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7 Nov 2005

Volume 87, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 192502 (2005); http://dx.doi.org/10.1063/1.2128478 (3 pages)

Ki-Suk Lee, SangKook Choi, and Sang-Koog Kim
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Uncooled tunable pyroelectric response of antiferroelectric Pb0.97La0.02(Zr0.65Sn0.22Ti0.13)O3 perovskite

Wai-Hung Chan, Zhengkui Xu, Jiwei Zhai, and Haydn Chen

Appl. Phys. Lett. 87, 192904 (2005); http://dx.doi.org/10.1063/1.2128483 (3 pages) | Cited 11 times

Online Publication Date: 3 November 2005

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Pb0.97La0.02(Zr0.65Sn0.22Ti0.13)O3 ceramic was confirmed to be in an antiferroelectric (AFE) phase at T<170 °C by macroscopic and microscopic studies. The electric-field-induced ferroelectric (FE) state was found to exhibit a much longer lifetime than the reasonable laboratory measuring time scale at T<60 °C, which has led to the frequent misinterpretation of this material system as FE. The dc bias dependence of the dielectric and pyroelectric properties was studied as a function of temperature. The poled sample exhibited a low dissipation factor (tan δ ∼ 0.03), a large transient pyroelectric coefficient of the order of 10−3–10−2 Cm−2 K−1, and excellent dc tunability at the FE-to-AFE transition temperature (39 °C/kV/mm). The possible application of this material to uncooled tunable pyroelectric thermal sensing is also discussed.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.70.+a Pyroelectric and electrocaloric effects
77.22.Ej Polarization and depolarization

Evidence for oxygen vacancy inducing spontaneous normal-relaxor transition in complex perovskite ferroelectrics

Guochu Deng, Guorong Li, Aili Ding, and Qingrui Yin

Appl. Phys. Lett. 87, 192905 (2005); http://dx.doi.org/10.1063/1.2125110 (3 pages) | Cited 28 times

Online Publication Date: 3 November 2005

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The relaxor ferroelectrics—0.3Pb(Zn1/3Nb2/3)O3–0.7(Pb,La)(Zr,Ti)O3—have been produced by sintering in reductive nitrogen ambient and postannealing in oxygen ambient. The two kinds of specimens exhibited great differences in the conductivity as a function of temperature, which indicated a high concentration of oxygen vacancies in the as-sintered specimen. On the other hand, this specimen underwent an evident spontaneous normal-relaxation transition, whereas the as-annealed one did not. The corresponding reason has been analyzed on the basis of the facts, which provide some evidence that the interior stresses due to oxygen deficiency induce the spontaneous normal-relaxor transition in the specimen sintered in reductive ambient.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.J- Point defects and defect clusters
77.80.-e Ferroelectricity and antiferroelectricity
61.72.Cc Kinetics of defect formation and annealing
62.20.-x Mechanical properties of solids

Effect of Y doping and composition-dependent elastic strain on the electrical properties of (Ba,Sr)TiO3 thin films deposited at 520 °C

Ruey-Ven Wang, Paul C. McIntyre, John D. Baniecki, Kenji Nomura, Takeshi Shioga, Kazuaki Kurihara, and Masatoshi Ishii

Appl. Phys. Lett. 87, 192906 (2005); http://dx.doi.org/10.1063/1.2125113 (3 pages) | Cited 17 times

Online Publication Date: 4 November 2005

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We demonstrate that large and simultaneous improvements in permittivity, tunability, and leakage current density of (Ba,Sr)TiO3 (BST)-based thin-film capacitors can be achieved by yttrium doping. We have found that, for a low deposition temperature (520 °C) sputtering process, Y-doped BST capacitors exhibit tenfold lower leakage current density (<10−9 A/cm2 at 100 KV/cm) and 70% higher permittivity than nominally undoped BST-based capacitors. Furthermore, this work suggests an intriguing correlation between dopant concentration-dependent elastic strain in the films and their enhanced dielectric properties.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.up Other materials
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.15.Cd Deposition by sputtering
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.F- Deformation and plasticity
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Axial Young’s modulus prediction of single-walled carbon nanotube arrays with diameters from nanometer to meter scales

C. H. Sun, F. Li, H. M. Cheng, and G. Q. Lu

Appl. Phys. Lett. 87, 193101 (2005); http://dx.doi.org/10.1063/1.2119409 (3 pages) | Cited 6 times

Online Publication Date: 31 October 2005

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Based on a self-similar array model, we systematically investigated the axial Young’s modulus (Yaxis) of single-walled carbon nanotube (SWNT) arrays with diameters from nanometer to meter scales by an analytical approach. The results show that the Yaxis of SWNT arrays decreases dramatically with the increases of their hierarchy number (s) and is not sensitive to the specific size and constitution when s is the same, and the specific Young’s modulus Yaxiss is independent of the packing configuration of SWNTs. Our calculations also show that the Yaxis of SWNT arrays with diameters of several micrometers is close to that of commercial high performance carbon fibers (CFs), but the Yaxiss of SWNT arrays is much better than that of high performance CFs.
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62.25.-g Mechanical properties of nanoscale systems
61.46.-w Structure of nanoscale materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Self-regenerative field emission source

Masaki Tanemura, J. Tanaka, K. Itoh, T. Okita, L. Miao, S. Tanemura, S. P. Lau, L. Huang, Y. Agawa, and M. Kitazawa

Appl. Phys. Lett. 87, 193102 (2005); http://dx.doi.org/10.1063/1.2126152 (3 pages) | Cited 11 times

Online Publication Date: 1 November 2005

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A self-regenerative field emission source was demonstrated. The emission source (cathode) consisted of carbon nanofibers (CNFs) grown on the tip of conical carbon protrusions on a graphite plate. CNFs were ∼ 25 nm in diameter, 0.3–2.5 μm in length and ∼ 1×106 mm−2 in site density. Initial emission characteristics showed a threshold field of 3.05 V/μm with a current density of 1 μA/cm2 and a field enhancement factor of 2860 from the Fowler-Nordheim plot assuming the work function of 4.6 eV for graphite. A lifetime test carried out for more than 40 h at a constant applied electric field of 10 V/μm in 10−4 Pa region disclosed a stable emission with a current density of 1.7–3.0×10−4 A/cm2 after a slight initial decrease in the emission current. Detailed morphological observations revealed that a thick layer of newly grown carbon fibers was formed on the cathode surface after the lifetime test which could be responsible for the observed stable and long-sustained emission under a nonultrahigh vacuum condition. Their growth was attributed to the surface diffusion of carbon atoms generated by sputtering of the carbon cathode with ionized residual gas molecules during the field emission process. Thus, the CNF-tipped carbon emitter was believed to be promising as a practical field electron emission source used under low vacuum.
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79.70.+q Field emission, ionization, evaporation, and desorption

Fabrication of one-dimensional GaAs channel-coupled InAs quantum dot memory device by selective-area metal-organic vapor phase epitaxy

Devaraj Nataraj, Noboru Ooike, Junichi Motohisa, and Takashi Fukui

Appl. Phys. Lett. 87, 193103 (2005); http://dx.doi.org/10.1063/1.2120905 (3 pages) | Cited 7 times

Online Publication Date: 1 November 2005

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Narrow wirelike openings were defined on SiO2-masked GaAs (001) substrates by electron-beam lithography and wet chemical etching methods. A one-dimensional GaAs channel-coupled InAs quantum dot memory device was fabricated in this opened area by the selective-area metal-organic vapor phase epitaxy. Drain current measurement by sweeping the gate voltage forward and backward showed clear hysteresis up to 180 K due to electrons charging into the quantum dots with a threshold voltage difference (ΔVth) of 165 mV at 20 K and 29 mV at 180 K. Comparison of experimental ΔVth values with the theoretically calculated ones showed that around 300 and 50 electrons were responsible for the memory operation at 20 and 180 K, respectively. Real time measurements showed that the write/erase states of the memory device were discriminated for more than 5 min at 20 K and about 100 s at 77 K.
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85.30.-z Semiconductor devices
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Synthesis and postgrowth doping of silicon nanowires

K. Byon, D. Tham, J. E. Fischer, and A. T. Johnson

Appl. Phys. Lett. 87, 193104 (2005); http://dx.doi.org/10.1063/1.2128070 (3 pages) | Cited 22 times

Online Publication Date: 1 November 2005

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High-quality silicon nanowires (SiNWs) were synthesized via a thermal evaporation method without the use of catalysts. Scanning electron microscopy and transmission electron microscopy showed that SiNWs were long and straight crystalline silicon with an oxide sheath. Field effect transistors were fabricated to investigate the electrical transport properties. Devices on as-grown material were p-channel with channel mobilities 1–10 cm2 V−1 s−1. Postgrowth vapor doping with bismuth converted these to n-channel behavior.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
85.30.Tv Field effect devices
81.16.-c Methods of micro- and nanofabrication and processing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.uf Ge and Si

Carbon-nanotube tips with edge made of a transition metal

Giannis Mpourmpakis, George E. Froudakis, Antonis N. Andriotis, and Madhu Menon

Appl. Phys. Lett. 87, 193105 (2005); http://dx.doi.org/10.1063/1.2126116 (3 pages) | Cited 11 times

Online Publication Date: 2 November 2005

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We show that transition metal atoms, when in contact with the open ends of single-wall carbon nanotubes can form stable tip structures. This allows one to combine the superior elastic and mechanical behavior of the nanotubes with the excellent electronic and electrical properties of transition metal systems to make high quality atomistic scanning probes for various nanotechnological applications. The geometry of the tip as well as the nature of the electronic states at the tip are found to be determined by the type of the transition metal atoms. We propose optimal tip materials for efficient probes based on a detailed electronic structure analysis using ab initio methods.
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61.46.-w Structure of nanoscale materials
73.20.At Surface states, band structure, electron density of states
71.15.-m Methods of electronic structure calculations

Nanoscale lateral epitaxial overgrowth of GaN on Si (111)

K. Y. Zang, Y. D. Wang, S. J. Chua, and L. S. Wang

Appl. Phys. Lett. 87, 193106 (2005); http://dx.doi.org/10.1063/1.2126138 (3 pages) | Cited 19 times

Online Publication Date: 3 November 2005

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We demonstrate that GaN can selectively grow by metalorganic chemical vapor deposition into the pores and laterally over the nanoscale patterned SiO2 mask on a template of GaN/AlN/Si. The nanoporous SiO2 on GaN surface with pore diameter of approximately 65 nm and pore spacing of 110 nm was created by inductively coupled plasma etching using anodic aluminum oxide template as a mask. Cross-section transmission electron microscopy shows that the threading-dislocation density was largely reduced in this nanoepitaxial lateral overgrowth region. Dislocations parallel to the interface are the dominant type of dislocations in the overgrown layer of GaN. A large number of the threading dislocations were filtered by the nanoscale mask, which leads to the dramatic reduction of the threading dislocations during the growth within the nano-openings. More importantly, due to the nanoscale size of the mask area, the very fast coalescence and subsequent lateral overgrowth of GaN force the threading dislocations to bend to the basal plane within the first 50 nm of the film thickness. The structure of overgrown GaN is a truncated hexagonal pyramid which is covered with six {1math01} side facets and (0001) top surface depending on the growth conditions.
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81.16.Nd Micro- and nanolithography
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Kk Vapor phase epitaxy; growth from vapor phase
85.40.Hp Lithography, masks and pattern transfer
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
68.37.Lp Transmission electron microscopy (TEM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials
81.05.Rm Porous materials; granular materials
68.55.-a Thin film structure and morphology

Self-assembled switches based on electroactuated multiwalled nanotubes

E. Dujardin, V. Derycke, M. F. Goffman, R. Lefèvre, and J. P. Bourgoin

Appl. Phys. Lett. 87, 193107 (2005); http://dx.doi.org/10.1063/1.2126805 (3 pages) | Cited 39 times

Online Publication Date: 3 November 2005

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A fabrication process for nanoelectromechanical systems (NEMS) based on multiwalled carbon nanotubes (CNTs) suspended across metallic trenches is described. The process is versatile and allows the production of CNT-NEMS with singly or doubly clamped nanotubes at an adjustable height above a bottom electrode. When a voltage bias is applied between the nanotube and the bottom electrode, the devices act as very efficient electrical switches. Surface functionalization of the bottom electrode with a self-assembled monolayer is implemented to improve the switching reversibility. Moreover, it opens opportunities to use these CNT-NEMS as a vertical cross-bar junction for molecular electronics studies.
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85.35.Kt Nanotube devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.Dn Self-assembly
81.07.De Nanotubes

Chemical sensors using peptide-functionalized conducting polymer nanojunction arrays

Alvaro Díaz Aguilar, Erica S. Forzani, Xiulan Li, Nongjian Tao, Larry A. Nagahara, Islamshah Amlani, and Raymond Tsui

Appl. Phys. Lett. 87, 193108 (2005); http://dx.doi.org/10.1063/1.2128038 (3 pages) | Cited 17 times

Online Publication Date: 3 November 2005

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We demonstrate a heavy metal-ion sensor for drinking water analysis using a conducting polymer nanojunction array. Each nanojunction is formed by bridging a pair of nanoelectrodes separated with a small gap (<60 nm) with electrodeposited peptide-modified polyanilines. The signal transduction mechanism of the sensor is based on the change in the nanojunction conductance as a result of polymer conformational changes induced by the metal-ion chelating peptide. The nanojunction sensor allows real-time detection of Cu2+ and Ni2+ at ppt range.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.63.Bd Nanocrystalline materials
61.41.+e Polymers, elastomers, and plastics
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution

Helical CdS nanowire ropes by simple aqueous chemical growth

Wenlong Wang and Fenglian Bai

Appl. Phys. Lett. 87, 193109 (2005); http://dx.doi.org/10.1063/1.2130377 (3 pages) | Cited 6 times

Online Publication Date: 4 November 2005

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Long and flexible crystalline CdS nanowire ropes were synthesized in bulk quantities via a simple aqueous chemical growth route, which has previously been successful for the growth of short CdS nanorods. The as-grown CdS nanoropes exhibit a unique helically twisted structural feature, as confirmed by both microscopic observation and circular dichroism spectroscopic characterization. The nucleation and growth kinetics of these related CdS one-dimensional(1D) nanocrystals was investigated by monitoring the temporal evolution of the UV-visible spectrum. It was found that cadmium and sulfide monomers were first nucleated out as “magic number” CdS nanoclusters in the initial nucleation stage, and then grew to regular sized CdS 1D nanocrystals during the subsequent Ostwald ripening process.
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81.05.Dz II-VI semiconductors
81.07.Vb Quantum wires
81.16.-c Methods of micro- and nanofabrication and processing
81.10.Dn Growth from solutions
78.67.Lt Quantum wires
61.46.-w Structure of nanoscale materials
78.20.Fm Birefringence
78.40.Ha Other nonmetallic inorganics

Initial nitride formation at Si/3C–SiC(100)3×2 interface by oxynitridation

C. Radtke, H. Enriquez, J. C. Arnault, P. Soukiassian, P. Moras, C. Crotti, and P. Perfetti

Appl. Phys. Lett. 87, 193110 (2005); http://dx.doi.org/10.1063/1.2130714 (3 pages) | Cited 3 times

Online Publication Date: 4 November 2005

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Nitric oxide interaction with 3C–SiC(100)3×2 and Si-3×2/3C–SiC(100)3×2 surfaces is investigated by synchrotron radiation-based core level photoemission spectroscopy. At 25 °C, NO exposures result in oxynitride formation, while annealing at 1000 °C removes oxygen leading to a nitride layer. Most interestingly, the results suggest stoichiometric Si3N4 layer formation at Si-3×2/3C–SiC(100)3×2 interface. This finding is of interest in limiting dopant diffusion and in defect passivation so critical at insulator/SiC interfaces.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
79.60.Jv Interfaces; heterostructures; nanostructures
81.65.Rv Passivation
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
61.66.Bi Elemental solids
61.66.Dk Alloys

Spontaneous formation of ordered nanocrystal arrays in films evaporated onto nanopore array substrates

Niravun Pavenayotin, M. D. Stewart, James M. Valles, Aijun Yin, and J. M. Xu

Appl. Phys. Lett. 87, 193111 (2005); http://dx.doi.org/10.1063/1.2130726 (3 pages) | Cited 10 times

Online Publication Date: 4 November 2005

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We have investigated the structure of films thermally evaporated onto anodic aluminum oxide substrates that are patterned with a hexagonal array of 34 and 80 nm diameter holes spaced by 100 nm. Over a range of film thicknesses, Pb and Sn films spontaneously self-assemble into an array of nanocrystals in registry with the underlying hole lattice. The development of the arrays with thickness indicates that surface energies drive coalescing grains to move over the holes. Materials that wet the substrate (Pd, Ge) or whose grains do not coalesce at the substrate temperature (Au) do not form arrays. Potential applications are discussed.
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81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.16.Rf Micro- and nanoscale pattern formation

Space-charge-limited bipolar flow in a nano-gap

W. S. Koh, L. K. Ang, S. P. Lau, and T. J. T. Kwan

Appl. Phys. Lett. 87, 193112 (2005); http://dx.doi.org/10.1063/1.2130526 (3 pages) | Cited 4 times

Online Publication Date: 4 November 2005

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This paper presents a quantum model of space-charge limited (SCL) bipolar flow in a nano-sized planar gap, including the effects of electron tunneling and exchange-correlation. It is found that the classical scaling of the SCL bipolar flow is no longer valid when the gap spacing D is comparable or smaller than the electron’s de Broglie wavelength at gap voltage Vg. The classical value of the SCL bipolar electron flow is greatly enhanced due to the electron tunneling through the space-charge electric potential created by both the electrons and ions. The space-charge effect of ions is less significant (compared to electron tunneling) in the deep quantum regime that the quantum SCL bipolar flow is nearly identical to the unipolar electron flow (or quantum Child-Langmuir law).
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77.22.Jp Dielectric breakdown and space-charge effects
73.63.-b Electronic transport in nanoscale materials and structures
73.40.Gk Tunneling
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Enhancement of iridium-based organic light-emitting diodes by spatial doping of the hole transport layer

Ying Wang, Weiying Gao, Slawomir Braun, William R. Salaneck, Fabrice Amy, Calvin Chan, and Antoine Kahn

Appl. Phys. Lett. 87, 193501 (2005); http://dx.doi.org/10.1063/1.2117623 (3 pages) | Cited 6 times

Online Publication Date: 31 October 2005

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The electroluminescence efficiency of Ir-based green emitter devices is very sensitive to the nature of the hole transport layer used. We show that by inserting a 1 nm layer of bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP) in a 4,4′-bis-(carbazol-9-yl)biphenyl (CBP) hole transport layer, a device that combines the positive attributes of both MPMP (high efficiency) and CBP (low injection voltage) is obtained. These results can be understood based on a combined ultraviolet photoemission spectroscopy/inverse photoemission spectroscopy study, which reveals the very low electron affinity and superior electron blocking capability of MPMP.
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85.60.Jb Light-emitting devices

Efficient white-light-emitting diodes based on polymer codoped with two phosphorescent dyes

Yunhua Xu, Junbiao Peng, Jiaxing Jiang, Wei Xu, Wei Yang, and Yong Cao

Appl. Phys. Lett. 87, 193502 (2005); http://dx.doi.org/10.1063/1.2119407 (3 pages) | Cited 62 times

Online Publication Date: 1 November 2005

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Efficient white-light-emitting diodes (WPLEDs) based on a polymer codoped with two phosphorescent dyes were fabricated by the spin-casting method. Polyhedral oligomeric silsesquioxane-terminated poly(9,9-dioctylfluorene) (PFO-poss) was used as the host and blue light emitter. Phosphorescent emitters, fac-tris[2-(4′-ter-butyl)phenylpyridine] iridium (III) [Ir(Bu-ppy)3] and bis-(1-phenylisoquinolyl)iridium(III)(1-trifluoro) acetylacetonate [(Piq)2Ir(acaF)] with green and red emission, respectively, were used as the guests. The electroluminescence spectrum can be tuned by changing concentration of the guests. The structure of the WPLEDs is indium tin oxide (ITO)/poly(ethlenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS)/ PVK/PFO-poss codoped with Ir(Bu-ppy)3 and (Piq)2Ir(acaF)/Ba/Al. The PVK layer [poly(N-vinylcarbazole)] acts as the function of blocking electron penetrating from PFO-poss to PEDOT. When the doping concentrations are 0.14 wt % for both Ir(Bu-ppy)3 and (Piq)2Ir(acaF), the efficient white-light emission with CIE coordinates of around (0.33, 0.33) is achieved. The current efficiency reaches 5.5 lm/W (9 cd/A), and the maximum luminance of 10 200 cd/m2 was gained at 11 V. The mechanisms of the WPLEDs with high efficiency are discussed.
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85.60.Jb Light-emitting devices
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
61.72.S- Impurities in crystals
61.72.up Other materials

High-performance flexible zinc tin oxide field-effect transistors

W. B. Jackson, R. L. Hoffman, and G. S. Herman

Appl. Phys. Lett. 87, 193503 (2005); http://dx.doi.org/10.1063/1.2120895 (3 pages) | Cited 73 times

Online Publication Date: 1 November 2005

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Flexible transistors were fabricated by sputter deposition of zinc tin oxide (ZTO) onto plasma-enhanced chemical vapor deposition gate dielectrics formed on flexible polyimide substrates with a blanket aluminum gate electrode. The flexible transistors exhibited high on-currents of 1 mA, on/off ratios of 106, subthreshold voltage slopes of 1.6 V/decade, turn-on voltages of −17 V, and mobilities of 14 cm2 V−1 s−1. Capacitance measurements indicate that the threshold voltage and subthreshold slope are primarily influenced by residual doping in the ZTO rather than by defects at the semiconductor/dielectric interface, and are useful for assessing contact resistance.
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85.30.Tv Field effect devices
61.72.uj III-V and II-VI semiconductors

Low-power memory device with NiSi2 nanocrystals embedded in silicon dioxide layer

P. H. Yeh, C. H. Yu, L. J. Chen, H. H. Wu, P. T. Liu, and T. C. Chang

Appl. Phys. Lett. 87, 193504 (2005); http://dx.doi.org/10.1063/1.2126150 (3 pages) | Cited 17 times

Online Publication Date: 2 November 2005

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A metal-oxide-semiconductor structure with NiSi2 nanocrystals embedded in the SiO2 layer has been fabricated. A pronounced capacitance-voltage hysteresis was observed with a memory window of 1 V under the 2 V programming voltage. The processing of the structure is compatible with the current manufacturing technology of semiconductor industry.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Photocurrent spectroscopy under depletion mode of transparent polymer field-effect transistors

S. Dutta and K. S. Narayan

Appl. Phys. Lett. 87, 193505 (2005); http://dx.doi.org/10.1063/1.2126151 (3 pages) | Cited 8 times

Online Publication Date: 2 November 2005

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The unique combination of voltage and light as the controlling parameters for charge transport in polymer-based field-effect transistors (PFETs) offers interesting strategies for light detection. Results of gate-voltage (Vg)-controlled intensity-modulated spectral response of the drain current in optically transparent PFETs are reported. The measurement and analysis of the results, obtained from light incident from the top and bottom side of the device, provide spatial information of the Vg-dependent photocarrier generation region. These measurements serve as a direct measure of the extent of the depletion.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds

Optimal design of microscaled scattering optical elements

Andreas Håkansson and José Sánchez-Dehesa

Appl. Phys. Lett. 87, 193506 (2005); http://dx.doi.org/10.1063/1.2126134 (3 pages) | Cited 9 times

Online Publication Date: 2 November 2005

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A method of inverse design is applied to generate an optical device that acts as a wavelength demultiplexer. The ultracompact device, only 2 μm thick, is designed to separate two wavelengths 1.55 μm and 1.50 μm, respectively, and consists of five layers of 0.4 μm×0.4 μm square-shaped bars etched in gallium arsenide. The expected cross talk is suppressed below −25 dB for both wavelengths. The proposed device is an example of a scattering optical element, a name here introduced to define a class of computer-generated optical devices and whose functionalities are based on the multiple scattering by their individual constituents. For realization of the aforementioned devices, two-dimensional photonic plates can be prepared by only a single integrated circuit processing procedure followed by micromanipulation assembling.
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42.15.Eq Optical system design
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
42.82.Bq Design and performance testing of integrated-optical systems

Single-quantum-well grating-gated terahertz plasmon detectors

E. A. Shaner, Mark Lee, M. C. Wanke, A. D. Grine, J. L. Reno, and S. J. Allen

Appl. Phys. Lett. 87, 193507 (2005); http://dx.doi.org/10.1063/1.2128057 (3 pages) | Cited 48 times

Online Publication Date: 2 November 2005

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A grating-gated field-effect transistor fabricated from a single-quantum well in a high-mobility GaAs–AlGaAs heterostructure is shown to function as a continuously electrically tunable photodetector of terahertz radiation via excitation of resonant plasmon modes in the well. Different harmonics of the plasmon wave vector are mapped, showing different branches of the dispersion relation. As a function of temperature, the resonant response magnitude peaks at around 30 K. Both photovoltaic and photoconductive responses have been observed under different incident power and bias conditions.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Tv Field effect devices
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
72.40.+w Photoconduction and photovoltaic effects

High-performance organic thin-film transistors with metal oxide/metal bilayer electrode

Chih-Wei Chu, Sheng-Han Li, Chieh-Wei Chen, Vishal Shrotriya, and Yang Yang

Appl. Phys. Lett. 87, 193508 (2005); http://dx.doi.org/10.1063/1.2126140 (3 pages) | Cited 133 times

Online Publication Date: 3 November 2005

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We demonstrate bilayer source-drain (S-D) electrodes for organic thin film transistors (OTFT). The bilayer consists of a transition metal oxide (MoO3,WO3, or V2O5) layer and a metal layer. The metal oxide layer, directly contacting the organic semiconducting layer, serves as the charge-injection layer. The overcoated metal layer is responsible for the conduction of charge carriers. We found that the metal oxide layer coupled between pentacene and metal layers played an important role in improving the field-effect transistor characteristics of OTFTs. Devices with the bilayer S-D electrodes showed enhanced hole-injection compared to those with only metal electrode. High field-effect mobility of 0.4 cm2/V s and on/off current ratios of 104 were obtained in the pentacene based TFTs using the bilayer S-D electrodes at a gate bias of −40 V. The improvement is attributed to the reduction in the contact barrier and the prevention of metal diffusion into the organic layer and/or unfavorable chemical reaction between the organic layer and the metal electrode.
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85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Double amorphous silicon-carbide p-layer structures producing highly stabilized pin-type protocrystalline silicon multilayer solar cells

Seung Yeop Myong, Koeng Su Lim, and Joshua M. Pears

Appl. Phys. Lett. 87, 193509 (2005); http://dx.doi.org/10.1063/1.2126802 (3 pages) | Cited 11 times

Online Publication Date: 3 November 2005

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We have applied double p-type amorphous silicon-carbide (p-a-SiC:H) layer structures to pin-type protocrystalline silicon (pc-Si:H) multilayer solar cells. The less-pronounced initial short-wavelength quantum efficiency variation against the biased voltage and the wide overlap of dark current—voltage (JD-V) and short-circuit current—open-circuit voltage (Jsc-Voc) characteristics prove that the double p-a-SiC:H layer structure successfully reduces recombination at the p/i interface. Therefore, we achieved highly stabilized efficiency of 9.0% without any backreflector.
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84.60.Jt Photoelectric conversion

Terahertz radiation from heavy-ion-irradiated In0.53Ga0.47As photoconductive antenna excited at 1.55 μm

N. Chimot, J. Mangeney, L. Joulaud, P. Crozat, H. Bernas, K. Blary, and J. F. Lampin

Appl. Phys. Lett. 87, 193510 (2005); http://dx.doi.org/10.1063/1.2126110 (3 pages) | Cited 32 times

Online Publication Date: 4 November 2005

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We investigate terahertz (THz) emission from heavy-ion-irradiated In0.53Ga0.47As photoconductive antennas excited at 1550 nm. The carrier lifetime in the highly irradiated In0.53Ga0.47As layer is less than 200 fs, the steady-state mobility is 490 cm2 V−1 s−1, and the dark resistivity is 3 Ω cm. The spectrum of the electric field radiating from the Br+-irradiated In0.53Ga0.47As antenna extends beyond 2 THz. The THz electric field magnitude is shown to saturate at high optical pump fluence, and the saturation fluence level increases with the irradiation dose, indicating that defect center scattering has a significant contribution to the transient mobility.
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84.40.Ba Antennas: theory, components and accessories
61.80.Jh Ion radiation effects
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