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24 Sep 2007

Volume 91, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 132501 (2007); http://dx.doi.org/10.1063/1.2786856 (3 pages)

V. Rose, X. M. Cheng, D. J. Keavney, J. W. Freeland, K. S. Buchanan, B. Ilic, and V. Metlushko
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Two coexisting mechanisms of dislocation reduction in an AlGaN layer grown using a thin GaN interlayer

J. Bai, T. Wang, P. J. Parbrook, Q. Wang, K. B. Lee, and A. G. Cullis

Appl. Phys. Lett. 91, 131903 (2007); http://dx.doi.org/10.1063/1.2790813 (3 pages) | Cited 10 times

Online Publication Date: 26 September 2007

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A significant dislocation reduction is achieved in an AlGaN layer grown on an AlN buffer by introducing a thin GaN interlayer. The mechanisms for the dislocation reduction are explored by transmission electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, and micro-Raman spectroscopy. The GaN interlayer grown on the AlN takes the form of platelets. The mechanisms of dislocation reduction in the platelet area and the area between the platelets are different. In the GaN platelets, due to the large misfit strain, the threading dislocations (TDs) in the AlN layer migrate into the interface and annihilate with each other. However, the GaN between the platelets is highly strained so that a higher density of TDs from AlN is incorporated into the upper layer. The coalescing of the platelets induced by the AlGaN growth makes the TDs in the areas between the platelets assemble and annihilate, resulting in additional dislocation reduction.
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68.55.-a Thin film structure and morphology
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.37.Ps Atomic force microscopy (AFM)
78.30.Fs III-V and II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Field-driven structural phase transition and sign-switching magnetocaloric effect in Ni–Mn–Sn

M. Pasquale, C. P. Sasso, L. Giudici, T. Lograsso, and D. Schlagel

Appl. Phys. Lett. 91, 131904 (2007); http://dx.doi.org/10.1063/1.2790829 (3 pages) | Cited 8 times

Online Publication Date: 26 September 2007

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Depending on the starting equilibrium temperature, the application of a magnetic field on a sample of Ni–Mn–Sn produces sample heating or cooling during adiabatic experiments. The competition between endothermal and exothermal effects is observed close to the martensite-to-austenite magnetostructural phase transition. A model assuming the coexistence of two phases and a field dependence of their volume allows to compute the evolution of entropy and heat capacity during the phase transition. The correct fitting of the results suggests that the field-induced reduction of the martensite-to-austenite transition temperature is responsible for the observed sign switching of the magnetocaloric effect.
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64.70.K- Solid-solid transitions
65.40.G- Other thermodynamical quantities
75.30.Sg Magnetocaloric effect, magnetic cooling
81.30.Kf Martensitic transformations

Air flow through carbon nanotube arrays

Ming Hu, Sergei Shenogin, Pawel Keblinski, and Nachiket Raravikar

Appl. Phys. Lett. 91, 131905 (2007); http://dx.doi.org/10.1063/1.2793174 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2007

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Using molecular dynamics simulations, we studied the air flow through carbon nanotube arrays. We found that for 1.4 nm diameter tubes separated by 25 nm, the air flow can be well described by the free molecular flow theory. We estimate that for such array, the pressure gradient is about 0.1 atm/μm at 1 atm air pressure and 5 m/s flow velocity, indicating that the flowing air can only pass through an array of no more than about 400 carbon nanotubes in series. Our findings provide design rules for arrays of nanotubes for thermal energy exchange with air.
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47.60.-i Flow phenomena in quasi-one-dimensional systems
47.27.te Turbulent convective heat transfer
47.85.-g Applied fluid mechanics
47.11.Mn Molecular dynamics methods

Direct synthesis of sp-bonded carbon chains on graphite surface by femtosecond laser irradiation

A. Hu, M. Rybachuk, Q.-B. Lu, and W. W. Duley

Appl. Phys. Lett. 91, 131906 (2007); http://dx.doi.org/10.1063/1.2793628 (3 pages) | Cited 19 times

Online Publication Date: 27 September 2007

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Microscopic phase transformation from graphite to sp-bonded carbon chains (carbyne) and nanodiamond has been induced by femtosecond laser pulses on graphite surface. UV/surface enhanced Raman scattering spectra and x-ray photoelectron spectra displayed the local synthesis of carbyne in the melt zone while nanocrystalline diamond and trans-polyacetylene chains form in the edge area of gentle ablation. These results evidence possible direct “writing” of variable chemical bonded carbons by femtosecond laser pulses for carbon-based applications.
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64.70.K- Solid-solid transitions
78.30.-j Infrared and Raman spectra
79.60.Jv Interfaces; heterostructures; nanostructures
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Deformation-induced rotational eutectic colonies containing length-scale heterogeneity in an ultrafine eutectic Fe83Ti7Zr6B4 alloy

Jin Man Park, Do Hyang Kim, Ki Buem Kim, and Won Tae Kim

Appl. Phys. Lett. 91, 131907 (2007); http://dx.doi.org/10.1063/1.2793189 (3 pages) | Cited 39 times

Online Publication Date: 27 September 2007

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Microstructural investigations of an ultrafine eutectic Fe83Ti7Zr6B4 alloy reveal that spherical eutectic colonies are composed of nanoeutectic areas which are encapsulated by submicron eutectic areas indicating length-scale heterogeneity of lamellar structure. Furthermore, formation of the wavy and discontinuous shear bands indicative of dissipation of the shear stress are possibly caused by a rotation of the eutectic colonies along the submicron eutectic areas during deformation, leading to developing typical dimples on the fracture surface. The rotation of the eutectic colonies containing the length-scale heterogeneity is proposed to be responsible for macroscopic plasticity of the ultrafine eutectic Fe83Ti7Zr6B4 alloy.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Characterization of Si nanostructures using a noncontact mode scanning near-field optical Raman microscope, with 100 nm spatial resolution and 5 nm depth resolution, using ultraviolet resonant Raman scattering

M. Yoshikawa, M. Murakami, and H. Ishida

Appl. Phys. Lett. 91, 131908 (2007); http://dx.doi.org/10.1063/1.2780114 (3 pages) | Cited 1 time

Online Publication Date: 28 September 2007

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The authors developed a noncontact mode scanning near-field Raman microscope (NC-SNORM) with a hollow pyramidal probe, using ultraviolet resonant Raman scattering, measured the stress distribution in very-large-scale integration standards made of silicon dioxide (SiO2) film and Si, and characterized Si nanodot structures. The authors found that the areas covered by SiO2 are under tensile stress and the areas not covered by SiO2 are under compressive stress. Compressive stress concentrates on the interface, about 100 nm wide, between the covered and noncovered areas. They measured near-field Raman spectra of the Si nanodot structures and found that the Raman intensities change periodically approximately every 100 nm.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Am Elemental semiconductors and insulators
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

A strong micropillar containing a low angle grain boundary

R. Maaß, S. Van Petegem, D. Grolimund, H. Van Swygenhoven, and M. D. Uchic

Appl. Phys. Lett. 91, 131909 (2007); http://dx.doi.org/10.1063/1.2784938 (3 pages) | Cited 13 times

Online Publication Date: 28 September 2007

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In situ white beam Laue diffraction experiments on focused ion beam machined single crystal 10 μm Ni pillars are performed to explore the relation between the initial and evolving microstructures and the subsequent flow response. The pillar has a flow stress that is at least in the upper bound of the scatter of the flow stresses obtained for similar Ni pillars. Detailed analysis of the Laue pattern suggests that the strength is in part due to the low angle grain boundary acting as a dislocation barrier.
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61.72.Mm Grain and twin boundaries
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Epitaxial growth of AlN films on Rh ultraviolet mirrors

S. Inoue, K. Okamoto, T. Nakano, J. Ohta, and H. Fujioka

Appl. Phys. Lett. 91, 131910 (2007); http://dx.doi.org/10.1063/1.2793187 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2007

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Epitaxial growth of AlN films on mirror polished Rh(111) substrates, with high reflectivity in the ultraviolet (UV) region and high thermal conductivity, was demonstrated using a low temperature growth technique employing pulsed laser deposition. It was found that AlN(0001) grows epitaxially on Rh(111) at 450 °C with an in-plane epitaxial relationship of AlN[11math0]‖Rh[1math0] Electron backscattering diffraction observations revealed that neither 30° rotational domains nor cubic phase domains were present in the AlN. X-ray reflectivity measurements revealed that no interfacial layer was present between the AlN films and Rh substrates and that the heterointerface was atomically abrupt, indicating that the Rh substrate still functioned as an UV mirror, even after AlN growth.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
42.79.Bh Lenses, prisms and mirrors
81.15.Fg Pulsed laser ablation deposition

Concomitant speed-of-sound tomography in photoacoustic imaging

Srirang Manohar, René G. H. Willemink, Ferdi van der Heijden, Cornelis H. Slump, and Ton G. van Leeuwen

Appl. Phys. Lett. 91, 131911 (2007); http://dx.doi.org/10.1063/1.2789689 (3 pages) | Cited 13 times

Online Publication Date: 28 September 2007

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We present a method to generate quantitative cross-sectional maps of acoustic propagation speed in tissue using the photoacoustic principle. The method is based on the interaction of laser-induced ultrasound from an extraneous absorber with the object under photoacoustic investigation. The propagation times of the ultrasound transients through the object at angles around 360° are measured using a multielement ultrasound detector. The geometry lends itself to fan-beam reconstruction allowing speed-of-sound tomograms to be generated. Simultaneously, conventional photoacoustic computed tomography can be performed as well. We demonstrate the concept showing results on phantoms carrying speed-of-sound distributions.
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87.63.D- Ultrasonography
43.80.Qf Medical diagnosis with acoustics
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
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Fluorine counter doping effect in B-doped Si

G. Impellizzeri, S. Mirabella, A. M. Piro, M. G. Grimaldi, F. Priolo, F. Giannazzo, V. Raineri, E. Napolitani, and A. Carnera

Appl. Phys. Lett. 91, 132101 (2007); http://dx.doi.org/10.1063/1.2790373 (3 pages) | Cited 7 times

Online Publication Date: 24 September 2007

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We investigated the effect of F on the electrical activity of B-doped junctions in preamorphized Si. It is shown that while the carrier dose introduced by B is reduced in the presence of F, no indication of B–F complexes formation can be found and B maintains its full substitutionality. Investigations on F-enriched crystalline Si demonstrated and quantified the n-type doping of F. These results clarify that the loss of holes in junctions coimplanted with B and F is not due to a chemical interaction between B and F, but simply to a dopant compensation effect.
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61.72.uf Ge and Si
72.20.-i Conductivity phenomena in semiconductors and insulators

A high-throughput thermoelectric power-factor screening tool for rapid construction of thermoelectric property diagrams

M. Otani, N. D. Lowhorn, P. K. Schenck, W. Wong-Ng, M. L. Green, K. Itaka, and H. Koinuma

Appl. Phys. Lett. 91, 132102 (2007); http://dx.doi.org/10.1063/1.2789289 (3 pages) | Cited 9 times

Online Publication Date: 24 September 2007

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The authors have developed a high-throughput screening tool that maps out thermoelectric power factors of combinatorial composition-spread film libraries. The screening tool allows one to measure the electrical conductivity and Seebeck coefficient of over 1000 sample points within 6 h. Seebeck coefficients of standard films measured with the screening tool are in good agreement with those measured by traditional thermoelectric measurement apparatus. The rapid construction of thermoelectric property diagrams is illustrated for two systems: (Zn, Al)–O binary composition-spread film on Al2O3 (0001) and (Ca,Sr,La)3Co4O9 ternary composition-spread film on Si (100).
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73.50.Lw Thermoelectric effects
73.61.Ng Insulators
72.20.Pa Thermoelectric and thermomagnetic effects

Radiation-induced decay of Shubnikov–de Haas oscillations in the regime of the radiation-induced zero-resistance states

R. G. Mani

Appl. Phys. Lett. 91, 132103 (2007); http://dx.doi.org/10.1063/1.2784963 (3 pages) | Cited 12 times

Online Publication Date: 25 September 2007

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Shubnikov–de Haas (SdH) oscillations decay under the influence of radiation in the regime of the radiation-induced zero-resistance states in GaAs/AlGaAs devices. Experiment demonstrates that the SdH amplitude scales linearly with the average background resistance in the vicinity of the radiation-induced resistance minima, which shows that the SdH amplitude vanishes in proportion to the background resistance at the centers of the radiation-induced zero-resistance states.
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72.20.My Galvanomagnetic and other magnetotransport effects

Temperature effects of Si interface passivation layer deposition on high-k III-V metal-oxide-semiconductor characteristics

InJo Ok, H. Kim, M. Zhang, F. Zhu, S. Park, J. Yum, H. Zhao, and Jack C. Lee

Appl. Phys. Lett. 91, 132104 (2007); http://dx.doi.org/10.1063/1.2790780 (3 pages) | Cited 11 times

Online Publication Date: 25 September 2007

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In this work, we studied the electrical characteristics of TaN/HfO2/GaAs metal-oxide-semiconductor capacitors with Si interface passivation layer (IPL) under various postdeposition anneal (PDA) conditions and various Si deposition temperatures/times. Using optimal Si IPL under reasonable PDA, post metal anneal conditions, and various Si deposition temperatures, excellent electrical characteristics with low frequency dispersion (<5%, and 50 mV) and reasonable Dit value ( ∼ 1012 eV−1 cm−2) can be obtained. It was found that higher temperature of Si IPL deposition and longer PDA time at 600 °C improved equivalent oxide thickness and leakage current.
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81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Shallow acceptors in GaN

T. A. G. Eberlein, R. Jones, S. Öberg, and P. R. Briddon

Appl. Phys. Lett. 91, 132105 (2007); http://dx.doi.org/10.1063/1.2776852 (2 pages) | Cited 6 times

Online Publication Date: 25 September 2007

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Recent high resolution photoluminescence studies of high quality Mg doped GaN show the presence of two acceptors. One is due to Mg and the other labeled A1 has a shallower acceptor defect. The authors investigate likely candidates for this shallow acceptor and conclude that CN is the most likely possibility. The authors also show that the CN is passivated by H and the passivated complex is more stable than MgGa–H.
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81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.65.Rv Passivation

Conductivity type conversion in ion-milled p-HgCdTe:As heterostructures grown by molecular beam epitaxy

I. I. Izhnin, S. A. Dvoretsky, N. N. Mikhailov, Yu. G. Sidorov, V. S. Varavin, K. D. Mynbaev, and M. Pociask

Appl. Phys. Lett. 91, 132106 (2007); http://dx.doi.org/10.1063/1.2789782 (3 pages) | Cited 8 times

Online Publication Date: 25 September 2007

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Conductivity type conversion in ion-milled As-doped p-HgCdTe heterostructures grown by molecular beam epitaxy on GaAs substrates has been studied. It was found that in these heterostructures, donor center concentration ( ∼ 1017 cm−3) after ion milling was much higher than that could have been expected as a result of interaction of interstitial mercury atoms, generated under the milling, with the As acceptors. One possible reason of the donor center formation is the activation of an intrinsic neutral defect, which was present in the HgCdTe:As prior to the ion milling. The nature of the donor centers formed is discussed.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.J- Point defects and defect clusters

Ge/Si heteronanocrystal floating gate memory

Bei Li, Jianlin Liu, G. F. Liu, and J. A. Yarmoff

Appl. Phys. Lett. 91, 132107 (2007); http://dx.doi.org/10.1063/1.2793687 (3 pages) | Cited 11 times

Online Publication Date: 27 September 2007

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Metal oxide semiconductor field effect transistor memories with Ge/Si heteronanocrystals (HNCs) as floating gate were fabricated and characterized. Ge/Si HNCs with density of 5×1011 cm−2 were grown on n-type Si (100) substrate with thin tunnel oxide on the top. Enhanced device performances including longer retention time, faster programming speed, and higher charge storage capability are demonstrated compared with Si nanocrystal (NC) memories. The erasing speed and endurance performance of Ge/Si HNC memories are similar to that of Si NC devices. The results suggest that Ge/Si HNCs may be an alternative to make further floating gate memory scaling down possible.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

Terahertz emission from vertically aligned InN nanorod arrays

H. Ahn, Y.-P. Ku, Y.-C. Wang, C.-H. Chuang, S. Gwo, and Ci-Ling Pan

Appl. Phys. Lett. 91, 132108 (2007); http://dx.doi.org/10.1063/1.2789183 (3 pages) | Cited 12 times

Online Publication Date: 27 September 2007

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Terahertz emission from indium nitride (InN) nanorods and InN film grown by molecular-beam epitaxy on Si(111) substrates has been investigated. Terahertz emission from InN nanorods is at least three times more intense than that from InN film and depends strongly on the size distribution of the nanorods. Surface electron accumulation at the InN nanorods effectively screens out the photo-Dember field in the accumulation layer formed under the surface. The nanorods with considerably large diameter than the thickness of accumulation layer are found to be dominant in the emission of terahertz radiation from InN nanorod arrays.
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78.67.Ch Nanotubes
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ey III-V semiconductors

Cu films containing insoluble Ru and RuNX on barrierless Si for excellent property improvements

J. P. Chu, C. H. Lin, and V. S. John

Appl. Phys. Lett. 91, 132109 (2007); http://dx.doi.org/10.1063/1.2790843 (3 pages) | Cited 21 times

Online Publication Date: 27 September 2007

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This letter reports superior properties of Ru- and RuNX-bearing Cu films deposited by cosputtering on barrierless Si substrates. After annealing at temperatures up to 680 °C for 1 h, low resistivity of ∼ 3 μΩ cm and minimal leakage currents as well as no detectable reaction at the Cu/Si interface have confirmed the excellent thermal stability of these Cu(Ru) and Cu(RuNX) films. Furthermore, the highly stable Cu(RuNX) film exhibits an outstanding adhesion property, proving to be a very promising candidate for the barrierless Cu metallization.
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61.72.Cc Kinetics of defect formation and annealing
73.61.At Metal and metallic alloys
68.60.Dv Thermal stability; thermal effects
81.15.Cd Deposition by sputtering
85.40.Ls Metallization, contacts, interconnects; device isolation

Conductivity of single ZnO nanorods after Ga implantation in a focused-ion-beam system

D. Weissenberger, M. Dürrschnabel, D. Gerthsen, F. Pérez-Willard, A. Reiser, G. M. Prinz, M. Feneberg, K. Thonke, and R. Sauer

Appl. Phys. Lett. 91, 132110 (2007); http://dx.doi.org/10.1063/1.2791006 (3 pages) | Cited 13 times

Online Publication Date: 27 September 2007

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ZnO nanorods were implanted with Ga+ ions in a combined scanning-electron-microscope/focused-ion-beam system with doses from 1011 to 1017 cm−2. Electrical resistance measurements performed on single ZnO nanorods yield first an increase of the resistance due to defect formation which lowers the electron mobility. Implantation doses exceeding 1015 cm−2 yield a strong decrease of the resistance to values significantly below the resistance before Ga+-ion implantation. Low specific resistivities of about 3×10−3 Ω cm are reached without additional annealing treatment after high-dose implantation.
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73.63.Bd Nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.72.uj III-V and II-VI semiconductors

Realization of In2O3 thin film transistors through reactive evaporation process

Dhananjay and Chih-Wei Chu

Appl. Phys. Lett. 91, 132111 (2007); http://dx.doi.org/10.1063/1.2789788 (3 pages) | Cited 13 times

Online Publication Date: 27 September 2007

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In2O3 thin films have been grown by reactive evaporation of indium in ambient oxygen. The films were structurally characterized by x-ray diffraction (XRD) and atomic force microscopy techniques. The results of XRD revealed that the films were polycrystalline in nature with preferred (222) orientation. The as-grown films were subjected to various annealing treatments to modulate the conductivity of the films for thin film transistors (TFTs). TFTs fabricated on SiO2 gate dielectric exhibited an on/off ratio of 104 and a field-effect mobility of 27 cm2/V s. High on-state current makes them potential candidates for flat-panel display devices.
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85.30.Tv Field effect devices
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Impact of V/III ratio on electrical properties of GaN thick films grown by hydride vapor-phase epitaxy

D. C. Oh, S. W. Lee, H. Goto, S. H. Park, I. H. Im, T. Hanada, M. W. Cho, and T. Yao

Appl. Phys. Lett. 91, 132112 (2007); http://dx.doi.org/10.1063/1.2786851 (3 pages) | Cited 8 times

Online Publication Date: 28 September 2007

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Impact of V/III ratio on electrical properties of GaN thick films are investigated, which are grown by hydride vapor-phase epitaxy. The authors note that the electron concentration of GaN films decreases with the increase of V/III ratio, while their electrical resistivity and electron mobility increase simultaneously. These indicate that enhancing V/III ratio suppresses electron-feeding sources in GaN films, which is not by generating electron-trapping centers but by reducing donor-type defects. On the other hand, it is shown that the linewidth of x-ray rocking curves in GaN films decreases and the near-band edge emission intensity of 10 K photoluminescence spectra increases as V/III ratio increases. These mean that higher V/III ratio condition helps for reducing crystalline point defects in GaN films. In terms of theoretical fitting into the temperature-dependence curves of electron mobilities, it is found that the electron transport of GaN films grown in lower V/III ratio condition is more hampered by defect scatterings. Consequently, it is suggested that the generation of donor-type defects in the GaN thick films is more suppressed by higher V/III ratios, which induces lower background electron concentration and higher electron mobility.
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73.61.Ey III-V semiconductors
72.20.Ht High-field and nonlinear effects
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Effect of void propagation on bump resistance due to electromigration in flip-chip solder joints using Kelvin structure

Y. W. Chang, T. H. Chiang, and Chih Chen

Appl. Phys. Lett. 91, 132113 (2007); http://dx.doi.org/10.1063/1.2790376 (3 pages) | Cited 5 times

Online Publication Date: 28 September 2007

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Three-dimensional modeling is employed to simulate various Kelvin structures for detecting the change in bump resistance due to void formation and propagation during electromigration in flip-chip solder joints. It is found that the Kelvin structures can sense the highest voltage drop when its voltage probes are placed at the current entrance into the bump on the chip side, and it is thus the most sensitive design to monitor void formation and propagation. When the bump resistance increases 20% of its initial value, the depletion percentage of contact opening ranges from 21.0% to 65.0%, depending on the position of the probes.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Direct observation of Schottky to Ohmic transition in Al-diamond contacts using real-time photoelectron spectroscopy

D. A. Evans, O. R. Roberts, A. R. Vearey-Roberts, D. P. Langstaff, D. J. Twitchen, and M. Schwitters

Appl. Phys. Lett. 91, 132114 (2007); http://dx.doi.org/10.1063/1.2790779 (3 pages) | Cited 4 times

Online Publication Date: 28 September 2007

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Real-time photoelectron spectroscopy and in situ electrical measurements have been applied to the formation of Al contacts on p-type diamond. At 294 K, an initially uniform Al film induces band bending in the diamond consistent with the measured (current-voltage) barrier height of 1.05 V. The temperature-induced transition to an Ohmic contact has been monitored in real time revealing a direct correlation between the onset of surface bonding at 755 K and an abrupt change in surface band bending. The reaction temperature is lower than previously believed, and there is a second transition point at 1020 K where the rates of change of both reaction and band bending increase sharply.
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73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Cg Contact resistance, contact potential

Tuning the contact resistance in nanoscale oligothiophene field effect transistors

A. Hoppe, J. Seekamp, T. Balster, G. Götz, P. Bäuerle, and V. Wagner

Appl. Phys. Lett. 91, 132115 (2007); http://dx.doi.org/10.1063/1.2790789 (3 pages) | Cited 6 times

Online Publication Date: 28 September 2007

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Nanoscale organic transistors for high frequency applications are often limited by contact resistances. We report on tuning of those resistances by shifting the transport level for dihexyl-n-thiophene (DHnT) semiconductors by variation of the number of thiophenes n from 4 to 7. The intrinsic mobility as well as contact resistance were determined from individual transfer curves of bottom-contact transistors with channel lengths down to 50 nm. Best values were found for DH7T with μ = 0.12 cm2/V s and Rc = 1 kΩ cm. While the contact resistance remains fairly constant for a given n as expected, the intrinsic mobility still decreases with decreasing channel length.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

High electron mobility in nearly lattice-matched AlInN/AlN/GaN heterostructure field effect transistors

Jinqiao Xie, Xianfeng Ni, Mo Wu, Jacob H. Leach, Ümit Özgür, and Hadis Morkoç

Appl. Phys. Lett. 91, 132116 (2007); http://dx.doi.org/10.1063/1.2794419 (3 pages) | Cited 43 times

Online Publication Date: 28 September 2007

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High electron mobility was achieved in Al1−xInxN/AlN/GaN (x = 0.20–0.12) heterostructure field effect transistors (HFETs) grown by metal-organic chemical vapor deposition. Reduction of In composition from 20% to 12% increased the room temperature equivalent two-dimensional-electron-gas density from 0.90×1013 to 1.64×1013 cm−2 with corresponding electron mobilities of 1600 and 1410 cm2/V s, respectively. The 10 K mobility reached 17 600 cm2/V s for the nearly lattice-matched Al0.82In0.18N/AlN/GaN heterostructure with a sheet carrier density of 9.6×1012 cm−2. For comparison, the AlInN/GaN heterostructure without the AlN spacer exhibited a high sheet carrier density (2.42×1013 cm−2) with low mobility (120 cm2/V s) at room temperature. The high mobility in our samples is in part attributed to ∼ 1 nm AlN spacer which significantly reduces the alloy scattering as well as provides a smooth interface. The HFETs having gate dimensions of 1.5×40 μm2 and a 5 μm source-drain separation exhibited a maximum transconductance of ∼ 200 mS/mm with good pinch-off characteristics and over 10 GHz current gain cutoff frequency.
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85.30.Tv Field effect devices
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