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27 Oct 2008

Volume 93, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 172501 (2008); http://dx.doi.org/10.1063/1.3005561 (3 pages)

Yan Wang, X. F. Han, and X.-G. Zhang
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Photovoltaic effect in micrometer-thick perovskite-type oxide multilayers on Si substrates

Hao Liu, Kun Zhao, Na Zhou, Huibin Lu, Meng He, Yanhong Huang, Kui-Juan Jin, Yueliang Zhou, Guozhen Yang, Songqing Zhao, Aijun Wang, and Wenxiu Leng

Appl. Phys. Lett. 93, 171911 (2008); http://dx.doi.org/10.1063/1.3010373 (3 pages) | Cited 10 times

Online Publication Date: 30 October 2008

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Micrometer-thick perovskite-type multilayer heterostructures with ten thousands of unit cells, [SrNb0.05Ti0.95O3/La0.9Sr0.1MnO3]3, have been fabricated on Si substrates. The structure exhibited nonlinear and rectifying current-voltage characteristics. Stable and temporal photovoltaic effects in the multilayer have been experimentally studied by using different wavelength light sources from ultraviolet to infrared, respectively. The photovoltage and photocurrent responsivities as a function of wavelength displayed that two cutoff wavelengths occurred corresponding to the band gaps of SrNb0.05Ti0.95O3 and Si and La0.9Sr0.1MnO3. Under the pulsed laser illumination the nanosecond response characterization of the present multilayer structure was obtained. Based on the band structure of the multilayers, a possible mechanism of photovoltaic process was proposed.
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73.63.-b Electronic transport in nanoscale materials and structures
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.40.+w Photoconduction and photovoltaic effects

Thermal expansion behavior study of Co nanowire array with in situ x-ray diffraction and x-ray absorption fine structure techniques

Guang Mo, Quan Cai, Longsheng Jiang, Wei Wang, Kunhao Zhang, Weidong Cheng, Xueqing Xing, Zhongjun Chen, and Zhonghua Wu

Appl. Phys. Lett. 93, 171912 (2008); http://dx.doi.org/10.1063/1.3012367 (3 pages) | Cited 4 times

Online Publication Date: 30 October 2008

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In situ x-ray diffraction and x-ray absorption fine structure techniques were used to study the structural change of ordered Co nanowire array with temperature. The results show that the Co nanowires are polycrystalline with hexagonal close packed structure without phase change up until 700 °C. A nonlinear thermal expansion behavior has been found and can be well described by a quadratic equation with the first-order thermal expansion coefficient of 4.3×10−6/°C and the second-order thermal expansion coefficient of 5.9×10−9/°C. The mechanism of this nonlinear thermal expansion behavior is discussed.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
78.70.Dm X-ray absorption spectra
68.65.La Quantum wires (patterned in quantum wells)

Photoluminescence lifetime and potential fluctuation in wurtzite Zn1−xCdxO alloy films

Kenji Yamamoto, Toshiya Ohashi, Takehiko Tawara, Hideki Gotoh, Atsushi Nakamura, and Jiro Temmyo

Appl. Phys. Lett. 93, 171913 (2008); http://dx.doi.org/10.1063/1.3013322 (3 pages) | Cited 4 times

Online Publication Date: 30 October 2008

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Carrier recombination dynamics in wurtzite Zn1−xCdxO alloy films has been studied by time-resolved photoluminescence (PL) to evaluate the potential fluctuation. Typical PL lifetime τ2 in Zn1−xCdxO is around 200 ps and gradually increases with a Cd content of up to 0.19. At a Cd content over 0.3, τ2 becomes roughly 50 ns. The degree of potential fluctuation E0 is increased from 9 to 157 meV with an increment in Cd content of 0.19. In contrast, at a Cd content over 0.3, E0 decreases to 35 meV with a Cd content of 0.55. This suggests that the potential fluctuation in Zn1−xCdxO with a high Cd content is greatly improved, which is qualitatively supported by the Zimmermann’s model [ R. Zimmermann, J. Cryst. Growth 101, 346 (1990) ].
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.47.jd Time resolved luminescence
68.55.ag Semiconductors
73.61.Ga II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Energy gap reduction in dilute nitride GaAsSbN

Yan-Ting Lin, Ta-Chun Ma, Tsung-Yi Chen, and Hao-Hsiung Lin

Appl. Phys. Lett. 93, 171914 (2008); http://dx.doi.org/10.1063/1.3009199 (3 pages) | Cited 8 times

Online Publication Date: 30 October 2008

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The energy gap of dilute nitride GaAsSbN has been studied. We found that the energy gap reduction induced by nitrogen incorporation is nearly independent of the Sb composition of the alloy, indicating that the conduction band and the valence band can be independently manipulated by incorporating N and Sb, respectively. A “double” band anticrossing (BAC) model, which is a combination of a BAC model for GaAsN and a valence BAC model for GaAsSb with the localized levels and hybridization parameters reported in literatures, has been proposed to fit the energy gap of annealed GaAsSbN samples. The as-grown samples, however, are with lower energy gaps, most likely resulting from the existence of substitutional N pairing and clustering in the alloys.
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71.20.Nr Semiconductor compounds
61.72.Cc Kinetics of defect formation and annealing

First-principles calculation of the effect of stress on the chemical activity of graphene

P. L. de Andres and J. A. Vergés

Appl. Phys. Lett. 93, 171915 (2008); http://dx.doi.org/10.1063/1.3010740 (3 pages) | Cited 13 times

Online Publication Date: 31 October 2008

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Graphene layers are stable, hard, and relatively inert. We study how tensile stress affects σ and π bonds and the resulting change in the chemical activity. Stress affects more strongly π bonds that can become chemically active and bind to adsorbed species more strongly. Upon stretch, single C bonds are activated in a geometry mixing 120° and 90°, an intermediate state between sp2 and sp3 bonding. We use ab initio density functional theory to study the adsorption of hydrogen on large clusters and two-dimensional periodic models for graphene. The influence of the exchange-correlation functional on the adsorption energy is discussed.
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68.35.Gy Mechanical properties; surface strains
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Bc Ab initio calculations of adsorbate structure and reactions

The Hall–Petch breakdown at high strain rates: Optimizing nanocrystalline grain size for impact applications

Jason R. Trelewicz and Christopher A. Schuh

Appl. Phys. Lett. 93, 171916 (2008); http://dx.doi.org/10.1063/1.3000655 (3 pages) | Cited 15 times

Online Publication Date: 31 October 2008

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The breakdown of Hall–Petch strength scaling is investigated in nanocrystalline Ni–W alloys at high strain rates, using dynamic hardness testing at grain sizes ranging from 3 to 150 nm. Whereas quasistatic tests show a strength plateau below about 15 nm, high-rate tests (indentation strain rate of ∼ 103 s−1) exhibit a pronounced strength peak and a regime of “inverse Hall–Petch” weakening. This effect is shown to be the result of a grain size-dependent rate sensitivity that exhibits a maximum at a grain size near 10–20 nm. High strain rates are also shown to promote shear banding at nanocrystalline grain sizes.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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Separation of the Schottky barrier and polarization effects on the photocurrent of Pt sandwiched Pb(Zr0.20Ti0.80)O3 films

Fengang Zheng, Jie Xu, Liang Fang, Mingrong Shen, and Xinglong Wu

Appl. Phys. Lett. 93, 172101 (2008); http://dx.doi.org/10.1063/1.3009563 (3 pages) | Cited 19 times

Online Publication Date: 27 October 2008

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Photoelectric behavior of Pt sandwiched Pb(Zr0.20Ti0.80)TiO3 (PZT) films deposited on Pt/Ti/SiO2/Si substrates by a sol-gel method was investigated by testing the short-circuit photocurrent under different film thicknesses. By poling the films step by step with increased magnitude and alternated direction of the dc electric field, interesting photoelectric behavior was found when the PZT films were in virgin or poled up/down state. The photocurrent was also strongly dependent on the film thickness. A simple model was proposed to separate the effects of interface Schottky barriers and bulk ferroelectric polarization of the film on the photocurrent of the Pt/PZT/Pt structure.
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73.30.+y Surface double layers, Schottky barriers, and work functions
77.22.Ej Polarization and depolarization
73.50.Pz Photoconduction and photovoltaic effects

Ni diffusion and its influence on electrical properties of AlxGa1−xN/GaN heterostructures

S. Huang, B. Shen, F. Lin, N. Ma, F. J. Xu, Z. L. Miao, J. Song, L. Lu, F. Liu, Y. Wang, Z. X. Qin, Z. J. Yang, and G. Y. Zhang

Appl. Phys. Lett. 93, 172102 (2008); http://dx.doi.org/10.1063/1.3010371 (3 pages) | Cited 1 time

Online Publication Date: 28 October 2008

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The effect of thermal annealing of Ni/AlxGa1−xN/GaN structures on electric properties of AlxGa1−xN/GaN heterostructures has been studied by means of temperature-dependent Hall measurements and deep level transient spectroscopy. It is found that the mobility of the two-dimensional electron gas (2DEG) decreases from 1530 to 986 cm2/V s at room temperature (RT) after annealing the Al0.25Ga0.75N/GaN heterostructure with a 10 nm thick Ni cap layer at 600 °C. The density of the 2DEG is also reduced by 2.0×1012 cm−2 at RT after the annealing, and decreases with increasing temperature between 100 and 460 K. It is determined that an acceptorlike deep level with an activation energy of 1.23 eV and apparent capture cross section of 2.8×10−13 cm2 is introduced into the heterostructures. We believe that the acceptorlike deep level is induced by Ni diffusion during the annealing, and it results in the significant degradation of the transport properties of the 2DEG in the heterostructures.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ns Metal-nonmetal contacts
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Fr Low-field transport and mobility; piezoresistance
81.40.Gh Other heat and thermomechanical treatments
71.10.Ca Electron gas, Fermi gas

Determination of the intershell conductance in a multiwall carbon nanotube

A. Stetter, J. Vancea, and C. H. Back

Appl. Phys. Lett. 93, 172103 (2008); http://dx.doi.org/10.1063/1.3006426 (3 pages) | Cited 4 times

Online Publication Date: 28 October 2008

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We have measured the current induced voltage drop along an individual multiwall carbon nanotube as a function of the distance to the current injecting electrode. The measurements have been performed at room temperature using scanning probe potentiometry combined with scanning electron microscopy. For a nanotube with an incomplete outer shell, a sharp potential jump was observed at the end of the outermost shell. The electric potential variation along the carbon nanotube has been used to determine the contact resistance between metal electrodes and the tube, the intrashell resistance, and the intershell conductance.
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73.63.Fg Nanotubes
73.40.Cg Contact resistance, contact potential

Resistance switching properties of sol-gel derived La0.67Ca0.33MnO3 thin films on F-doped SnO2 conducting glass

Ting Zhang, Zhaohui Su, Hongju Chen, Linghong Ding, and Weifeng Zhang

Appl. Phys. Lett. 93, 172104 (2008); http://dx.doi.org/10.1063/1.3011029 (3 pages) | Cited 9 times

Online Publication Date: 29 October 2008

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The electric-pulse-induced resistance switching of the Au–La0.67Ca0.33MnO3(LCMO)-FTO (fluorine-doped tin oxide) heterostructures was studied by electrochemical workstation. A distinct current-voltage characteristic of the device with pronounced reproducible nonlinearity, asymmetry, and hysteresis was observed at room temperature. The current-voltage characteristics suggest a Poole–Frenkel and space-charge-limited current type mechanism controlled by Au/LCMO interface traps. The resistance switching behavior shows obvious multilevel resistance switching. The present results suggest a possible application of Ag-LCMO-FTO system as multilevel memory devices.
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73.40.Ns Metal-nonmetal contacts
73.20.-r Electron states at surfaces and interfaces
73.61.Ng Insulators
68.55.aj Insulators
72.20.Ht High-field and nonlinear effects
82.45.Mp Thin layers, films, monolayers, membranes

Rectification effect and electron transport property of CdS/Si nanoheterostructure based on silicon nanoporous pillar array

Hai Jun Xu and Xin Jian Li

Appl. Phys. Lett. 93, 172105 (2008); http://dx.doi.org/10.1063/1.3002297 (3 pages) | Cited 6 times

Online Publication Date: 29 October 2008

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A CdS/Si nanoheterostructure was prepared by growing CdS nanocrystallites onto silicon nanoporous pillar array. A rectification effect with an onset voltage of ∼ 1 V, a forward current density of ∼ 170 mA cm−2 at 4.5 V, a leakage current density of ∼ 8×10−2 mA cm−2, and a reverse breakdown voltage of ∼ 8 V was observed. The rectifying ratio was evaluated to be ∼ 215 at ±4.5 V. The electron transport across the nanoheterostructure was found to be mainly controlled by sulfur vacancies and obey the trap-limited model. These results indicate that CdS/Si nanoporous pillar array might be a promising material in fabricating photoelectronic nanodevices.
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73.40.Ei Rectification
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.jd Vacancies
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing

Intermixing and chemical structure at the interface between n-GaN and V-based contacts

S. Pookpanratana, R. France, M. Bär, L. Weinhardt, O. Fuchs, M. Blum, W. Yang, J. D. Denlinger, T. D. Moustakas, and C. Heske

Appl. Phys. Lett. 93, 172106 (2008); http://dx.doi.org/10.1063/1.2992199 (3 pages) | Cited 6 times

Online Publication Date: 29 October 2008

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The interface between n-type GaN and V-based contacts was characterized by soft x-ray spectroscopy. We have investigated the chemical interface structure before and after a rapid thermal annealing (RTA) step, which is crucial for the formation of an Ohmic contact. X-ray photoelectron and x-ray excited Auger electron spectra suggest that RTA induces an accumulation of metallic Ga at the surface. Using x-ray emission spectroscopy, we find that the probed nitrogen atoms are in a VN-like environment, indicating that vanadium interacts with nitrogen atoms from the GaN to form VN.
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73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing
78.70.En X-ray emission spectra and fluorescence
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Narrow inhomogeneous broadening of V-groove quantum wires grown on vicinal substrates

N. Moret, D. Y. Oberli, B. Dwir, A. Rudra, P. Gallo, and E. Kapon

Appl. Phys. Lett. 93, 172107 (2008); http://dx.doi.org/10.1063/1.2976555 (3 pages) | Cited 3 times

Online Publication Date: 30 October 2008

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Significant reduction in inhomogeneous broadening of GaAs/AlGaAs V-groove quantum wires (QWRs) is achieved by growing them on vicinal (001) GaAs substrates misaligned by several degrees with respect to the [1math0] groove direction. Low temperature photoluminescence spectra exhibit QWR linewidths as low as 3.7 meV for subband separation of 41 meV and 3 meV for subband separation of 27 meV. Atomic force microscopy evidences a change in the growth dynamics as compared with QWRs made on exact (001) GaAs substrates. The impact of the different growth dynamics on the wire interface structure is discussed.
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78.67.Lt Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
78.55.Cr III-V semiconductors
68.35.bg Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Tunable graphene system with two decoupled monolayers

H. Schmidt, T. Lüdtke, P. Barthold, E. McCann, V. I. Fal’ko, and R. J. Haug

Appl. Phys. Lett. 93, 172108 (2008); http://dx.doi.org/10.1063/1.3012369 (3 pages) | Cited 22 times

Online Publication Date: 30 October 2008

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The use of two truly two-dimensional gapless semiconductors, monolayer and bilayer graphene, as current-carrying components in field-effect transistors (FETs) gives access to special types of nanoelectronic devices. Here, we report on the development of graphene-based FETs containing two decoupled graphene monolayers manufactured from a single one folded during the exfoliation process. The transport characteristics of these devices differ markedly from those manufactured from a single-crystal bilayer. By analyzing Shubnikov–de Haas oscillations, we demonstrate the possibility to independently control the carrier densities in both layers using top and bottom gates, despite there being only a nanometer scale separation between them.
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73.23.-b Electronic transport in mesoscopic systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
73.43.-f Quantum Hall effects

Fully transparent nonvolatile memory employing amorphous oxides as charge trap and transistor’s channel layer

Huaxiang Yin, Sunil Kim, Chang Jung Kim, Ihun Song, Jaechul Park, Sangwook Kim, and Youngsoo Park

Appl. Phys. Lett. 93, 172109 (2008); http://dx.doi.org/10.1063/1.3012386 (3 pages) | Cited 15 times

Online Publication Date: 30 October 2008

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A fully transparent nonvolatile memory with the conventional sandwich gate insulator structure was demonstrated. Wide band gap amorphous GaInZnO (a-GIZO) thin films were employed as both the charge trap layer and the transistor channel layer. An excellent program window of 3.5 V with a stressing time of 100 ms was achieved through the well-known Fowler–Nordheim tunneling method. Due to the similar energy levels extracted from the experimental data, the asymmetrical program/erase characteristics are believed to be the result of the strong trapping of the injected negative charges in the shallow donor levels of the GIZO film.
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84.30.Sk Pulse and digital circuits

In situ verification of single-domain III-V on Si(100) growth via metal-organic vapor phase epitaxy

Henning Döscher, Thomas Hannappel, Bernardette Kunert, Andreas Beyer, Kerstin Volz, and Wolfgang Stolz

Appl. Phys. Lett. 93, 172110 (2008); http://dx.doi.org/10.1063/1.3009570 (3 pages) | Cited 11 times

Online Publication Date: 31 October 2008

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Reflectance anisotropy spectroscopy (RAS) was used in situ for the quantification of antiphase domains on surfaces of thin GaP films deposited onto Si(100) by metal-organic vapor phase epitaxy (MOVPE). The preparation of a single-domain GaP/Si(100) surface was determined via the analysis of RAS peak intensities in reference to the well-known P-rich surface reconstruction of homoepitaxially grown GaP(100). Both preprocessed Si(100) substrates and MOVPE as-grown GaP/Si(100) films were also characterized ex situ by atomic force microscopy to identify the formation of mono- and diatomic surface steps and to analyze of the domain distribution, respectively.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.37.Ps Atomic force microscopy (AFM)
68.35.bg Semiconductors

Reproducible growth of p-type ZnO:N using a modified atomic layer deposition process combined with dark annealing

L. Dunlop, A. Kursumovic, and J. L. MacManus-Driscoll

Appl. Phys. Lett. 93, 172111 (2008); http://dx.doi.org/10.1063/1.3000604 (3 pages) | Cited 30 times

Online Publication Date: 31 October 2008

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Nitrogen doped ZnO (ZnO:N) films were deposited by atmospheric atomic layer deposition (ALD) between 100 and 300 °C. Postannealing was required to remove compensating defects. After a low temperature dark annealing, originally n-type films became p-type. Films deposited at low temperatures ( ⩽ 150 °C) have low hole mobilities (μ) of 0.2–0.4 cm2 V−1 s−1 and moderate hole concentrations (np) of around 1×1015 cm−3. Higher temperature deposited films ( ≥ 200 °C) have higher μ values (6 cm2 V−1 s−1) but np values <1×1013 cm−3. This crossover in transport properties can be explained by the opposing effects of deposition temperature on nitrogen doping level and distribution, and film crystallinity.
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68.55.ag Semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
72.20.Fr Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.80.Ey III-V and II-VI semiconductors

Metal modulation epitaxy growth for extremely high hole concentrations above 1019 cm−3 in GaN

Gon Namkoong, Elaissa Trybus, Kyung Keun Lee, Michael Moseley, W. Alan Doolittle, and David C. Look

Appl. Phys. Lett. 93, 172112 (2008); http://dx.doi.org/10.1063/1.3005640 (3 pages) | Cited 14 times

Online Publication Date: 31 October 2008

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The free hole carriers in GaN have been limited to concentrations in the low 1018 cm−3 range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ∼ 10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ∼ 1.5×1019 cm−3.
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81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Zero-field spin splitting in AlxGa1−xN/GaN heterostructures with various Al compositions

Ning Tang, Bo Shen, Kui Han, Fang-Chao Lu, Fu-Jun Xu, Zhi-Xin Qin, and Guo-Yi Zhang

Appl. Phys. Lett. 93, 172113 (2008); http://dx.doi.org/10.1063/1.3012361 (3 pages) | Cited 5 times

Online Publication Date: 31 October 2008

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The zero-field spin splitting in AlxGa1−xN/GaN heterostructures with various Al compositions has been investigated at low temperatures and high magnetic fields. The zero-field spin-splitting energy and the spin-orbit coupling parameter are obtained by means of beating pattern Shubnikov–de Haas measurements. It is found that the spin-orbit coupling parameter can be tuned by the polarization-induced electric field. The AlxGa1−xN/GaN heterostructure is one of the promising materials for the spin-polarized field effect transistor.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.25.-b Spin polarized transport
81.05.Ea III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Dependency of threshold switching on density of localized states of Ge2Sb2Te5 thin films for phase change random access memory

Seung Wook Ryu, Jong Ho Lee, Yong Bae Ahn, Choon Hwan Kim, Byung Joon Choi, Cheol Seong Hwang, and Hyeong Joon Kim

Appl. Phys. Lett. 93, 172114 (2008); http://dx.doi.org/10.1063/1.3012366 (3 pages) | Cited 10 times

Online Publication Date: 31 October 2008

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The threshold switching of Ge2Sb2Te5 (GST) films for phase change random access memory applications was investigated by measuring the variation in the threshold voltage (VT) with the crystallinity of the GST films and photon energy absorption spectra. As the GST film was amorphized, VT increased to approximately 1 V and its electrical resistance increased. The optical band gap and Urbach edge of the GST increased from 0.66 to 0.97 eV and from 12 to 65 meV, respectively, upon its amorphization. It was experimentally confirmed that the threshold switching is associated with the density of localized states of the GST.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

The effect of KrF laser annealing within an ultrashort time on metal-alumina-nitride-oxide-silicon-type flash memory devices

Sungho Heo, Man Chang, Yongkyu Ju, Seungjae Jung, and Hyunsang Hwang

Appl. Phys. Lett. 93, 172115 (2008); http://dx.doi.org/10.1063/1.3012381 (3 pages) | Cited 1 time

Online Publication Date: 31 October 2008

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The effect of laser annealing (LA) within an ultrashort time on metal-alumina-nitride-oxide-silicon-type flash memory device is investigated. Conventional high-temperature annealing leads to the degrading quality of high-k blocking oxide due to the long annealing time. On the contrary, an optimized LA at an energy of 500 mJ/cm2 can effectively improve the blocking efficiency due to the reduction in leakage current density. Using the results of x-ray photoemission spectroscopy and high-resolution cross-sectional transmission electron microscopy, this improvement was attributed to the minimized decomposition of the Al2O3 layer and the interfacial layer growth between Al2O3 and Si3N4.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Spatially resolved electronic properties of MgO/GaAs(001) tunnel barrier studied by ballistic electron emission microscopy

S. Guézo, P. Turban, C. Lallaizon, J. C. Le Breton, P. Schieffer, B. Lépine, and G. Jézéquel

Appl. Phys. Lett. 93, 172116 (2008); http://dx.doi.org/10.1063/1.3012571 (3 pages) | Cited 5 times

Online Publication Date: 31 October 2008

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The spatially resolved electronic structure of the epitaxial Au/MgO/GaAs(001) tunnel junction has been studied by ballistic electron emission microscopy. The Schottky barrier height of Au on the MgO/GaAs heterostructure is determined to be 3.90 eV, in good agreement with spatially averaged x-ray photoelectron spectroscopy measurements. Locally, two well-defined conduction channels are observed for electrons energies of 2.5 and 3.8 eV, i.e., below the conduction band minimum of the oxide layer. These conduction channels are attributed to band of defect states in the band-gap of the tunnel barrier related to oxygen vacancies in the MgO layer. These defect states are responsible for the low barrier height measured on magnetic tunnel junctions with epitaxial MgO(001) tunnel barriers.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.jd Vacancies
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.20.At Surface states, band structure, electron density of states

Substrate misorientation induced strong increase in the hole concentration in Mg doped GaN grown by metalorganic vapor phase epitaxy

T. Suski, E. Litwin-Staszewska, R. Piotrzkowski, R. Czernecki, M. Krysko, S. Grzanka, G. Nowak, G. Franssen, L. H. Dmowski, M. Leszczynski, P. Perlin, B. Łucznik, I. Grzegory, and R. Jakieła

Appl. Phys. Lett. 93, 172117 (2008); http://dx.doi.org/10.1063/1.3013352 (3 pages) | Cited 9 times

Online Publication Date: 31 October 2008

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We demonstrate that relatively small GaN substrate misorientation can strongly change hole carrier concentration in Mg doped GaN layers grown by metalorganic vapor phase epitaxy. In this work intentionally misoriented GaN substrates (up to 2° with respect to ideal 〈0001〉 plane) were employed. An increase in the hole carrier concentration to the level above 1018 cm−3 and a decrease in GaN:Mg resistivity below 1 Ω cm were achieved. Using secondary ion mass spectroscopy we found that Mg incorporation does not change with varying misorientation angle. This finding suggests that the compensation rate, i.e., a decrease in unintentional donor density, is responsible for the observed increase in the hole concentration. Analysis of the temperature dependence of electrical transport confirms this interpretation.
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73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.55.ag Semiconductors

On the explanation of the barrier heights of InP Schottky contacts by metal-induced gap states

Winfried Mönch

Appl. Phys. Lett. 93, 172118 (2008); http://dx.doi.org/10.1063/1.3009283 (3 pages) | Cited 6 times

Online Publication Date: 31 October 2008

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The barrier heights of metal-semiconductor or Schottky contacts are explained by the continuum of metal-induced gap states (MIGSs). A verification of the theoretically predicted values requires experimental barrier heights of Schottky contacts, which are not only intimate, abrupt, and free of impurities but also laterally homogeneous. Such data may be obtained from current-voltage and capacitance-voltage characteristics. Results of corresponding studies with Ag, Au, Cr, Pd, and Ti contacts on InP were recently published. The barrier heights of the respective laterally homogeneous Schottky contacts evaluated from those experimental data quantitatively confirm the predictions of the MIGS theory.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts

Resistance dependence of photovoltaic effect in Au/SrTiO3:Nb(0.5 wt %) Schottky junctions

D. S. Shang, J. R. Sun, L. Shi, Z. H. Wang, and B. G. Shen

Appl. Phys. Lett. 93, 172119 (2008); http://dx.doi.org/10.1063/1.3009285 (3 pages) | Cited 4 times

Online Publication Date: 31 October 2008

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Photoresponse in the Au/SrTiO3:0.5 wt % Nb Schottky junction with an electric field–tunable resistance between ∼ 70 kΩ and ∼ 900 MΩ has been experimentally studied. The most remarkable observation is the strong dependence of the open-circuit photovoltage on junction resistance and the invariance of the short-circuit photocurrent during resistance switching. These results, combined with a theoretical calculation based on the equivalent circuit model consisting of a diode in parallel with a resistor, suggest the occurrence of filamentary conductive channels across the interface of the junction under the impact of electric pulses, whereas the remaining Schottky barrier keeps completely unchanged.
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72.40.+w Photoconduction and photovoltaic effects
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
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