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29 Nov 2010

Volume 97, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 223101 (2010); http://dx.doi.org/10.1063/1.3519844 (3 pages)

Jin-Kyu Yang, Svetlana V. Boriskina, Heeso Noh, Michael J. Rooks, Glenn S. Solomon, Luca Dal Negro, and Hui Cao
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Stokes–Einstein relation in dense metallic glass-forming melts

S. M. Chathoth and K. Samwer

Appl. Phys. Lett. 97, 221910 (2010); http://dx.doi.org/10.1063/1.3523361 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2010

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Quasielastic neutron scattering has been used to investigate atomic motion in a very fragile binary metallic melt and a multicomponent bulk glass-forming metallic melt. Both melts show a breakdown of the Stokes–Einstein relation and display a change in the slope of In D dependence on In(η/T). We also observed that the values for the exponent in the fractional Stokes–Einstein relation are not in the commonly observed range for Cu46Zr42Al7Y5 melts. At low temperatures, the deviation from the Stokes–Einstein law is very significant and can be expressed in the form of a power law with exponent ξ = −1.82±0.08. The change in the slope is found to be associated with a change in friction coefficient while increasing the packing density of the melt. The abrupt change in the value of friction coefficient is independent of packing density, but it occurs at a common value of ζ = (3.2±0.1)×10−12 kg s−1 in these melts.
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61.25.Mv Liquid metals and alloys
81.40.Pq Friction, lubrication, and wear
66.10.cg Mass diffusion, including self-diffusion, mutual diffusion, tracer diffusion, etc.
62.20.Qp Friction, tribology, and hardness

High-pressure hydrogen materials compatibility of piezoelectric films

K. J. Alvine, V. Shutthanandan, W. D. Bennett, C. C. Bonham, D. Skorski, S. G. Pitman, M. E. Dahl, and C. H. Henager, Jr.

Appl. Phys. Lett. 97, 221911 (2010); http://dx.doi.org/10.1063/1.3517445 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2010

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Hydrogen is well known for materials compatibility issues, including blistering and embrittlement in metals, which are challenges for its use as the next-generation “green” fuel. Beyond metals, hydrogen also degrades piezoelectric materials used as actuators used in direct injection hydrogen internal combustion engines. We present the materials compatibility studies of piezoelectric films in high-pressure hydrogen environments. Absorption of high-pressure hydrogen and composition changes were studied with an elastic recoil detection analysis and Rutherford back-scattering spectrometry in lead zirconate titanate and barium titanate thin films. Hydrogen surface degradation in the form of blistering and Pb mixing was also observed.
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62.50.-p High-pressure effects in solids and liquids
77.55.hj PZT
61.05.Np Atom, molecule, and ion scattering (for structure determination only)
81.65.-b Surface treatments

Direct-gap photoluminescence with tunable emission wavelength in Ge1−ySny alloys on silicon

J. Mathews, R. T. Beeler, J. Tolle, C. Xu, R. Roucka, J. Kouvetakis, and J. Menéndez

Appl. Phys. Lett. 97, 221912 (2010); http://dx.doi.org/10.1063/1.3521391 (3 pages) | Cited 16 times

Online Publication Date: 2 December 2010

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Direct-gap photoluminescence has been observed at room temperature in Ge1−ySny alloys grown on (001) Si substrates. The emission wavelength is tunable over a 90 meV (200 nm) range by increasing the Sn concentration from y = 0 to y = 0.03. A weaker feature at lower energy is assigned to the indirect gap transitions, and the separation between the direct and indirect emission peaks is found to decrease as a function of y, as expected for these alloys. These results suggest that Ge1−ySny alloys represent an attractive alternative to Ge for the fabrication of laser devices on Si.
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78.55.Hx Other solid inorganic materials
71.20.Nr Semiconductor compounds

Ga induced superstructures as templates for lattice matched hetroepitaxial growth of GaN on Si(111) substrate

Praveen Kumar, Jithesh Kuyyalil, and S. M. Shivaprasad

Appl. Phys. Lett. 97, 221913 (2010); http://dx.doi.org/10.1063/1.3522830 (3 pages) | Cited 2 times

Online Publication Date: 3 December 2010

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High quality GaN is grown by plasma assisted molecular beam epitaxy on Ga induced superstructural phases of Si(111)7×7. Three stable surface phases induced by Ga adsorption, viz., (1×1), (6.3×6.3), and (√3×√3)R30°, are employed as templates to grow epitaxial (0001) GaN thin films. GaN grown on Si(√3×√3)R30°-Ga is found to be highly crystalline with intense (0002) x-ray diffraction and photoluminescence peaks with low full width at half maximum, low surface roughness, and stoichiometric surface composition. The high quality of these GaN films formed at a low temperature of 400 °C is explained by the integral (×2) lattice matching between the unit cell of GaN and the (√3×√3) phase. The experiments demonstrate a plausible approach of adsorbate induced surface modifications as templates for III-V hetroepitaxy on Si surfaces.
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68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.43.Mn Adsorption kinetics
68.35.bg Semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Conformal GaP layers on Si wire arrays for solar energy applications

Adele C. Tamboli, Manav Malhotra, Gregory M. Kimball, Daniel B. Turner-Evans, and Harry A. Atwater

Appl. Phys. Lett. 97, 221914 (2010); http://dx.doi.org/10.1063/1.3522895 (3 pages)

Online Publication Date: 3 December 2010

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We report conformal, epitaxial growth of GaP layers on arrays of Si microwires. Silicon wires grown using chlorosilane chemical vapor deposition were coated with GaP grown by metal-organic chemical vapor deposition. The crystalline quality of conformal, epitaxial GaP/Si wire arrays was assessed by transmission electron microscopy and x-ray diffraction. Hall measurements and photoluminescence show p- and n-type doping with high electron mobility and bright optical emission. GaP pn homojunction diodes on planar reference samples show photovoltaic response with an open circuit voltage of 660 mV.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
73.61.-r Electrical properties of specific thin films
85.30.Kk Junction diodes
78.66.-w Optical properties of specific thin films

Single-mode waveguiding in bundles of self-assembled semiconductor nanowires

J. Zhang, A. A. Lutich, A. S. Susha, A. L. Rogach, F. Jäckel, and J. Feldmann

Appl. Phys. Lett. 97, 221915 (2010); http://dx.doi.org/10.1063/1.3524219 (3 pages) | Cited 1 time

Online Publication Date: 3 December 2010

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We report on waveguiding in bundles of parallel oriented semiconductor nanowires, self-assembled from colloidal CdTe nanocrystals in solution at room temperature. Individual bundles, as narrow as 170 nm, act as single-mode, subwavelength waveguides for red visible light. Losses are dominated by reabsorption and allow waveguiding over distances of micrometers. This renders self-assembled NW bundles candidates for low-cost, short-distance optical interconnects in hybrid electronic-photonic circuits.
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42.82.Et Waveguides, couplers, and arrays
42.82.Ds Interconnects, including holographic interconnects
42.70.-a Optical materials
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Investigation on the formation mechanism of p-type Li–N dual-doped ZnO

B. Y. Zhang, B. Yao, Y. F. Li, Z. Z. Zhang, B. H. Li, C. X. Shan, D. X. Zhao, and D. Z. Shen

Appl. Phys. Lett. 97, 222101 (2010); http://dx.doi.org/10.1063/1.3518059 (3 pages) | Cited 5 times

Online Publication Date: 29 November 2010

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Lithium and nitrogen dual-doped ZnO films [ZnO:(Li, N)] with Li concentrations of 0%–11.2% were grown on sapphire by plasma-assisted molecular beam epitaxy, and a stable p-type ZnO:(Li, N) film was obtained by doping 6.1% of Li. The p-type conductivity of ZnO:(Li, N) is attributed to the formation of the Lii–NO complex, which depresses the compensation of Lii donor for LiZn acceptor and the generation of (N2)O donors. It is demonstrated that the Lii–NO complex can form an impurity band above the valance band maximum, resulting in a decrease in the ionization energy of the acceptor and an improvement in the conductivity and stability of the p-type ZnO:(Li, N).
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68.55.A- Nucleation and growth
81.05.Dz II-VI semiconductors
61.72.U- Doping and impurity implantation
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.55.ag Semiconductors
61.72.uj III-V and II-VI semiconductors

Effect of top metal contact on electrical transport through individual multiwalled carbon nanotubes

Neha Kulshrestha, Abhishek Misra, Senthil Srinivasan, Kiran Shankar Hazra, Reeti Bajpai, Soumyendu Roy, Gayatri Vaidya, and D. S. Misra

Appl. Phys. Lett. 97, 222102 (2010); http://dx.doi.org/10.1063/1.3518063 (3 pages)

Online Publication Date: 29 November 2010

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The effect of position of top metal contact on the electrical transport through individual multiwalled carbon nanotubes (MWNTs) has been investigated using gas injection system in situ in scanning electron microscope to deposit the top platinum metal contacts at different desired sites on the side contacted MWNTs in bridging structure. Current-voltage measurements reveal a significant improvement in electrical properties of the tubes after the top contact is made. This improvement has been found to be independent of position of top contact, i.e., whether the top contact is made on the ends or at any other site of the tube.
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73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
61.46.Fg Nanotubes

Trapping effect evaluation of gateless AlGaN/GaN heterojunction field-effect transistors using transmission-line-model method

Cheng-Yu Hu (胡成余), Tamotsu Hashizume (橋詰保), Kota Ohi (大井幸多), and Masafumi Tajima (田島正文)

Appl. Phys. Lett. 97, 222103 (2010); http://dx.doi.org/10.1063/1.3506583 (3 pages) | Cited 1 time

Online Publication Date: 29 November 2010

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An electric-field-dependent trapping effect was observed in our AlGaN/GaN transmission-line-model (TLM) structure. Therefore, we adopted a “gradual voltage stress” scheme to induce a similar trapping effect, that is, a similar sheet resistance variation (ΔRSH) for all intervals of our AlGaN/GaN TLM structure. By measuring the TLM structure under “gradual voltage stress” (stressed TLM measurement), we investigated the trapping effects in gateless AlGaN/GaN heterojunction field-effect transistors. 10 nm of Al2O3 passivation film substantially decreased the voltage-stress-induced ΔRSH, suggesting surface traps were involved. The feasibility and reproducibility of the stressed TLM measurement method was confirmed with repeated passivation.
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85.30.Tv Field effect devices
81.65.Rv Passivation
81.05.Ea III-V semiconductors

Effects of oxidation on surface chemical states and barrier height of AlGaN/GaN heterostructures

Masataka Higashiwaki, Srabanti Chowdhury, Brian L. Swenson, and Umesh K. Mishra

Appl. Phys. Lett. 97, 222104 (2010); http://dx.doi.org/10.1063/1.3522649 (3 pages) | Cited 11 times

Online Publication Date: 29 November 2010

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The effects of oxidation on the surface structure and chemical bonding states of AlGaN/GaN heterostructures were investigated using x-ray photoelectron spectroscopy (XPS). In comparing Al 2p core-level XPS spectra among as-grown and annealed samples, we found that Al atoms on the surface were highly oxidized after rapid thermal annealing (RTA) at high temperature; not only in an O2 but also in an N2 gas atmosphere. The Al oxidation level was almost identical for the samples annealed at 800 °C, irrespective of the annealing atmosphere and time; yet there was a strong dependence on the annealing temperature. The dependence of surface barrier height on the annealing condition is associated with Al oxidation behavior. Before the RTA, the barrier height increased together with the AlGaN thickness, indicating an unpinned Fermi level and the existence of low-density and distributed surface donor states. After the high-temperature RTA, however, the height is maintained at a certain value, regardless of the thickness, due to Fermi level pinning by high-density donor states. These results can be explained by the formation of two types of oxide structures providing different types of donor states.
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81.05.Ea III-V semiconductors
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
79.60.Jv Interfaces; heterostructures; nanostructures

Schottky and tunneling behavior of Fe/MgO/Ge(100) structures

J.-B. Laloë, M. C. Hickey, J. Chang, and J. S. Moodera

Appl. Phys. Lett. 97, 222105 (2010); http://dx.doi.org/10.1063/1.3518071 (3 pages) | Cited 2 times

Online Publication Date: 30 November 2010

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We investigated interface and electrical properties of Ge-based Schottky and tunnel diodes with crystalline MgO barriers. Following a simple cleaning procedure not requiring a high-temperature anneal, x-ray data indicated smooth interfaces and that the MgO tunnel barrier was highly textured. Transport characteristics were fitted using a self-consistent field Simmons–Schottky current-voltage model, yielding the Schottky and tunnel barrier heights for the devices and the distribution of tunneling currents. Considering the Fermi-level depinning and the ratio of Schottky to tunneling currents for each barrier thickness, we find that a MgO thickness of 15 Å yields the best transport properties in this system.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Tv Field effect devices

Trapping of electrons in metal oxide-polymer memory diodes in the initial stage of electroforming

Benjamin F. Bory, Stefan C. J. Meskers, René A. J. Janssen, Henrique L. Gomes, and Dago M. de Leeuw

Appl. Phys. Lett. 97, 222106 (2010); http://dx.doi.org/10.1063/1.3520517 (3 pages) | Cited 2 times

Online Publication Date: 30 November 2010

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Metal oxide-polymer diodes require electroforming before they act as nonvolatile resistive switching memory diodes. Here we investigate the early stages of the electroforming process in Al/Al2O3/poly(spirofluorene)/Ba/Al diodes using quasistatic capacitance-voltage measurements. In the initial stage, electrons are injected into the polymer and then deeply trapped near the poly(spirofluorene)-Al2O3 interface. For bias voltages below 6 V, the number of trapped electrons is found to be CoxideV/q with Coxide as the geometrical capacitance of the oxide layer. This implies a density of traps for the electrons at the polymer-metal oxide interface larger than 3×1017 m−2.
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84.30.Sk Pulse and digital circuits
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
84.47.+w Vacuum tubes
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.10.Fq Growth from melts; zone melting and refining
82.45.-h Electrochemistry and electrophoresis

Dual dielectric tunnel barrier in silicon-rich silicon nitride charge-trap nonvolatile memory

Eunkyeom Kim, Taekyung Yim, Seungman An, Won-Ju Cho, and Kyoungwan Park

Appl. Phys. Lett. 97, 222107 (2010); http://dx.doi.org/10.1063/1.3521260 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2010

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We investigated a tunnel barrier with dual (SiO2 and SiNx) dielectric layers in charge-trap nonvolatile memories to improve the program/erase speed and charge retention characteristics. Threshold voltage shift measurements performed for various stress voltages and time durations revealed that these devices had a large memory window (2–6 V) and long retention time (>10 years). With a decrease in the SiO2 layer thickness, the program speed increased but the erase speed decreased. The change in the program/erase speed and charge retention characteristics with the relative thickness ratio could be attributed to the asymmetric shape of the tunnel barrier. The tunneling currents were explained on the basis of Fowler–Nordheim tunneling and Frenkel–Poole emission in the asymmetric tunnel barrier.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Mechanism of ultrahigh Mn concentration in epitaxially grown wurtzite Ga1−xMnxN

Z. T. Chen, L. Wang, X. L. Yang, C. D. Wang, and G. Y. Zhang

Appl. Phys. Lett. 97, 222108 (2010); http://dx.doi.org/10.1063/1.3521278 (3 pages)

Online Publication Date: 30 November 2010

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The mechanism of Mn doping in epitaxially grown wurtzite Ga1−xMnxN has been investigated by using first-principles calculations. Although the Mn solubility limit is calculated to be as low as 0.032% under thermodynamical equilibrium, it can be increased by about two orders due to the role of growth surface, reaching several atomic percent, and can be further increased by hydrogen passivation. This work indicates that Ga1−xMnxN can be grown epitaxially with Mn concentration as high as that were used in most theoretical predictions, making it reasonable to expect practical room-temperature ferromagnetic Ga1−xMnxN suitable for spin injector.
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68.55.ag Semiconductors
61.72.uj III-V and II-VI semiconductors
82.60.Hc Chemical equilibria and equilibrium constants
81.65.Rv Passivation
72.25.Dc Spin polarized transport in semiconductors

Fabrication of p-channel thin-film transistors using CuO active layers deposited at low temperature

Sang-Yun Sung, Se-Yun Kim, Kwang-Min Jo, Joon-Hyung Lee, Jeong-Joo Kim, Sang-Gon Kim, Kyoung-Hoon Chai, S. J. Pearton, D. P. Norton, and Young-Woo Heo

Appl. Phys. Lett. 97, 222109 (2010); http://dx.doi.org/10.1063/1.3521310 (3 pages) | Cited 5 times

Online Publication Date: 30 November 2010

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We investigated copper oxides for use as an active layer of p-channel field-effect thin-film transistors (TFTs). Cu2O thin films deposited at room temperature using rf magnetron sputtering were transformed to a CuO phase after an annealing treatment in air above 200 °C. The optical bandgaps of the Cu2O and CuO were 2.44 and 1.41 eV, respectively. The bottom gate structured TFTs fabricated using CuO active layers operated in a p-type enhancement mode with an on/off ratio of ∼ 104 and field-effect mobility of 0.4 cm2/V⋅s.
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85.30.Tv Field effect devices

High mobility two-dimensional electron gases in nitride heterostructures with high Al composition AlGaN alloy barriers

Guowang Li, Yu Cao, Huili Grace Xing, and Debdeep Jena

Appl. Phys. Lett. 97, 222110 (2010); http://dx.doi.org/10.1063/1.3523358 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2010

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We report high-electron mobility nitride heterostructures with >70% Al composition AlGaN alloy barriers grown by molecular beam epitaxy. Direct growth of such AlGaN layers on GaN resulted in hexagonal trenches and a low mobility polarization-induced charge. By applying growth interruption at the heterojunction, the surface morphology improved dramatically and the room temperature two-dimensional electron gas (2DEG) mobility increased by an order of magnitude, exceeding 1300 cm2/V s. The 2DEG density was tunable at 0.4–3.7×1013/cm2 by varying the total barrier thickness (t). Surface barrier heights of the heterostructures were extracted and exhibited dependence on t.
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72.20.Ht High-field and nonlinear effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.47.-b Solid-gas/vacuum interfaces: types of surfaces

18.7% efficient laser-doped solar cell on p-type Czochralski silicon

Z. Hameiri, L. Mai, A. Sproul, and S. R. Wenham

Appl. Phys. Lett. 97, 222111 (2010); http://dx.doi.org/10.1063/1.3515866 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2010

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The use of laser doping in solar cell fabrication has received increased attention in recent years, especially due to its ability to form a selective emitter without subjecting the wafer to prolonged high-temperature processes. At the University of New South Wales, a laser doping method was developed that combines the formation of the selective emitter with a self-aligned metallization pattern. This letter reports 18.7% efficient laser-doped solar cells, fabricated on large area commercial-grade p-type Czochralski silicon, and analyzes the loss mechanisms.
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88.40.jj Silicon solar cells

Room temperature single-electron memory and light sensor with three-dimensionally positioned InAs quantum dots

S. Göpfert, L. Worschech, S. Lingemann, C. Schneider, D. Press, S. Höfling, and A. Forchel

Appl. Phys. Lett. 97, 222112 (2010); http://dx.doi.org/10.1063/1.3520522 (3 pages)

Online Publication Date: 1 December 2010

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The authors report on the fabrication and characterization of single-electron memories based on site-controlled InAs quantum dots (QDs) embedded in a GaAs/AlGaAs quantum-wire transistor. By using a hole structure template on a modulation-doped GaAs/AlGaAs heterostructure in combination with etching techniques, two single InAs QDs were centrally positioned in a quantum-wire transistor so that pronounced shifts of the transistor threshold occur by charging of the QDs with single electrons. Single-electron read and write functionalities up to room temperature were observed. The memory function can be also controlled by light with a wavelength in the telecommunication range.
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85.35.Gv Single electron devices
85.60.Gz Photodetectors (including infrared and CCD detectors)

p-n junctions on Ga-face GaN grown by NH3 molecular beam epitaxy with low ideality factors and low reverse currents

Christophe A. Hurni, Oliver Bierwagen, Jordan R. Lang, Brian M. McSkimming, Chad S. Gallinat, Erin C. Young, David A. Browne, Umesh K. Mishra, and James S. Speck

Appl. Phys. Lett. 97, 222113 (2010); http://dx.doi.org/10.1063/1.3521388 (3 pages) | Cited 8 times

Online Publication Date: 1 December 2010

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A comprehensive analysis of forward and reverse current of Ga-face GaN p-n junctions grown by NH3 molecular beam epitaxy (NH3-MBE) on metal organic chemical vapor deposition (MOCVD) GaN:Fe on sapphire is presented. NH3-MBE has a great potential for growing low leakage vertical devices due to its nitrogen-rich growth. Diodes with the lowest n-doping of n ∼ 3.5×1017 cm−3 exhibit an extremely low reverse current of 2.6×10−7 A/cm2 at −40 V and an ideality factor of 1.3, which is lower than the state-of-the-art Ga-face p-n junctions grown on sapphire by MOCVD. An explanation for the difficulty for observing low ideality factors in GaN is presented.
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85.30.Kk Junction diodes
85.40.Sz Deposition technology
85.40.Ry Impurity doping, diffusion and ion implantation technology

Anomalous Hall mobility kink observed in Mg-doped InN: Demonstration of p-type conduction

N. Ma, X. Q. Wang, F. J. Xu, N. Tang, B. Shen, Y. Ishitani, and A. Yoshikawa

Appl. Phys. Lett. 97, 222114 (2010); http://dx.doi.org/10.1063/1.3522892 (3 pages) | Cited 8 times

Online Publication Date: 2 December 2010

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The p-type conduction in Mg-doped InN film is identified by an anomalous Hall mobility kink observed at ∼ 600 K in temperature-dependent Hall-effect measurements. The good agreement between experimental results and ensemble Monte Carlo simulation confirms the p-type bulk conduction under the surface electron accumulation layer. Furthermore, it is found that there is an exponential relationship between the hole concentration in the p-type bulk layer and the reciprocal kink temperature, which provides an effective way to evaluate the hole concentration in Mg-doped InN bulk layer through Hall-effect measurements.
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73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Enhancing the electron mobility via delta-doping in SrTiO3

Y. Kozuka, M. Kim, H. Ohta, Y. Hikita, C. Bell, and H. Y. Hwang

Appl. Phys. Lett. 97, 222115 (2010); http://dx.doi.org/10.1063/1.3524198 (3 pages) | Cited 4 times

Online Publication Date: 2 December 2010

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We fabricated high-mobility δ-doped structures in SrTiO3 thin films in order to investigate the low temperature electronic transport properties of confined carriers in this system. An enhancement of the electron mobility above the bulk value was observed as the doped layer thickness decreased. High-field Hall measurements revealed that this mobility enhancement originates from higher-mobility electrons in the undoped clean regions, which have quantum-mechanically broadened from the doped layer. Because of the absence of apparent lattice misfit between the layers, this structure is highly suitable for investigating two-dimensional electron gases in SrTiO3.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Fq High-field and nonlinear effects
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Ht High-field and nonlinear effects

Polarization-mediated remote surface roughness scattering in ultrathin barrier GaN high-electron mobility transistors

Yu Cao, Huili Xing, and Debdeep Jena

Appl. Phys. Lett. 97, 222116 (2010); http://dx.doi.org/10.1063/1.3521258 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2010

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Ultrathin AlN/GaN heterojunctions are highly attractive for high-frequency transistor applications. In this work, remote surface roughness (RSR) scattering mediated by the high polarization is studied as a new scattering mechanism in such structures. In both depletion-mode and enhancement-mode devices with ultrathin AlN barriers, RSR scattering can be of the same order as polar optical phonons, the dominant scattering mechanism at room temperature. The study indicates that to achieve high-performance high-electron mobility transistors, the surface roughness during processing is as critical as maintaining a sharp heterojunction.
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85.30.Tv Field effect devices
63.20.-e Phonons in crystal lattices
68.35.bg Semiconductors

Ultrafast resistive switching in SrTiO3:Nb single crystal

X. T. Zhang, Q. X. Yu, Y. P. Yao, and X. G. Li

Appl. Phys. Lett. 97, 222117 (2010); http://dx.doi.org/10.1063/1.3524216 (3 pages) | Cited 4 times

Online Publication Date: 3 December 2010

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The resistive switching effect of the SrTiO3:Nb (0.05wt %, 0.5 wt %, and 1 wt % Nb) single crystals contact with Ag and Pt, respectively, was studied by in situ monitoring the voltage drop (Vs) across the samples. For Ag/SrTiO3:Nb junction, the response time is as short as 5 ns, which is two orders of magnitude short than that of the Pt/SrTiO3:Nb junction. The effect of metal electrodes on the response time has been discussed, which is related to the barrier height of the junction.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
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Current induced effective magnetic field and magnetization reversal in uniaxial anisotropy (Ga,Mn)As

M. Endo, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 97, 222501 (2010); http://dx.doi.org/10.1063/1.3520514 (3 pages) | Cited 2 times

Online Publication Date: 29 November 2010

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The authors investigate the current density and temperature dependence of current induced effective magnetic field Heff through spin-orbit interaction in a ferromagnetic semiconductor Ga0.92Mn0.08As having uniaxial magnetic anisotropy. The change of the magnitude of apparent magnetic anisotropy induced by Heff that is dependent on the current direction and density is observed by transport measurements using the planar Hall effect. The authors show the 180° magnetization switching through Heff by applying pulsed current.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.My Galvanomagnetic and other magnetotransport effects

Observation of coupled vortex gyrations by 70-ps-time- and 20-nm-space-resolved full-field magnetic transmission soft x-ray microscopy

Hyunsung Jung, Young-Sang Yu, Ki-Suk Lee, Mi-Young Im, Peter Fischer, Lars Bocklage, Andreas Vogel, Markus Bolte, Guido Meier, and Sang-Koog Kim

Appl. Phys. Lett. 97, 222502 (2010); http://dx.doi.org/10.1063/1.3517496 (3 pages) | Cited 5 times

Online Publication Date: 29 November 2010

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We employed time- and space-resolved full-field magnetic transmission soft x-ray microscopy to observe vortex-core gyrations in a pair of dipolar-coupled vortex-state Permalloy (Ni80Fe20) disks. The 70 ps temporal and 20 nm spatial resolution of the microscope enabled us to simultaneously measure vortex gyrations in both disks and to resolve the phases and amplitudes of both vortex-core positions. We observed their correlation for a specific vortex-state configuration. This work provides a robust and direct method of studying vortex gyrations in dipolar-coupled vortex oscillators.
Show PACS
07.85.Tt X-ray microscopes
75.30.Cr Saturation moments and magnetic susceptibilities
85.70.-w Magnetic devices
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