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28 Nov 2005

Volume 87, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 221108 (2005); http://dx.doi.org/10.1063/1.2137458 (3 pages)

V. Barna, S. Ferjani, A. De Luca, R. Caputo, N. Scaramuzza, C. Versace, and G. Strangi
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Trapping-detrapping defects in single crystal diamond films grown by chemical vapor deposition

A. Balducci, Marco Marinelli, E. Milani, M. E. Morgada, G. Prestopino, M. Scoccia, A. Tucciarone, and G. Verona-Rinati

Appl. Phys. Lett. 87, 222101 (2005); http://dx.doi.org/10.1063/1.2135384 (3 pages) | Cited 5 times

Online Publication Date: 21 November 2005

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High-quality single-crystal diamond films were homoepitaxially grown by chemical vapor deposition onto low cost high-pressure high-temperature diamond substrates. The transport properties of the obtained samples were studied by photoresponse characterization. Fast ultraviolet (5 ns) laser pulses at 215 nm were used as a probe. The time evolution of the photoinduced current was observed to closely reproduce the laser pulse shape, thus indicating a time response lower than the adopted laser pulse duration. Very stable and reproducible response was measured, so that neither priming nor memory effects are observed. However, a minor slow component shows up in the charge-integrated sample response, whose temperature dependence was investigated in a −25–+50 °C range. A systematic speed up of this slow component of the sample signal is observed, indicating the presence of shallow centers producing trapping-detrapping effects. The experimental results are discussed in the framework of a trapping-detrapping model affecting the charge transport mechanism and an activation energy of Ea = 0.4 eV was derived for the shallow trapping centers.
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71.55.Cn Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.50.Pz Photoconduction and photovoltaic effects
73.61.Cw Elemental semiconductors

β-Ga2O3 nanowires: Synthesis, characterization, and p-channel field-effect transistor

Pai-Chun Chang, Zhiyong Fan, Wei-Yu Tseng, A. Rajagopal, and Jia G. Lu

Appl. Phys. Lett. 87, 222102 (2005); http://dx.doi.org/10.1063/1.2135867 (3 pages) | Cited 19 times

Online Publication Date: 21 November 2005

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Quasione-dimensional Ga2O3 nanowires are synthesized via catalytic chemical vapor deposition method. Their morphology and crystal structure are characterized by electron microscopy and x-ray diffraction techniques, and their optical property is studied by photoluminescence measurement. To develop their future application in nanoelectronic devices, the as-grown Ga2O3 nanowires are doped with zinc to increase its carrier concentration and subsequently fabricated into field-effect transistors. Electron transport measurements show that the doped nanowires exhibit p-type semiconducting behavior with a significant enhancement of conductivity.
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81.07.Bc Nanocrystalline materials
85.30.Tv Field effect devices
68.65.La Quantum wires (patterned in quantum wells)
73.21.Hb Quantum wires
73.63.Nm Quantum wires
78.67.Lt Quantum wires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Hc Catalytic methods
82.30.Vy Homogeneous catalysis in solution, polymers and zeolites
68.37.Lp Transmission electron microscopy (TEM)
78.55.Hx Other solid inorganic materials
61.72.up Other materials

Steady-state and transient electron transport within bulk wurtzite indium nitride: An updated semiclassical three-valley Monte Carlo simulation analysis

Stephen K. O’Leary, Brian E. Foutz, Michael S. Shur, and Lester F. Eastman

Appl. Phys. Lett. 87, 222103 (2005); http://dx.doi.org/10.1063/1.2135876 (3 pages) | Cited 35 times

Online Publication Date: 21 November 2005

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Recent experimentation, performed on bulk wurtzite InN, suggests that the energy gap, the effective mass of the electrons in the lowest-energy valley, and the nonparabolicity coefficient of the lowest-energy valley are not as originally believed for this material. Using a semiclassical three-valley Monte Carlo simulation approach, we analyze the steady-state and transient electron transport that occurs within bulk wurtzite InN using a revised set of material parameters, this revised set of parameters taking into account this recently observed phenomenology. We find that the peak electron drift velocity is considerably greater than that found previously. The impact that this revised set of parameters has upon the transient electron transport is also found to be significant.
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72.20.Fr Low-field transport and mobility; piezoresistance
71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Phonon localization in periodic uniaxially nanostructured silicon

Sylvain G. Cloutier, Rodney S. Guico, and Jimmy M. Xu

Appl. Phys. Lett. 87, 222104 (2005); http://dx.doi.org/10.1063/1.2135881 (3 pages) | Cited 11 times

Online Publication Date: 21 November 2005

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Phonon spectroscopy of low-dimensional silicon nanostructures may help identify and understand their unique physical properties for potentially enabling new applications. High-resolution Raman spectroscopy reveals that fabrication of such nanostructures can lead to the creation of nanosize crystallites at the silicon interface due to the introduction of defect centers which is most likely responsible for local crystal-symmetry breaking and phonon localization. By examining these nanocrystallites created in periodic crystalline silicon nanodot arrays formed in silicon-on-insulator and their dispersive and power-dependent phonon spectra, we found clear evidence of spatial phonon localization, which in turn suggests a breaking of the fundamental phonon-selection rule limiting radiative recombination in silicon’s indirect band structure.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Hv Other nonmetallic inorganics
61.72.-y Defects and impurities in crystals; microstructure
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Average energy dissipated by mega-electron-volt hydrogen and helium ions per electron-hole pair generation in 4H-SiC

Alessandro Lo Giudice, Franco Fizzotti, Claudio Manfredotti, Ettore Vittone, and Filippo Nava

Appl. Phys. Lett. 87, 222105 (2005); http://dx.doi.org/10.1063/1.2135507 (3 pages) | Cited 6 times

Online Publication Date: 21 November 2005

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The pulse height response for He and H ions with energies between 1 and 6 MeV incident upon n-type 4H-SiC epitaxial Schottky diodes has been investigated. The average amount of energy, ε, given up by the incident radiation to form electron-hole pair in this material was obtained by comparison with the average energy loss per pair in silicon detectors and it was found to be (7.78±0.05) eV at room temperature. This value is smaller than that foreseen by Klein’s semiempirical linear relationship between ε and the semiconductor band gap.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices

Hydrogen sensing at room temperature with Pt-coated ZnO thin films and nanorods

L. C. Tien, P. W. Sadik, D. P. Norton, L. F. Voss, S. J. Pearton, H. T. Wang, B. S. Kang, F. Ren, J. Jun, and J. Lin

Appl. Phys. Lett. 87, 222106 (2005); http://dx.doi.org/10.1063/1.2136070 (3 pages) | Cited 96 times

Online Publication Date: 21 November 2005

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A comparison is made of the sensitivities for detecting hydrogen with Pt-coated single ZnO nanorods and thin films of various thicknesses (20–350 nm). The Pt-coated single nanorods show a current response of approximately a factor of 3 larger at room temperature upon exposure to 500 ppm H2 in N2 than the thin films of ZnO. The power consumption with both types of sensors can be very small (in the nW range) when using discontinuous coatings of Pt. Once the Pt coating becomes continuous, the current required to operate the sensors increases to the μW range. The optimum ZnO thin film thickness under our conditions was between 40–170 nm, with the hydrogen sensitivity falling off outside this range. The nanorod sensors show a slower recovery in air after hydrogen exposure than the thin films, but exhibit a faster response to hydrogen, consistent with the notion that the former adsorb relatively more hydrogen on their surface. Both ZnO thin and nanorods cannot detect oxygen.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
68.55.-a Thin film structure and morphology
81.65.-b Surface treatments

Modulation in optical second harmonic generation signal from channel of pentacene field effect transistors during device operation

Takaaki Manaka, Eunju Lim, Ryosuke Tamura, and Mitsumasa Iwamoto

Appl. Phys. Lett. 87, 222107 (2005); http://dx.doi.org/10.1063/1.2136075 (3 pages) | Cited 20 times

Online Publication Date: 21 November 2005

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The channel formation process of the pentacene field effect transistor (FET) was shown by the optical second harmonic generation (SHG) ascribed to the electric field induced SHG. The SHG signal probed successfully and nondestructively the off and on states. The enhancement of the SHG signal at the off state was observed with applying the source-drain voltage in the absence of the gate voltage, whereas it remarkably decayed with applying the gate voltage, indicating the channel formation. At the channel formation, holes injected from the source electrode changed the potential profile in pentacene film at the off state and the SHG signal was suppressed.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
85.30.Tv Field effect devices

Epitaxial, ferromagnetic Cu2−xMnxO films on (001) Si by near-room-temperature electrodeposition

Y. L. Liu, S. Harrington, K. A. Yates, M. Wei, M. G. Blamire, J. L. MacManus-Driscoll, and Y. C. Liu

Appl. Phys. Lett. 87, 222108 (2005); http://dx.doi.org/10.1063/1.2136349 (3 pages) | Cited 6 times

Online Publication Date: 21 November 2005

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∼ 1 micron thick Cu2−xMnxO films were grown both on Au-coated and uncoated (001) Si from sulphate solutions at 60 °C, several hundred degrees lower than normally used for growth of dilute magnetic semiconductors. The Mn concentration in the films was controlled very sensitively by controlling both the ratio of Mn:Cu in solution and the deposition potential. An optimum Mn concentration of 0.3% in the films produced saturation magnetization values of 0.6 μB/Mn at room temperature. The Cu2−xMnxO films were semiconducting with resistivitity value lower than the undoped film. Photoluminscence measurements showed that Mn substitutes on the Cu lattice sites.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Pq Electrodeposition, electroplating
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors

Blends of semiconductor polymer and small molecular crystals for improved-performance thin-film transistors

D. M. Russell, C. J. Newsome, S. P. Li, T. Kugler, M. Ishida, and T. Shimoda

Appl. Phys. Lett. 87, 222109 (2005); http://dx.doi.org/10.1063/1.2136356 (3 pages) | Cited 14 times

Online Publication Date: 21 November 2005

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Incorporating dihexyl-quarterthiophene (DH4T) into the active layer of a poly(3-hexylthiophene) thin-film transistor can enhance the mobility by a factor of 10. The DH4T concentration dependence shows the improvement in mobility is due to the formation of crystals within the blend film, which occur at a critical concentration of 29% DH4T. Application of percolation theory reveals that transport in blend devices is limited by the mobility of the poly(3-hexylthiophene) (P3HT) and by the crystal packing. With improved polymer performance, the mobility in blend films is expected to approach 1 cm2/V s.
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85.30.Tv Field effect devices

Double injection as a technique to study charge carrier transport and recombination in bulk-heterojunction solar cells

G. Juška, K. Arlauskas, G. Sliaužys, A. Pivrikas, A. J. Mozer, N. S. Sariciftci, M. Scharber, and R. Österbacka

Appl. Phys. Lett. 87, 222110 (2005); http://dx.doi.org/10.1063/1.2137454 (3 pages) | Cited 16 times

Online Publication Date: 22 November 2005

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Ambipolar charge carrier mobility and recombination in bulk-heterojunction solar cells based on the mixture of regioregular poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) has been studied using injection current transients. The experimental results demonstrate double injection with bimolecular recombination limiting the injection current. We found that charge carrier bimolecular recombination is significantly reduced compared to Langevin recombination. We have measured the temperature and electric field dependence of the reduced bimolecular recombination coefficient and the results suggest that the electron and hole pathways are different and the recombination is controlled by the probability of the carriers to meet at the polymer/PCBM interface.
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84.60.Jt Photoelectric conversion
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
85.65.+h Molecular electronic devices

Nanoscale stress analysis of strained-Si metal-oxide-semiconductor field-effect transistors by quantitative electron diffraction contrast imaging

J. Li, D. Anjum, R. Hull, G. Xia, and J. L. Hoyt

Appl. Phys. Lett. 87, 222111 (2005); http://dx.doi.org/10.1063/1.2135388 (3 pages) | Cited 6 times

Online Publication Date: 22 November 2005

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A technique that uses quantitative electron diffraction contrast imaging (EDCI) to measure stress with a spatial resolution on the order of 10 nm and sensitivity on the order of tens of MPa is applied to strained-Si metal-oxide-semiconductor field-effect transistors. This is accomplished by utilizing transmission electron microscopy and focused ion beam micromachining in conjunction with finite element modeling and electron diffraction contrast simulations. Our techniques enable quantitative interpretation of EDCI intensity, as a function of the magnitude of the local stress field. Analysis shows that the stress distribution in the strained-Si channel is very sensitive to the stress state of the surrounding materials, especially TiSi2, which can modify the stress distribution in the channel by well over 100 MPa.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Deep levels in n-type AlGaN grown by hydride vapor-phase epitaxy on sapphire characterized by deep-level transient spectroscopy

J. Osaka, Y. Ohno, S. Kishimoto, K. Maezawa, and T. Mizutani

Appl. Phys. Lett. 87, 222112 (2005); http://dx.doi.org/10.1063/1.2137901 (3 pages) | Cited 7 times

Online Publication Date: 22 November 2005

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Deep levels in unintentionally doped n-type Al0.09Ga0.91N and Al0.17Ga0.83N films grown on sapphire by hydride vapor-phase epitaxy were characterized using capacitance deep-level transient spectroscopy and were compared to the reported electron traps in GaN grown by various techniques. It was shown that at least three dominant deep levels exist in each sample. The Al mole fraction dependence of their activation energy suggested that each of these three levels has the same origin as the three dominant well known point-defect-related deep levels in GaN, respectively. It is thought that deep levels in GaN change their electric characteristics in low Al content AlGaN.
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71.55.Eq III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Formation of p-n homojunctions in n-ZnO bulk single crystals by diffusion from a Zn3P2 source

Soohwan Jang, Jau-Jiun Chen, B. S. Kang, F. Ren, D. P. Norton, S. J. Pearton, J. Lopata, and W. S. Hobson

Appl. Phys. Lett. 87, 222113 (2005); http://dx.doi.org/10.1063/1.2137988 (3 pages) | Cited 15 times

Online Publication Date: 22 November 2005

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p-n junctions have been formed in lightly n-type (1017 cm−3) bulk, single-crystal ZnO substrates by diffusion of P from a Cd3P2, arsenic and red phosphorous dopant source in a closed-ampoule system. The P incorporation depth was found to be ∼ 200 nm after diffusion at 550 °C for 30 min, as determined by secondary ion mass spectrometry profiling. The resulting structures show rectification, with on-off current ratios of ∼ 70 at +3/−5 V. The forward current ideality factor was ≥ 2, consistent with multiple current transport mechanisms present in the junction, such as defect-assisted tunneling and conventional carrier recombination in the space-charge region via midgap deep levels. The forward turn-on voltage, VF was ∼ 4 V at 300 K with a specific on-state resistance (RON) of ∼ 21 mΩ cm2. The activation energy of the forward current at low forward biases was ∼ 1.4 eV. This is also consistent with carrier recombination in the space charge region via a midgap deep level.
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66.30.J- Diffusion of impurities
71.55.Gs II-VI semiconductors
73.61.Ga II-VI semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uj III-V and II-VI semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
73.40.Ei Rectification
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Ferroelectric switch for spin injection

M. Ye. Zhuravlev, S. S. Jaswal, E. Y. Tsymbal, and R. F. Sabirianov

Appl. Phys. Lett. 87, 222114 (2005); http://dx.doi.org/10.1063/1.2138365 (3 pages) | Cited 46 times

Online Publication Date: 23 November 2005

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A method for the switching of the spin polarization of the electric current injected into a semiconductor is proposed, based on injecting spins from a diluted magnetic semiconductor through a ferroelectric tunnel barrier. We show that the reversal of the electric polarization of the ferroelectric results in a sizable change in the spin polarization of the injected current, thereby providing a two-state electrical control of this spintronic device. We also predict a possibility of switching of tunneling magnetoresistance in magnetic tunnel junctions with a ferroelectric barrier and coexistence of tunneling magnetoresistance and giant electroresistance effects in these multiferroic tunnel junctions.
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77.80.Fm Switching phenomena
72.25.Dc Spin polarized transport in semiconductors
75.47.Pq Other materials

Efficient blue electroluminescent device using tetra(β-naphthyl)silane as a hole-blocking material

Gui Yu, Xinjun Xu, Yunqi Liu, Zuoquan Jiang, Shiwei Yin, Zhigang Shuai, Daoben Zhu, Xiaobang Duan, and Ping Lu

Appl. Phys. Lett. 87, 222115 (2005); http://dx.doi.org/10.1063/1.2138812 (3 pages) | Cited 13 times

Online Publication Date: 23 November 2005

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We report an efficient blue light-emitting diode (LED) using N, N′-bis(1-naphthyl)-N, N′-diphenylbenzidine as an emitting layer and tetra(β-naphthyl)silane (TNS) as a hole-blocking layer (HBL). We find that the hole-blocking performance, thermal stability, and film-forming ability of TNS are improved over those of the prototypical hole-blocking material 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The device that used TNS as the HBL exhibits a narrower light emission and higher current efficiency (2.5 cd/A) as compared with the device containing BCP as the HBL. TNS should be promising as an excellent hole-blocking layer in LEDs.
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85.60.Jb Light-emitting devices
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