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28 May 2007

Volume 90, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 90, 221101 (2007); http://dx.doi.org/10.1063/1.2743884 (3 pages)

Siyka I. Shopova, Hongying Zhou, Xudong Fan, and Po Zhang
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Thermodynamic properties and interfacial layer characteristics of HfO2 thin films deposited by plasma-enhanced atomic layer deposition

Inhoe Kim, Seoungwoo Kuk, Seokhoon Kim, Jinwoo Kim, Hyeongtag Jeon, M.-H. Cho, and K.-B. Chung

Appl. Phys. Lett. 90, 222101 (2007); http://dx.doi.org/10.1063/1.2743749 (3 pages) | Cited 4 times

Online Publication Date: 29 May 2007

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The thermodynamic properties and interfacial characteristics of HfO2 thin films that were deposited by the direct plasma atomic layer deposition (DPALD) method are investigated. The as-deposited HfO2 films that were deposited by the DPALD method show crystallization of the HfO2 layers, which initiates at approximately the 35th cycle (about 2.8 nm) of the DPALD process. Medium-energy ion scattering analysis reveals that the direct O2 plasma causes a compositional change in the interfacial layer as the process progresses. With an increase in the number of process cycles, the Si content decreases and the O content increases at that position, so that the HfO2-like Hf-silicate layer is formed on top of the interfacial layer. The enhanced physical reactivity of the oxygen ions in the direct plasma and the Hf-silicate layer may be the driving forces that accelerate the early crystallization of the HfO2 layer in the DPALD process in the as-deposited state.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
65.40.G- Other thermodynamical quantities
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
52.77.Dq Plasma-based ion implantation and deposition

Three-level structure design and optically controlled current in coupled quantum dots

Weidong Chu, Suqing Duan, and Jia-Lin Zhu

Appl. Phys. Lett. 90, 222102 (2007); http://dx.doi.org/10.1063/1.2743906 (3 pages) | Cited 12 times

Online Publication Date: 29 May 2007

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Two-mode photon-assisted transport through coupled nonidentical quantum dots is studied by designing the level structure of the system. It is found that a Λ-type three-level structure can be formed by modulating the shape and size of dots or by applying electric field. Based on the three-level system, current antiresonance phenomenon occurs due to the effect of coherent population trapping. Using the asymmetry of quantum dots, oscillating current can be produced by rotating the polarization direction of linearly polarized microwave.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
73.21.La Quantum dots

Excimer laser irradiation induced suppression of off-state leakage current in organic transistors

Wei-Yang Chou, Shih-Ting Lin, Horng-Long Cheng, Fu-Ching Tang, Yow-Jon Lin, Chang-Feng You, and Yu-Wu Wang

Appl. Phys. Lett. 90, 222103 (2007); http://dx.doi.org/10.1063/1.2743925 (3 pages) | Cited 3 times

Online Publication Date: 29 May 2007

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The authors report the suppression of the off-state leakage current and subthreshold swing (SS) in inkjet-printed poly(3-hexylthiophene) thin-film transistors with asymmetric work function source and drain electrodes. Indium tin oxide (ITO) material was used as source/drain electrodes and the source electrode was irradiated by KrF excimer laser. The dominant mechanisms for the suppressive Ioff could be attributed to the increase in the work function of ITO source irradiated by the excimer laser. Lower trap state density formed on the laser irradiated source electrode. Holes could be easily injected into the channel at small lateral electric field resulting in smaller threshold voltage and SS.
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85.30.Tv Field effect devices
85.60.-q Optoelectronic devices

Nickel nanocrystals with HfO2 blocking oxide for nonvolatile memory application

F. M. Yang, T. C. Chang, P. T. Liu, U. S. Chen, P. H. Yeh, Y. C. Yu, J. Y. Lin, S. M. Sze, and J. C. Lou

Appl. Phys. Lett. 90, 222104 (2007); http://dx.doi.org/10.1063/1.2743926 (3 pages) | Cited 32 times

Online Publication Date: 29 May 2007

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A distributed charge storage with Ni nanocrystals embedded in the SiO2 and HfO2 layer has been fabricated in this study. The mean size and aerial density of the Ni nanocrystals are estimated to be about 5 nm and 3.9×1012/cm2, respectively. The nonvolatile memory device with Ni nanocrystals exhibits 1 V threshold voltage shift under 4 V write operation. The device has a long retention time with a small charge lose rate. Besides, the endurance of the memory device is not degraded up to 106 write/erase cycles.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.30.Sk Pulse and digital circuits

H2S exposure of a (100)Ge surface: Evidences for a (2×1) electrically passivated surface

M. Houssa, D. Nelis, D. Hellin, G. Pourtois, T. Conard, K. Paredis, K. Vanormelingen, A. Vantomme, M. K. Van Bael, J. Mullens, M. Caymax, M. Meuris, and M. M. Heyns

Appl. Phys. Lett. 90, 222105 (2007); http://dx.doi.org/10.1063/1.2743385 (3 pages) | Cited 10 times

Online Publication Date: 30 May 2007

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The experimental study of the bonding geometry of a (100)Ge surface exposed to H2S in the gas phase at 330 °C shows that 1 ML S coverage with (2×1) surface reconstruction can be achieved. The amount of S on the Ge surface and the observed surface periodicity can be explained by the formation of disulfide bridges between Ge–Ge dimers on the surface. First-principles molecular dynamics simulations confirm the preserved (2×1) reconstruction after dissociative adsorption of H2S molecules on a (100)Ge (2×1) surface, and predict the formation of (S–H)–(S–H) inter-Ge dimer bridges, i.e., disulfide bridges interacting via hydrogen bonding. The computed energy band gap of this atomic configuration is shown to be free of surface states, a very important finding for the potential application of Ge in future high performance integrated circuits.
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81.65.Rv Passivation
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Bc Ab initio calculations of adsorbate structure and reactions
71.20.Mq Elemental semiconductors

Interaction of dislocations with vacancies in silicon: Electronic effects

M. M. de Araýýjo, J. F. Justo, and R. W. Nunes

Appl. Phys. Lett. 90, 222106 (2007); http://dx.doi.org/10.1063/1.2743909 (3 pages) | Cited 1 time

Online Publication Date: 30 May 2007

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The authors report on an ab initio investigation of the interaction of vacancies with the core of 90° partial dislocation in silicon. For the single-period and the double-period core reconstructions, they find the vacancy formation energies at the core sites to be lower than in the crystalline environment. Moreover, they find that the vacancy-dislocation coupling does not change the U-negative nature of a vacancy in silicon, but leads to quantitative changes in the relative stability of different charge states, as the Fermi level sweeps the electronic band gap in this material.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Bb Theories and models of crystal defects
71.20.Mq Elemental semiconductors
71.15.-m Methods of electronic structure calculations

Transparent metallic Sb-doped SnO2 nanowires

Qing Wan, Eric N. Dattoli, and Wei Lu

Appl. Phys. Lett. 90, 222107 (2007); http://dx.doi.org/10.1063/1.2743746 (3 pages) | Cited 40 times

Online Publication Date: 30 May 2007

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The authors report the growth and characterization of single-crystalline, degenerately Sb-doped SnO2 (SnO2:Sb) nanowires. The in situ doped SnO2:Sb nanowires are transparent conductors with resistivities down to 4.1×10−4 Ω cm and failure-current densities up to 2.1×107 A/cm2. High carrier concentrations (>1020 cm−3) and minimal environmental effects were also observed and attributed to effective Sb doping. The SnO2:Sb nanowires can be obtained at large quantities using a low-cost vapor transport method and may provide a suitable alternative to indium tin oxide as transparent conducting oxide materials. Field emission devices with SnO2:Sb nanowire cathodes and anodes exhibited an ultralow turn-on voltage of 2 V.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Bc Nanocrystalline materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
73.63.Bd Nanocrystalline materials

Concentration-dependent mobility in organic field-effect transistors probed by infrared spectromicroscopy of the charge density profile

A. D. Meyertholen, Z. Q. Li, D. N. Basov, M. M. Fogler, M. C. Martin, G. M. Wang, A. S. Dhoot, D. Moses, and A. J. Heeger

Appl. Phys. Lett. 90, 222108 (2007); http://dx.doi.org/10.1063/1.2745223 (3 pages) | Cited 4 times

Online Publication Date: 31 May 2007

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The authors show that infrared imaging of the charge density profile in organic field-effect transistors (FETs) can probe transport characteristics which are difficult to access by conventional contact-based measurements. Specifically, they carry out experiments and modeling of infrared spectromicroscopy of poly(3-hexylthiophene) (P3HT) FETs in which charge injection is affected by a relatively low resistance of the gate insulators. They conclude that the mobility of P3HT has a power-law density dependence, which is consistent with the activated transport in disorder-induced tails of the density of states.
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85.30.Tv Field effect devices

Memory effect of CdSe/ZnS nanoparticles embedded in a conducting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] polymer layer

Fushan Li, Dong-Ick Son, Han-Moe Cha, Seung-Mi Seo, Bong-Jun Kim, Hyuk-Ju Kim, Jae-Hun Jung, and Tae Whan Kim

Appl. Phys. Lett. 90, 222109 (2007); http://dx.doi.org/10.1063/1.2745219 (3 pages) | Cited 22 times

Online Publication Date: 31 May 2007

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Capacitance-voltage (C-V) measurements on Au/a conducting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] polymer layer containing core/shell CdSe/ZnS nanoparticles (hybrid layer)/indium tin oxide (ITO) coated glass and Al/hybrid layer/ITO coated glass capacitors at 300 K showed metal-insulator-semiconductor behavior with a large flatband voltage shift. This shift was due to the existence of the CdSe/ZnS nanoparticles, indicative of trapping, storing, and emission of charge carriers in the CdSe/ZnS nanoparticles. Symmetric and asymmetric C-V characteristics appeared in the Al/hybrid layer/ITO coated glass and Au/hybrid layer/ITO coated glass capacitors, respectively. A dipolar carrier trapping model is proposed to explain the symmetric behavior in the C-V curve.
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84.30.Sk Pulse and digital circuits
84.32.Tt Capacitors

Room-temperature ferromagnetic and ferroelectric behavior in polycrystalline ZnO-based thin films

Yuan-Hua Lin, Minghao Ying, Ming Li, Xiaohui Wang, and Ce-Wen Nan

Appl. Phys. Lett. 90, 222110 (2007); http://dx.doi.org/10.1063/1.2745247 (3 pages) | Cited 23 times

Online Publication Date: 31 May 2007

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Polycrystalline ZnO-based thin films with Li and/or Co doping have been prepared by a sol-gel spin-coating method on silicon substrates. Magnetization measurements reveal that Li-doped ZnO film shows paramagnetic behavior. However, the Co-doped ZnO thin films show obvious room-temperature ferromagnetic properties, and ferromagnetic properties can be enhanced by the Li codoping, which may be ascribed to indirect exchange via Li-related defects. All ZnO-based films exhibit ferroelectric behavior, and ferroelectric properties can be tuned by the dopants.
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77.80.-e Ferroelectricity and antiferroelectricity
61.72.up Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals

Band discontinuity measurements of the wafer bonded InGaAs/Si heterojunction

Kyle S. McKay, Felix P. Lu, Jungsang Kim, Changhyun Yi, April S. Brown, and Aaron R. Hawkins

Appl. Phys. Lett. 90, 222111 (2007); http://dx.doi.org/10.1063/1.2745254 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2007

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p-type InGaAs/Si heterojunctions were fabricated through a wafer fusion bonding process. The relative band alignment between the two materials at the heterointerface was determined using current-voltage (I-V) measurements and applying thermionic emission-diffusion theory. The valence and conduction band discontinuities for the InGaAs/Si interface were determined to be 0.48 and −0.1 eV, respectively, indicating a type-II band alignment.
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73.20.At Surface states, band structure, electron density of states
79.40.+z Thermionic emission
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

PbTe nanocomposites synthesized from PbTe nanocrystals

J. Martin, G. S. Nolas, W. Zhang, and L. Chen

Appl. Phys. Lett. 90, 222112 (2007); http://dx.doi.org/10.1063/1.2745218 (3 pages) | Cited 52 times

Online Publication Date: 1 June 2007

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Dense lead telluride (PbTe) nanocomposites were prepared from PbTe nanocrystals synthesized employing an aqueous solution-phase reaction. This approach reproducibly synthesizes 100–150 nm nanocrystals with a high yield of over 2 g per batch. Densification using spark plasma sintering dimensionally integrated nanoscale grains within a bulk matrix, resulting in a uniform dispersion of nonconglomerated nanocrystals. Transport properties of PbTe nanocomposites were evaluated through temperature dependent resistivity, Hall, Seebeck coefficient, and thermal conductivity measurements. These nanocomposites show an enhancement in the thermoelectric properties compared to bulk polycrystalline PbTe with similar carrier concentrations. Our results also indicate a strong sensitivity to stoichiometry, surface oxygen adsorption, and porosity.
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81.16.Be Chemical synthesis methods
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.43.Mn Adsorption kinetics
52.77.-j Plasma applications
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