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7 Feb 2005

Volume 86, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 063101 (2005); http://dx.doi.org/10.1063/1.1861133 (3 pages)

Choongho Yu, Qing Hao, Sanjoy Saha, Li Shi, Xiangyang Kong, and Z. L. Wang
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GaN metal-oxide-semiconductor high-electron-mobility-transistor with atomic layer deposited Al2O3 as gate dielectric

P. D. Ye, B. Yang, K. K. Ng, J. Bude, G. D. Wilk, S. Halder, and J. C. M. Hwang

Appl. Phys. Lett. 86, 063501 (2005); http://dx.doi.org/10.1063/1.1861122 (3 pages) | Cited 24 times

Online Publication Date: 31 January 2005

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We report on a GaN metal-oxide-semiconductor high-electron-mobility-transistor (MOS-HEMT) using atomic-layer-deposited (ALD) Al2O3 as the gate dielectric. Compared to a conventional GaN high-electron-mobility-transistor (HEMT) of similar design, the MOS-HEMT exhibits several orders of magnitude lower gate leakage and several times higher breakdown voltage and channel current. This implies that the ALD Al2O3∕AlGaN interface is of high quality and the ALD Al2O3∕AlGaN∕GaN MOS-HEMT is of high potential for high-power rf applications. In addition, the high-quality ALD Al2O3 gate dielectric allows the effective two-dimensional (2D) electron mobility at the AlGaN∕GaN heterojunction to be measured under a high transverse field. The resulting effective 2D electron mobility is much higher than that typical of Si, GaAs or InGaAs metal-oxide-semiconductor field-effect-transistors (MOSFETs).
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Dn Low-field transport and mobility; piezoresistance

Device annealing effect in organic solar cells with blends of regioregular poly(3-hexylthiophene) and soluble fullerene

Youngkyoo Kim, Stelios A. Choulis, Jenny Nelson, Donal D. C. Bradley, Steffan Cook, and James R. Durrant

Appl. Phys. Lett. 86, 063502 (2005); http://dx.doi.org/10.1063/1.1861123 (3 pages) | Cited 243 times

Online Publication Date: 31 January 2005

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Here we report enhanced efficiency bulk heterojunction organic solar cells using blend films of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) that are subjected to a thermal annealing process. Blend films (P3HT:PCBM = 1:1 by weight) were prepared using chlorobenzene and 1,2-dichlorobenzene in order to investigate the role of the solvent. Irrespective of the chosen solvent, the optimal device annealing temperature was found to be 140 °C. The highest power conversion efficiency, 3% under air mass 1.5 simulated solar illumination (100 mW/cm2), was achieved by device annealing at 140 °C for 15 min using blend films prepared from chlorobenzene (2.3% for 1,2-dichlorobenzene).
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84.60.Jt Photoelectric conversion
85.65.+h Molecular electronic devices
61.72.Cc Kinetics of defect formation and annealing

Room temperature tunneling transport through Si nanodots in silicon rich silicon nitride

Zingway Pei, Alex Y. K. Su, H. L. Hwang, and H. L. Hsiao

Appl. Phys. Lett. 86, 063503 (2005); http://dx.doi.org/10.1063/1.1861129 (3 pages) | Cited 9 times

Online Publication Date: 31 January 2005

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Devices containing Si nanodots (NDs) were made in an α-SiNx:H/Si NDs/α-SiNx:H structure to explore the transport characteristics. The Si NDs were embedded in a silicon nitride matrix and were produced by using a plasma enhanced chemical vapor deposition technique. Room temperature Si NDs related electron and hole tunneling transport were observed in these devices. Negative differential resistance in the current–voltage characteristics was observed for the hole tunneling. The peak-to-valley ratio was as high as 13.9. Transmission electron microscopy reveals that only one Si ND exists in the current transport direction. The Si NDs are ∼ 5 nm in diameter. A model with a double barrier band diagram is suggested to explain the Si NDs related transport.
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85.30.Kk Junction diodes
73.40.Gk Tunneling
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Tuning of electron injections for n-type organic transistor based on charge-transfer compounds

Y. Takahashi, T. Hasegawa, Y. Abe, Y. Tokura, K. Nishimura, and G. Saito

Appl. Phys. Lett. 86, 063504 (2005); http://dx.doi.org/10.1063/1.1863434 (3 pages) | Cited 49 times

Online Publication Date: 1 February 2005

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A high mobility ( ∼ 1.0 cm2/V s) n-type organic field-effect transistor is devised in terms of the combination of semiconducting and metallic charge-transfer (CT) compounds, namely, DBTTF-TCNQ crystals as channels and TTF-TCNQ thin films as electrodes for carrier injections on top of the crystals. Comparison of the field-effect properties for devices with conventional electrode materials indicates the successful demonstration of the interface band engineering with use of the CT materials.
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85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds

Origin of dark counts in In0.53Ga0.47As/In0.52Al0.48As avalanche photodiodes operated in Geiger mode

G. Karve, S. Wang, F. Ma, X. Li, J. C. Campbell, R. G. Ispasoiu, D. S. Bethune, W. P. Risk, G. S. Kinsey, J. C. Boisvert, T. D. Isshiki, and R. Sudharsanan

Appl. Phys. Lett. 86, 063505 (2005); http://dx.doi.org/10.1063/1.1861498 (3 pages) | Cited 9 times

Online Publication Date: 1 February 2005

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A dark count rate in InP-based single photon counting avalanche photodiodes is a limiting factor to their efficacy. The temperature dependence of the dark count rate was studied to understand its origin in In0.53Ga0.47As/In0.52Al0.48As separate-absorption-charge-multiplication avalanche photodiodes. The dark count rate was observed to be a very weak function of temperature in the range from 77 K to 300 K. Various mechanisms for dark count generation were considered. Simulations of band-to-band tunneling in the In0.52Al0.48As multiplication layer were found to agree well with the experimental temperature dependence of dark count rate at various excess biases. To reduce tunneling-induced dark counts, a suitable design change to the detector structure is proposed.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.50.Pz Photoconduction and photovoltaic effects
73.40.Gk Tunneling
73.50.Fq High-field and nonlinear effects
29.40.Wk Solid-state detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Improvement of efficiency and stability of polymer light-emitting devices by modifying indium tin oxide anode surface with ultrathin tetrahedral amorphous carbon film

B. J. Chen, X. W. Sun, B. K. Tay, L. Ke, and S. J. Chua

Appl. Phys. Lett. 86, 063506 (2005); http://dx.doi.org/10.1063/1.1796527 (3 pages) | Cited 10 times

Online Publication Date: 1 February 2005

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Poly(p-phenylene vinylene)-based polymer light-emitting devices using different thicknesses of tetrahedral amorphous carbon ultrathin films between indium tin oxide and polyethylenedioxythiophene hole transporting layer have been fabricated. The device with a 0.5 nm tetrahedral amorphous carbon (ta-C) layer has the highest luminance and current efficiency compared to that of other devices. The current efficiency of a standard device without a ta-C layer is 1.1 cd/A at 5 V, however, the current efficiency of a device with a ta-C layer thickness of 0.5 nm is 2.7 cd/A; the current efficiency is improved about 2.5 times compared to the standard device. The improvement of the efficiency is due to blocking the hole injection from anode and balancing the hole and electron current. The lifetime of a device with a ta-C layer is significantly much longer than the standard device, and the device with a 0.5 nm ta-C layer has the longest lifetime.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
78.66.Nk Insulators

Microsqueeze force sensor useful as contact-free profilometer and viscometer

Stefano Oberti, Andreas Stemmer, David Juncker, Urs Duerig, and Heinz Schmid

Appl. Phys. Lett. 86, 063507 (2005); http://dx.doi.org/10.1063/1.1862328 (3 pages)

Online Publication Date: 1 February 2005

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We present a sensor for measuring viscous friction forces in liquids proximal to a substrate. The sensor is implemented as a mechanical oscillator that is damped by the liquid squeezed in the gap between the sensor head and the substrate. Force versus distance curves were recorded ranging from 100 μm down to a few microns and are in agreement with the expected power law for the damping curve. The viscosity ratios of different liquids were measured with the sensor and are in accordance with values in the literature. Moreover, the topography of an immersed substrate was recorded with micrometer lateral and vertical resolution by scanning the sensor in constant height mode above the surface.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
47.80.-v Instrumentation and measurement methods in fluid dynamics
83.85.Jn Viscosity measurements
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
05.45.Xt Synchronization; coupled oscillators
68.35.B- Structure of clean surfaces (and surface reconstruction)

nlinImproving spatial resolution of convergent beam electron diffraction strain mapping in silicon microstructures

A. Armigliato, R. Balboni, and S. Frabboni

Appl. Phys. Lett. 86, 063508 (2005); http://dx.doi.org/10.1063/1.1855408 (3 pages) | Cited 14 times

Online Publication Date: 2 February 2005

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Despite the use of nanometer-sized probes in field emission transmission electron microscopes, the spatial resolution in strain analysis performed by convergent beam electron diffraction is limited in one direction by the need for tilting the cross-sectional sample in the electron microscope off the vertical ⟨110⟩ direction. We demonstrate that it is possible to improve this resolution by using the ⟨340⟩ zone axis, instead of the ⟨230⟩ one, which has recently become of common use in the analysis of silicon microdevices. Quantitative strain information with good sensitivity and accuracy can be obtained in the new axis. An example of application to the two-dimensional strain mapping in shallow trench isolation structures, obtained with a scanning attachment and a high-angle annular dark-field detector, is reported.
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61.05.jm Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction
07.10.Pz Instruments for strain, force, and torque
68.37.Lp Transmission electron microscopy (TEM)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Three-layered organic solar cells incorporating a nanostructure-optimized phthalocyanine:fullerene codeposited interlayer

Kouji Suemori, Takahiro Miyata, Masaaki Yokoyama, and Masahiro Hiramoto

Appl. Phys. Lett. 86, 063509 (2005); http://dx.doi.org/10.1063/1.1863451 (3 pages) | Cited 53 times

Online Publication Date: 2 February 2005

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Three-layered organic solar cells incorporating a codeposited interlayer of fullerene and metal-free phthalocyanine, whose nanostructure was optimized by controlling the substrate temperature during coevaporation, showed a photoelectric conversion efficiency of 2.5% under illumination with simulated solar light. The three-layered cells were concluded to have a p-i-n-like energetic structure.
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84.60.Jt Photoelectric conversion
85.65.+h Molecular electronic devices
73.50.Pz Photoconduction and photovoltaic effects

Evolution of leakage paths in HfO2/SiO2 stacked gate dielectrics: A stable direct observation by ultrahigh vacuum conducting atomic force microscopy

K. Kyuno, K. Kita, and A. Toriumi

Appl. Phys. Lett. 86, 063510 (2005); http://dx.doi.org/10.1063/1.1862779 (3 pages) | Cited 17 times

Online Publication Date: 3 February 2005

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A conducting atomic force microscopy (C-AFM) in ultrahigh vacuum (UHV) is used to directly observe the evolution of leakage path in HfO2/SiO2 stacked gate dielectrics. Thanks to the UHV environment, reproducible results for both positive and negative tip biases are obtained without material formation on the surface, which has been a problem for atmospheric C-AFM. It is found that the density of leakage spots increases exponentially as a function of tip bias and that it is a large factor for leakage current increase.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)

Internal photoemission in solar blind AlGaN Schottky barrier photodiodes

Jean-Yves Duboz, Nicolas Grandjean, Franck Omnes, Mauro Mosca, and Jean-Luc Reverchon

Appl. Phys. Lett. 86, 063511 (2005); http://dx.doi.org/10.1063/1.1862780 (3 pages) | Cited 3 times

Online Publication Date: 3 February 2005

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We have analyzed the photoresponse of solar blind AlGaN Schottky barrier photodiodes below the alloy band gap energy, in the 3.5–4.5 eV range, and we show that it is dominated by internal photoemission. The n-type Schottky barrier height is shown to increase linearly with the band gap energy of the AlGaN alloy. The amplitude of the internal photoemission signal is about 20 times smaller than the value given by the Fowler theory based on a free electron model. We explain this result by taking into account the interband transitions and the ballistic transport of photoexcited electrons in the metal. This low value of internal photoemission allows us to achieve a spectral rejection ratio between 280 and 320 nm of more than 3 decades.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.De Semiconductor-device characterization, design, and modeling
72.40.+w Photoconduction and photovoltaic effects

Magnetization dynamics and thermal stability in patterned media

J. Moritz, B. Dieny, J. P. Nozières, R. J. M. van de Veerdonk, T. M. Crawford, D. Weller, and S. Landis

Appl. Phys. Lett. 86, 063512 (2005); http://dx.doi.org/10.1063/1.1861973 (3 pages) | Cited 10 times

Online Publication Date: 3 February 2005

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The dynamic coercivity of patterned media with perpendicular magnetic anisotropy is measured over ten orders of magnitude using magnetic field pulses from magnetic recording heads with pulse widths in the range 150 ps to 1 s. The local field generated by write heads allows the study of the switching dynamics of individual bits. Existing models have been applied for a quantitative analysis of the data. As a result, we found the written bits are stable for at least 10 years. Individual dot magnetization switching has been achieved with subnanosecond pulses showing that very-high-data-rate recording is possible in patterned media.
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75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Stability of fully deuterated amorphous silicon thin-film transistors

Shufan Lin, Andrew J. Flewitt, William I. Milne, Ralf B. Wehrspohn, and Martin J. Powell

Appl. Phys. Lett. 86, 063513 (2005); http://dx.doi.org/10.1063/1.1862755 (3 pages) | Cited 4 times

Online Publication Date: 4 February 2005

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The threshold voltage stability of fully deuterated (a-Si:D) and hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) is compared. The difference in the kinetic energy of D+ and H+ ions upon impact with the growing surface during radio-frequency plasma-enhanced chemical vapor deposition leads to material having different physical properties for the same nominal deposition conditions. However, a-Si:D and a-Si:H grown at the same growth rate by adjusting the gas pressure have almost identical properties. By using the growth rate as a normalizing parameter for comparing a-Si:H and a-Si:D TFTs, it is shown that there is no difference in the stability of a-Si:D compared with a-Si:H TFTs. This study rules out the possibility of a giant isotopic effect in amorphous silicon TFTs, and supports the model for Si dangling bond defect creation in a-Si:H where the breaking of weak Si–Si bonds is the rate-limiting step.
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85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.55.Cn Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
78.66.Jg Amorphous semiconductors; glasses

The effect of C60 doping on the device performance of organic light-emitting diodes

Jun Yeob Lee and Jang Hyuk Kwon

Appl. Phys. Lett. 86, 063514 (2005); http://dx.doi.org/10.1063/1.1861962 (3 pages) | Cited 13 times

Online Publication Date: 4 February 2005

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The effect of C60 doping in the hole transport layer on the device performance of phosphorescent light-emitting diodes was investigated by changing the C60 content from 0% to 3%. Doping of C60 in 1,3,5-tris(N,N-bis-(4,5-methoxyphenyl)-aminophenyl)benzol resulted in efficient hole injection and low driving voltage at high luminance. In addition, the lifetime of the phosphorescent device was improved significantly by introducing a C60 molecule in the hole transport layer. The C60-doped device showed an extended lifetime of 1400 h compared with 700 h of the undoped device.
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85.60.Jb Light-emitting devices
85.65.+h Molecular electronic devices
78.55.Hx Other solid inorganic materials
61.72.up Other materials
72.20.Fr Low-field transport and mobility; piezoresistance
85.40.Ry Impurity doping, diffusion and ion implantation technology
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.S- Impurities in crystals

Visualization of electrons and holes localized in gate thin film of metal SiO2–Si3N4–SiO2 semiconductor-type flash memory using scanning nonlinear dielectric microscopy after writing-erasing cycling

Koichiro Honda, Sunao Hashimoto, and Yasuo Cho

Appl. Phys. Lett. 86, 063515 (2005); http://dx.doi.org/10.1063/1.1862333 (3 pages) | Cited 10 times

Online Publication Date: 4 February 2005

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We applied scanning nonlinear dielectric microscopy and succeeded in clarifying the position of the electrons/holes in the gate SiO2–Si3N4–SiO2 (ONO) film of the metal-ONO-semiconductor-type flash memory after the write-erase cycling operation. The electrons were found in the Si3N4 part of the ONO film. The holes, on the other hand, were found in the Si3N4 film as well as at the bottom SiO2 film. We also showed that neither injected electrons nor injected holes accumulate during the write-erase cycling. This indicates that the remaining carrier in the ONO film is space charge and would not be expected to continue to increase infinitely with repeated injections and that most of the injected carriers would recombine with each other. After recombination, they exist separately and are electrically neutralized only.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices
68.37.-d Microscopy of surfaces, interfaces, and thin films
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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