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28 Feb 2005

Volume 86, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 093101 (2005); http://dx.doi.org/10.1063/1.1870108 (3 pages)

G. S. Paraoanu and A. M. Halvari
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Near- and mid-infrared detection using GaAs∕InxGa1−xAs∕InyGa1−yAs multiple step quantum wells

M. P. Touse, G. Karunasiri, K. R. Lantz, H. Li, and T. Mei

Appl. Phys. Lett. 86, 093501 (2005); http://dx.doi.org/10.1063/1.1871350 (3 pages) | Cited 17 times

Online Publication Date: 23 February 2005

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A dual-band multiple-quantum-well infrared photodetector capable of simultaneously detecting wavelengths near 0.9 μm and 10 μm has been fabricated using GaAs∕InGaAs step quantum wells. The detection of the near (0.82–0.95 μm)- and mid (9–11 μm)-infrared wavelength bands was achieved using interband and intersubband transitions. The measured peak responsivities of the near- and mid-infrared bands were 0.4 A∕W and 1 A∕W, respectively, at 0.8 V bias across the device. The broken symmetry of the step quantum well allows transitions from the ground states of heavy and light holes to the first-excited electron state allowing the photoexcited carriers to be efficiently collected. The estimated values of the detectivities for near- and mid-infrared bands at 40 K and 0.8 V bias are approximately 4.5×109 cm(Hz)1/2/W and 1.1×1010 cm(Hz)1/2/W, respectively.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects

Flexible organic photovoltaics using conducting polymer electrodes

Gary P. Kushto, Woohong Kim, and Zakya H. Kafafi

Appl. Phys. Lett. 86, 093502 (2005); http://dx.doi.org/10.1063/1.1867568 (3 pages) | Cited 41 times

Online Publication Date: 23 February 2005

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Single heterojunction, small-molecule organic photovoltaic devices (OPVs) have been prepared on fully flexible thermoplastic substrates using prepatterned conducting polymer electrodes( ∼ 450 Ω/◻). OPVs were fabricated via sequential vacuum vapor deposition of layers of the organic electron donating/hole transporting material: N,N′-(α-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine and the electron accepting/transporting material: C60. The resulting photovoltaic cells exhibit white-light power conversion efficiencies of 1% (AM1.5, 97 mW/cm2), virtually identical to those fabricated on prepatterned tin-doped indium oxide/glass substrates.
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84.60.Jt Photoelectric conversion
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.60.Bt Optoelectronic device characterization, design, and modeling

Performance improvement of polycrystalline diamond ultraviolet photodetectors by room-temperature plasma treatment

S. G. Wang, P. J. Sellin, A. Lohstroh, and Qing Zhang

Appl. Phys. Lett. 86, 093503 (2005); http://dx.doi.org/10.1063/1.1868862 (3 pages)

Online Publication Date: 23 February 2005

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Enhancement of ultraviolet (UV) photoresponsivity in chemical-vapor-deposited (CVD) diamond photodetectors was observed by posttreatment in a plasma of oxygen and carbon tetrafluoride at room temperature. This room-temperature plasma posttreatment was found to be an efficient process in suppressing the extrinsic photoresponse of CVD diamond UV photodetectors in the visible region. Nearly four orders of magnitude difference in the photoresponsivity between the UV and visible light regions were obtained. The results of photoluminescence mapping and Raman spectra indicate that this performance improvement may have resulted from the effective removal of the sp2-bonded carbon impurities and passivation of the silicon-vacancy defects in the diamond.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.55.Ap Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
81.65.Rv Passivation
71.55.Cn Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Improvement in performance of transparent organic light-emitting diodes with increasing sputtering power in the deposition of indium tin oxide cathode

Choong-Heui Chung, Young-Wook Ko, Yong-Hae Kim, Choong-Yong Sohn, Hye Yong Chu, and Jin Ho Lee

Appl. Phys. Lett. 86, 093504 (2005); http://dx.doi.org/10.1063/1.1869534 (3 pages) | Cited 12 times

Online Publication Date: 23 February 2005

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The performance of transparent organic light-emitting diodes (OLEDs) can be substantially improved by increasing the rf sputtering power in the deposition of an indium tin oxide cathode. This dependence of device performance on sputtering power is quite different from that reported for transparent OLEDs. The effect is attributed to sputtering induced substrate-heating resulting in chemical reactions at the Al–LiF–Alq3 interface and electron injection enhancement. By effectively dissipating the energy of sputtered particles, device damage can be taken away. The findings herein show that a transparent OLED having better electron injection properties than a conventional OLED can be fabricated.
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85.60.Jb Light-emitting devices
85.30.-z Semiconductor devices
81.15.Cd Deposition by sputtering
78.60.Fi Electroluminescence

Electroluminescence of 2,4-bis(4-(2′-thiophene-yl)phenyl)thiophene in organic light-emitting field-effect transistors

Takahito Oyamada, Hiroyuki Sasabe, Chihaya Adachi, Suguru Okuyama, Noriyuki Shimoji, and Kazumi Matsushige

Appl. Phys. Lett. 86, 093505 (2005); http://dx.doi.org/10.1063/1.1870105 (3 pages) | Cited 38 times

Online Publication Date: 24 February 2005

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We succeeded in observing electroluminescence (EL) of 2,4-bis(4-(2′-thiophene-yl)phenyl)thio-phene (TPTPT) as an active layer in an organic field-effect transistor (OFET). In particular, an OFET with a short channel of dSD = 0.8 μm demonstrated higher EL efficiency than one with a much longer channel (dSD = 9.8 μm). We observed a maximum EL quantum efficiency (ηmax) of 6.4×10−3 % in the short-channel-length device at an applied source-drain voltage of Vd = −100 V and a gate voltage of Vg = −40 V. From the OFET characteristics, although the TPTPT layer demonstrated typical p-type operation, the occurrence of EL clearly indicated simultaneous hole and electron injection from the source and drain electronics, respectively, under high Vd and Vg.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
78.60.Fi Electroluminescence
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Reaction-dispersive proton transport model for negative bias temperature instabilities

M. Houssa, M. Aoulaiche, S. De Gendt, G. Groeseneken, M. M. Heyns, and A. Stesmans

Appl. Phys. Lett. 86, 093506 (2005); http://dx.doi.org/10.1063/1.1871357 (3 pages) | Cited 24 times

Online Publication Date: 24 February 2005

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Negative bias temperature instabilities in p-channel metal-oxide-semiconductor field effect transistors are modeled by taking into account the generation of Pb0 centers at the (100)Si/SiO2 interface, followed by the dispersive transport of protons away from the interface. It is shown that the characteristic time, oxide electric field, and temperature dependence of the threshold voltage shifts observed in these devices can be very well reproduced by the model. The general belief that the transport of positively charged species cannot explain negative bias temperature instabilities thus appears to be incorrect.
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85.30.De Semiconductor-device characterization, design, and modeling
85.30.Tv Field effect devices
66.30.H- Self-diffusion and ionic conduction in nonmetals
71.55.Cn Elemental semiconductors
71.55.Ht Other nonmetals

Bendable single crystal silicon thin film transistors formed by printing on plastic substrates

E. Menard, R. G. Nuzzo, and J. A. Rogers

Appl. Phys. Lett. 86, 093507 (2005); http://dx.doi.org/10.1063/1.1866637 (3 pages) | Cited 71 times

Online Publication Date: 25 February 2005

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Bendable, high performance single crystal silicon transistors have been formed on plastic substrates using an efficient dry transfer printing technique. In these devices, free standing single silicon objects, which we refer to as microstructured silicon (μs‐Si), are picked up, using a conformable rubber stamp, from the top surface of a wafer from which they are generated. The μs‐Si is then transferred, to a specific location and with a controlled orientation, onto a thin plastic sheet. The efficiency of this method is demonstrated by the fabrication of an array of thin film transistors that exhibit excellent electrical properties: average device effective mobilities, evaluated in the linear regime, of ∼ 240 cm2/V s, and threshold voltages near 0 V. Frontward and backward bending tests demonstrate the mechanical robustness and flexibility of the devices.
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85.30.Tv Field effect devices
73.61.Cw Elemental semiconductors
68.35.Gy Mechanical properties; surface strains
73.50.Dn Low-field transport and mobility; piezoresistance
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Improved performance and stability of organic light-emitting devices with Al–Cu alloy cathode

I.-Ching Chen, Shiao-Wen Hwang, and Chin H. Chen

Appl. Phys. Lett. 86, 093508 (2005); http://dx.doi.org/10.1063/1.1879103 (3 pages) | Cited 3 times

Online Publication Date: 25 February 2005

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We have developed a stable green organic electroluminescent (EL) device by using an Al–Cu alloy as a cathode, which has better performance and reliability than the device with an Al cathode. The device with an Al–Cu alloy cathode achieved an EL efficiency of 3.78 cd/A(2.18 lm/W) at 20 mA/cm2 and the operating voltage was 5.46 V, while device with Al cathode had an EL efficiency of 3.1 cd/A(1.34 lm/W) and 7.3 V at the same drive condition. The Al–Cu device achieved a 20% decay lifetime (t80) of 1234 h at an initial brightness of 756 cd/m2, which is twice the lifetime of conventional device with the state-of-the-art LiF/Al cathode.
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85.60.Jb Light-emitting devices
85.60.Ha Photomultipliers; phototubes and photocathodes

Conductivity switching characteristics and reset currents in NiO films

S. Seo, M. J. Lee, D. H. Seo, S. K. Choi, D.-S. Suh, Y. S. Joung, I. K. Yoo, I. S. Byun, I. R. Hwang, S. H. Kim, and B. H. Park

Appl. Phys. Lett. 86, 093509 (2005); http://dx.doi.org/10.1063/1.1872217 (3 pages) | Cited 79 times

Online Publication Date: 25 February 2005

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Conductivity switching phenomena controlled by external voltages have been investigated for various NiO films deposited by dc reactive sputtering methods. Pt/NiO/Pt capacitor structures with top electrodes of different diameters have showed increasing off-state current with the diameter of a top electrode and nearly the same on-state current independent of the diameter. Local conductivity switching behaviors have been observed in a series structure consisting of two Pt/NiO/Pt capacitors with different resistance values. By reasoning out conductivity switching mechanisms from the switching characteristics and introducing multilayers consisting of NiO layers with different resistance values, we have reduced the reset current by two orders of magnitude.
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73.61.Le Other inorganic semiconductors
84.32.Dd Connectors, relays, and switches
81.15.Cd Deposition by sputtering

Physical model for frequency-dependent dynamic charge trapping in metal-oxide-semiconductor field effect transistors with HfO2 gate dielectric

C. Shen, M. F. Li, H. Y. Yu, X. P. Wang, Y.-C. Yeo, D. S. H. Chan, and D.-L. Kwong

Appl. Phys. Lett. 86, 093510 (2005); http://dx.doi.org/10.1063/1.1874312 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2005

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In this letter, we report on a physical model to explain the frequency dependence of dynamic charge trapping in metal-oxide-semiconductor (MOS) transistors with ultrathin HfO2 gate dielectrics. For transistors operating in a complementary MOS inverter circuit with a given gate voltage amplitude, we observed a reduction of charge trapping when the stress frequency is increased. This can be explained by the traps in the high-k HfO2 dielectric have the property of negative-U centers. One trap can capture two electrons sequentially, and the trap energy is reduced as a result of lattice relaxation. Results of calculation using the model show excellent agreement with all experiment data.
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85.30.Tv Field effect devices
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.30.De Semiconductor-device characterization, design, and modeling
68.60.Bs Mechanical and acoustical properties
71.55.Ht Other nonmetals
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