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19 Oct 2009

Volume 95, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 95, 162501 (2009); http://dx.doi.org/10.1063/1.3248257 (3 pages)

W. W. Lei, D. Liu, P. W. Zhu, X. H. Chen, Q. Zhao, G. H. Wen, Q. L. Cui, and G. T. Zou
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Even-odd parity oscillations in spin polarization of a quantum dot array

Xing-Tao An and Jian-Jun Liu

Appl. Phys. Lett. 95, 163501 (2009); http://dx.doi.org/10.1063/1.3250433 (3 pages) | Cited 4 times

Online Publication Date: 19 October 2009

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We propose a quantum dot (QD) array device which contains a bridge coupling between two leads. Due to the quantum interference and the Rashba spin-orbit interaction, the spin of the electrons through the device is polarized. Moreover, we find odd-even parity oscillations of spin polarization of the electrons through the system. We study the spin accumulations in every QD and find that there is difference between the spin accumulations of the QDs directly and indirectly coupling to leads. These results demonstrate that the bridge coupling is a flexible and feasible way to manipulate the electron spin of the QD array.
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85.35.Ds Quantum interference devices
73.63.Kv Quantum dots
73.21.La Quantum dots
73.23.-b Electronic transport in mesoscopic systems
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Mechanism of carrier injection in (Ni/Au)/p-AlxGa1−xN:Mg(0 ≤ x<0.1) Ohmic contacts

S. Nikishin, I. Chary, B. Borisov, V. Kuryatkov, Yu. Kudryavtsev, R. Asomoza, S. Yu. Karpov, and M. Holtz

Appl. Phys. Lett. 95, 163502 (2009); http://dx.doi.org/10.1063/1.3242420 (3 pages) | Cited 1 time

Online Publication Date: 19 October 2009

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We report the mechanism of current injection in (Ni/Au)/p-AlxGa1−xN:Mg(0 ≤ x<0.1) Ohmic contacts based on the temperature dependence of hole concentrations (p) and specific contact resistance (ρc). The injection mechanism is found to be thermionic emission in all cases. A model is developed to describe the temperature dependences of p and ρc for Mg concentrations from 1019 to 1020 cm−3. The model takes into account splitting in the valence band structure, hole activation energy, and Schottky barrier height. For GaN (AlGaN) these are found to be 132–140 (135–150) meV and 66–88 (84–93) meV, respectively.
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73.40.Ns Metal-nonmetal contacts
72.20.-i Conductivity phenomena in semiconductors and insulators
79.40.+z Thermionic emission
73.40.Cg Contact resistance, contact potential
73.20.At Surface states, band structure, electron density of states
81.05.Bx Metals, semimetals, and alloys
81.05.Ea III-V semiconductors

Magnetic tunnel junction on a ferroelectric substrate

N. A. Pertsev and H. Kohlstedt

Appl. Phys. Lett. 95, 163503 (2009); http://dx.doi.org/10.1063/1.3253706 (3 pages) | Cited 17 times

Online Publication Date: 23 October 2009

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The concept of a magnetic tunnel junction fabricated on a ferroelectric substrate is described theoretically. It is shown that the application of a moderate electric field to a substrate having strong piezoelectric response may induce an in-plane magnetization rotation in a ferromagnetic electrode made of a highly magnetostrictive cubic material with small magnetocrystalline anisotropy. Remarkably, an abrupt change of the junction’s electrical resistance can result from the substrate-induced magnetization reorientation in the free ferromagnetic layer. Hence the described hybrid multiferroic device may be employed as an electric-write nonvolatile magnetic memory cell with nondestructive readout.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity

Efficiency droop behavior of direct current aged GaN-based blue light-emitting diodes

Xianjie Shao, Hai Lu, Dunjun Chen, Zili Xie, Rong Zhang, and Youdou Zheng

Appl. Phys. Lett. 95, 163504 (2009); http://dx.doi.org/10.1063/1.3254237 (3 pages) | Cited 5 times

Online Publication Date: 23 October 2009

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By direct current (dc) stressing, GaN-based blue light-emitting diodes (LEDs) with different density of nonradiative recombination centers in the active region of InGaN/GaN multiple quantum wells were obtained and studied for injection-current-induced efficiency droop. It is found that with increasing stressing time, the overall quantum efficiency of the aged LEDs drops while the peak-efficiency-current shifts toward higher magnitude. At selected injection current levels, the electroluminescence spectra of the aged LEDs show little change in peak position and shape. The shift in peak-efficiency-current, which follows the same trend as the degree of luminescence decay, is explained by a rate-equation model in which the newly created defects by dc stressing enlarge the dominant low-current region of nonradiative recombinations.
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85.60.Jb Light-emitting devices
81.07.St Quantum wells
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