg Semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Le Other inorganic semiconductors
85.30.Tv Field effect devices

Hole mobility in Mg-doped p-type InN films

Xinqiang Wang, Song-Bek Che, Yoshihiro Ishitani, and Akihiko Yoshikawa

Appl. Phys. Lett. 92, 132108 (2008); http://dx.doi.org/10.1063/1.2906374 (3 pages) | Cited 23 times

Online Publication Date: 2 April 2008

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Mg-doped p-type InN layers with different thicknesses were grown under the same growth/doping conditions so that their net acceptor concentrations were almost the same (3–6)×1018 cm−3, which were confirmed by electrolyte capacitance-voltage measurements. The conductivity of p-InN region embedded under high density surface electrons could be extracted through the slope of total sheet conductivity against thickness, which was about 8.1 Ω−1 cm−1. Then, corresponding hole mobility was determined to be about 17–36 cm2/V s for the hole concentrations of about (1.4–3.0)×1018 cm−3 obtained by providing the hole effective mass and Mg acceptor activation energy as 0.42m0 and 61 meV, respectively.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Diffusion and thermal stability of hydrogen in ZnO

Junhyeok Bang and K. J. Chang

Appl. Phys. Lett. 92, 132109 (2008); http://dx.doi.org/10.1063/1.2906379 (3 pages) | Cited 30 times

Online Publication Date: 2 April 2008

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We perform both first-principles calculations and kinetic Monte Carlo (kMC) simulations to study the diffusion and thermal stability of hydrogen in ZnO. The migration energy of a substitutional hydrogen (HO) is 1.7 eV, much higher than the value of 0.4–0.5 eV for an interstitial hydrogen (Hi). Using as input the calculated energy barriers for H diffusion, kMC simulations show that while Hi diffuses out at low temperature, the thermal stability of HO is maintained up to 475 °C, in good agreement with the annealing data. In addition, our calculations suggest that injected hydrogen from air turns into HO, causing n-type conductivity.
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66.30.Dn Theory of diffusion and ionic conduction in solids
61.72.jj Interstitials
66.30.Lw Diffusion of other defects
72.80.Ey III-V and II-VI semiconductors

P-type semiconducting gas sensing behavior of nanoporous rf sputtered CaCu3Ti4O12 thin films

E. Joanni, R. Savu, P. R. Bueno, E. Longo, and J. A. Varela

Appl. Phys. Lett. 92, 132110 (2008); http://dx.doi.org/10.1063/1.2905810 (3 pages) | Cited 8 times

Online Publication Date: 4 April 2008

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The fabrication of nanoporous sputtered CaCu3Ti4O12 thin films with high gas sensitivity is reported in this work. The porous microstructure and the nanocrystalline nature of the material promoted the diffusion of the atmosphere into the film, shortening the response time of the samples. Behaving as p-type semiconductor, the material presents enhanced sensitivity even at low working temperatures. Impedance spectroscopy measurements were performed in order to investigate the mechanisms responsible for the performance of the devices.
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81.05.Rm Porous materials; granular materials
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
82.80.-d Chemical analysis and related physical methods of analysis
66.30.Pa Diffusion in nanoscale solids
61.43.Gt Powders, porous materials

Huge positive magnetoresistance in a gated AlGaAs/GaAs high electron mobility transistor structure at high temperatures

C.-T. Liang, Yen Shung Tseng, Jau-Yang Wu, Sheng-Di Lin, Chun-Kai Yang, Yu-Ru Li, Kuang Yao Chen, Po-Tsun Lin, and Li-Hung Lin

Appl. Phys. Lett. 92, 132111 (2008); http://dx.doi.org/10.1063/1.2906360 (3 pages)

Online Publication Date: 4 April 2008

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Magnetoresistivity measurements on a gated AlGaAs/GaAs high electron mobility transistor (HEMT) structure were performed at high temperatures T. By changing the applied gate voltage Vg, we can investigate the observed huge positive magnetoresistance (PMR) at different effective disorder and density inhomogeneity within the same HEMT structure. The observed PMR value increases with increasing disorder in the depletion mode (Vg ⩽ 0). Moreover, the PMR value is not limited by the quality of the HEMT structure at T = 80 K. Such results pave the way for low-cost, high-throughput GaAs-based HEMT fabrication for future magnetic sensing and recording devices fully compatible with the mature HEMT technology.
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85.30.Tv Field effect devices

Ordered n-type ZnO nanorod arrays

Huijuan Zhou, Johannes Fallert, Janos Sartor, Roman J. B. Dietz, Claus Klingshirn, Heinz Kalt, Daniel Weissenberger, Dagmar Gerthsen, Haibo Zeng, and Weiping Cai

Appl. Phys. Lett. 92, 132112 (2008); http://dx.doi.org/10.1063/1.2907197 (3 pages) | Cited 20 times

Online Publication Date: 4 April 2008

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Using indium as catalyst for growth and simultaneously as doping source, ordered arrays of n-type ZnO single crystal nanorods have been perpendicularly grown on p-GaN/Al2O3 substrates with a vapor phase transport growth method. The low temperature photoluminescence measurements of the n-ZnO nanorods show dominant In-related neutral donor bound exciton emission in the ultraviolet region. Electrical transport measurements performed on single n-ZnO nanorods yield resistances of about 50–200 kΩ and a typical specific resistivity of 2.0×10−2 Ω cm. The resistivity is one order of magnitude reduced by introducing In compared to the nominally undoped ZnO nanorods.
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81.16.-c Methods of micro- and nanofabrication and processing
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Et II-VI semiconductors
73.63.-b Electronic transport in nanoscale materials and structures
73.22.Lp Collective excitations
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