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11 Feb 2013

Volume 102, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 063701 (2013); http://dx.doi.org/10.1063/1.4790115 (5 pages)

In-Tsang Lin, Hong-Chang Yang, and Jyh-Horng Chen
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Lanthanide impurities in wide bandgap semiconductors: A possible roadmap for spintronic devices

G. Caroena, W. V. M. Machado, J. F. Justo, and L. V. C. Assali

Appl. Phys. Lett. 102, 062101 (2013); http://dx.doi.org/10.1063/1.4791787 (4 pages)

Online Publication Date: 11 February 2013

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The electronic properties of lanthanide (from Eu to Tm) impurities in wurtzite gallium nitride and zinc oxide were investigated by first principles calculations, using an all electron methodology plus a Hubbard potential correction. The results indicated that the 4f-related energy levels remain outside the bandgap in both materials, in good agreement with a recent phenomenological model, based on experimental data. Additionally, zinc oxide doped with lanthanide impurities became an n-type material, showing a coupling between the 4f-related spin polarized states and the carriers. This coupling may generate spin polarized currents, which could lead to applications in spintronic devices.
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61.72.uj III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds
72.25.Dc Spin polarized transport in semiconductors
72.80.Ey III-V and II-VI semiconductors

Gamma irradiation impact on electronic carrier transport in AlGaN/GaN high electron mobility transistors

C. Schwarz, A. Yadav, M. Shatkhin, E. Flitsiyan, L. Chernyak, V. Kasiyan, L. Liu, Y. Y. Xi, F. Ren, S. J. Pearton, C. F. Lo, J. W. Johnson, and E. Danilova

Appl. Phys. Lett. 102, 062102 (2013); http://dx.doi.org/10.1063/1.4792240 (3 pages) | Cited 1 time

Online Publication Date: 11 February 2013

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AlGaN/GaN high electron mobility transistors were irradiated with 60Co gamma-rays to doses up to 1000 Gy, in order to analyze the effects of irradiation on the devices' transport properties. Temperature-dependent electron beam-induced current measurements, conducted on the devices before and after exposure to gamma-irradiation, allowed for the obtaining of activation energies related to radiation-induced defects due to nitrogen vacancies. DC current-voltage measurements were also conducted on the transistors to assess the impact of gamma-irradiation on transfer, gate, and drain characteristics.
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85.30.Tv Field effect devices

High performance InGaZnO thin film transistor with InGaZnO source and drain electrodes

Hung-Chi Wu and Chao-Hsin Chien

Appl. Phys. Lett. 102, 062103 (2013); http://dx.doi.org/10.1063/1.4789997 (4 pages)

Online Publication Date: 11 February 2013

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This work demonstrates In-Ga-Zn-O (IGZO) as source and drain electrodes in IGZO-thin film transistors (TFTs). The fabricated TFT depicts excellent electrical properties; its mobility is 18.02 (cm2/V s), threshold voltage (Vth) is 0.3 (V), on/off ratio is 1.63 × 108 and subthreshold swing (S.S.) is 239 (mV/decade). We find using rapid thermal annealing treatment can convert IGZO into an effective conductor, and the transparency of IGZO remained almost unchanged. We also find sufficient thermal budget is needed for getting stable transfer curve and output characteristic; otherwise, current fluctuation in on-state can be easily observed. With IGZO electrodes, fully transparent IGZO-TFTs can be thus realized on a glass substrate.
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85.30.Tv Field effect devices
82.45.Fk Electrodes

Rapid hot-electron energy relaxation in lattice-matched InAlN/AlN/GaN heterostructures

J.-Z. Zhang, A. Dyson, and B. K. Ridley

Appl. Phys. Lett. 102, 062104 (2013); http://dx.doi.org/10.1063/1.4792276 (4 pages)

Online Publication Date: 12 February 2013

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Hot-electron energy relaxation is theoretically studied for a typical lattice-matched InAlN/AlN/GaN heterostructure, including effects of non-equilibrium phonons and screening from the mobile electrons in the GaN channel. A dramatic fall of relaxation time occurs at low electron temperatures (<500 K) due to the exponentially increased phonon generation as well as fast decreased screening and hot-phonon effect. At high electron temperatures (>1500 K), on the other hand, the hot-phonon effect is very weak because of short optical phonon lifetimes (experimental value ∼0.1 ps), and the electron relaxation is dictated by the screened electron-phonon interactions which alone yield a nearly constant relaxation time ∼0.1 ps. With increasingly fast optical-phonon decay, therefore the high-temperature electron relaxation time decreases slowly with the electron temperature, with its limiting value set entirely by the screened electron-phonon interactions alone. The calculated dependence of the relaxation time on the electron temperature and the high-temperature relaxation times ∼0.1 ps are in good agreement with experimental results.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
63.20.kd Phonon-electron interactions
71.38.-k Polarons and electron-phonon interactions
72.20.Fr Low-field transport and mobility; piezoresistance

Pressure-induced phase transformation of In2Se3

Anya M. Rasmussen, Samuel T. Teklemichael, Elham Mafi, Yi Gu, and Matthew D. McCluskey

Appl. Phys. Lett. 102, 062105 (2013); http://dx.doi.org/10.1063/1.4792313 (4 pages)

Online Publication Date: 13 February 2013

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In2Se3 has potential as a phase-change material for memory applications. Understanding its phase diagram is important to achieve controlled switching between phases. Using x-ray diffraction and a diamond-anvil cell, the pressure-dependent structural properties of In2Se3 powder were studied at room temperature. α-In2Se3 transforms into the β phase at 0.7 GPa, an order of magnitude lower than phase-transition critical pressures in typical semiconductors. The β phase persists upon decompression to ambient pressure. Raman spectroscopy experiments confirm this result. The bulk moduli are reported and the c/a ratio for the β phase is shown to have a highly nonlinear dependence on pressure.
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64.70.K- Solid-solid transitions
78.30.Hv Other nonmetallic inorganics
81.30.Dz Phase diagrams of other materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.50.-p High-pressure effects in solids and liquids

Band alignment between Ta2O5 and metals for resistive random access memory electrodes engineering

V. Y.-Q. Zhuo, Y. Jiang, M. H. Li, E. K. Chua, Z. Zhang, J. S. Pan, R. Zhao, L. P. Shi, T. C. Chong, and J. Robertson

Appl. Phys. Lett. 102, 062106 (2013); http://dx.doi.org/10.1063/1.4792274 (5 pages)

Online Publication Date: 13 February 2013

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Band alignment of resistive random access memory (RRAM) switching material Ta2O5 and different metal electrode materials was examined using high-resolution X-ray photoelectron spectroscopy. Schottky and hole barrier heights at the interface between electrode and Ta2O5 were obtained, where the electrodes consist of materials with low to high work function (Φm,vac from 4.06 to 5.93 eV). Effective metal work functions were extracted to study the Fermi level pinning effect and to discuss the dominant conduction mechanism. An accurate band alignment between electrodes and Ta2O5 is obtained and can be used for RRAM electrode engineering and conduction mechanism study.
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84.30.Sk Pulse and digital circuits

Visible single-photon emission from a nitrogen impurity center in AlAs

M. Jo, T. Mano, T. Kuroda, Y. Sakuma, and K. Sakoda

Appl. Phys. Lett. 102, 062107 (2013); http://dx.doi.org/10.1063/1.4792315 (3 pages)

Online Publication Date: 14 February 2013

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We report visible single-photon emission from a nitrogen impurity center in AlAs grown on GaAs(001). Sharp emission lines are observed at 2.1–2.2 eV, below the X-conduction bandedge of AlAs from N δ-doped AlAs. The quadratic increase in the photoluminescence intensity with the N concentration reveals that the nitrogen impurity centers consist of NN pairs. Polarization analysis reveals that the peak at 2.191 eV consists of different pair configurations, while the peak at 2.165 eV contains only a single pair configuration along the 〈110〉 direction. Photon correlation measurement gives the second-order correlation function g(2)(0) = 0.33, demonstrating single-photon statistics in emissions from an NN pair.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
61.72.jn Color centers
61.72.uj III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors

Polarization induced hole doping in graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy

Shibin Li, Ting Zhang, Jiang Wu, Yajie Yang, Zhiming Wang, Zhiming Wu, Zhi Chen, and Yadong Jiang

Appl. Phys. Lett. 102, 062108 (2013); http://dx.doi.org/10.1063/1.4792685 (3 pages)

Online Publication Date: 14 February 2013

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Polarization induced hole doping on the order of ∼1018 cm−3 is achieved in linearly graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy. Graded AlxGa1−xN and conventional Al0.7Ga0.3N layers grown on AlN are beryllium (Be) doped via epitaxial growth. The hole concentration in graded AlxGa1−xN:Be (x = 0.7 ∼ 1) layers demonstrates that polarization generates hole charges from Be dopant. The Al0.7Ga0.3N layer is not conductive owing to the absence of carriers generated from the Be dopant without the inducement of polarization. Polarization doping provides an approach to high efficiency p-type doping in high Al composition AlGaN.
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68.55.ag Semiconductors
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Cu3BiS3 as a potential photovoltaic absorber with high optical efficiency

Mukesh Kumar and Clas Persson

Appl. Phys. Lett. 102, 062109 (2013); http://dx.doi.org/10.1063/1.4792751 (4 pages) | Cited 2 times

Online Publication Date: 15 February 2013

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Cu3BiS3 is a potential photovoltaic material. Employing a first-principles approach, we calculate the structural, electronic, and optical properties of Cu3BiS3, and we demonstrate that Cu3BiS3 is an indirect band gap semiconductor in contrast to similar chalcogenide semiconductors. The fundamental band gap energy is estimated to be Eg ≈ 1.5–1.7 eV. The analysis reveals that Cu3BiS3 has a much stronger absorption coefficient (>105 cm−1) compared to other Cu-S based materials like CuInS2 and Cu2ZnSnS4. This is explained by the presence of localized Bi 6p states in the band gap region, generating a flat lowest conduction band.
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71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.66.Fn Inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Green to blue polarization compensated c-axis oriented multi-quantum wells by AlGaInN barrier layers

A. Dadgar, L. Groh, S. Metzner, S. Neugebauer, J. Bläsing, T. Hempel, F. Bertram, J. Christen, A. Krost, Z. Andreev, and B. Witzigmann

Appl. Phys. Lett. 102, 062110 (2013); http://dx.doi.org/10.1063/1.4793185 (4 pages)

Online Publication Date: 15 February 2013

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We report on an over 50% reduction in polarization field strength in c-axis oriented InGaN multi-quantum wells (MQW) by applying quaternary AlGaInN barrier layers with better polarization matching to InGaN than GaN barriers. With the reduction in polarization fields, a strong blue-shift in photoluminescence is observed in agreement with theoretical expectation and simulations. By gracing incidence x-ray diffraction measurements, we demonstrate that partial relaxation already occurs for GaN/InGaN MQWs. As a consequence, the requirement of higher In-content layers for green light emission is in conflict with increasing strain leading to lattice relaxation.
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78.67.De Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
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