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28 May 2007

Volume 90, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

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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A low-noise ferrite magnetic shield

T. W. Kornack, S. J. Smullin, S.-K. Lee, and M. V. Romalis

Appl. Phys. Lett. 90, 223501 (2007); http://dx.doi.org/10.1063/1.2737357 (3 pages) | Cited 18 times

Online Publication Date: 29 May 2007

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Ferrite materials provide magnetic shielding performance similar to commonly used high permeability metals but have lower intrinsic magnetic noise generated by thermal Johnson currents due to their high electrical resistivity. Measurements inside a ferrite shield with a spin-exchange relaxation-free atomic magnetometer reveal a noise level of 0.75 fT Hz−1/2, 25 times lower than what would be expected in a comparable μ-metal shield. The authors identify a 1/f component of the magnetic noise due to magnetization fluctuations and derive general relationships for the Johnson current noise and magnetization noise in cylindrical ferromagnetic shields in terms of their conductivity and complex magnetic permeability.
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41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
07.55.Nk Magnetic shielding in instruments

Contribution of water vapor to slider air-bearing pressure in hard disk drives

Yansheng Ma and Bo Liu

Appl. Phys. Lett. 90, 223502 (2007); http://dx.doi.org/10.1063/1.2743745 (3 pages) | Cited 6 times

Online Publication Date: 29 May 2007

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Water vapor in humid air contributes to slider air-bearing pressure in a totally different way from that of dry air. Water vapor pressure keeps constant in slider-disk interface and is identical to the water vapor pressure outside the interface. The simulated slider flying height and attitude in humid air are different from that in dry air and the higher the relative humidity the bigger the differences.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
89.20.Kk Engineering

Surface recombination velocity reduction in type-II InAs/GaSb superlattice photodiodes due to ammonium sulfide passivation

Jian V. Li, Shun Lien Chuang, Edward Aifer, and Eric M. Jackson

Appl. Phys. Lett. 90, 223503 (2007); http://dx.doi.org/10.1063/1.2743905 (3 pages) | Cited 5 times

Online Publication Date: 29 May 2007

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The surface recombination velocity (SRV) of minority electrons in a type-II InAs/GaSb superlattice photodiode is quantitatively investigated using the electron beam induced current technique and its value used to evaluate the effects of two different passivation methods. Before passivation, the SRV was determined to be (5.0±0.2)×104 cm/s. The SRVs of two samples passivated at room temperature are compared with that of the unpassivated sample. One passivation method, using a neutralized (NH4)2S solution for 60 min, reduces the SRV by a factor of 2. The other passivation method, using 4% (NH4)2S solution for 30 min, reduces the SRV by more than one order of magnitude.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Hole-versus electron-based operations in SiGe nanocrystal nonvolatile memories

J. S. de Sousa, V. N. Freire, and J.-P. Leburton

Appl. Phys. Lett. 90, 223504 (2007); http://dx.doi.org/10.1063/1.2741598 (3 pages) | Cited 11 times

Online Publication Date: 30 May 2007

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A comparative study between electron- and hole-based data storage operations in Si1−xGex nanocrystal nonvolatile memories is presented. The authors show that the valence band-edge alignment is ideally suited for holes storage, which allows for extremely long retention times for alloy composition x>0 without affecting the programming performances.
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85.30.-z Semiconductor devices
84.30.Sk Pulse and digital circuits

High efficiency phosphorescent organic light-emitting diodes using carbazole-type triplet exciton blocking layer

Sung Hyun Kim, Jyongsik Jang, and Jun Yeob Lee

Appl. Phys. Lett. 90, 223505 (2007); http://dx.doi.org/10.1063/1.2742788 (3 pages) | Cited 42 times

Online Publication Date: 31 May 2007

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Device performances of green phosphorescent organic light-emitting diodes using (4,4′-N,N′-dicarbazole)biphenyl (CBP) and N,N′-dicarbazolyl-3,5-benzene (mCP) as an exciton blocking layer were investigated. CBP and mCP were introduced between hole transport layer and emitting layer to block triplet exciton quenching and efficient hole transport to emitting layer. The efficiency of green devices could be improved by more than three times by using mCP exciton blocking layer.
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85.60.Jb Light-emitting devices
71.35.-y Excitons and related phenomena

Enhanced microwave transmission through a patterned metal film

R. J. Kelly, M. J. Lockyear, J. R. Suckling, J. R. Sambles, and C. R. Lawrence

Appl. Phys. Lett. 90, 223506 (2007); http://dx.doi.org/10.1063/1.2745202 (3 pages) | Cited 4 times

Online Publication Date: 31 May 2007

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Selective transmission of radiation through a two-dimensional array of subwavelength slits in an otherwise opaque thin metal film is presented at microwave frequencies. Individual slits are modified with the addition of perpendicular cuts, which interestingly and perhaps counterintuitively leads to resonant transmission when the incident radiation is polarized parallel to the slits. Finite element modeling of the structure shows the transmission of radiation polarized parallel to the slit direction to be a result of induced surface currents exciting a zeroth-order Fabry-Pérot mode.
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78.70.Gq Microwave and radio-frequency interactions
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Photocurrent gain in 4H-SiC interdigit Schottky UV detectors with a thermally grown oxide layer

A. Sciuto, F. Roccaforte, S. Di Franco, V. Raineri, S. Billotta, and G. Bonanno

Appl. Phys. Lett. 90, 223507 (2007); http://dx.doi.org/10.1063/1.2745208 (3 pages) | Cited 7 times

Online Publication Date: 31 May 2007

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A large photocurrent increase in 4H-SiC interdigit Schottky UV detectors was observed in the presence of a thermally grown silicon oxide layer. In particular, internal quantum efficiency higher than unity indicated the presence of an internal gain strictly correlated with the presence of the superficial oxide on SiC. Moreover, a long recovery time, in the range of 10–19 s, was evaluated by fall-time photocurrent measurements due to the detrapping of charges in the oxide after the irradiation switching off. The photoresponse of the device was analytically described considering the lowering of the surface potential barrier due to charges trapped at the oxide/semiconductor interface.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.De Semiconductor-device characterization, design, and modeling
85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes

Low roll-off of efficiency at high current density in phosphorescent organic light emitting diodes

Jae-Wook Kang, Se-Hyung Lee, Hyung-Dol Park, Won-Ik Jeong, Kyung-Mo Yoo, Young-Seo Park, and Jang-Joo Kim

Appl. Phys. Lett. 90, 223508 (2007); http://dx.doi.org/10.1063/1.2745224 (3 pages) | Cited 68 times

Online Publication Date: 31 May 2007

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The authors demonstrate that the reduction of quantum efficiency with increasing current density in phosphorescent light emitting diodes (PhOLEDs) is related to the formation of excitons in hole transporting layer based on the analysis of emission spectra and exciton formation zone. Low roll-off of efficiency in a PhOLED was achieved using dual emitting layers (D-EMLs) by confining the exciton formation near the interface between the emitting layers. The external quantum efficiency was maintained almost constant up to 22 mA/cm2 (10 000 cd/m2) by adopting the D-EMLs in Ir(ppy)3 based PhOLEDs, resulting in high external quantum efficiency (ηext = 13.1%) at high luminance.
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85.60.Jb Light-emitting devices
71.35.-y Excitons and related phenomena

Nanocomposite field effect transistors based on zinc oxide/polymer blends

Zong-Xiang Xu, V. A. L. Roy, Peter Stallinga, Michele Muccini, Stefano Toffanin, Hei-Feng Xiang, and Chi-Ming Che

Appl. Phys. Lett. 90, 223509 (2007); http://dx.doi.org/10.1063/1.2740478 (3 pages) | Cited 31 times

Online Publication Date: 1 June 2007

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The authors have examined the field effect behavior of nanocomposite field effect transistors containing ZnO (zinc oxide) tetrapods or nanocrystals dispersed in a polymer matrix of poly[2-methoxy,5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). The electrical characteristics of ZnO tetrapods/MEH-PPV composite devices exhibit an increase in hole mobility up to three orders of magnitude higher than the polymer MEH-PPV device.
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85.30.Tv Field effect devices

Investigation of point defect generation in dry etched InP ridge waveguide structures

M. Avella, J. Jiménez, F. Pommereau, J. P. Landesman, and A. Rhallabi

Appl. Phys. Lett. 90, 223510 (2007); http://dx.doi.org/10.1063/1.2743384 (3 pages) | Cited 5 times

Online Publication Date: 1 June 2007

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Waveguides engraved in InP by dry etching, reactive ion etching and inductively coupled plasma (ICP), were studied by cathodoluminescence. The dry etching processes were found to induce nonradiative recombination centers, which reduce the luminescence emission from the ridge structures. In addition, the ICP process introduced intrinsic defects, probably In vacancy related defects, which were generated at the dielectric cap/InP interface at the ridge top.
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84.40.Az Waveguides, transmission lines, striplines
81.65.Cf Surface cleaning, etching, patterning
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.J- Point defects and defect clusters
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Short-wavelength intersubband electroabsorption modulation based on electron tunneling between GaN/AlN coupled quantum wells

L. Nevou, N. Kheirodin, M. Tchernycheva, L. Meignien, P. Crozat, A. Lupu, E. Warde, F. H. Julien, G. Pozzovivo, S. Golka, G. Strasser, F. Guillot, E. Monroy, T. Remmele, and M. Albrecht

Appl. Phys. Lett. 90, 223511 (2007); http://dx.doi.org/10.1063/1.2745211 (3 pages) | Cited 15 times

Online Publication Date: 1 June 2007

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Room temperature intersubband electroabsorption modulation in GaN/AlN coupled quantum wells is demonstrated at short infrared wavelengths, covering the fiber-optics telecommunication wavelength range. Electroabsorption modulation with opposite sign is observed at λ = 1.2–1.67 μm and λ = 2.1–2.4 μm. The electromodulation originates from electron tunneling between a wide well (reservoir) and a narrow well separated by an ultrathin AlN barrier. Both the intersubband absorption and the modulation spectroscopic measurements are in good agreement with the simulations. The maximum modulation depth is ∼ 44% at λ = 2.2 μm. The −3 dB cutoff frequency limited by the RC time constant is 11.5 MHz for 700×700 μm2 mesas.
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78.67.De Quantum wells
73.63.Hs Quantum wells
78.20.Jq Electro-optical effects
73.40.Gk Tunneling

Enhanced performance of solution-processed regioregular poly(3-hexylthiophene) thin-film transistors using planar bottom-contact architecture

Mingsheng Xu, Keita Nagai, Masakazu Nakamura, Kazuhiro Kudo, and Masaaki Iizuka

Appl. Phys. Lett. 90, 223512 (2007); http://dx.doi.org/10.1063/1.2745221 (3 pages) | Cited 6 times

Online Publication Date: 1 June 2007

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The authors report on the solution-processed planar bottom-contact (pBC) organic thin-film transistors and contact effect on gate threshold voltage incorporating regioregular poly(3-hexylthiophene) active layer. By employing pBC configuration, the transistors on SiO2/Si without surface modification show much higher mobility, lower threshold voltage, and narrower dispersion of threshold voltage when compared to the conventional bottom-contact counterparts. The high mobility and lower threshold voltage are attributed to an improved contact at the interface between the source/drain electrodes and the poly(3-hexylthiophene) active layer.
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85.30.Tv Field effect devices

Nonvolatile polycrystalline silicon thin film transistor memory using silicon-rich silicon nitride as charge storage layer

Z. Pei, A. Chung, and H. L. Hwang

Appl. Phys. Lett. 90, 223513 (2007); http://dx.doi.org/10.1063/1.2745265 (3 pages) | Cited 3 times

Online Publication Date: 1 June 2007

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In this work, the authors report a memory device based on a Si thin film transistor (TFT) structure by incorporating silicon-rich silicon nitride (SRSN) film in the gate dielectric stacks as the charge storage layer. The SRSN film has a lower barrier for hole injection than the barrier for electron injection. Therefore, the memory window is dominated by hole injection. The memory window for TFT nonvolatile memory at steady state as large as 6.8 V is observed, and the memory window is around 3 V under pulse operation. In addition, this TFT memory has no significant degradation after 500 times of switching operation.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Rectifying property and giant positive magnetoresistance of Fe3O4/SiO2/Si heterojunction

T. L. Qu, Y. G. Zhao, H. F. Tian, C. M. Xiong, S. M. Guo, and J. Q. Li

Appl. Phys. Lett. 90, 223514 (2007); http://dx.doi.org/10.1063/1.2743937 (3 pages) | Cited 8 times

Online Publication Date: 1 June 2007

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Fe3O4/SiO2/Si heterojunction was fabricated by growing Fe3O4 film on an n-typed Si wafer with the native SiO2 buffer layer using the pulsed laser deposition. Transmission electron microcopic study shows the high quality of the heterojunction interfaces and the SiO2 layer is 2.5 nm thick. This junction shows a backward diodelike rectifying behavior and an anomalously giant positive magnetoresistance (MR) for the large reverse bias voltages. The temperature dependence of MR shows a peak around the Verwey transition temperature with a maximum MR of 87% under a −2 V bias voltage. The results were discussed by considering the band structure of the heterojunction and the effect of the reverse bias voltage.
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73.40.Ei Rectification
75.47.De Giant magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
73.20.At Surface states, band structure, electron density of states
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