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23 Apr 2012

Volume 100, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 171903 (2012); http://dx.doi.org/10.1063/1.4704193 (3 pages)

Y. Peng and K. Kempa
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Structure stabilities and transitions in polyhedral metal nanocrystals: An atomic-bond-relaxation approach

Ai Zhang, Ziming Zhu, Yan He, and Gang Ouyang

Appl. Phys. Lett. 100, 171912 (2012); http://dx.doi.org/10.1063/1.4706260 (5 pages) | Cited 2 times

Online Publication Date: 26 April 2012

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We present an atomic-bond-relaxation (ABR) method to illustrate a deeper insight on structure stabilities and transitions of metal nanocrystals with polyhedral structure based on the thermodynamic consideration. It has been found that the end effects in polyhedral nanocrystals induced by the atoms located at edges, side facets, and vertexes play the dominant roles for their structure performances. The theoretical predictions are well consistent with the experimental measurements and simulations, which suggest the ABR model can be an effective method to understand solid-solid phase transition of polyhedral metal nanocrystals.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.70.Nd Structural transitions in nanoscale materials
82.60.Qr Thermodynamics of nanoparticles

Large-area nanostructured substrates for surface enhanced Raman spectroscopy

Andriy Shevchenko, Victor Ovchinnikov, and Anna Shevchenko

Appl. Phys. Lett. 100, 171913 (2012); http://dx.doi.org/10.1063/1.4707158 (4 pages) | Cited 1 time

Online Publication Date: 26 April 2012

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We demonstrate substantial enhancement of Raman transitions of organic molecules by nanostructured gold-coated substrates at the excitation wavelength of 785 nm and experimentally study the factors that influence the enhancement. The substrates are fabricated by using a robust and cost-effective nanopatterning technique that allows us to create high-density gold- or silver-coated nanopillars simultaneously on the whole surface of a standard silicon wafer.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.30.Am Elemental semiconductors and insulators
78.68.+m Optical properties of surfaces
81.16.Rf Micro- and nanoscale pattern formation

Capping effect of GaAsSb and InGaAsSb on the structural and optical properties of type II GaSb/GaAs quantum dots

Jun He, Feng Bao, and Jinping Zhang

Appl. Phys. Lett. 100, 171914 (2012); http://dx.doi.org/10.1063/1.4707385 (4 pages) | Cited 2 times

Online Publication Date: 26 April 2012

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We systematically study the influence of group V intermixing on the structural and optical properties of type II GaSb/GaAs quantum dots (QDs) capped by selected capping layers. Compared to GaSb QDs capped directly by a GaAs layer, we observe a strong enhancement of photoluminescence (PL) intensity and a significant red-shift of the photoluminescence peak energy to 1.35 μm at 300 K by the introduction of a GaAsSb capping layer. In addition, Z-contrast cross sectional transmission electron microscopy shows Sb segregation and group V mixing is greatly suppressed by GaAsSb or InGaAsSb capping layers. The new capping layers offers the possibility of controlling optical properties of type II GaSb/GaAs quantum dots and this opens up new means for achieving high efficient GaSb/GaAs quantum dot solar cell.
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78.67.Hc Quantum dots
81.30.Mh Solid-phase precipitation
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
64.75.Ef Mixing

Shift of Ag diffusion profiles in CdTe by metal/semiconductor interfaces

H. Wolf, J. Kronenberg, F. Wagner, M. Deicher, Th. Wichert, and ISOLDE Collaboration

Appl. Phys. Lett. 100, 171915 (2012); http://dx.doi.org/10.1063/1.4709393 (3 pages)

Online Publication Date: 27 April 2012

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Metal layers deposited on the surface of the semiconductor CdTe effect a shift of the concentration profile of Ag dopants in CdTe by several 100 μm during diffusion anneal at about 550 K. Radio-tracer experiments using 111Ag show that this effect occurs in the case of Al, Ni, Cu, and Au layers. A preliminary explanation relates the effect to an enhancement of the diffusion of Ag atoms in CdTe caused by Cd self-interstitials that are generated at the metal/semiconductor interface.
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66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
61.72.jj Interstitials
61.72.uj III-V and II-VI semiconductors

Symmetrically tunable optical properties of InGaN/GaN multiple quantum disks by an external stress

H. Y. Shih, Y. F. Chen, and T. Y. Lin

Appl. Phys. Lett. 100, 171916 (2012); http://dx.doi.org/10.1063/1.4709397 (4 pages)

Online Publication Date: 27 April 2012

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The influence of an external stress on the optical properties of InGaN/GaN multiple quantum disks (MQDs) has been investigated. As a transversal force is applied on the MQDs, both photoluminescence and Raman scattering spectra are altered due to the piezoelectric potential accompanied by the quantum confined Stark effect. Quite interestingly, it is found that the optical spectra possess a sixfold symmetry about the c-axis. This intriguing phenomenon can be attributed to the inherent nature of hexagonal lattice as well as the good flexibility of the composite consisting of polydimethylsiloxane and MQDs. Our results can provide an alternative route to optimize and extend the application of nitride-based devices.
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81.05.Ea III-V semiconductors
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.20.Jq Electro-optical effects

Stress relaxation and critical thickness for misfit dislocation formation in (10math0) and (30math) InGaN/GaN heteroepitaxy

Po Shan Hsu, Matthew T. Hardy, Erin C. Young, Alexey E. Romanov, Steven P. DenBaars, Shuji Nakamura, and James S. Speck

Appl. Phys. Lett. 100, 171917 (2012); http://dx.doi.org/10.1063/1.4707160 (4 pages) | Cited 1 time

Online Publication Date: 27 April 2012

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Cathodoluminescence imaging was used to study the onset of plastic relaxation and critical thickness for misfit dislocation (MD) formation by basal plane (BP) or nonbasal plane (NBP) slip in In0.09Ga0.91N/GaN heterostructures grown on nonpolar (10math0) and semipolar (30math) substrates. Layers grown on both orientations were shown to stress relax initially via generation of NBP MDs as a result of prismatic slip on inclined m-planes. Analysis of the resolved shear stress on the two slip planes (i.e., basal and an inclined m-plane) reveals a crossover at which the resolved shear stress on the m-planes becomes larger than that on the BP.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
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Electrical properties of the amorphous interfacial layer between Al electrodes and epitaxial NiO films

Jae Hyuck Jang, Ji-Hwan Kwon, Seung Ran Lee, Kookrin Char, and Miyoung Kim

Appl. Phys. Lett. 100, 172101 (2012); http://dx.doi.org/10.1063/1.4704917 (3 pages)

Online Publication Date: 23 April 2012

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The amorphous interfacial layer (a-IL) between Al electrode and epitaxial NiO films were studied using electron energy-loss spectroscopy (EELS) and energy-dispersive x-ray spectroscopy. Two distinct properties were found in the a-IL, i.e., a lower metallic and an upper insulating layer. EELS results revealed that the metallic Ni atoms were responsible for the conducting nature of the lower oxide amorphous layer. The resistance behavior of Al/a-IL/epi-NiO was changed from a high to a low resistance state after forming process. The resistance change could be explained by the formation of a nanocrystalline metal alloy in the insulating amorphous layer.
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73.40.Ns Metal-nonmetal contacts
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
79.20.Uv Electron energy loss spectroscopy

Local micro-photoreflectance spectroscopy measurements on type II InGaAlAs/GaAsSb/InP heterojunction bipolar transistor: Correlation with electrical characteristics

H. Chouaib and C. Bru-Chevallier

Appl. Phys. Lett. 100, 172102 (2012); http://dx.doi.org/10.1063/1.4705408 (4 pages)

Online Publication Date: 24 April 2012

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Micro-photoreflectance (micro-PR) is performed on patterned type II InGaAlAs/GaAsSb/InP heterojunction bipolar transistor to locally measure the built-in electric fields. The results show that the efficiency of the electric field modulation correlates with the ideality factor extracted from the electrical characteristics (Gummel characteristics). The Franz-Keldysh oscillations (FKO) completely disappear at the emitter/base heterojunction on devices with high ideality factor (nearly 2), whereas typical FKO spectra are seen on samples with ideality factor ∼1. Such behavior is attributed to the type II recombination across the InGaAlAs/GaAsSb interface which can reduce the photovoltage effect. Prior to the micro-PR experiments, photoluminescence is performed to demonstrate that the InGaAlAs/GaAsSb interface nature is of type II as well as to estimate the band offset discontinuity ΔEC.
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85.30.Pq Bipolar transistors
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Negative electron mobility in diamond

J. Isberg, M. Gabrysch, S. Majdi, and D. J. Twitchen

Appl. Phys. Lett. 100, 172103 (2012); http://dx.doi.org/10.1063/1.4705434 (4 pages) | Cited 2 times

Online Publication Date: 24 April 2012

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By measuring the drift velocity of electrons in diamond as a function of applied electric field, we demonstrate that ultra-pure diamond exhibits negative differential electron mobility in the [100] direction below 140 K. Negative electron mobility is normally associated with III–V or II–VI semiconductors with an energy difference between different conduction band valleys. The observation of negative mobility in diamond, an elemental group IV semiconductor, is explained in terms of repopulation effects between different equivalent conduction band valleys using a model based on the Boltzmann equation.
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72.20.Fr Low-field transport and mobility; piezoresistance
71.20.Tx Fullerenes and related materials; intercalation compounds
81.05.ug Diamond
72.80.Cw Elemental semiconductors

Electrical activation and electron spin resonance measurements of implanted bismuth in isotopically enriched silicon-28

C. D. Weis, C. C. Lo, V. Lang, A. M. Tyryshkin, R. E. George, K. M. Yu, J. Bokor, S. A. Lyon, J. J. L. Morton, and T. Schenkel

Appl. Phys. Lett. 100, 172104 (2012); http://dx.doi.org/10.1063/1.4704561 (4 pages) | Cited 7 times

Online Publication Date: 24 April 2012

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We have performed continuous wave and pulsed electron spin resonance measurements of implanted bismuth donors in isotopically enriched silicon-28. Donors are electrically activated via thermal annealing with minimal diffusion. Damage from bismuth ion implantation is repaired during thermal annealing as evidenced by narrow spin resonance linewidths (Bpp = 12μT) and long spin coherence times (T2 = 0.7 ms, at temperature T = 8 K). The results qualify ion implanted bismuth as a promising candidate for spin qubit integration in silicon.
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72.20.My Galvanomagnetic and other magnetotransport effects
76.30.Lh Other ions and impurities
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing

Basal plane dislocation multiplication via the Hopping Frank-Read source mechanism in 4H-SiC

H. Wang, F. Wu, S. Byrappa, S. Sun, B. Raghothamachar, M. Dudley, E. K. Sanchez, D. Hansen, R. Drachev, S. G. Mueller, and M. J. Loboda

Appl. Phys. Lett. 100, 172105 (2012); http://dx.doi.org/10.1063/1.4704679 (4 pages)

Online Publication Date: 24 April 2012

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Synchrotron white beam x-ray topography (SWBXT) observations are reported of single-ended Frank-Read sources in 4H-SiC. These result from inter-conversion between basal plane dislocations (BPDs) and threading edge dislocations (TEDs) brought about by step interactions on the growth interface resulting in a dislocation comprising several glissile BPD segments on parallel basal planes interconnected by relatively sessile TED segments. Under stress, the BPD segments become pinned by the TED segments producing single ended Frank-Read sources. Since the BPDs appear to “hop” between basal planes, this apparently dominant multiplication mechanism for BPDs in 4H-SiC is referred to as the “Hopping” Frank-Read source mechanism.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
72.20.Ee Mobility edges; hopping transport
72.80.Jc Other crystalline inorganic semiconductors

Doping characterization for germanium-based microelectronics and photovoltaics using the differential Hall technique

N. S. Bennett and N. E. B. Cowern

Appl. Phys. Lett. 100, 172106 (2012); http://dx.doi.org/10.1063/1.4705293 (4 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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In this coming decade, complementary metal-oxide-semiconductor microelectronic devices may undergo a major change with the implementation of germanium channels. Likewise, the performance of photovoltaic cells based on elemental semiconductors will continue to be optimized. Both technologies will rely on a detailed and thorough understanding of electrical properties, and here, precise doping characterization will play a key role. The differential Hall technique combines resistivity and Hall-effect measurements with successive surface layer removal, allowing one to measure independent carrier concentration and mobility depth profiles. In this Letter, we apply the technique for both microelectronic- and photovoltaic-relevant doping structures in germanium. Controllable and uniform layer removal is achieved with tailored depth resolution (<1–20 nm) for a range of doping structures (30–600 nm).
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85.40.Ry Impurity doping, diffusion and ion implantation technology
85.60.Bt Optoelectronic device characterization, design, and modeling

Hybrid-orientation Ge-on-insulator structures on (100) Si platform by Si micro-seed formation combined with rapid-melting growth

Masashi Kurosawa, Naoyuki Kawabata, Taizoh Sadoh, and Masanobu Miyao

Appl. Phys. Lett. 100, 172107 (2012); http://dx.doi.org/10.1063/1.4705733 (5 pages) | Cited 4 times

Online Publication Date: 25 April 2012

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Hybrid-integration of (111), (110), and (100) Ge-on-insulator (GOI) on an Si chip is essential to merge III-V semiconductor optical-devices as well as high-speed Ge transistors onto Si-large-scale integrated-circuits. We clarify important-parameters to control Ni-metal-induced lateral crystallization and Al-induced layer-exchange crystallization. This achieves artificial (110) and (111) Si micro-seed on insulating-film. Together with Si substrate as (100) Si seed, multi-crystal-seeds with different orientations are aligned on a Si chip. Then, SiGe-mixing triggered rapid-melting-growth of amorphous-Ge is examined from these multi-crystal-seeds. This enables simultaneous Ge lateral-crystallization with (111), (110), and (100) orientations. High-quality, hybrid-orientation GOIs without defects are demonstrated on Si platform.
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68.55.ag Semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Optical and structural studies of homoepitaxially grown m-plane GaN

S. Khromov, B. Monemar, V. Avrutin, Xing Li, H. Morkoç, L. Hultman, and G. Pozina

Appl. Phys. Lett. 100, 172108 (2012); http://dx.doi.org/10.1063/1.4706258 (4 pages)

Online Publication Date: 25 April 2012

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Cathodoluminescence (CL) and transmission electron microscopy studies of homoepitaxially grown m-plane Mg-doped GaN layers are reported. Layers contain basal plane and prismatic stacking faults (SFs) with ∼106 cm−1 density. Broad emission peaks commonly ascribed to SFs were found to be insignificant in these samples. A set of quite strong, sharp lines were detected in the same spectral region of 3.36–3.42 eV. The observed peaks are tentatively explained as excitons bound to some impurity defects, which can also be related to SFs. Donor-acceptor pair (DAP) recombination involving Si or O and Mg was ruled out by fitting DAP energies and CL mapping.
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78.66.Fd III-V semiconductors
61.72.Nn Stacking faults and other planar or extended defects
71.55.Eq III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.55.Cr III-V semiconductors

Spatial distribution of structural degradation under high-power stress in AlGaN/GaN high electron mobility transistors

Libing Li, Jungwoo Joh, J. A. del Alamo, and Carl V. Thompson

Appl. Phys. Lett. 100, 172109 (2012); http://dx.doi.org/10.1063/1.4707163 (3 pages) | Cited 1 time

Online Publication Date: 25 April 2012

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The two-dimensional spatial distribution of structural degradation of AlGaN/GaN high electron mobility transistors was investigated under high-power electrical stressing using atomic force and scanning electron microscopy. It was found that pits form on the surface of the GaN cap layer at the edges of the gate fingers in the middle of the device. The average pit area and density increase gradually from the edge to the center of the fingers and are more common along inner fingers than fingers. It was also found that pit formation and growth are thermally activated.
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85.30.Tv Field effect devices

Realization of high-quality HfO2 on In0.53Ga0.47As by in-situ atomic-layer-deposition

T. D. Lin (林宗達), Y. H. Chang (張宇行), C. A. Lin (林俊安), M. L. Huang (黃懋霖), W. C. Lee (李威縉), J. Kwo (郭瑞年), and M. Hong (洪銘輝)

Appl. Phys. Lett. 100, 172110 (2012); http://dx.doi.org/10.1063/1.4706261 (4 pages) | Cited 4 times

Online Publication Date: 26 April 2012

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High κ dielectric of HfAlO/HfO2 was an in-situ atomic-layer-deposited directly on molecular beam epitaxy grown In0.53Ga0.47As surface without using pre-treatments or interfacial passivation layers, where HfAlO (HfO2:Al2O3 ∼ 4:1) with high re-crystallization temperature was employed as the top oxide layer. The HfAlO (∼4.5 nm)/HfO2 (0.8 nm)/In0.53Ga0.47As metal oxide semiconductor capacitors have exhibited an oxide/In0.53Ga0.47As interface free of arsenic-related defective bonding, thermodynamic stability at 800 °C, and low leakage current densities of <10−7 A/cm2 at ±1 MV/cm. The interfacial trap density (Dit) spectra in absence of mid-gap peaks were obtained by temperature-dependent capacitance and conductance with Dit’s of 2–3 × 1012 eV−1 cm−2 below and 6–12 × 1011 eV−1 cm−2 above the mid-gap of In0.53Ga0.47As, respectively. An equivalent oxide thickness of less than 1 nm has been achieved by reducing the HfAlO thickness to ∼2.7 nm with the same initial HfO2 thickness of ∼0.8 nm.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.Px Epitaxial and superlattice films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Two-photon excitation in an intermediate band solar cell structure

Nazmul Ahsan, Naoya Miyashita, Muhammad Monirul Islam, Kin Man Yu, Wladek Walukiewicz, and Yoshitaka Okada

Appl. Phys. Lett. 100, 172111 (2012); http://dx.doi.org/10.1063/1.4709405 (4 pages) | Cited 11 times

Online Publication Date: 27 April 2012

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We present evidence for the production of photocurrent due to two-photon excitation in an intermediate band solar cell structure. The structure consists of an n-GaNAs intermediate band layer sandwiched between a p-AlGaAs emitter and an n-AlGaAs barrier layer with suitable doping level to block electron escaping from the intermediate band to the bottom n-GaAs substrate. Multi-band transitions observed in two-photon excitation experiments are explained using photo-modulated reflectance spectrum, and further support for intermediate band solar cell operation of this structure is given by current-voltage measurements.
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88.40.jm Thin film III-V and II-VI based solar cells
88.40.H- Solar cells (photovoltaics)
72.40.+w Photoconduction and photovoltaic effects

High carrier mobility in transparent Ba1−xLaxSnO3 crystals with a wide band gap

X. Luo, Y. S. Oh, A. Sirenko, P. Gao, T. A. Tyson, K. Char, and S.-W. Cheong

Appl. Phys. Lett. 100, 172112 (2012); http://dx.doi.org/10.1063/1.4709415 (5 pages) | Cited 4 times

Online Publication Date: 27 April 2012

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We discovered that perovskite (Ba,La)SnO3 can have excellent carrier mobility even though its band gap is large. The Hall mobility of Ba0.98La0.02SnO3 crystals with the n-type carrier concentration of ∼8-10 × 1019 cm−3 is found to be ∼103 cm2 V−1 s−1 at room temperature, and the precise measurement of the band gap Δ of a BaSnO3 crystal shows Δ = 4.05 eV, which is significantly larger than those of other transparent conductive oxides. The high mobility with a wide band gap indicates that (Ba,La)SnO3 is a promising candidate for transparent conductor applications and also epitaxial all-perovskite multilayer devices.
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72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

GaAs/AlGaAs resonant tunneling diodes with a GaInNAs absorption layer for telecommunication light sensing

F. Hartmann, F. Langer, D. Bisping, A. Musterer, S. Höfling, M. Kamp, A. Forchel, and L. Worschech

Appl. Phys. Lett. 100, 172113 (2012); http://dx.doi.org/10.1063/1.4709421 (3 pages)

Online Publication Date: 27 April 2012

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Al0.6Ga0.4As/GaAs/Al0.6Ga0.4As double-barrier resonant-tunneling diodes (RTD) were grown by molecular beam epitaxy with a nearby, lattice-matched Ga0.89In0.11N0.04As0.96 absorption layer. RTD mesas with ring contacts and an aperture for optical excitation of charge carriers were fabricated on the epitaxial layers. Electrical and optical properties of the RTDs were investigated for different thicknesses of a thin GaAs spacer layer incorporated between the AlGaAs tunnel barrier adjacent to the GaInNAs absorption layer. Illumination of the RTDs with laser light of 1.3 μm wavelength leads to a pronounced photo-effect with a sensitivities of around 103 A/W.
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85.30.Kk Junction diodes
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Surface photoluminescence and magnetism in hydrothermally grown undoped ZnO nanorod arrays

Xiaoyong Xu, Chunxiang Xu, Yi Lin, Tao Ding, Shengjiang Fang, Zengliang Shi, Weiwei Xia, and Jingguo Hu

Appl. Phys. Lett. 100, 172401 (2012); http://dx.doi.org/10.1063/1.4705412 (5 pages) | Cited 6 times

Online Publication Date: 23 April 2012

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ZnO nanorod arrays were synthesized by a hydrothermal method on the Si substrate with ZnO thin film as seed layer prepared by magnetron sputtering. The presence of -OH ligands on the surface of the as-grown sample was confirmed, and its dominant role in both suppressing the visible emission and boosting the room-temperature ferromagnetism (FM) was revealed. Through alternative H2 and O2 annealing to remove the -OH ligands, reconstruct surface-states and tune the oxygen occupancy in ZnO nanorods, the clear correlation between the characteristic green emission and ferromagnetism was established.
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81.16.-c Methods of micro- and nanofabrication and processing
68.55.ag Semiconductors
81.15.Cd Deposition by sputtering
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors

Role of donor-acceptor complexes and impurity band in stabilizing ferromagnetic order in Cu-doped SnO2 thin films

Yongfeng Li, Rui Deng, Yufeng Tian, Bin Yao, and Tom Wu

Appl. Phys. Lett. 100, 172402 (2012); http://dx.doi.org/10.1063/1.4705419 (4 pages) | Cited 7 times

Online Publication Date: 23 April 2012

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Our complementary magnetic and photoluminescence measurements reveal the correlation between the donor-acceptor complex and the ferromagnetic order in Cu-doped SnO2 thin films. Oxygen vacancies (VO) and Cu dopants form defect complexes of donor-acceptor pairs, and the associated spin-polarized impurity band leads to the narrowing of bandgap. Electronic structure calculations based on the first-principles method demonstrate that the Cu-VO complex has low formation energy and can stabilize the ferromagnetic coupling. Our results suggest that intrinsic defects and their complexes with dopants play a key role for establishing the ferromagnetic order in doped wide-bandgap oxides.
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61.72.up Other materials
75.50.Dd Nonmetallic ferromagnetic materials
61.72.jd Vacancies
75.50.Pp Magnetic semiconductors
71.20.Nr Semiconductor compounds
78.55.Hx Other solid inorganic materials

The role of Ni-Mn hybridization on the martensitic phase transitions in Mn-rich Heusler alloys

Mahmud Khan, J. Jung, S. S. Stoyko, Arthur Mar, Abdiel Quetz, Tapas Samanta, Igor Dubenko, Naushad Ali, Shane Stadler, and K. H. Chow

Appl. Phys. Lett. 100, 172403 (2012); http://dx.doi.org/10.1063/1.4705422 (4 pages) | Cited 2 times

Online Publication Date: 23 April 2012

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Room temperature x-ray diffraction, dc magnetization, and ac susceptibility measurements have been performed on a series of Mn rich Ni50Mn37-xCrxSb13 and Ni50+xMn37-xSb13 Heusler alloys. Depending on the value of x, the room temperature crystal structures of the samples are either L21 cubic or orthorhombic. It is a commonly accepted idea that the martensitic transition temperatures in Ni-Mn-Z (Z = Ga, In, Sb, Sn) based Heusler alloys decrease (increase) with decreasing (increasing) valence electron concentration, e/a. However, the present work shows that regardless of the change in e/a, the martensitic transition temperature (TM) decreases with increasing Cr or Ni concentration. These results support the model where, in the case of Mn rich Heusler alloys, it is the hybridization between the Ni atoms and the Mn atoms in the Z sites that plays the dominant role in driving the martensitic transformation.
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81.30.Kf Martensitic transformations
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.kd Metals and alloys
61.66.Dk Alloys

Phase diagram of magnetic domain walls in spin valve nano-stripes

N. Rougemaille, V. Uhlíř, O. Fruchart, S. Pizzini, J. Vogel, and J. C. Toussaint

Appl. Phys. Lett. 100, 172404 (2012); http://dx.doi.org/10.1063/1.4704665 (4 pages)

Online Publication Date: 23 April 2012

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We investigate numerically the transverse versus vortex phase diagram of head-to-head domain walls in Co/Cu/Py spin valve nano-stripes (Py: permalloy), in which the Co layer is mostly single domain while the Py layer hosts the domain wall. The range of stability of the transverse wall is shifted towards larger thickness compared to single Py layers, due to a magnetostatic screening effect between the two layers. An approached analytical scaling law is derived, which reproduces faithfully the phase diagram.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures

Reversible switching of room temperature ferromagnetism in CeO2-Co nanoparticles

J. Sacanell, M. A. Paulin, V. Ferrari, G. Garbarino, and A. G. Leyva

Appl. Phys. Lett. 100, 172405 (2012); http://dx.doi.org/10.1063/1.4705045 (3 pages) | Cited 2 times

Online Publication Date: 23 April 2012

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We investigated the reversible ferromagnetic (FM) behavior of pure and Co doped CeO2 nanopowders. The as-sintered samples displayed an increasing paramagnetic contribution upon Co doping. Room temperature FM is obtained simply by performing thermal treatments in vacuum at temperatures as low as 500 °C and it can be switched off by performing thermal treatments in oxidizing conditions. The FM contribution is enhanced as we increase the time of the thermal treatment in vacuum. Those systematic experiments establish a direct relation between ferromagnetism and oxygen vacancies and open a path for developing materials with tailored properties.
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75.78.Jp Ultrafast magnetization dynamics and switching
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Wx Nanopowders

Effect of oxidizing the ferromagnetic electrode in magnetic tunnel junctions on tunneling magnetoresistance

Sungjung Joo, K. Y. Jung, B. C. Lee, Tae-Suk Kim, K. H. Shin, Myung-Hwa Jung, K.-J. Rho, J.-H. Park, Jinki Hong, and K. Rhie

Appl. Phys. Lett. 100, 172406 (2012); http://dx.doi.org/10.1063/1.4704557 (3 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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The ferromagnetic layer in magnetic tunnel junctions (MTJs) was oxidized with varying O2 concentrations, and the corresponding effect on spin-dependent transport was studied. As expected from our previous results for MTJs with an over-oxidized AlOx tunnel barrier, a partially oxidized ferromagnetic layer plays an important role in spin-dependent transport. As the temperature is lowered, the junction resistance increases dramatically, and the tunneling magnetoresistance (TMR) is strongly suppressed. Increasing the O2 concentration enhances the increase of resistance and suppression of TMR. This work supports our previous conclusion that oxidizing the ferromagnetic layer generates localized magnetic moments, which act as a scattering center for spin-polarized tunneling electrons.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
81.65.Mq Oxidation
82.45.-h Electrochemistry and electrophoresis
72.25.-b Spin polarized transport
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