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5 Feb 2007

Volume 90, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 063114 (2007); http://dx.doi.org/10.1063/1.2457525 (3 pages)

Thomas J. Mullen, Charan Srinivasan, J. Nathan Hohman, Susan D. Gillmor, Mitchell J. Shuster, Mark W. Horn, Anne M. Andrews, and Paul S. Weiss
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Structure of shock waves in glass fiber reinforced polymer matrix composites

Liren Tsai, Vikas Prakash, A. M. Rajendran, and Dattatraya P. Dandekar

Appl. Phys. Lett. 90, 061909 (2007); http://dx.doi.org/10.1063/1.2435340 (3 pages) | Cited 3 times

Online Publication Date: 6 February 2007

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Glass fiber reinforced polymer (GRP) composites are attractive candidates for future combat vehicle armor systems. Due to their complex architecture, shock waves in GRP undergo geometric and material dispersion as well as attenuation with distance of shock wave propagation. In the present study a series of plate impact experiments is conducted to investigate the structure of shock waves in the GRP. The effects of material and geometric dispersion as well as the GRP’s hydrodynamic response on the attenuation of the shock waves are considered. It is observed that the hydrodynamic effects dictate the structure of shock waves in the GRP.
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62.50.-p High-pressure effects in solids and liquids

Size dependence of effective Young’s modulus of nanoporous gold

Anant Mathur and Jonah Erlebacher

Appl. Phys. Lett. 90, 061910 (2007); http://dx.doi.org/10.1063/1.2436718 (3 pages) | Cited 42 times

Online Publication Date: 7 February 2007

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Nanoporous gold (NPG) is a brittle, three-dimensional, random structure of Au with nanometer scale open porosity that is made by dealloying Au/Ag alloys in acid. In this work, Young’s modulus of NPG with controlled porosity variation between 3 and 40 nm is determined by mechanical testing of ∼ 100 nm thick, free standing, large-grained, stress-free films of NPG using a buckling-based method [ C. Stafford et al., Nat. Mater. 3, 545 (2005) ]. Results showing a dramatic rise in the effective Young’s modulus of NPG with decreasing ligament size, especially below 10 nm are presented, and possible reasons for this behavior are discussed.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
68.55.-a Thin film structure and morphology

Thermal activation in Au-based bulk metallic glass characterized by high-temperature nanoindentation

Bing Yang, Jeffrey Wadsworth, and Tai-Gang Nieh

Appl. Phys. Lett. 90, 061911 (2007); http://dx.doi.org/10.1063/1.2459383 (3 pages) | Cited 19 times

Online Publication Date: 7 February 2007

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High-temperature nanoindentation experiments have been conducted on a Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass from 30 to 140 °C, utilizing loading rates ranging from 0.1 to 100 mN/s. Generally, the hardness decreased with increasing temperature. An inhomogeneous-to-homogeneous flow transition was clearly observed when the test temperature approached the glass transition temperature. Analyses of the pop-in pattern and hardness variation showed that the inhomogeneous-to-homogeneous transition temperature was loading-rate dependent. Using a free-volume model, the authors deduced the size of the basic flow units and the activation energy for the homogeneous flow. In addition, the strain rate dependency of the transition temperature was predicted.
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81.05.Kf Glasses (including metallic glasses)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

In-plane optical anisotropy in self-assembled Ge quantum dots induced by interfacial chemical bonds

C. M. Wei, T. T. Chen, Y. F. Chen, Y. H. Peng, and C. H. Kuan

Appl. Phys. Lett. 90, 061912 (2007); http://dx.doi.org/10.1063/1.2459506 (3 pages) | Cited 1 time

Online Publication Date: 7 February 2007

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In-plane optical anisotropy has been observed in self-assembled Ge quantum dots (QDs). It is found that the photoluminescence (PL) spectrum polarized along [110] exhibits different features compared to that corresponding to [1math0]. Besides, the polarized PL spectrum is able to reveal a detailed fine structure much more pronounced than that in the unpolarized spectrum. It is shown that the observed optical anisotropy is a result of the inherent property of the type-II band alignment of Ge QDs embedded in Si matrix. The light emission arises from the recombination of electrons and holes across the interface, and it thus reflects the anisotropic nature of the interfacial chemical bonds.
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78.67.Hc Quantum dots
78.55.Ap Elemental semiconductors

Strain relaxation mechanism in a reverse compositionally graded SiGe heterostructure

L. H. Wong, J. P. Liu, F. Romanato, C. C. Wong, and Y. L. Foo

Appl. Phys. Lett. 90, 061913 (2007); http://dx.doi.org/10.1063/1.2472135 (3 pages) | Cited 10 times

Online Publication Date: 7 February 2007

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A concept of compositional reverse-grading (RG) in SiGe/Si heteroepitaxy has been proposed, in which the graded layer lattice mismatch starts at the highest value at the RG/Si interface and decreases to a final mismatch at the SiGe/RG interface. Using various characterization techniques, the authors show that this low-dislocation-density strain relaxation mechanism relies on the large nucleation rates of misfit dislocations at the abrupt RG/Si interface and the reduction of threading dislocations at the SiGe/RG interface by facilitating glide. The RG concept enables the growth of high-quality relaxed epitaxial layer on a thin buffer layer, suitable as a substrate for many microelectronic and optoelectronic applications.
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68.35.Gy Mechanical properties; surface strains
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Concentration-dependent near-infrared quantum cutting in GdBO3:Tb3+,Yb3+ nanophosphors

Q. Y. Zhang, C. H. Yang, Z. H. Jiang, and X. H. Ji

Appl. Phys. Lett. 90, 061914 (2007); http://dx.doi.org/10.1063/1.2472195 (3 pages) | Cited 55 times

Online Publication Date: 7 February 2007

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An efficient near-infrared (NIR) quantum-cutting (QC), involving the emission of two low-energy NIR photons from an absorbed visible photon via a cooperative downconversion mechanism in GdBO3:Tb3+,Yb3+ nanophosphors, has been demonstrated. Upon excitation of Tb3+ with a visible photon at 486 nm, two NIR photons could be emitted by Yb3+ through cooperative energy transfer from Tb3+ to two Yb3+ ions. The dependence of Yb3+ doping concentration on the visible and NIR emissions, decay lifetime, and quantum efficiencies from the QC phosphors has been investigated. Calculations indicate that the optimal NIR quantum efficiency approaches 182% before reaching concentration quenching threshold. Application of the QC nanophosphors in silicon-based solar cells might greatly enhance its response.
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42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.55.Hx Other solid inorganic materials
61.72.S- Impurities in crystals

Perfectly tetragonal, tensile-strained Ge on Ge1−ySny buffered Si(100)

Y.-Y. Fang, J. Tolle, R. Roucka, A. V. G. Chizmeshya, John Kouvetakis, V. R. D’Costa, and José Menéndez

Appl. Phys. Lett. 90, 061915 (2007); http://dx.doi.org/10.1063/1.2472273 (3 pages) | Cited 20 times

Online Publication Date: 7 February 2007

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High-quality, tensile-strained Ge layers with variable thickness (>30 nm) have been deposited at low temperature (350–380 °C) on Si(100) via fully relaxed Ge1−ySny buffers. The precise strain state of the epilayers is controlled by varying the Sn content of the buffer, yielding tunable tensile strains up to 0.25% for y = 0.025. Combined Raman analysis and high resolution x-ray diffraction using multiple off-axis reflections reveal unequivocally that the symmetry of tensile Ge is perfectly tetragonal, while the strain state of the buffer ( ∼ 200 nm thick) remains essentially unchanged. A downshift of the direct gap consistent with tensile strain has been observed.
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68.60.Bs Mechanical and acoustical properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
71.20.Mq Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators

Structural properties of epitaxial γ-Al2O3 (111) thin films on 4H-SiC (0001)

Carey M. Tanner, Monica Sawkar-Mathur, Jun Lu, Hans-Olof Blom, Michael F. Toney, and Jane P. Chang

Appl. Phys. Lett. 90, 061916 (2007); http://dx.doi.org/10.1063/1.2435978 (3 pages) | Cited 7 times

Online Publication Date: 8 February 2007

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Al2O3 thin films were grown on 4H-SiC (0001) by thermal atomic layer deposition and were crystallized to the γ-Al2O3 phase by rapid thermal annealing in N2 at 1100 °C. The films were found to be chemically stable during processing based on x-ray photoelectron spectroscopy. The change in film structure was initially confirmed by reflection high-energy electron diffraction. As shown by high-resolution transmission electron microscopy images, the abrupt interface of the as-deposited films with the 4H-SiC substrate was preserved during crystallization, indicating no interfacial reaction. Selected area electron diffraction and synchrotron-based x-ray diffraction established an epitaxial relationship of γ-Al2O3 (111) ‖ 4H-SiC (0001) and in-plane orientation of γ-Al2O3 (1math0) ‖ 4H-SiC (11math0). No other alumina phases or orientations were observed and no in-plane misorientation was observed in the 27 Å Al2O3 films. The full width at half maximum of the γ-Al2O3 (222) rocking curve is 0.056°, indicating a lack of mosaic spread and a high-quality crystalline film. Twinning around the γ-Al2O3 [111] axis was the only defect observed in these films.
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68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Cc Kinetics of defect formation and annealing
61.72.Mm Grain and twin boundaries
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Fabrication and low temperature thermoelectric properties of NaxCoO2 (x = 0.68 and 0.75) epitaxial films by the reactive solid-phase epitaxy

W. J. Chang, C. C. Hsieh, T. Y. Chung, S. Y. Hsu, K. H. Wu, T. M. Uen, J.-Y. Lin, J. J. Lin, C.-H. Hsu, Y. K. Kuo, H. L. Liu, M. H. Hsu, Y. S. Gou, and J. Y. Juang

Appl. Phys. Lett. 90, 061917 (2007); http://dx.doi.org/10.1063/1.2437131 (3 pages) | Cited 2 times

Online Publication Date: 8 February 2007

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The authors have fabricated NaxCoO2 thin films via lateral diffusion of sodium into Co3O4 (111) epitaxial films (reactive solid-phase epitaxy [ Ohta et al., Cryst. Growth Des. 5, 25 (2005) ]). The environment of thermal diffusion is key to the control of the sodium content in thin films. From the results of x-ray diffraction and in-plane ρab, the epitaxial growth and the sodium contents of these films were identified. The thermoelectric measurements show a large thermoelectric power similar to that observed in single crystals. The quasiparticle scattering rate is found to approach zero at low temperatures, consistent with the small residual resistivity, indicating high quality of the NaxCoO2 thin films.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Np Solid phase epitaxy; growth from solid phases
68.55.A- Nucleation and growth
72.20.Pa Thermoelectric and thermomagnetic effects
73.61.Ng Insulators

Vibrational study of hydrogen bonding to ion irradiated diamond surfaces

M. Bertin, A. Lafosse, R. Azria, Sh. Michaelson, O. Ternyak, and A. Hoffman

Appl. Phys. Lett. 90, 061918 (2007); http://dx.doi.org/10.1063/1.2457302 (3 pages) | Cited 9 times

Online Publication Date: 8 February 2007

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High resolution electron energy loss spectroscopy has been used to probe hydrogenated diamond film surfaces exposed to 1 keV Ar+ ions at a dose of ∼ 1015 cm−2 and thermal annealing. The defects induced on the upper atomic layers were identified with regard to the different hydrogenated species hybridization states as well as their thermal stability. Ion irradiation resulted in the coexistence of a partially hydrogenated disordered near surface region including CH species bonded in sp, sp2, and sp3 bonding configurations and CC dimers. Thermal annealing of the ion beam irradiated hydrogenated surface leads to complete hydrogen desorption at ∼ 650 °C. This temperature is significantly lower compared to a well defined diamond surface for which an annealing temperature above 900 °C is needed.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
68.49.Jk Electron scattering from surfaces
79.20.Uv Electron energy loss spectroscopy
68.43.Mn Adsorption kinetics

Epitaxial gadolinium nitride thin films

J. W. Gerlach, J. Mennig, and B. Rauschenbach

Appl. Phys. Lett. 90, 061919 (2007); http://dx.doi.org/10.1063/1.2472538 (3 pages) | Cited 15 times

Online Publication Date: 8 February 2007

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GdN thin films are deposited on MgO(100) by low-energy ion-beam-assisted molecular-beam epitaxy at elevated temperatures. Elemental analysis by secondary-ion mass spectrometry proves that a protective layer is imperative to avoid oxidation of the GdN films in air. In situ surface structural investigation of the growing GdN films by reflection high-energy electron diffraction reveals epitaxial film growth. This result is confirmed by x-ray diffraction structure and texture analysis. Accordingly, the GdN films on MgO(100) exhibit cube-on-cube epitaxy. Due to the epitaxial growth the crystalline quality of the films is by far higher than that of films previously reported of in literature.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Strain distribution of thin InN epilayers grown on (0001) GaN templates by molecular beam epitaxy

A. Delimitis, Ph. Komninou, G. P. Dimitrakopulos, Th. Kehagias, J. Kioseoglou, Th. Karakostas, and G. Nouet

Appl. Phys. Lett. 90, 061920 (2007); http://dx.doi.org/10.1063/1.2470496 (3 pages) | Cited 5 times

Online Publication Date: 8 February 2007

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A structural characterization of thin InN films is performed to determine the post-growth strain distribution, using electron microscopy techniques. A 60° misfit dislocation network at the InN/GaN interface effectively accommodates the lattice mismatch. The InN in-plane lattice parameter, which remained practically constant throughout the epilayer thickness, was precisely determined by electron diffraction analysis, and cross-section and plan-view lattice images. Image analysis using the geometric phase and projection methods revealed a uniform distribution of the residual tensile strain along the growth and lateral directions. The in-plane strain is primarily attributed to InN island coalescence during the initial stages of growth.
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68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Intermolecular elastic and plastic characteristics of organic phthalocyanine thin films evaluated by nanoindentation

Moriyasu Kanari, Hirotaka Kawamata, Takashi Wakamatsu, and Ikuo Ihara

Appl. Phys. Lett. 90, 061921 (2007); http://dx.doi.org/10.1063/1.2472041 (3 pages) | Cited 3 times

Online Publication Date: 9 February 2007

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Although small molecule organic thin films have been applied to electronics, very few experimental results have been reported in respect to their mechanical properties. Here the authors report experimental results in which three types of phthalocyanine (Pc) thin films were investigated for mechanical characteristics using a nanoindentation. Indentation hardness of zinc Pc(ZnPc) thin films was significantly higher than those of metal-free Pc(H2Pc) and copper Pc(CuPc) thin films by a factor of approximately 1.7 times. From the mechanical prarameters, the critical bending radius is evaluated in the range of 4.0–5.7 mm for the Pc films on a polymer base film.
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68.60.Bs Mechanical and acoustical properties
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
62.20.Qp Friction, tribology, and hardness
62.20.F- Deformation and plasticity

Marcasite osmium nitride with high bulk modulus: First-principles calculations

Yuan Xu Wang, Masao Arai, and Taizo Sasaki

Appl. Phys. Lett. 90, 061922 (2007); http://dx.doi.org/10.1063/1.2472540 (3 pages) | Cited 24 times

Online Publication Date: 9 February 2007

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The authors propose marcasite OsN2 as a structure of the experimentally synthesized orthorhombic OsN2 compound. From the first-principles calculations, they find that the marcasite structure is more stable than the fluorite and pyrite ones and its lattice constants are in good agreement with the experiment. The calculated elastic constants for marcasite OsN2 satisfy the stability condition. The band structure shows that marcasite OsN2 is metallic. There is a pseudogap around the Fermi level of the total density of states of marcasite OsN2, which may contribute to its stability. The appearance of the pseudogap is mainly caused by the anisotropic connectivity of OsN6 octahedra.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.66.Fn Inorganic compounds
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Organic nanochannel field-effect transistor with organic conductive wires

Masatoshi Sakai, Masakazu Nakamura, and Kazuhiro Kudo

Appl. Phys. Lett. 90, 062101 (2007); http://dx.doi.org/10.1063/1.2454286 (3 pages) | Cited 8 times

Online Publication Date: 5 February 2007

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The authors fabricated an organic nanochannel field-effect transistor (FET) that is self-wired with highly conductive organic conductors. The advantages of the transistor are a short channel (approximately 400 nm in length) and spontaneous formation of an active layer of the FET. Further, in principle, the carrier-injection barrier is absent at the interface of the organic metal and organic semiconductor. Thus, the transistor is highly conductive despite the narrow cross section of the channel. The FET characteristics of the nanochannel transistor exhibit the n-channel enhancement mode behavior.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

(In,Ga)As gated-vertical quantum dot with an Al2O3 insulator

T. Kita, D. Chiba, Y. Ohno, and H. Ohno

Appl. Phys. Lett. 90, 062102 (2007); http://dx.doi.org/10.1063/1.2437060 (3 pages) | Cited 3 times

Online Publication Date: 5 February 2007

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The authors fabricated a gated-vertical (In,Ga)As quantum dot with an Al2O3 gate insulator deposited using atomic layer deposition and investigated its electrical transport properties at low temperatures. The gate voltage dependence of the dI/dV−V characteristics shows clear Coulomb diamonds at 1.1 K. The metal-insulator gate structure allowed the authors to control the number of electrons in the quantum dot from 0 to a large number estimated to be about 130.
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73.63.Kv Quantum dots
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.21.La Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Role of valence-band Co 3d states on ferromagnetism in Zn1−xCoxO nanorods

J. W. Chiou, H. M. Tsai, C. W. Pao, K. P. Krishna Kumar, J. H. Chen, D. C. Ling, F. Z. Chien, W. F. Pong, M.-H. Tsai, J. J. Wu, M.-H. Yang, S. C. Liu, I.-H. Hong, C.-H. Chen, H.-J. Lin, et al.

Appl. Phys. Lett. 90, 062103 (2007); http://dx.doi.org/10.1063/1.2432234 (3 pages) | Cited 4 times

Online Publication Date: 5 February 2007

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This work investigates the electronic and ferromagnetic properties of Zn1−xCoxO nanorods using x-ray absorption, x-ray magnetic circular dichroism, and scanning photoelectron microscopy methods. The magnetic moment of Co ions in Zn1−xCoxO nanorods is found greatly reduced relative to that of the Co metal. The intensities of valence-band features near the valence-band maximum/Fermi level (EF) of ferromagnetic nanorods are substantially larger than those of weaker ferromagnetic nanorods, suggesting that the occupation of near-EF valence-band Co 3d states is important in determining the ferromagnetic behavior in Zn1−xCoxO nanorods.
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73.20.At Surface states, band structure, electron density of states
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Cr Saturation moments and magnetic susceptibilities
78.70.Dm X-ray absorption spectra

Influence of spontaneous polarization on the electrical and optical properties of bulk, single crystal ZnO

M. W. Allen, P. Miller, R. J. Reeves, and S. M. Durbin

Appl. Phys. Lett. 90, 062104 (2007); http://dx.doi.org/10.1063/1.2450642 (3 pages) | Cited 39 times

Online Publication Date: 5 February 2007

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Hall effect, photoluminescence, and Schottky diode measurements were made on the Zn-polar and O-polar faces of undoped, bulk, single crystal, c-axis ZnO wafers. Significant polarity related differences were observed in the PL and Schottky diode characteristics of low carrier concentration, hydrothermally grown wafers. Increased emission from free exciton recombinations and from recombinations between 3.3725 and 3.3750 eV was observed on the Zn-polar face. Conversely, emission between 3.3640 and 3.3680 eV was more intense on the O-polar face. The barrier heights of silver oxide Schottky diodes were approximately 130 meV larger on the Zn-polar face compared to the O-polar face.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.30.+y Surface double layers, Schottky barriers, and work functions
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena

Temperature sensor using thermal transport properties in the subthreshold regime of an organic thin film transistor

Soyoun Jung, Taeksoo Ji, and Vijay K. Varadan

Appl. Phys. Lett. 90, 062105 (2007); http://dx.doi.org/10.1063/1.2450646 (3 pages) | Cited 23 times

Online Publication Date: 5 February 2007

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In this letter, a temperature sensor based on an organic thin film transistor is proposed and discussed in terms of its linearity and reliability of the variation in the subthreshold drain current with temperature. The saturation mobility exhibits thermally activated hopping and temperature-deactivated behavior in different temperature ranges, but the saturation current shows very little change compared to the subthreshold current that is linearly varied with temperature from 273 to 453 K. In addition, sensor reliability can be ensured by placing a time delay between consecutive measurements to release the charges trapped in the dielectric/semiconductor interface, the so-called bias-stress effect.
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07.20.Dt Thermometers
85.30.Tv Field effect devices

Influence of defects in n−-GaN layer on the responsivity of Schottky barrier ultraviolet photodetectors

D. G. Zhao, D. S. Jiang, J. J. Zhu, Z. S. Liu, S. M. Zhang, J. W. Liang, Hui Yang, X. Li, X. Y. Li, and H. M. Gong

Appl. Phys. Lett. 90, 062106 (2007); http://dx.doi.org/10.1063/1.2450658 (3 pages) | Cited 3 times

Online Publication Date: 5 February 2007

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The influence of defects on the responsivity of GaN Schottky barrier ultraviolet photodetectors with n−-GaN/n+-GaN layer structures is investigated. It is found that employing undoped GaN instead of Si-doped GaN as the n−-GaN layer brings about a higher responsivity due to a lower Ga vacancy concentration. On the other hand, the dislocations may increase the recombination of electron-hole pairs and enhance the surface recombination in the photodetectors. Employing undoped GaN and reducing the dislocation density in the n−-GaN layer are necessary to improve the responsivity of Schottky barrier photodetectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.30.+y Surface double layers, Schottky barriers, and work functions

Enhanced and retarded diffusion of arsenic in silicon by point defect engineering

Ning Kong, Sanjay K. Banerjee, Taras A. Kirichenko, Steven G. H. Anderson, and Mark C. Foisy

Appl. Phys. Lett. 90, 062107 (2007); http://dx.doi.org/10.1063/1.2450663 (3 pages) | Cited 8 times

Online Publication Date: 5 February 2007

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Arsenic enhanced or retarded diffusion is observed by overlapping the dopant region with, respectively, interstitial-rich and vacancy-rich regions produced by Si implants. Enhanced diffusion can be attributed to interstitial-mediated diffusion during postimplant annealing. Two possible mechanisms for diffusion retardation, interstitial-vacancy recombination and dopant clustering, are analyzed in additional experiments. The point defect engineering approach demonstrated in this letter could be applied to fabrication of n-type ultrashallow junctions.
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66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing

Ambipolar conduction in transistors using solution grown InAs nanowires with Cd doping

Qingling Hang, Fudong Wang, William E. Buhro, and David B. Janes

Appl. Phys. Lett. 90, 062108 (2007); http://dx.doi.org/10.1063/1.2457249 (3 pages) | Cited 8 times

Online Publication Date: 6 February 2007

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Nanowire field effect transistors have been fabricated using Cd doped InAs nanowires synthesized using a solution-liquid-solid technique. Both n-channel and p-channel characteristics have been observed, which implies that the surface Fermi level is not pinned in the conduction band. The observation of a p channel is attributed to the passivation of surface states by surface ligands introduced during nanowire synthesis and to the effects of heavy acceptor doping. Devices in which the surface ligands are removed by O2 plasma treatment exhibit only n-channel conduction, which would be consistent with surface Fermi level pinning in the conduction band.
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85.30.Tv Field effect devices

Transport characterization of the magnetic anisotropy of (Ga,Mn)As

K. Pappert, S. Hümpfner, J. Wenisch, K. Brunner, C. Gould, G. Schmidt, and L. W. Molenkamp

Appl. Phys. Lett. 90, 062109 (2007); http://dx.doi.org/10.1063/1.2437075 (3 pages) | Cited 24 times

Online Publication Date: 6 February 2007

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The rich magnetic anisotropy of compressively strained (Ga,Mn)As has attracted great interest recently. Here the authors discuss a sensitive method to visualize and quantify the individual components of the magnetic anisotropy using transport. A set of high resolution transport measurements is compiled into color coded resistance polar plots, which constitute a fingerprint of the symmetry components of the anisotropy. As a demonstration of the sensitivity of the method, they show that these typically reveal the presence of both the [math10] and the [010] uniaxial magnetic anisotropy component in (Ga,Mn)As layers, even when most other techniques reveal only one of these components.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ey III-V semiconductors
75.30.Gw Magnetic anisotropy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Deformation potential carrier-phonon scattering in semiconducting carbon nanotube transistors

G. Pennington, N. Goldsman, A. Akturk, and A. E. Wickenden

Appl. Phys. Lett. 90, 062110 (2007); http://dx.doi.org/10.1063/1.2437127 (3 pages) | Cited 17 times

Online Publication Date: 6 February 2007

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Theoretical calculations of carrier transport in semiconducting single-walled carbon nanotubes are compared with recent experiments. Considering carrier-phonon scattering, a deformation potential coupling constant of 14 eV is determined. Theory predicts the low-field mobility, conductance, and on resistance of field-effect transistors as a function of nanotube diameter and temperature. When the device is in the on state, the mean free path (Lm-on) varies linearly with tube diameter and inversely with temperature. Intersubband scattering is found to strongly decrease Lm-on when a few subbands are occupied.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Pentacene-based thin film transistors with titanium oxide-polystyrene/polystyrene insulator blends: High mobility on high K dielectric films

Cecile Jung, Ashok Maliakal, Alexander Sidorenko, and Theo Siegrist

Appl. Phys. Lett. 90, 062111 (2007); http://dx.doi.org/10.1063/1.2450660 (3 pages) | Cited 20 times

Online Publication Date: 6 February 2007

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High K titanium oxide-polystyrene TiO2-PS nanocomposite has been blended with PS to generate gate dielectric films with permittivities ranging from 2.5 to 8 in order to investigate permittivity effects on pentacene thin film transistor performance. An order of magnitude increase in saturation mobility is observed for TiO2-PS (K = 8) as compared to PS devices (K = 2.5). Morphological differences for pentacene grown on TiO2-PS/PS dielectrics are thought to be responsible for the observed mobility enhancements. The high performance of pentacene on TiO2-PS devices suggests that high permittivity films are compatible with high mobility devices.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
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