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7 Mar 2005

Volume 86, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 86, 103102 (2005); http://dx.doi.org/10.1063/1.1875734 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, and Motoichi Ohtsu
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Improved stability of organic electroluminescent devices by doping styrylamines in hole or electron transporting layer

Meng-Ting Lee, Chi-Hung Liao, Chih-Hung Tsai, and Chin H. Chen

Appl. Phys. Lett. 86, 103501 (2005); http://dx.doi.org/10.1063/1.1881796 (3 pages) | Cited 5 times

Online Publication Date: 28 February 2005

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The stability of green organic electroluminescent devices has been improved by doping styrylamine derivate, p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph) in hole or electron transporting layer. Compared with the undoped device, the stability of the electron transporting layer has increased by a factor of 1.8 without affecting the electroluminescence efficiency of 11 cd/A and color (CIEx,y = 0.34, 0.62). The enhanced stability is believed to derive from the hole trapping nature of DSA-Ph which can reduce the residual hole carriers in tris(8-hydroquinolinato)aluminum (Alq3) and suppress the formation of fluorescent quencher of Alq3 cationic species.
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85.60.Jb Light-emitting devices
78.66.Li Other semiconductors
78.60.Fi Electroluminescence
73.61.Ph Polymers; organic compounds
61.72.up Other materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Modification of the electric conduction at the pentacene/SiO2 interface by surface termination of SiO2

Iwao Yagi, Kazuhito Tsukagoshi, and Yoshinobu Aoyagi

Appl. Phys. Lett. 86, 103502 (2005); http://dx.doi.org/10.1063/1.1875749 (3 pages) | Cited 77 times

Online Publication Date: 28 February 2005

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A surface treatment method has been developed for the SiO2/Si substrate to control the electrical properties of pentacene thin-film transistors (TFTs). The surface treatment is performed by spin-coating 1,1,1,3,3,3-hexamethyldisilazane liquid, resulting in a drastic improvement of the off current although the surface treatment never shows a pronounced morphological change in the pentacene channel in comparison with the one on the nontreated substrate. The off current improvement directly enhances the transistor performance especially in the TFTs with a few monolayers channel thickness. The off current suppression could be caused by the reduction of the interfacial floating charge trapped at the pentacene/SiO2 interface.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Cf Surface cleaning, etching, patterning

Low-voltage operation of a pentacene field-effect transistor with a polymer electrolyte gate dielectric

Matthew J. Panzer, Christopher R. Newman, and C. Daniel Frisbie

Appl. Phys. Lett. 86, 103503 (2005); http://dx.doi.org/10.1063/1.1880434 (3 pages) | Cited 80 times

Online Publication Date: 28 February 2005

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Large operating voltages are often required to switch organic field-effect transistors (OFETs) on and off because commonly used gate dielectric layers provide low capacitive coupling between the gate electrode and the semiconductor. We present here a pentacene OFET gated by a solution-deposited polymer electrolyte film in which the current was modulated over four orders of magnitude using gate voltages less than 2 V. A subthreshold slope of 180 mV per decade of current was observed during transistor turn on at a source-drain bias of −1 V; the estimated dielectric layer specific capacitance was 5 μF/cm2. Sweep rate-dependent hysteresis may be attributed to a combination of ion migration and charge carrier trapping effects. Strategies to improve switching speeds for polymer electrolyte-gated OFETs are also discussed.
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85.30.Tv Field effect devices
77.55.-g Dielectric thin films
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Strained silicon thin-film transistors fabricated on glass

J. J. Lee, J. S. Maa, D. J. Tweet, and S. T. Hsu

Appl. Phys. Lett. 86, 103504 (2005); http://dx.doi.org/10.1063/1.1880444 (3 pages) | Cited 2 times

Online Publication Date: 28 February 2005

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Strained-Si thin-film transistors were fabricated on glass substrate by direct transfer of a 35 nm strained Si film onto glass. The strained Si films were originally grown on a relaxed SiGe layer on Si substrate. The tensile strain for the strained Si on glass (SSOG) was found to be 0.80%±0.02%. The effective electron mobility of the fabricated NMOS TFTs is 820 cm2/V s. These devices show low interface charge densities at the bonding interface and at the gate oxide interface, as confirmed by the low subthreshold swing of 77 mV/dec for the 0.5 μm SSOG device.
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85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Cw Elemental semiconductors
68.55.-a Thin film structure and morphology

Nickel nanocrystal formation on HfO2 dielectric for nonvolatile memory device applications

Jong Jin Lee, Yoshinao Harada, Jung Woo Pyun, and Dim-Lee Kwong

Appl. Phys. Lett. 86, 103505 (2005); http://dx.doi.org/10.1063/1.1881778 (3 pages) | Cited 33 times

Online Publication Date: 3 March 2005

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This letter presents the formation of nickel nanocrystal on HfO2 high-k dielectric and its application to the nonvolatile memory devices. The effects of the initial nickel layer thickness and annealing temperature on nickel nanocrystal formation are investigated. The n-metal-oxide-semiconductor field-effect transistor with nickel nanocrystals and HfO2 tunneling dielectrics is fabricated and its programming, data retention, and endurance properties are characterized to demonstrate its advantages for nonvolatile memory device applications.
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85.30.Tv Field effect devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.07.Bc Nanocrystalline materials
84.30.Sk Pulse and digital circuits
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Cd Deposition by sputtering
81.16.-c Methods of micro- and nanofabrication and processing
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling
77.80.Dj Domain structure; hysteresis
61.46.-w Structure of nanoscale materials
84.32.Tt Capacitors

Mixed host organic light-emitting devices with low driving voltage and long lifetime

Jiun-Haw Lee, Chih-I. Wu, Shun-Wei Liu, Ching-An Huang, and Yih Chang

Appl. Phys. Lett. 86, 103506 (2005); http://dx.doi.org/10.1063/1.1879093 (3 pages) | Cited 35 times

Online Publication Date: 3 March 2005

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In this letter, we present and analyze the device performance of the mixed host (MH) organic light-emitting devices (OLEDs). The host of the emitting layer (EML) material in this device consists of a hole transport layer (HTL) and an electron transport layer (ETL) fabricated by coevaporation. The bipolar transport characteristic of the MH layer helps to reduce the driving voltage. Device lifetime is increased due to the elimination of the sharp boundary of the HTL/EML interface. Combining the MH structure with a high mobility electron ETL material, bis(10-hydroxybenzo[h]qinolinato)beryllium, the OLED has shown a brightness of 27 600 cd/m2 at a driving voltage of 5 V, and a lifetime four times longer than that of a conventional OLED.
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85.60.Jb Light-emitting devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Ee Mobility edges; hopping transport

Highly efficient polymer light-emitting devices using ambipolar phosphorescent polymers

Mitsunori Suzuki, Shizuo Tokito, Fumio Sato, Takeshi Igarashi, Kunio Kondo, Tamami Koyama, and Tetsuhiko Yamaguchi

Appl. Phys. Lett. 86, 103507 (2005); http://dx.doi.org/10.1063/1.1879102 (3 pages) | Cited 62 times

Online Publication Date: 3 March 2005

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We report on highly efficient polymer light-emitting devices (PLEDs) achieved using a phosphorescent polymer, which is a copolymer that has bis(2-phenylpyridine)iridium (acetylacetonate) [Ir(ppy)2(acac)], N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a side group. The phosphorescent polymer has an ambipolar charge-transport ability. An increase in PBD unit concentration allows an improvement in the efficiency of the PLEDs. Ba and Cs were used for electron-injection layers as well as Ca, to improve the electron injection. An external quantum efficiency of 11.8% and a power efficiency of 38.6 lm/W were obtained by using Cs. The results indicate that this can be attributed to an improvement in the charge balance of electrons and holes.
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85.60.Jb Light-emitting devices
85.65.+h Molecular electronic devices
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence

A prototype protein field-effect transistor

Siu-Tung Yau and Guoguang Qian

Appl. Phys. Lett. 86, 103508 (2005); http://dx.doi.org/10.1063/1.1880445 (3 pages) | Cited 5 times

Online Publication Date: 3 March 2005

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Electrical conduction in a macroscopic assembly of apoferritin, a non-redox protein, has been characterized using a three-terminal prototype device. Our result shows an ohmic conduction near zero bias. The ohmic conduction can be controlled using an electric field applied to the protein assembly via the gate terminal of the device. The transconductance of the protein device shows a highly nonlinear dependence on the gate voltage. The transconductance curve indicates that the device has the attributes of an n-channel metal-oxide-semiconductor field-effect transistor with electrons as charge carriers. The input/output dynamic response of the device has been demonstrated.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
87.14.E- Proteins

A Si-based quantum-dot light-emitting diode

M. Jo, K. Ishida, N. Yasuhara, Y. Sugawara, K. Kawamoto, and S. Fukatsu

Appl. Phys. Lett. 86, 103509 (2005); http://dx.doi.org/10.1063/1.1882757 (3 pages) | Cited 10 times

Online Publication Date: 4 March 2005

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A Si-based light-emitting diode (LED) containing strained GaSb quantum dots (QDs) embedded in Si within the active region was fabricated by means of Si molecular-beam epitaxy. An external quantum efficiency of 0.3% was obtained for near bandedge luminescence at 11 K. The high luminosity of Si-based QD-LED was also evidenced by the fact that direct imaging on an infrared camera of standard sensitivity was successful. Characteristics of the QD-LED operating at room temperature are described.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Defect density and diffusion length of holes in nanocrystalline silicon devices

Vikram L. Dalal and Puneet Sharma

Appl. Phys. Lett. 86, 103510 (2005); http://dx.doi.org/10.1063/1.1873062 (3 pages) | Cited 8 times

Online Publication Date: 4 March 2005

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We report on the measurement of doping density, defect density, and minority carrier diffusion length in nanocrystalline Si p+nn+ solar cell devices fabricated using very high frequency (VHF) and electron-cyclotron-resonance (ECR) plasma deposition techniques. Doping and midlevel defect densities were estimated from a measurement of capacitance versus voltage at different frequencies. The as grown layers were always n-type. The doping in as-grown base layers could be reduced by either compensating the material during growth with ppm levels of boron, or increased by adding ppm levels of phosphorus. It was found that there was a distinct correlation between shallow donor density, and deep defect density, situated at 0.35–0.5 eV below the conduction band, even in unintentionally doped materials. Increasing doping increased the midlevel defect density. The diffusion length of holes was measured using combinations of capacitance and quantum efficiency measurements. The nanocrystalline Si p–n junction is shown to be a diffusion controlled, and not a drift-controlled device.
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71.55.Cn Elemental semiconductors
84.60.Jt Photoelectric conversion
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

GaN-based photocathodes with extremely high quantum efficiency

Shoichi Uchiyama, Yasufumi Takagi, Minoru Niigaki, Hirofumi Kan, and Haruyasu Kondoh

Appl. Phys. Lett. 86, 103511 (2005); http://dx.doi.org/10.1063/1.1883707 (3 pages) | Cited 13 times

Online Publication Date: 4 March 2005

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We have fabricated phototubes with photocathodes consisting of the Mg-doped GaN films. The spectral shapes of the response and the quantum efficiency (QE) strongly depend on the Mg-doping concentration. The calibrated QE of the photocathode is maximized to be 71.9% at a photon energy of 5.4 eV by a Mg-doping concentration of 3.0×1019 cm−3. Consequently, a phototube with the GaN-based photocathode is realized to demonstrate a very high QE, more than 50% and sharp cutoff characteristic over three orders of magnitude.
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85.60.Ha Photomultipliers; phototubes and photocathodes
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals

Flexible, organic, ion-sensitive field-effect transistor

Andrea Loi, Ileana Manunza, and Annalisa Bonfiglio

Appl. Phys. Lett. 86, 103512 (2005); http://dx.doi.org/10.1063/1.1873051 (3 pages) | Cited 36 times

Online Publication Date: 4 March 2005

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Organic ion-sensitive field-effect transistors assembled on flexible plastic films have been fabricated. A thin Mylar™ foil acts both as substrate and gate dielectric. The active layer is vacuum-sublimed on one side of the foil, prepatterned with bottom-contact Au source and drain electrodes. The opposite side of the insulating film is in contact with an electrolytic solution that together with a reference electrode forms an ionic gate. A sensitivity of the device to the pH of the electrolyte solution has been observed. Thanks to the flexibility of the substrate and the low cost of the employed technology, this device opens the way for flexible sensors that can be employed in a variety of innovative applications.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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