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12 Apr 2010

Volume 96, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 96, 153701 (2010); http://dx.doi.org/10.1063/1.3385388 (3 pages)

Sinan Keten and Markus J. Buehler
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Size dependence of transverse electric transport in single ZnO nanoneedles

Ya Yang, Junjie Qi, Wen Guo, Jing Zhao, Xueqiang Wang, and Yue Zhang

Appl. Phys. Lett. 96, 152101 (2010); http://dx.doi.org/10.1063/1.3386571 (3 pages) | Cited 1 time

Online Publication Date: 12 April 2010

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We report a size dependence of transverse electric transport in single ZnO nanoneedles with diameters ranging from 5 to 50 nm. Under the same voltages, the measured transverse current through the single ZnO nanoneedle was found to decrease dramatically with the decreasing diameters from 50 to 20 nm, and no current were detected when the diameters are smaller than 20 nm. A spherical electric transport model is proposed to explore the origin of the size dependence.
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73.63.Nm Quantum wires
72.80.Ey III-V and II-VI semiconductors
72.10.-d Theory of electronic transport; scattering mechanisms

High stability of amorphous hafnium-indium-zinc-oxide thin film transistor

Eugene Chong, Kyoung Chul Jo, and Sang Yeol Lee

Appl. Phys. Lett. 96, 152102 (2010); http://dx.doi.org/10.1063/1.3387819 (3 pages) | Cited 33 times

Online Publication Date: 12 April 2010

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Time dependence of the threshold voltage (Vth) shift in amorphous hafnium-indium-zinc oxide (a-HIZO) thin film transistor has been reported under on-current bias temperature stress measured at 60 °C. X-ray photoelectron spectroscopy results show the decrease in oxygen vacancies by Hf metal cations in a-HIZO systems after annealing process. High stability of a-HIZO systems has been observed due to low charge injection from the channel layer. Hf metal cations have been effectively incorporated into the IZO thin films as a suppressor against both the oxygen deficiencies and the carrier generation.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
73.61.Jc Amorphous semiconductors; glasses
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.Cc Kinetics of defect formation and annealing
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Anharmonic effects in ZnO optical phonons probed by Raman spectroscopy

Marius Millot, Ramon Tena-Zaera, Vicente Munoz-Sanjose, Jean-Marc Broto, and Jesus Gonzalez

Appl. Phys. Lett. 96, 152103 (2010); http://dx.doi.org/10.1063/1.3387843 (3 pages) | Cited 3 times

Online Publication Date: 12 April 2010

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We report Raman spectroscopy measurements on ZnO crystals grown by the vapor transport method and annealed. Vacuum annealing is found to yield single crystals with ultra low density of defects. We focus on the optical E2 phonon linewidth temperature dependence in the 10–500 K range. The linewidth decrease at low temperature is analyzed and discussed in the light of anharmonic up- and down-conversion processes, unveiling strongly different behaviors for the two E2 phonons.
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81.10.Bk Growth from vapor
78.55.Et II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
63.20.Ry Anharmonic lattice modes
78.30.Fs III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors

Quantum capacitance and density of states of graphene

S. Dröscher, P. Roulleau, F. Molitor, P. Studerus, C. Stampfer, K. Ensslin, and T. Ihn

Appl. Phys. Lett. 96, 152104 (2010); http://dx.doi.org/10.1063/1.3391670 (3 pages) | Cited 13 times

Online Publication Date: 12 April 2010

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We report on measurements of the quantum capacitance in graphene as a function of charge carrier density. A resonant LC-circuit giving high sensitivity to small capacitance changes is employed. The density of states, which is directly proportional to the quantum capacitance, is found to be significantly larger than zero at and around the charge neutrality point. This finding is interpreted to be a result of potential fluctuations with amplitudes of the order of 100 meV in good agreement with scanning single-electron transistor measurements on bulk graphene and transport studies on nanoribbons.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.61.Wp Fullerenes and related materials
73.50.Dn Low-field transport and mobility; piezoresistance
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
72.80.Vp Electronic transport in graphene

Effect of antisite defects on band structure and thermoelectric performance of ZrNiSn half-Heusler alloys

Pengfei Qiu, Jiong Yang, Xiangyang Huang, Xihong Chen, and Lidong Chen

Appl. Phys. Lett. 96, 152105 (2010); http://dx.doi.org/10.1063/1.3396981 (3 pages) | Cited 9 times

Online Publication Date: 14 April 2010

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Band structures for ZrNiSn with Zr/Sn antisite defects are calculated with ab initio methods. Antisite defects shrink the band gap and enhance the density of states slope near the Fermi level, which are favorable to electrical transport properties for intrinsic semiconductors. The degree of Zr/Sn antisite defects are controlled by annealing time experimentally, and measurements show low electrical resistivity and high Seebeck coefficient for unannealed ZrNiSn, which benefits from the modified electronic structure caused by antisite defects. The maximum ZT is 0.64 at 800 K for unannealed ZrNiSn, which is the highest value for ZrNiSn systems without exterior doping.
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71.20.Be Transition metals and alloys
61.72.J- Point defects and defect clusters
71.15.-m Methods of electronic structure calculations
72.15.Jf Thermoelectric and thermomagnetic effects
61.72.Cc Kinetics of defect formation and annealing
71.55.Ak Metals, semimetals, and alloys

Space-charge electric field in photorefractive multiple quantum wells

Xiangxue Zhang, Mohammad Samiullah, and Ping Yu

Appl. Phys. Lett. 96, 152106 (2010); http://dx.doi.org/10.1063/1.3367728 (3 pages) | Cited 1 time

Online Publication Date: 14 April 2010

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We have developed a graphical method to determine the space-charge electric field in photorefractive multiple quantum wells when the photocurrent is dominated by the drift current. The minima and maxima of the space-charge electric field due to space modulated light intensity are obtained from photocurrent measurements under uniform illumination. In addition, we find that the space-charge field depends nonlinearly on the applied electric field and the intensity of light, and changes sharply with the intensity up to a critical intensity beyond which it remains unchanged.
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77.22.Jp Dielectric breakdown and space-charge effects
73.63.Hs Quantum wells
72.40.+w Photoconduction and photovoltaic effects
78.67.De Quantum wells
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Atomic resolution in tunneling induced light emission from GaAs(110)

Maria Reinhardt, Guillaume Schull, Philipp Ebert, and Richard Berndt

Appl. Phys. Lett. 96, 152107 (2010); http://dx.doi.org/10.1063/1.3360203 (3 pages) | Cited 2 times

Online Publication Date: 14 April 2010

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A cryogenic scanning tunneling microscope is used to induce band edge luminescence from GaAs(110). The emission intensity varies within the unit mesh of the surface. This atomic resolution reflects variations of the efficiency of hole injection into states at the valence band maximum. Moreover, the hole injection efficiency is modulated by local potential fluctuations due to dopants.
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78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
68.47.Fg Semiconductor surfaces
68.35.bg Semiconductors

Fermi level depinning at the germanium Schottky interface through sulfur passivation

Arun V. Thathachary, K. N. Bhat, Navakanta Bhat, and M. S. Hegde

Appl. Phys. Lett. 96, 152108 (2010); http://dx.doi.org/10.1063/1.3387760 (3 pages) | Cited 7 times

Online Publication Date: 15 April 2010

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We demonstrate the depinning of Fermi level on both p- and n-type germanium after sulfur passivation by aqueous (NH4)2S treatment. Schottky contacts realized using metals with a wide range of work functions produce nearly ideal behavior confirming that the Fermi level is depinned. Examination of the passivated surface using x-ray photoelectron spectroscopy reveals bonding between Ge and sulfur. It is shown that good Ohmic contacts to n-type Ge and a hole barrier height (ϕBp) of 0.6 eV to p-type Ge can be achieved after this passivation treatment, with Zr Schottky contacts. This is the highest ϕBp reported so far.
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73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Rv Passivation
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Ns Metal-nonmetal contacts

Determination of the sign of g factors for conduction electrons using time-resolved Kerr rotation

C. L. Yang, Junfeng Dai, W. K. Ge, and Xiaodong Cui

Appl. Phys. Lett. 96, 152109 (2010); http://dx.doi.org/10.1063/1.3402769 (3 pages) | Cited 2 times

Online Publication Date: 16 April 2010

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The knowledge of electron g factor is essential for spin manipulation in the field of spintronics and quantum computing. While there exist technical difficulties in determining the sign of g factor in semiconductors by the established magneto-optical spectroscopic methods. We develop a technique to precisely measure the sign and the amplitude of electron g factor in semiconductors using time resolved Kerr rotation.
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07.60.Rd Visible and ultraviolet spectrometers
78.67.De Quantum wells
78.20.Jq Electro-optical effects
78.47.D- Time resolved spectroscopy (>1 psec)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.21.Fg Quantum wells
78.66.Fd III-V semiconductors
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