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6 Oct 2008

Volume 93, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 141901 (2008); http://dx.doi.org/10.1063/1.2990662 (3 pages)

J. H. Han, K. B. Kim, S. Yi, J. M. Park, S. W. Sohn, T. E. Kim, D. H. Kim, J. Das, and J. Eckert
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Observation of individual dopants in a thin silicon layer by low temperature Kelvin Probe Force Microscope

Maciej Ligowski, Daniel Moraru, Miftahul Anwar, Takeshi Mizuno, Ryszard Jablonski, and Michiharu Tabe

Appl. Phys. Lett. 93, 142101 (2008); http://dx.doi.org/10.1063/1.2992202 (3 pages) | Cited 19 times

Online Publication Date: 6 October 2008

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Detection of individual dopants in the thin silicon layer using Kelvin Probe Force Microscopy is presented. The analysis of the surface potential images taken at low temperatures (13 K) on n-type and p-type samples reveals local potential fluctuations that can be attributed to single phosphorus and boron atoms, respectively. Results are confirmed by simulation of surface potential induced by dopants and by the back gate voltage dependence of the measured potential.
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68.35.bg Semiconductors
68.37.Ps Atomic force microscopy (AFM)
61.72.S- Impurities in crystals

Gated armchair nanotube and metallic field effect

Wei Ren, T. H. Cho, T. C. Leung, and C. T. Chan

Appl. Phys. Lett. 93, 142102 (2008); http://dx.doi.org/10.1063/1.2998394 (3 pages) | Cited 6 times

Online Publication Date: 7 October 2008

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We propose a useful metallic field effect element based on the electric field control of armchair single-wall carbon nanotube. The electron conduction channels are enhanced by imposing a transverse gate voltage. Multiple Dirac points have been revealed theoretically by our density functional and tight binding calculations. Our electron transport results show that the performance of such unique transistors depends mainly on the diameter of nanotube exploited. The critical field strength required decreases rapidly with the tube diameter.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices

Phase separation and optical properties in oxygen-rich InN films

A. Dixit, C. Sudakar, R. Naik, G. Lawes, J. S. Thakur, E. F. McCullen, G. W. Auner, and V. M. Naik

Appl. Phys. Lett. 93, 142103 (2008); http://dx.doi.org/10.1063/1.2963498 (3 pages) | Cited 4 times

Online Publication Date: 7 October 2008

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We have investigated the properties of sputter deposited InN thin films prepared from an In-metal (InN-MT) and an In2O3 target (InN-OT). The excess oxygen present in the InN-OT films alters the microstructure by introducing additional disorder. Depth dependent x-ray photoelectron spectroscopy measurements indicate the presence of higher concentrations of oxygen in InN-OT. Raman spectra show evidence for the presence of an In2O3 secondary phase in both samples. Although the InN-OT film has a higher oxygen concentration, both films show similar electrical and optical properties.
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68.35.Dv Composition, segregation; defects and impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.Nq Composition and phase identification
79.60.Ht Disordered structures
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Magnetoelectric bistabilities in ferromagnetic resonant tunneling structures

Christian Ertler

Appl. Phys. Lett. 93, 142104 (2008); http://dx.doi.org/10.1063/1.2998697 (3 pages) | Cited 1 time

Online Publication Date: 7 October 2008

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The conditions for the occurrence of pronounced magnetoelectric bistabilities in the resonant tunneling through a ferromagnetic quantum well are theoretically investigated. The bistability appears due to the mutual feedback of the carriers Coulomb interaction and the carriers exchange coupling with magnetic impurities in the well. It is shown that the well Curie temperature depends strongly on the relative alignment of the quantum well level and the reservoirs chemical potentials, which can be modified electrically. Switching between a “current-on/magnetism-off” and a “current-off/magnetism-on” mode becomes possible if the well temperature lies in-between the bistable values of the well Curie temperature.
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75.80.+q Magnetomechanical effects, magnetostriction
73.63.Hs Quantum wells
73.40.Gk Tunneling
75.30.Et Exchange and superexchange interactions
75.30.Hx Magnetic impurity interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Enhancing electron transport in Si:P delta-doped devices by rapid thermal anneal

K. E. J. Goh, Y. Augarten, L. Oberbeck, and M. Y. Simmons

Appl. Phys. Lett. 93, 142105 (2008); http://dx.doi.org/10.1063/1.2996582 (3 pages) | Cited 3 times

Online Publication Date: 8 October 2008

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We address the use of rapid thermal anneal (RTA) to enhance electron mobility and phase coherent transport in Si:P δ-doped devices encapsulated by low temperature Si molecular beam epitaxy while minimizing dopant diffusion. RTA temperatures of 500–700 °C were applied to δ-doped layers encapsulated at 250 °C. From 4.2 K magnetotransport measurements, we find that the improved crystal quality after RTA increases the mobility/mean free path by ∼ 40% and the phase coherence length by ∼ 25%. Our results suggest that the initial capping layer has near optimal crystal quality and transport improvement achieved by a RTA is limited.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Charging effect of Al2O3 thin films containing Al nanocrystals

Y. Liu, T. P. Chen, W. Zhu, M. Yang, Z. H. Cen, J. I. Wong, Y. B. Li, S. Zhang, X. B. Chen, and S. Fung

Appl. Phys. Lett. 93, 142106 (2008); http://dx.doi.org/10.1063/1.2994695 (3 pages) | Cited 5 times

Online Publication Date: 9 October 2008

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In this work, Al2O3 thin film containing Al nanocrystals (nc-Al) is deposited on Si substrate by radio frequency sputtering to form a metal-insulator-semiconductor structure. Both electron and hole trapping in nc-Al are observed. The charge storage ability of the nc-Al/Al2O3 thin films provides the possibility of memory applications. Charging in the nc-Al also leads to a change in the dc resistance of the thin films, namely, the electron trapping in the nc-Al leads to an increase in the resistance, whereas the resistance is reduced if there is hole trapping in the nc-Al.
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68.55.aj Insulators
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Cd Deposition by sputtering
73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Spin bias measurement based on a quantum point contact

Yanxia Xing, Qing-feng Sun, and Jian Wang

Appl. Phys. Lett. 93, 142107 (2008); http://dx.doi.org/10.1063/1.2999587 (3 pages) | Cited 12 times

Online Publication Date: 9 October 2008

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Electron charge transport through a quantum point contact (QPC) driven by an asymmetric spin bias (SB) is studied. A large charge current is induced when the transmission coefficient of the QPC jumps from one integer plateau to the next. Furthermore, for an open external circuit, the induced charge bias instead of the charge current is found to be quite large. It provides an efficient and practical way to detect SB by using a very simple device, a QPC or a STM tip. In addition, with the aid of magnetic field, polarization direction of the SB can also be determined.
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73.63.Rt Nanoscale contacts
72.25.-b Spin polarized transport
73.23.-b Electronic transport in mesoscopic systems

Low extended defect density nonpolar m-plane GaN by sidewall lateral epitaxial overgrowth

Kwang-Choong Kim, Mathew C. Schmidt, Feng Wu, Melvin B. McLaurin, Asako Hirai, Shuji Nakamura, Steven P. DenBaars, and James S. Speck

Appl. Phys. Lett. 93, 142108 (2008); http://dx.doi.org/10.1063/1.2908978 (3 pages) | Cited 4 times

Online Publication Date: 9 October 2008

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Sidewall lateral epitaxial overgrowth (SLEO) is demonstrated by metal organic chemical vapor deposition for nonpolar {1math00} m-plane GaN films. m-plane GaN films were grown by metal organic chemical vapor deposition on m-plane 6H SiC substrates with an AlN initiation layer. Subsequently, an SiO2 stripe dielectric pattern was formed with 2 μm window openings parallel to the [11math0] a-direction and an 8 μm mask and then the m-plane GaN was etched through the window openings to reveal Ga-face (0001) and N-face (000math) sidewalls. The SLEO growth was achieved in two growth steps—lateral growth from the sidewalls and subsequent growth through and then over the dielectric mask openings. In comparison to planar m-plane GaN films grown on 6H SiC, the threading dislocation density was reduced from low 1010 to 3×108 cm−2 and the stacking fault density was reduced by one order of magnitude.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects
61.72.Lk Linear defects: dislocations, disclinations

Interface as the origin of ferromagnetism in cobalt doped ZnO film grown on silicon substrate

Z. G. Yin, N. F. Chen, Y. Li, X. W. Zhang, Y. M. Bai, C. L. Chai, Y. N. Xie, and J. Zhang

Appl. Phys. Lett. 93, 142109 (2008); http://dx.doi.org/10.1063/1.2989128 (3 pages) | Cited 3 times

Online Publication Date: 10 October 2008

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We have investigated the magnetic properties of Co-doped zinc oxide (ZnO) film deposited on silicon substrate by magnetron sputtering. Co ions have a valence of 2+ and substitute for Zn sites in the lattice. By using a chemical etching method, an extrinsic ferromagnetism was demonstrated. The observed ferromagnetism is neither associated with magnetic precipitates nor with contamination, but originates from the silicon/silicon oxide interface. This interface ferromagnetism is characterized by being temperature independent and by having a parallel magnetic anisotropy.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
75.30.Gw Magnetic anisotropy
81.15.Cd Deposition by sputtering
75.50.Dd Nonmetallic ferromagnetic materials

Two insulating phases in compressed Pr1−xCaxMnO3 thin films

M. Filippi, W. Prellier, P. Auban-Senzier, and C. R. Pasquier

Appl. Phys. Lett. 93, 142110 (2008); http://dx.doi.org/10.1063/1.2993347 (3 pages) | Cited 7 times

Online Publication Date: 10 October 2008

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The temperature-dependent resistivity of two Pr1−xCaxMnO3 (x = 0.5 and 0.6) thin films grown on LaAlO3 has been studied as a function of hydrostatic pressure (up to 2.5 GPa) and magnetic field (up to 9 T). Both samples show a monotonic decrease in the resistivity with an increase in pressure, corresponding to a change of −35% at 2.5 GPa. No pressure induced metal-to-insulator transition was observed in the temperature-dependent resistivity. The nontrivial interaction between high pressure and magnetic field reveals that the effect of pressure cannot be simply rescaled to that of a specific field, as has been reported for the corresponding bulk material. We propose an interpretation of the data based on phase separation, where two different insulating phases coexist: the charge ordered phase, which is sensitive to both magnetic field and pressure, and a second insulating phase that can be tuned by magnetic field. Such a result demonstrates that phase separation can be manipulated in thin films by independent application of magnetic field and/or external pressure.
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73.61.Ng Insulators
72.60.+g Mixed conductivity and conductivity transitions

Transparent Al–Zn–Sn–O thin film transistors prepared at low temperature

Doo-Hee Cho, Shinhyuk Yang, Chunwon Byun, Jaeheon Shin, Min Ki Ryu, Sang-Hee Ko Park, Chi-Sun Hwang, Sung Mook Chung, Woo-Seok Cheong, Sung Min Yoon, and Hye-Yong Chu

Appl. Phys. Lett. 93, 142111 (2008); http://dx.doi.org/10.1063/1.2998612 (3 pages) | Cited 50 times

Online Publication Date: 10 October 2008

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We have fabricated transparent bottom gate thin film transistors (TFTs) using Al-doped zinc tin oxide (AZTO) as active layers. The AZTO active layer was deposited by rf magnetron sputtering at room temperature. The AZTO TFT showed good TFT performance without postannealing. The field effect mobility and the subthreshold swing were improved by postannealing below 180 °C. The AZTO TFT exhibited a field effect mobility (μFET) of 10.1 cm2/V s, a turn-on voltage (Von) of 0.4 V, a subthreshold swing (S/S) of 0.6 V/decade, and an on/off ratio (Ion/Ioff) of 109.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology
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