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25 May 2009

Volume 94, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 213101 (2009); http://dx.doi.org/10.1063/1.3139865 (3 pages)

Chul-Ho Lee, Jinkyoung Yoo, Young Joon Hong, Jeonghui Cho, Yong-Jin Kim, Seong-Ran Jeon, Jong Hyeob Baek, and Gyu-Chul Yi
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Hot-electron characteristics in chemically resolved electrical measurements of thin silica and SiON layers

A. Rozenblat, Y. Rosenwaks, and H. Cohen

Appl. Phys. Lett. 94, 213501 (2009); http://dx.doi.org/10.1063/1.3141454 (3 pages)

Online Publication Date: 26 May 2009

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We use the recently developed chemically resolved electrical measurements (CREM) to sensitively measure hot-electron transport characteristics in thin dielectric layers. By comparing bare gate-oxide layers, SiO2 and SiON, pronounced differences are revealed that are absent from standard contact measurements and from CREM conducted on top metallic pads. The “on pad” and standard measurements obey a similar defect-assisted “Poole–Frenkel” transport, whereas I ∼ Vα characterizes the hot-electron transport through the bare overlayer, with a clear thickness dependence of α. These unique CREM features offer useful advantages in gate-oxide characterization.
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72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
77.55.-g Dielectric thin films
73.61.Ng Insulators

Endurance enhancement of Cu-oxide based resistive switching memory with Al top electrode

Hangbing Lv, Ming Wang, Haijun Wan, Yali Song, Wenjing Luo, Peng Zhou, Tingao Tang, Yinyin Lin, R. Huang, S. Song, J. G. Wu, H. M. Wu, and M. H. Chi

Appl. Phys. Lett. 94, 213502 (2009); http://dx.doi.org/10.1063/1.3142392 (3 pages) | Cited 20 times

Online Publication Date: 26 May 2009

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We investigated the switching performance of Cu-oxide films with Al, Pt, and Ti electrodes. Compared with Pt electrode, the Al electrode shows better stability, preferable endurance, and larger resistance ratio. An interface AlOx layer is detected by transmission electron microscopy and Auger electron spectroscopy. This layer can strongly affect the movement of oxygen vacancies. However, the sample with pure Ti electrode almost has no switching characteristics. Ti/TiN electrode with thin Ti exhibits good switching behavior. The thickness control of Ti layer is quite critical. So we suggest that the oxygen diffusion in electrode is another important factor for switching performance.
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73.40.Rw Metal-insulator-metal structures
72.60.+g Mixed conductivity and conductivity transitions
79.20.Fv Electron impact: Auger emission
68.35.Ct Interface structure and roughness
66.30.Lw Diffusion of other defects
61.72.jd Vacancies

Enhancement in hole current density on polarization in poly(3-hexylthiophene):cadmium selenide quantum dot nanocomposite thin films

Kusum Kumari, Suresh Chand, V. D. Vankar, and Vikram Kumar

Appl. Phys. Lett. 94, 213503 (2009); http://dx.doi.org/10.1063/1.3142393 (3 pages) | Cited 4 times

Online Publication Date: 26 May 2009

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We demonstrate the effect of polarization on space charge limited J-V behavior in poly(3-hexylthiophene) (P3HT):cadmium selenide (CdSe) ( ∼ 5 nm) quantum dot nanocomposite thin films in hole-only device configuration, indium tin oxide/poly(ethylene-dioxthiophene):polystyrenesulphonate/P3HT:CdSe/Au. Current density has been found to enhance in these hybrid films on polarization. This has been attributed to decrease in characteristic trap energy from 32 to 27 meV, trap density from 1.7×1018 to 1×1018 cm−3 and increase in hole mobility from 2.6×10−6 to 7.7×10−6 cm2 V−1 s−1 due to field induced enhanced order by dipolar alignment and/or trapping of charge carriers at the nanoscale interfacial boundaries of P3HT and CdSe quantum dots.
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73.63.Kv Quantum dots
73.63.Bd Nanocrystalline materials
73.50.Dn Low-field transport and mobility; piezoresistance
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
77.22.Ej Polarization and depolarization

Improved performance of InAlN-based Schottky solar-blind photodiodes

Z. T. Chen, S. X. Tan, Y. Sakai, and T. Egawa

Appl. Phys. Lett. 94, 213504 (2009); http://dx.doi.org/10.1063/1.3142870 (3 pages) | Cited 14 times

Online Publication Date: 26 May 2009

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The authors report the growth of InxAl1−xN with high crystal quality by metal organic chemical vapor deposition, the Pd/InxAl1−xN Schottky contacts with reverse current densities as low as 6.0×10−7 A/cm2 at −5 V and 2.1×10−5 A/cm2 at −10 V, and consequently significant improvement in the performance of InAlN-based Schottky solar-blind photodiodes with peak responsivity of 133 mA/W at 242 nm, corresponding to a quantum efficiency of 68.5%. The illumination is detectable under the intensity as weak as 10 nW/cm2. The rejection ratios by 300 nm are one order of magnitude for 10 nW/cm2 illumination and three orders of magnitude for 1 μW/cm2 illumination.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Bt Optoelectronic device characterization, design, and modeling
85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling
85.40.Sz Deposition technology

Metal-oxide-semiconductor field-effect-transistors on indium phosphide using HfO2 and silicon passivation layer with equivalent oxide thickness of 18 Å

Yen-Ting Chen, Han Zhao, Jung Hwan Yum, Yanzhen Wang, and Jack C. Lee

Appl. Phys. Lett. 94, 213505 (2009); http://dx.doi.org/10.1063/1.3143629 (3 pages) | Cited 12 times

Online Publication Date: 26 May 2009

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In this letter, we demonstrate the electrical properties of metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field-effect transistors (MOSFETs) on InP using atomic layer deposited HfO2 gate dielectric and a thin silicon interface passivation layer (Si IPL). Compared with single HfO2, the use of Si IPL results in better interface quality with InP substrate, as illustrated by smaller frequency dispersion and reduced hysteresis. MOSFETs with Si IPL show much higher drive current and transconductance, improved subthreshold swing, interface-trap density and gate leakage current with equivalent oxide thickness scaling down to 18 Å.
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85.30.Tv Field effect devices
84.32.Tt Capacitors

Pressure dependent resonant frequency of micromechanical drumhead resonators

D. R. Southworth, H. G. Craighead, and J. M. Parpia

Appl. Phys. Lett. 94, 213506 (2009); http://dx.doi.org/10.1063/1.3141731 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2009

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We examine the relationship between squeeze film effects and resonance frequency in drum-type resonators. We find that the resonance frequency increases linearly with pressure as a result of the additional restoring force contribution from compression of gas within the drum cavity. We demonstrate trapping of the gas by squeeze film effects and geometry. The pressure sensitivity is shown to scale inversely with cavity height and sound radiation is found to be the predominant loss mechanism near and above atmospheric pressure. Drum resonators exhibit linearity and sensitivity suitable to barometry from below 10 Torr up to several atmospheres.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.30.-k Measurements common to several branches of physics and astronomy
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems

The conductance method in a bottom-up approach applied on hafnium oxide/silicon interfaces

J. Piscator, B. Raeissi, and O. Engström

Appl. Phys. Lett. 94, 213507 (2009); http://dx.doi.org/10.1063/1.3138125 (3 pages) | Cited 4 times

Online Publication Date: 27 May 2009

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Starting from basic statistical properties of interface states, we demonstrate the influence of energy dependent interface state distributions and thermal emission rates including their capture cross sections on measured differential conductance data for Al/HfO2/SiOx/Si structures. Theoretical plots calculated this way reproduce experimental conductance data without correction for lateral surface potential variations. Close to the silicon conduction band edge, we find an energy dependence of the capture cross sections revealing the existence of electron states with capture processes deviating from the multiphonon mechanisms found for the deeper lying states at interfaces between high-k dielectrics and silicon.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
63.20.kg Phonon-phonon interactions
73.20.-r Electron states at surfaces and interfaces

Formation of Cu nanocrystals on 3-mercaptopropyltrimethoxysilane monolayer by pulsed iodine-assisted chemical vapor deposition for nonvolatile memory applications

Heejung Park, Ara Kim, Chiyoung Lee, Jang-Sik Lee, and Jaegab Lee

Appl. Phys. Lett. 94, 213508 (2009); http://dx.doi.org/10.1063/1.3139072 (3 pages) | Cited 4 times

Online Publication Date: 27 May 2009

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We fabricated nonvolatile nanocrystal flash memory using Cu nanocrystals deposited at 110 °C by pulsed iodine-assisted chemical vapor deposition (CVD) as the charge storage elements. The Cu nanocrystals are deposited on 3-mercaptopropyltrimethoxysilane (MPTMS) coated SiO2 (4 nm) thermally grown on Si, followed by the coating of MPTMS on the Cu nanoparticles to immobilize the Cu atoms. This novel device structure is simply fabricated by pulsed CVD and exhibits a threshold voltage shift of 1.9 V after the application of a voltage pulse (erase: −14 V, 1 ms/program: 40 V, 1 ms) to the gate and has reliable data retention characteristics.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials
84.30.Sk Pulse and digital circuits
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.35.-p Nanoelectronic devices
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

p-Si/β-FeSi2/n-Si double-heterostructure light-emitting diodes achieving 1.6 μm electroluminescence of 0.4 mW at room temperature

Mitsushi Suzuno, Tomoaki Koizumi, and Takashi Suemasu

Appl. Phys. Lett. 94, 213509 (2009); http://dx.doi.org/10.1063/1.3147168 (3 pages) | Cited 6 times

Online Publication Date: 28 May 2009

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Electroluminescence at an emission power of over 0.4 mW is achieved at an emission wavelength of 1.6 μm using a p-Si/β-FeSi2/n-Si double-heterostructure light-emitting diode. This emission power is obtained at room temperature under current injection of 460 mA, corresponding to an external quantum efficiency of approximately 0.1%. Photoluminescence and time-resolved photoluminescence measurements for devices with different thicknesses of β-FeSi2 indicate that radiative recombination rate increased as the thickness of the β-FeSi2 active layer is increased.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.47.jd Time resolved luminescence
81.05.Cy Elemental semiconductors
81.05.Hd Other semiconductors
78.55.Hx Other solid inorganic materials

Reduction in Shockley–Read–Hall generation-recombination in AlInSb light-emitting-diodes using spatial patterning of the depletion region

G. R. Nash and T. Ashley

Appl. Phys. Lett. 94, 213510 (2009); http://dx.doi.org/10.1063/1.3147207 (3 pages)

Online Publication Date: 28 May 2009

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A technique for the reduction in Shockley–Read–Hall recombination in semiconductor diodes, in which areas of the depletion region are removed, is described and preliminary results obtained using AlInSb light-emitting-diodes (LEDs) are presented. Both the electrical and optical characteristics of the devices were significantly improved by removing parts of the depletion region using dry etching, with an average increase in the zero bias differential resistance and LED emission at low currents by a factor of 2.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

A spatial light modulator for terahertz beams

Wai Lam Chan, Hou-Tong Chen, Antoinette J. Taylor, Igal Brener, Michael J. Cich, and Daniel M. Mittleman

Appl. Phys. Lett. 94, 213511 (2009); http://dx.doi.org/10.1063/1.3147221 (3 pages) | Cited 35 times

Online Publication Date: 28 May 2009

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We design and implement a multipixel spatial modulator for terahertz beams using active terahertz metamaterials. Our first-generation device consists of a 4×4 pixel array, where each pixel is an array of subwavelength-sized split-ring resonator elements fabricated on a semiconductor substrate, and is independently controlled by applying an external voltage. Through terahertz transmission experiments, we show that the spatial modulator has a uniform modulation depth of around 40% across all pixels, and negligible crosstalk, at the resonant frequency. This device can operate under small voltage levels, at room temperature, with low power consumption and reasonably high switching speed.
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42.79.Hp Optical processors, correlators, and modulators

High responsivity A-plane GaN-based metal-semiconductor-metal photodetectors for polarization-sensitive applications

A. Navarro, C. Rivera, J. Pereiro, E. Muñoz, B. Imer, S. P. DenBaars, and J. S. Speck

Appl. Phys. Lett. 94, 213512 (2009); http://dx.doi.org/10.1063/1.3143230 (3 pages) | Cited 5 times

Online Publication Date: 28 May 2009

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The fabrication and characterization of metal-semiconductor-metal polarization-sensitive photodetectors based on A-plane GaN grown on R-plane sapphire substrates is reported. These photodetectors take advantage of the in-plane crystal anisotropy, which results in linear dichroism near the band gap energy. The high resistivity of the A-plane GaN material leads to extremely low dark currents. For an optimized finger spacing of 1 μm, dark current density and responsivity at 30 V are 0.3 nA/mm2 and 2 A/W, respectively. A maximum polarization sensitivity ratio of 1.8 was determined. In a differential configuration, the full width at half maximum of the polarization-sensitive region is 8.5 nm.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Bx Metals, semimetals, and alloys
81.05.Ea III-V semiconductors

Hybrid electro-optic polymer/sol-gel waveguide directional coupler switches

Y. Enami, D. Mathine, C. T. DeRose, R. A. Norwood, J. Luo, A. K-Y. Jen, and N. Peyghambarian

Appl. Phys. Lett. 94, 213513 (2009); http://dx.doi.org/10.1063/1.3141452 (3 pages) | Cited 11 times

Online Publication Date: 29 May 2009

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We report electro-optic (EO) switches using transversely tapered hybrid EO/sol-gel waveguide directional couplers. The length of the active region critically reduces to 1.5 mm with transverse tapers, which is shorter by a factor of 5 than the active region with vertical tapers. The transitions are performed from a sol-gel core to two EO polymer cores with gradual index changes using gray-scaled photobleaching. The device shows the lowest switching voltage and an active length product (VsLa) of 2.9 V cm with a guest–host EO polymer AJLS102, compared to hybrid waveguide switches and modulators with vertical taper and higher EO coefficients.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Micromachined single-level nonplanar polycrystalline SiGe thermal microemitters for infrared dynamic scene projection

V. K. Malyutenko, O. Yu. Malyutenko, V. Leonov, and C. Van Hoof

Appl. Phys. Lett. 94, 213514 (2009); http://dx.doi.org/10.1063/1.3148645 (3 pages)

Online Publication Date: 29 May 2009

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The technology for self-supported membraneless polycrystalline SiGe thermal microemitters, their design, and performance are presented. The 128-element arrays with a fill factor of 88% and a 2.5-μm-thick resonant cavity have been grown by low-pressure chemical vapor deposition and fabricated using surface micromachining technology. The 200-nm-thick 60×60 μm2 emitting pixels enforced with a U-shape profile pattern demonstrate a thermal time constant of 2–7 ms and an apparent temperature of 700 K in the 3–5 and 8–12 μm atmospheric transparency windows. The application of the devices to the infrared dynamic scene simulation and their benefit over conventional planar membrane-supported emitters are discussed.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.20.-n Thermal instruments and apparatus
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.82.Et Waveguides, couplers, and arrays
42.72.Ai Infrared sources
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)
81.20.Wk Machining, milling
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