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3 Dec 2007

Volume 91, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 91, 232101 (2007); http://dx.doi.org/10.1063/1.2818712 (3 pages)

T. Kita, D. Chiba, Y. Ohno, and H. Ohno
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A highly efficient wide-band-gap host material for blue electrophosphorescent light-emitting devices

Dong Ryeol Whang, Youngmin You, Se Hun Kim, Won-Ik Jeong, Young-Seo Park, Jang-Joo Kim, and Soo Young Park

Appl. Phys. Lett. 91, 233501 (2007); http://dx.doi.org/10.1063/1.2821116 (3 pages) | Cited 27 times

Online Publication Date: 3 December 2007

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We report on an efficient wide-band-gap host material for blue electrophosphorescence devices, namely, 1,2-trans-di-9-carbazolylcyclobutane (DCz). Photophysical studies show that lower-energy excimer formation between the carbazole units can be efficiently suppressed in a DCz film, thus maintaining its high triplet-state energy and inducing an exothermic energy transfer from DCz to iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic). Electrophosphorescent devices comprising a FIrpic:DCz emitting layer exhibit a superior performance with a maximum external quantum efficiency of 9.8%, a maximum luminance efficiency of 21.5 cd/A, and a maximum power efficiency of 15.0 lm/W at 0.01 mA/cm2.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics

Hydrogen annealing of arrays of planar and vertically stacked Si nanowires

E. Dornel, T. Ernst, J. C. Barbé, J. M. Hartmann, V. Delaye, F. Aussenac, C. Vizioz, S. Borel, V. Maffini-Alvaro, C. Isheden, and J. Foucher

Appl. Phys. Lett. 91, 233502 (2007); http://dx.doi.org/10.1063/1.2818678 (3 pages) | Cited 12 times

Online Publication Date: 3 December 2007

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Four level matrices of round, 35 nm in diameter Si nanowires (NWs) are obtained thanks to a top-down approach. In particular, we report optimized H2 annealing conditions (800 to 900 °C) in order to reconstruct the plasma-etched surfaces of the suspended nanowires. The nanowire shape evolution has been studied in scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The side roughness decrease and the rounding of the NWs have been quantified. The instability of the anchors of the NWs to the contact regions has been evidenced and confirmed by surface diffusion simulations.
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81.07.Vb Quantum wires
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
68.65.La Quantum wires (patterned in quantum wells)

Hydrogen shuttling near Hf-defect complexes in Si/SiO2/HfO2 structures

A. G. Marinopoulos, I. Batyrev, X. J. Zhou, R. D. Schrimpf, D. M. Fleetwood, and S. T. Pantelides

Appl. Phys. Lett. 91, 233503 (2007); http://dx.doi.org/10.1063/1.2820380 (3 pages) | Cited 3 times

Online Publication Date: 4 December 2007

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We propose that a defect complex comprising a suboxide Hf–Si bond and an interfacial dangling bond is responsible for the stress-induced buildup of interface traps in Si/SiO2/HfO2 capacitors. With the aid of first-principles calculations, we show that these defects possess a symmetric double-well energy minimum with a moderate intervening barrier. The calculated activation energies suggest a relatively easy hopping of H atoms between the two energy minima (a field-aided shuttling mechanism). This mechanism can explain the experimentally measured oscillations of interface-trap densities during switched-bias conditions following x-ray irradiation or constant-voltage stress.
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71.55.-i Impurity and defect levels
61.80.Cb X-ray effects
73.21.Ac Multilayers
84.32.Tt Capacitors

Modified substrate-current model for high voltage n-channel metal-oxide-semiconductor transistor and its implication on transistor design

Mingzhi Dai, A. Yap, K. Huang, S. Y. Huang, J. Wang, S. Wang, I. Jiang, W. J. Zhang, L. Yi, A. Cheng, S. H. Liu, and K. Y. Liao

Appl. Phys. Lett. 91, 233504 (2007); http://dx.doi.org/10.1063/1.2817751 (3 pages) | Cited 2 times

Online Publication Date: 4 December 2007

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A simple analytical model with two high-electric-field regions, instead of only one shifted high-electric-field region (the Kirk effect), is proposed to explain the unusual substrate-current behavior in very short high voltage n-channel metal-oxide-semiconductor transistors. This model agrees well with the experimental data in terms of the substrate-current dependence on VGS, VDS, process, and structures.
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85.30.De Semiconductor-device characterization, design, and modeling

Degradation of low frequency noise in SiGe- and SiGeC-surface channel p-type metal-oxide-semiconductor field effect transistor due to consuming the Si cap

R. Yang, Y. Z. Xiong, W. Y. Loh, J. D. Ye, M. B. Yu, C. Shen, J. J. Yang, K. T. Chua, K. M. Hoe, G. Q. Lo, N. Balasubramanian, and D. L. Kwong

Appl. Phys. Lett. 91, 233505 (2007); http://dx.doi.org/10.1063/1.2819071 (3 pages) | Cited 1 time

Online Publication Date: 6 December 2007

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This letter reports on the noise degradation mechanism in SiGe- and SiGeC-surface channel p-type metal-oxide-semiconductor field-effect transistors (pMOSFETs). Compared to their Si reference, the surface SiGe pMOSFETs show only slightly lower or even comparable noise (at low gate bias), while the SiGeC devices exhibit higher noise amplitude for the full bias range, unlike previously reported buried SiGe pMOSFETs with significantly improved noise over their Si control. The degradation can be attributed to Si-cap consumption and thus the cancellation of buried channel operation. [C] incorporation further degrades noise characteristics due to inferior quality of epilayer and higher interface trap density.
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85.30.Tv Field effect devices

Evolution of phase change memory characteristics with operating cycles: Electrical characterization and physical modeling

Joy Sarkar and Bob Gleixner

Appl. Phys. Lett. 91, 233506 (2007); http://dx.doi.org/10.1063/1.2821845 (3 pages) | Cited 14 times

Online Publication Date: 6 December 2007

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The authors report an improvement in electrical characteristics with operational cycles of phase change memory cells having Ge2Sb2Te5 as the active material. An increase in amorphous-state resistance and threshold voltage and decrease in crystalline-state resistance with cycling are observed, which can be explained by gradual compositional change of the memory material driven by the energy input during programming operations. It is also found that melting of the active volume is critical for such improvement in the electrical characteristics. A physical model is proposed based on an expanding cell active volume with operating cycles to self-consistently explain the reported electrical data.
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61.43.Dq Amorphous semiconductors, metals, and alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Highly efficient p-i-n white organic light emitting devices with tandem structure

Meng-Huan Ho, Teng-Ming Chen, Pu-Cheng Yeh, Shiao-Wen Hwang, and Chin H. Chen

Appl. Phys. Lett. 91, 233507 (2007); http://dx.doi.org/10.1063/1.2822398 (3 pages) | Cited 20 times

Online Publication Date: 6 December 2007

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Highly efficient tandem p-i-n white organic light emitting devices have been fabricated. Utilizing an optical transparent bilayer with doped organic p-n junction that consists of 4,7-diphenyl-1,10-phenanthroline: 2% cesium carbonate (Cs2CO3)/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine: 50% v/v tungsten oxide (WO3) as the connecting layer, the tandem p-i-n white device achieved an electroluminescence efficiency of 23.9 cd/A and a power efficiency of 7.8 lm/W at 20 mA/cm2 with a Commission Internationale de l’Eclairage coordinates of (0.30, 0.43). The electroluminescent color of this tandem p-i-n white organic light-emitting diode device will not change significantly with respect to drive current variation and forward viewing angle.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Kk Junction diodes
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Dual broadband photodetector based on interband and intersubband transitions in InAs quantum dots embedded in graded InGaAs quantum wells

Brandon S. Passmore, Jiang Wu, M. O. Manasreh, and G. J. Salamo

Appl. Phys. Lett. 91, 233508 (2007); http://dx.doi.org/10.1063/1.2822412 (3 pages) | Cited 4 times

Online Publication Date: 6 December 2007

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Two broadband photoresponse from InAs quantum dots embedded in graded InGaAs quantum well photodetectors were observed in the spectral regions of 4–12 μm (midinfrared band) and 0.5–1.0 μm (near-infrared-visible band). The midinfrared band is attributed to the intersubband transitions within the quantum dots and was observed at temperatures less than 80 K. The near-infrared-visible band is attributed to interband transitions and is observed in the temperature range of 77–300 K. The room temperature detectivity of the near-infrared-visible band is estimated to be on the order of ∼ 3.0×108 cm math/W with a bias voltage less than 1.0 V.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
78.30.Fs III-V and II-VI semiconductors

Photovoltaic response of a polymer p-i-n junction

Yanguang Zhang, Yufeng Hu, and Jun Gao

Appl. Phys. Lett. 91, 233509 (2007); http://dx.doi.org/10.1063/1.2822993 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2007

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We report the photovoltaic characterization of a polymer p-i-n junction, realized by in situ electrochemical doping and thermal cycling. The planar, “frozen” p-i-n junction exhibits record-high open-circuit voltage up to 2.25 V, and in-plane short-circuit current density in excess of 10 mA/cm2 under simulated sunlight ( ∼ 300 mW/cm2). Our results suggest that built-in potential close to the polymer energy gap in magnitude can be obtained in a polymer device structure without the use of dissimilar electrodes, and large short-circuit current density is possible without the use of strong electron acceptors, which limits the open-circuit voltage.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.60.-q Optoelectronic devices

Study of anode work function modified by self-assembled monolayers on pentacene/fullerene organic solar cells

Chung-Ting Tseng, Yu-Hung Cheng, Ming-Chang M. Lee, Chien-Chung Han, Chien-Hong Cheng, and Yu-Tai Tao

Appl. Phys. Lett. 91, 233510 (2007); http://dx.doi.org/10.1063/1.2823579 (3 pages) | Cited 14 times

Online Publication Date: 6 December 2007

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The authors investigated the anode work function modified by series of self-assembled monolayers comprising alkanethiols and perfluorinated alkanethiols with different alkyl lengths on pentacene/fullerene thin-film organic solar cells. Via selecting different types of self-assembled molecules, the anode work function can be tailored for modifying the interfacial barrier. The measured open-circuit voltages indicated reduced anode work function that tends to form Schottky contact. The maximal open-circuit voltage and short-circuit current were measured to be 0.4 V and 17.7 mA/cm2, respectively, in the case of anode work function modified by perfluorinated alkanethiols. The power conversion efficiency is 2.24%.
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73.30.+y Surface double layers, Schottky barriers, and work functions
84.60.Jt Photoelectric conversion

A Cu-based alloyed Ohmic contact system on n-type GaAs

Ke-Shian Chen, Edward Yi Chang, Chia-Ching Lin, Cheng-Shih Lee, Wei-Ching Huang, and Ching-Ting Lee

Appl. Phys. Lett. 91, 233511 (2007); http://dx.doi.org/10.1063/1.2819687 (3 pages)

Online Publication Date: 7 December 2007

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An alloyed Pd/Ge/Cu Ohmic contact to n-type GaAs is reported for the first time. The Pd/Ge/Cu Ohmic contact exhibited a very low specific contact resistance of 5.73×10−7 Ω cm2 at a low annealing temperature of 250 °C. This result is comparable to the reported Pd/Ge and Au/Ge/Ni Ohmic contact systems to n-type GaAs with doping concentrations about 1×1018 cm−3. The Ohmic contact formation mechanisms and microstructure evolution were investigated using secondary ion mass spectrometry, x-ray diffraction, transmission electron microscopy, and energy dispersive spectrometer. The Ohmic contact behavior was related to the formation of Cu3Ge and PdGaxAsy compounds after annealing.
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72.80.Ey III-V and II-VI semiconductors
73.40.Ns Metal-nonmetal contacts
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Negative differential resistance induced by intermolecular interaction in a bimolecular device

Meng-Qiu Long, Ke-Qiu Chen, Lingling Wang, B. S. Zou, and Z. Shuai

Appl. Phys. Lett. 91, 233512 (2007); http://dx.doi.org/10.1063/1.2822423 (3 pages) | Cited 33 times

Online Publication Date: 7 December 2007

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Using nonequilibrium Green’s functions in combination with the density-functional theory, we study the electronic transport properties of the molecular device constructed by two cofacial oligo(phenylene ethynylene) molecules and gold electrodes. The results show that negative differential resistance can be observed when the intermolecular distance closes to a certain value. We propose that a combination of the splitting of the molecular orbitals due to the intermolecular interaction and the change of the coupling between the molecules and the electrodes at different biases might be responsible for the negative differential resistance behavior.
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85.65.+h Molecular electronic devices
02.30.-f Function theory, analysis

Backward rectifying and forward Schottky behavior at Au/Nb-1.0 wt %-doped SrTiO3 interface

Yimin Cui and Rongming Wang

Appl. Phys. Lett. 91, 233513 (2007); http://dx.doi.org/10.1063/1.2823583 (3 pages) | Cited 7 times

Online Publication Date: 7 December 2007

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The Au/Nb-1.0 wt %-doped SrTiO3 junctions were successfully fabricated by magnetic controlled sputtering and annealing process. Backward diodelike behaviors were observed in as-prepared junction and the one annealed at 350 °C. Transition to Schottky behavior was found in the junction annealed at 750 °C; the Schottky junction shows linear capacitance-voltage (C−2-V) relationship in the reverse condition with barrier heights determined to be 1.6 eV. The results of current-voltage (I-V) measurements reveal that high temperature annealing can alter interface barrier and thereby ameliorate the stability of leakage current remarkably.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
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