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17 Jul 2006

Volume 89, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 031107 (2006); http://dx.doi.org/10.1063/1.2222329 (3 pages)

Jiaguang Han, Zhiyuan Zhu, Sanith Ray, Abul K. Azad, Weili Zhang, Mingxia He, Shihong Li, and Yiping Zhao
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Solid phase epitaxy during Ge condensation from amorphous SiGe layer on silicon-on-insulator substrate

S. Balakumar, C. H. Tung, G. Q. Lo, R. Kumar, N. Balasubramanian, D. L. Kwong, Gao Fei, and S. J. Lee

Appl. Phys. Lett. 89, 032101 (2006); http://dx.doi.org/10.1063/1.2222343 (3 pages) | Cited 5 times

Online Publication Date: 17 July 2006

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We report the solid phase epitaxial growth of silicon germanium (SiGe) layer during condensation/oxidation of sputter deposited amorphous SiGe layer on Si on insulator (SOI). The amorphous SiGe layer was first converted into polycrystalline film by preannealing and high temperature oxidation process. The solid phase epitaxial growth occurs during further oxidation/annealing process of polycrystalline SiGe on the Si on insulator substrate. A final thickness of about 1040 Å of single crystalline SiGe is achieved with initial amorphous SiGe and SOI of thickness of 1000 and 740 Å, respectively SiGe with 60% Ge concentration was achieved on further condensation followed by cyclic annealing to eliminate the defects formed in the layer.
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81.15.Np Solid phase epitaxy; growth from solid phases
68.55.-a Thin film structure and morphology
64.70.F- Liquid-vapor transitions
81.65.Mq Oxidation

Vertical quantum wire realized with double cleaved-edge overgrowth

S. F. Roth, H. J. Krenner, D. Schuh, M. Bichler, and M. Grayson

Appl. Phys. Lett. 89, 032102 (2006); http://dx.doi.org/10.1063/1.2222347 (3 pages) | Cited 1 time

Online Publication Date: 17 July 2006

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A quantum wire is fabricated on (001) GaAs at the intersection of two overgrown cleaves. The wire is contacted at each end to n+-GaAs layers via two-dimensional (2D) leads. A side gate controls the density of the wire revealing conductance quantization. The step height is strongly reduced from 2e2/h due to the 2D lead series resistance. We characterize the 2D density and mobility for both cleave facets with four-point measurements. The density on the first facet is modulated by the substrate potential, depleting a 2 μm wide strip that defines the wire length. Microphotoluminescence shows an extra peak consistent with one-dimensional electron states at the corner.
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68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires
73.21.Hb Quantum wires
81.07.Vb Quantum wires
78.55.Cr III-V semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Study of void formation due to electromigration in flip-chip solder joints using Kelvin bump probes

Y. W. Chang, S. W. Liang, and Chih Chen

Appl. Phys. Lett. 89, 032103 (2006); http://dx.doi.org/10.1063/1.2226989 (3 pages) | Cited 18 times

Online Publication Date: 17 July 2006

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Kelvin bump probes were fabricated in flip-chip solder joints, and they were employed to monitor the void formation during electromigration. We found that voids started to form at approximately 5% of the failure time under 0.8 A at 150 °C, and the bump resistance increased only 0.02 mΩ in the initial stage of void formation. Three-dimensional simulation was performed to examine the increase in bump resistance at different stages of void formation, and it fitted the experimental results quite well. This technique provides a systematic way for investigating the void formation during electromigration.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Mobility comparison between front and back channels in ultrathin silicon-on-insulator metal-oxide-semiconductor field-effect transistors by the front-gate split capacitance-voltage method

Akiko Ohata, Sorin Cristoloveanu, and Mikael Cassé

Appl. Phys. Lett. 89, 032104 (2006); http://dx.doi.org/10.1063/1.2222255 (3 pages) | Cited 3 times

Online Publication Date: 18 July 2006

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The mobilities of the front and back channels in ultrathin silicon-on-insulator metal-oxide-semiconductor field-effect transistors with a thin (2 nm) gate oxide were compared. From front-gate split capacitance-voltage measurements, it was confirmed that the effective mobility of the front channel is lower than that of the back channel. A detailed analysis shows that this lowering strongly depends on the electron density, suggesting the presence of additional Coulomb scattering centers at the front channel.
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85.30.Tv Field effect devices

Anomalous attenuation of the positive temperature coefficient of resistivity in a carbon-black-filled polymer composite with electrically conductive in situ microfibrils

Xiang-Bin Xu, Zhong-Ming Li, Kun Dai, and Ming-Bo Yang

Appl. Phys. Lett. 89, 032105 (2006); http://dx.doi.org/10.1063/1.2222339 (3 pages) | Cited 17 times

Online Publication Date: 19 July 2006

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The positive temperature coefficient of resistivity (PTCR) of in situ microfibrillar carbon black∕poly (ethylene terephthalate)∕polyethylene composite attenuates dramatically after a sufficient time of isothermal treatment without oxygen above the melting region of polyethylene. The inhomogeneous surface microstructure and the large size of the microfibrils are the key factors controlling PTCR attenuation, through which a model is proposed to explain this anomalous phenomenon. An effective approach is accordingly developed to prepare recyclable semicrystalline thermoplastic based electrically conductive polymer composite with steady conductivity in wide temperature range.
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81.05.Qk Reinforced polymers and polymer-based composites
72.80.Tm Composite materials
81.40.Gh Other heat and thermomechanical treatments

Strain monitoring in InAs–AlxGa1−xAsySb1−y structures grown by molecular beam epitaxy

Gregory E. Triplett, April S. Brown, and Gary S. May

Appl. Phys. Lett. 89, 032106 (2006); http://dx.doi.org/10.1063/1.2226998 (3 pages)

Online Publication Date: 19 July 2006

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A study of strained InAs–AlxGa1−xAsySb1−y quantum well structures produced by molecular beam epitaxy is presented. The ability to manipulate quantum well strain by way of the AlxGa1−xAsySb1−y buffer is examined using statistical experimental design. Results show that anion composition in the buffer (with a target lattice constant, a = 6.12 Å) varies by as much as 3% in the 450–500 °C growth temperature range. The data reveal interrelationships between strain, structural characteristics, and conductivity. Results demonstrate that these relationships exist and can be modeled empirically and exploited for the design of near-infrared optoelectronic devices.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Fg Quantum wells
73.63.Hs Quantum wells

Nanoscale electrical characterization of organic photovoltaic blends by conductive atomic force microscopy

Olivier Douhéret, Laurence Lutsen, Ann Swinnen, Martin Breselge, Koen Vandewal, Ludwig Goris, and Jean Manca

Appl. Phys. Lett. 89, 032107 (2006); http://dx.doi.org/10.1063/1.2227846 (3 pages) | Cited 29 times

Online Publication Date: 20 July 2006

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Conductive atomic force microscopy (CAFM) is introduced to perform electrical characterization of organic photovoltaic blends with high spatial resolution. Reference blends used in organic bulk heterojunction solar cells are investigated. The ability of CAFM to electrically evidence phase separated donor and acceptor regions is demonstrated. Furthermore, local spectroscopy is performed to analyze charge transport mechanisms in the blends. Significant modifications of the electrical properties of the semiconducting polymers are shown to occur after blending with fullerene derivatives. Finally, the sensitivity of CAFM to photoelectrical phenomena is revealed. Current variations of few picoamperes are locally observed under illumination of P3HT:PCBM.
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73.61.Ph Polymers; organic compounds

Optical spin injection in CuGaSe2/GaAs films

G. Itskos, R. Murray, A. Meeder, N. Papathanasiou, and M. Ch. Lux-Steiner

Appl. Phys. Lett. 89, 032108 (2006); http://dx.doi.org/10.1063/1.2233684 (3 pages) | Cited 2 times

Online Publication Date: 20 July 2006

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We have investigated polarization-resolved photoluminescence in epitaxially grown CuGaSe2/GaAs(001) films. Spin-polarized excitons are optically excited both below and above the characteristic crystal field splitting of the chalcopyrite. At low temperatures, a large exciton spin polarization of 35% is measured under resonant pumping but this is reduced by an order of magnitude and reverses its sign for nonresonant excitation. The measurements suggest that optical pumping within a small energy window just above the band gap results in the preferential generation of light holes and electrons that exhibit a long spin relaxation time, comparable to the recombination time in CuGaSe2.
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78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.25.Dc Spin polarized transport in semiconductors

In-polar InN grown by plasma-assisted molecular beam epitaxy

Chad S. Gallinat, Gregor Koblmüller, Jay S. Brown, Sarah Bernardis, James S. Speck, Grace D. Chern, Eric D. Readinger, Hongen Shen, and Michael Wraback

Appl. Phys. Lett. 89, 032109 (2006); http://dx.doi.org/10.1063/1.2234274 (3 pages) | Cited 71 times

Online Publication Date: 20 July 2006

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We study the effect of different deposition conditions on the properties of In-polar InN grown by plasma-assisted molecular beam epitaxy. GaN buffer layers grown in the Ga-droplet regime prior to the InN deposition significantly improved the surface morphology of InN films grown with excess In flux. Using this approach, In-polar InN films have been realized with room temperature electron mobilities as high as 2250 cm2/V s. We correlate electron concentrations in our InN films with the unintentionally incorporated impurities, oxygen and hydrogen. A surface electron accumulation layer of 5.11×1013 cm−2 is measured for In-polar InN. Analysis of optical absorption data provides a band gap energy of ∼ 0.65 eV for the thickest InN films.
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81.05.Ea III-V semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.-a Thin film structure and morphology
52.77.Dq Plasma-based ion implantation and deposition
73.50.Dn Low-field transport and mobility; piezoresistance

Alloy disorder effects on the room temperature optical properties of Ga1−xInxNyAs1−y quantum wells

Bhavtosh Bansal, Abdul Kadir, Arnab Bhattacharya, B. M. Arora, and Rajaram Bhat

Appl. Phys. Lett. 89, 032110 (2006); http://dx.doi.org/10.1063/1.2227618 (3 pages) | Cited 6 times

Online Publication Date: 20 July 2006

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The effect of alloy disorder on optical density of states and average room-temperature carrier statistics in Ga1−xInxNyAs1−y quantum wells is discussed. A redshift between the peak of the room-temperature photoluminescence and the surface photovoltage spectra that systematically increases with nitrogen content y is observed. The relationship between this Stokes shift and the absorption linewidth in different samples suggests that the photoexcited carriers undergo a continuous transition—from quasithermal equilibrium with the lattice to complete trapping by quantum dot like potential fluctuations—with increase in nitrogen fraction. The “electron temperatures” inferred from photoluminescence spectra are consistent with this interpretation.
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78.67.De Quantum wells
73.63.Hs Quantum wells
78.55.Cr III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena

High electrical conductivity of layered cobalt oxide Ca3Co4O9 epitaxial films grown by topotactic ion-exchange method

Kenji Sugiura, Hiromichi Ohta, Kenji Nomura, Masahiro Hirano, Hideo Hosono, and Kunihito Koumoto

Appl. Phys. Lett. 89, 032111 (2006); http://dx.doi.org/10.1063/1.2234277 (3 pages) | Cited 29 times

Online Publication Date: 21 July 2006

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Epitaxial film of a layered cobalt oxide, Ca3Co4O9, was fabricated on a (0001) face of an α-Al2O3 substrate by a topotactic ion-exchange method using a γ-Na0.8CoO2 epitaxial film as a precursor. High-resolution x-ray diffraction and atomic force microscope measurements revealed that the film was high-quality (001)-oriented Ca3Co4O9 with stepped and terraced surface morphology. The film exhibits a high electrical conductivity of 2.95×102 S cm−1 and a large Seebeck coefficient of ∼ +125 μV K−1, which leads to the thermoelectric power factor (TPF) of 4.5×10−4 W m−1 K−2 at 300 K, potentially usable as a building block of the multilayered film structure with an enhanced TPF value.
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73.50.Lw Thermoelectric effects
68.55.-a Thin film structure and morphology
72.20.Pa Thermoelectric and thermomagnetic effects

First-principles theory of tunneling currents in metal-oxide-semiconductor structures

X.-G. Zhang, Zhong-Yi Lu, and Sokrates T. Pantelides

Appl. Phys. Lett. 89, 032112 (2006); http://dx.doi.org/10.1063/1.2234283 (3 pages) | Cited 4 times

Online Publication Date: 21 July 2006

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Ultrathin gate-oxide films and alternate dielectrics call for accurate modeling of tunneling currents. Available models, based on the effective-mass approximation, yield good fits to finite-bias data, but fail for infinitesimal biases. Here we report a first-principles theory of tunneling currents. We show that the conductance at infinitesimal bias is a ground-state property and can be calculated accurately using density-functional theory and the local-density approximation for exchange and correlation. At finite biases, a discontinuity in the exchange-correlation potential must be properly included. Challenges for both theory and experiments are identified.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Effective work function modification of atomic-layer-deposited-TaN film by capping layer

K. Choi, H. N. Alshareef, H. C. Wen, H. Harris, H. Luan, Y. Senzaki, P. Lysaght, P. Majhi, and B. H. Lee

Appl. Phys. Lett. 89, 032113 (2006); http://dx.doi.org/10.1063/1.2234288 (3 pages) | Cited 26 times

Online Publication Date: 21 July 2006

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We demonstrate that the metallic capping layer has a strong impact on the effective work function (EWF) of the metal gate. Specifically, the EWF of atomic-layer-deposited (ALD)-TaN could be increased from 4.5 to 4.8 eV with chemical-vapor-deposited-TiN capping, which is sufficient amount of work function modification for silicon on insulator based devices. A strong interdiffusion of Ti atoms into the ALD-TaN film is observed and correlated well with the changes in the EWF change. Ti capping experiments confirm that the Ti interdiffusion can actually modify the EWF of Ti/ALD-TaN stack.
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73.30.+y Surface double layers, Schottky barriers, and work functions
66.30.Ny Chemical interdiffusion; diffusion barriers

Nonlinear optical transitions of GaAs/AlGaAs asymmetric double-well structures

E. H. Kim, Y. H. Shin, Yongmin Kim, S. J. Noh, C. H. Perry, J. A. Simmons, S. A. Crooker, and T. Takamasu

Appl. Phys. Lett. 89, 032114 (2006); http://dx.doi.org/10.1063/1.2220533 (3 pages) | Cited 1 time

Online Publication Date: 21 July 2006

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A thin AlGaAs barrier (2.5 nm) inserted into a GaAs/AlGaAs single heterojunction formed a square and a wedge-shaped triangular quantum well in the conduction band. In such a structure, the valence band does not have tunnel-coupled energy levels. Hence, the photogenerated valence holes tend to move to the GaAs flatband region. This asymmetric quantum structure showed intense nonlinear photoluminescence emission behavior with external excitation power and magnetic field. Increasing the external laser power simply caused the number of photogenerated holes to increase near the interface close to the quantum well, which then recombined with the conduction band electrons. External magnetic fields resulted in an increased Coulomb attraction which generated dynamic movement of valence holes. The migration of unbound holes to the interface region from the GaAs flatband area produced highly nonlinear optical transitions in magnetic fields.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
71.20.Nr Semiconductor compounds
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