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27 Mar 2006

Volume 88, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages)

Premila Mohan, Junichi Motohisa, and Takashi Fukui
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Schottky diodes from asymmetric metal-nanotube contacts

Chenguang Lu, Lei An, Qiang Fu, Jie Liu, Hong Zhang, and James Murduck

Appl. Phys. Lett. 88, 133501 (2006); http://dx.doi.org/10.1063/1.2190707 (3 pages) | Cited 20 times

Online Publication Date: 29 March 2006

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Carbon nanotube Schottky diodes were fabricated using asymmetric metal-nanotube contacts. These devices were prepared from semiconducting single-walled carbon nanotubes contacted by one Al or Ti electrode and one Au electrode. Nanotubes formed a low resistance contact with the Au electrode and a Schottky contact with the Al or Ti electrode. Electronic transport through the Schottky barriers was determined by the competition between tunneling and thermionic emission, which could be tuned by a back gate voltage.
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85.30.Kk Junction diodes
85.35.Kt Nanotube devices
85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling

Low-cost fabrication of submicron all polymer field effect transistors

J. Z. Wang, J. Gu, F. Zenhausern, and H. Sirringhaus

Appl. Phys. Lett. 88, 133502 (2006); http://dx.doi.org/10.1063/1.2191088 (3 pages) | Cited 24 times

Online Publication Date: 29 March 2006

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All polymer field effect transistors have been fabricated combining nanoimprint lithography and inkjet printing. Trenches with hydrophilic bottoms confined by hydrophobic walls with considerable height are patterned by nanoimprint lithography. Conducting polymer solutions were then delivered into these trench liquid containers by inkjet printing. Dried conducting polymer in nearby trenches forms source-drain electrodes with the channel length accurately defined by the gap in between the designed two trenches. Top-gate all polymer field effect transistors with submicron channel lengths were successfully realized by such low-cost process.
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81.16.Nd Micro- and nanolithography
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
85.30.Tv Field effect devices

Afterpulsing in Geiger-mode avalanche photodiodes for 1.06 μm wavelength

K. E. Jensen, P. I. Hopman, E. K. Duerr, E. A. Dauler, J. P. Donnelly, S. H. Groves, L. J. Mahoney, K. A. McIntosh, K. M. Molvar, A. Napoleone, D. C. Oakley, S. Verghese, C. J. Vineis, and R. D. Younger

Appl. Phys. Lett. 88, 133503 (2006); http://dx.doi.org/10.1063/1.2189187 (3 pages) | Cited 18 times

Online Publication Date: 29 March 2006

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We consider the phenomenon of afterpulsing in avalanche photodiodes (APDs) operating in gated and free-running Geiger mode. An operational model of afterpulsing and other noise characteristics of APDs predicts the noise behavior observed in the free-running mode. We also use gated-mode data to investigate possible sources of afterpulsing in these devices. For 30-μm-diam, 1.06-μm-wavelength InGaAsP/InP APDs operated at 290 K and 4 V overbias, we obtained a dominant trap lifetime of τd = 0.32 μs, a trap energy of 0.11 eV, and a baseline dark count rate 245 kHz.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling

Spectroscopic strain measurement methodology: Degree-of-polarization photoluminescence versus photocurrent spectroscopy

Jens W. Tomm, Tran Quoc Tien, and Daniel T. Cassidy

Appl. Phys. Lett. 88, 133504 (2006); http://dx.doi.org/10.1063/1.2189189 (3 pages) | Cited 2 times

Online Publication Date: 29 March 2006

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A methodological approach to strain analysis in semiconductor devices is presented. Two methods, degree-of-polarization of photoluminescence and photocurrent spectroscopy, are compared by analyzing a spatially inhomogeneous strained test sample, namely, a high-power diode laser array that is affected by packaging-induced stress. Both methods concordantly reveal a −0.1% uniaxial compression in the vicinity of the midpoint of the active region of the device, demonstrating the compatibility of and justifying the assumptions involved in the two different approaches. Furthermore, we discuss some distinctive details of the processing-induced strains observed in the vicinities of metallized contacts and grooves involved in the device design.
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85.30.De Semiconductor-device characterization, design, and modeling
42.55.Px Semiconductor lasers; laser diodes

Photoemission investigation on copper phthalocyanine:fullerene blend film

L. Lozzi, S. Santucci, and S. La Rosa

Appl. Phys. Lett. 88, 133505 (2006); http://dx.doi.org/10.1063/1.2186742 (3 pages) | Cited 7 times

Online Publication Date: 30 March 2006

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The electronic structure of thin blend films composed by copper phthalocyanine (CuPc) and fullerene (C60) have been studied by soft x-ray photoemission spectroscopy. Several samples with different C60/CuPc concentration ratios were prepared by thermal evaporation in ultrahigh vacuum conditions. As the C60 concentration increases, strong shifts of the CuPc highest occupied molecular orbital (HOMO) level towards the Fermi level and of the C60 HOMO level to higher binding energies have been observed. This experimental result suggests that there is a sizeable interaction between CuPc and C60 molecules that can be interpreted in terms of a charge transfer from C60 to CuPc. These shifts play an important role in the application of the CuPc:C60 blend films for instance in the construction of solar cells on flexible substrates.
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79.60.-i Photoemission and photoelectron spectra
73.20.At Surface states, band structure, electron density of states
84.60.Jt Photoelectric conversion
71.20.Rv Polymers and organic compounds
71.20.Tx Fullerenes and related materials; intercalation compounds
81.05.ub Fullerenes and related materials

Controllable gas-liquid phase flow patterns and monodisperse microbubbles in a microfluidic T-junction device

J. H. Xu, S. W. Li, Y. J. Wang, and G. S. Luo

Appl. Phys. Lett. 88, 133506 (2006); http://dx.doi.org/10.1063/1.2189570 (3 pages) | Cited 28 times

Online Publication Date: 30 March 2006

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This letter describes the gas-liquid phase flow patterns and the mechanism of generation of monodisperse microbubbles in a T-junction microfluidic device using the crossflowing shear-rupturing technique. The bubble size is ranged from 100 to 500 μm. The air phase states as isolate air slugs, “pearl necklaces,” periodic isolate bubbles, zig-zag bubble patterns, and multiple-bubble layer can be observed in the wider measured channel. The bubble size relates with the continuous phase flow velocity and viscosity as Vb∝1/(μcuc), while being almost independent of surface tension γ and air phase flow rate Qg, for the conditions used in this work. The bubble formation mechanism by using the crossflowing shear-rupturing technique is different from the hydrodynamic flow focusing and both geometry-dominated breakup techniques. Our system provides independent control of both the size and volume fraction of dispersed bubbles.
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47.54.De Experimental aspects
47.55.Ca Gas/liquid flows
47.55.db Drop and bubble formation
47.55.df Breakup and coalescence
47.61.Jd Multiphase flows
47.85.Np Fluidics

Gate electrode processes in an electrolyte-gated transistor: Non-Faradaically versus Faradaically coupled conductivity modulation of a polyacetylene ionomer

Fuding Lin and Mark C. Lonergan

Appl. Phys. Lett. 88, 133507 (2006); http://dx.doi.org/10.1063/1.2190077 (3 pages) | Cited 13 times

Online Publication Date: 30 March 2006

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The significance of gate electrode processes to the transfer characteristics of electrochemical transistors is demonstrated using a device based on a polyacetylene ionomer. Two regimes of operation are identified. The first involves a conventional redox process where two Faradaic processes balance: oxidative doping of the polymer to modulate conductivity is coupled to reduction at the gate electrode. The second involves a nonconventional hybrid mode of operation: doping is coupled to the charging of an ionic double layer at the gate electrode, which is a non-Faradaic process. The implications of these two regimes on the design and performance of electrochemical transistors are discussed.
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85.30.Tv Field effect devices
82.45.Fk Electrodes
82.45.Gj Electrolytes
61.72.up Other materials

Ambipolar organic field-effect transistors with air stability, high mobility, and balanced transport

Haibo Wang, Jun Wang, Xuanjun Yan, Jianwu Shi, Hongkun Tian, Yanhou Geng, and Donghang Yan

Appl. Phys. Lett. 88, 133508 (2006); http://dx.doi.org/10.1063/1.2190445 (3 pages) | Cited 30 times

Online Publication Date: 30 March 2006

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Ambipolar organic field-effect transistors (OFETs) based on the organic heterojunction of copper-hexadecafluoro-phthalocyanine (F16CuPc) and 2,5-bis(4-biphenylyl) bithiophene (BP2T) were fabricated. The ambipolar OFETs eliminated the injection barrier for the electrons and holes though symmetrical Au source and drain electrodes were used, and exhibited air stability and balanced ambipolar transport behavior. High field-effect mobilities of 0.04 cm2/V s for the holes and 0.036 cm2/V s for the electrons were obtained. The capacitance-voltage characteristic of metal-oxide-semiconductor (MOS) diode confirmed that electrons and holes are transported at F16CuPc and BP2T layers, respectively. On this ground, complementary MOS-like inverters comprising two identical ambipolar OFETs were constructed.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Electrically addressing a single self-assembled quantum dot

D. J. P. Ellis, A. J. Bennett, A. J. Shields, P. Atkinson, and D. A. Ritchie

Appl. Phys. Lett. 88, 133509 (2006); http://dx.doi.org/10.1063/1.2190451 (3 pages) | Cited 13 times

Online Publication Date: 30 March 2006

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We report on the use of an aperture in an aluminum oxide layer to restrict current injection into a single self-assembled InAs quantum dot from an ensemble of such dots within a large mesa. The insulating aperture is formed through the wet oxidation of a layer of AlAs. Under photoluminescence we observe that only one quantum dot in the ensemble exhibits a Stark shift, and that the same single dot is visible under electroluminescence. Autocorrelation measurements performed on the electroluminescence confirm that we are observing emission from a single quantum dot.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
78.60.Fi Electroluminescence
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects

Spatially resolved and temperature dependent thermal tuning rates of high-power diode laser arrays

Michael Kreissl, Tran Quoc Tien, Jens W. Tomm, D. Lorenzen, Anna Kozlowska, Mateusz Latoszek, Myriam Oudart, and Julien Nagle

Appl. Phys. Lett. 88, 133510 (2006); http://dx.doi.org/10.1063/1.2190454 (3 pages) | Cited 1 time

Online Publication Date: 30 March 2006

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Thermal tuning properties of passively cooled 808 nm emitting high-power diode laser bars are analyzed. Data from standard devices packaged on Cu heat sinks and identical devices mounted on expansion-matched Cu–W heat sinks are compared. For a standard device, we find up to one-fifth of the thermal tuning rate of −(0.56±0.04) meV K−1 to be caused by pressure tuning driven by the relaxation of compressive packaging-induced stress for increasing temperatures. For devices packaged on expansion-matched heat sinks the observed tuning rate of −(0.46±0.01) meV K−1 represents almost the genuine thermal tuning rate of the semiconductor device structure. Thus this technology potentially leads to improved device properties.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems

Wide range pressure sensor based on a piezoelectric bimorph microcantilever

V. Mortet, R. Petersen, K. Haenen, and M. D’Olieslaeger

Appl. Phys. Lett. 88, 133511 (2006); http://dx.doi.org/10.1063/1.2190462 (3 pages) | Cited 11 times

Online Publication Date: 30 March 2006

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Since the development of the atomic force microscope, interest in microfabricated cantilevers has grown. Cantilevers are excellent micromechanical sensors. In this work, we use a commercially available piezoelectric bimorph cantilever as pressure and temperature sensor. The piezoelectric layer acts as both sensor and actuator. The sensor detects the change in the resonance frequencies due to the drag force of the surrounding gas. The frequency shift of the resonant modes is measured as a function of the pressure and the temperature. The results show that both pressure and temperature can be measured simultaneously using the piezoelectric bimorph cantilever’s resonant frequencies.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Oxidation of Si(001) with a hyperthermal O-atom beam at room temperature: Suboxide distribution and residual order structure

Masahito Tagawa, Chie Sogo, Kumiko Yokota, Akitaka Yoshigoe, Yuden Teraoka, and Takayoshi Shimura

Appl. Phys. Lett. 88, 133512 (2006); http://dx.doi.org/10.1063/1.2190467 (3 pages) | Cited 2 times

Online Publication Date: 30 March 2006

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Synchrotron radiation photoelectron spectroscopy (SR-PES) and crystal truncation rod (CTR) scattering profiles were used to investigate an ultrathin SiO2 overlayer on a Si(001) surface formed by a 5 eV O-atom beam at room temperature. The SR-PES spectra indicated that the suboxides in the O-atom-beam oxidized film were concentrated on the SiO2 surface rather than at the Si/SiO2 interface. The CTR scattering data of the O-atom-beam oxidation film had a lower intensity near (1 1 L) (0.3<L<0.8), suggesting a lower content of the SiO2 ordered structure in the oxide film. An inverse diffusion of the interstitial Si atoms in the oxidation kinetics can explain the data.
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81.65.Mq Oxidation
68.47.Fg Semiconductor surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
66.30.Lw Diffusion of other defects

Observation of deep level defects within the waveguide of red-emitting high-power diode lasers

Claus Ropers, Tran Quoc Tien, Christoph Lienau, Jens W. Tomm, Peter Brick, Norbert Linder, Bernd Mayer, Martin Müller, Sönke Tautz, and Wolfgang Schmid

Appl. Phys. Lett. 88, 133513 (2006); http://dx.doi.org/10.1063/1.2190815 (3 pages) | Cited 10 times

Online Publication Date: 30 March 2006

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The waveguides of 650 nm emitting high-power laser diodes are analyzed regarding the presence of deep level defects by photoelectrical techniques, namely, photocurrent spectroscopy, laser beam induced current, and near-field optical beam induced current (NOBIC). Deep level configurations in pristine devices and the kinetics of defect creation during device operation are monitored and discussed. The localization of the defects within the epitaxial layer sequence is done by NOBIC. We show that light, which is confined within the laser waveguide, interacts with the deep level defects detected. This demonstrates that the presence of deep level defects directly affects the device properties.
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42.55.Px Semiconductor lasers; laser diodes

Photonic crystal laser lift-off GaN light-emitting diodes

Aurélien David, Tetsuo Fujii, Brendan Moran, Shuji Nakamura, Steven P. DenBaars, Claude Weisbuch, and Henri Benisty

Appl. Phys. Lett. 88, 133514 (2006); http://dx.doi.org/10.1063/1.2189159 (3 pages) | Cited 59 times

Online Publication Date: 31 March 2006

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We report on the fabrication and study of laser lift-off GaN-based light-emitting diodes, thinned down to the microcavity regime, incorporating two-dimensional photonic crystal diffraction gratings. Angle-resolved measurements reveal the photonic behavior of the devices, which strongly depends on the GaN thickness. Data point out the detrimental role of metal absorption. We explore theoretically the possibility to limit this loss channel.
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85.60.Jb Light-emitting devices
42.62.-b Laser applications
42.70.Qs Photonic bandgap materials
42.79.Dj Gratings
85.30.De Semiconductor-device characterization, design, and modeling

Organic nonvolatile memory by dopant-configurable polymer

Qianxi Lai, Zuhua Zhu, Yong Chen, Satish Patil, and Fred Wudl

Appl. Phys. Lett. 88, 133515 (2006); http://dx.doi.org/10.1063/1.2191874 (3 pages) | Cited 31 times

Online Publication Date: 31 March 2006

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We report an organic, nonvolatile memory based on dopant concentration-induced conductance changes in a conjugated polymer. Consisting of a polymer poly [2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV)/ionic conductor (RbAg4I5) bilayer sandwiched between two metal electrodes, the device is electrically switched between its low-conductance “off” state and high-conductance “on” state reversibly and repeatedly with on/off ratios above two orders of magnitude and pulse durations as short as 1 μs when a voltage exceeding its threshold values (>+3.5 V or <−3.8 V) is applied. The conductance change is attributed to the injection/depletion of iodide dopant ions in the MEH-PPV layer by the applied electric field.
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84.30.Sk Pulse and digital circuits
85.30.-z Semiconductor devices

Phosphorus-doped SiC as an excellent p-type Si surface passivation layer

S. Janz, S. Riepe, M. Hofmann, S. Reber, and S. Glunz

Appl. Phys. Lett. 88, 133516 (2006); http://dx.doi.org/10.1063/1.2191954 (2 pages) | Cited 12 times

Online Publication Date: 31 March 2006

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The passivation properties of phosphorus-doped amorphous silicon carbide (a-SixC1−x) layers on monocrystalline Si wafers (floating zone, 1 Ω cm) have been investigated. The cleaning and the deposition process were performed in our two source (microwave, radio frequency) plasma-enhanced chemical vapor deposition reactor. In situ plasma etching and deposition at 350 °C without any following annealing step led to extraordinary low surface recombination velocities of less than 5 cm/s for injection levels between 1×1014 and 1×1015 cm−3. Characterization of the a-SixC1−x layer was done with quasi-steady-state photoconductance, microwave-detected photoconductance, and carrier density imaging techniques. For injection levels of more than 1×1015 cm−3 the effective lifetime was limited only by intrinsic Auger recombination.
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81.65.Rv Passivation
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
79.20.Fv Electron impact: Auger emission
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