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15 Nov 2004

Volume 85, Issue 20, pp. 4561-4807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4768 (2004); http://dx.doi.org/10.1063/1.1818331 (3 pages)

G. Walter, N. Holonyak, M. Feng, and R. Chan
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Mn diffusion in Ga1−xMnxAs∕GaAs superlattices

A. Mikkelsen, L. Ouattara, H. Davidsson, E. Lundgren, J. Sadowski, and O. Pacherova

Appl. Phys. Lett. 85, 4660 (2004); http://dx.doi.org/10.1063/1.1818338 (3 pages) | Cited 5 times

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Ga1−xMnxAs∕GaAs superlattices with Mn concentrations of 1% and 5% in the Ga1−xMnxAs layers and a GaAs spacer thickness of 4 and 60 GaAs monolayers have been studied by cross-sectional scanning tunneling microscopy. By achieving atomic resolution of the superlattices, we observe individual Mn atoms in the Ga1−xMnxAs layers and in the GaAs spacer. We find that about 20% of the total amount of Mn diffuses from the GaMnAs layers into the GaAs spacer layers. Our results can be related to previous measurements of the magnetic properties of short period Ga1−xMnxAs∕GaAs superlattices.

Reduction of contact resistance in pentacene thin-film transistors by direct carrier injection into a-few-molecular-layer channel

Nobuhide Yoneya, Makoto Noda, Nobukazu Hirai, Kazumasa Nomoto, Masaru Wada, and Jiro Kasahara

Appl. Phys. Lett. 85, 4663 (2004); http://dx.doi.org/10.1063/1.1814443 (3 pages) | Cited 54 times

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We found an abrupt reduction of contact resistance, Rc, in pentacene bottom-contact thin-film transistors (TFTs) with Au/Ti source/drain (S/D) electrodes when Ti thickness is below ∼3 nm. Our results suggest that the direct ohmic contact with a few molecular layer channel is a key to reduce the Rc of the S/D electrodes. We propose a Au/self-assembled monolayer electrode structure enabling direct ohmic contact with these few molecular layer channels, and achieved high-performance bottom-contact TFTs with an extrinsic mobility of 1.1 cm2∕V s, an on/off ratio of 106, and a subthreshold swing of 0.3 V/decade.

Memory effect from charge trapping in layered organic structures

Sung Hoon Kang, Todd Crisp, Ioannis Kymissis, and Vladimir Bulović

Appl. Phys. Lett. 85, 4666 (2004); http://dx.doi.org/10.1063/1.1819991 (3 pages) | Cited 26 times

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We demonstrate organic light emitting devices (OLEDs) with a charge trap layer that show memory behavior. These OLEDs demonstrate that organic heterojunction structures can controllably trap and release electronic charges. The trap layer is either 5-nm-thick clustered silver islands, or a 10-nm-thick organic laser dye DCM2 ([2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-9-yl)-ethenyl]-4H-pyran-4-ylidene] propane-dinitrile) doped into TPD (N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine). Predictions of the energy band structure indicate that both DCM2 sites and the metal islands can trap charge, consistent with the measured current–voltage characteristics. Trap sites are charged by applying reverse bias over the OLEDs. For devices with DCM2 traps we observe quenching of DCM2 photoluminescence upon charging, which allows us to quantify the charged trap density as approximately 10% of the trap sites or 1018 cm−3. From time resolved measurements we observe that the charge retention time exceeds 2 h.

Silicon doping dependence of highly conductive n-type Al0.7Ga0.3N

K. Zhu, M. L. Nakarmi, K. H. Kim, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 85, 4669 (2004); http://dx.doi.org/10.1063/1.1825055 (3 pages) | Cited 8 times

Online Publication Date: 16 November 2004

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Highly conductive Si-doped n-type Al0.7Ga0.3N alloys were grown by metalorganic chemical vapor deposition on sapphire substrates. Variable temperature Hall-effect measurements have been employed to study the electrical properties for samples with nominal Si dopant concentration (NSi) from 2.6 to 6.8×1019 cm−3. For the sample with NSi=6.0×1019 cm−3, we have achieved n-type resistivity of 0.0075 Ω cm with an electron concentration of 3.3×1019 cm−3 and mobility of 25 cm2∕V s at room temperature. For the same sample, the effective donor (Si) activation energy E0 was determined to be as low as 10 meV. E0 increases to 25 meV as NSi is reduced to 2.6×1019 cm−3, which can be explained by the bandgap renormalization effect. This implies that heavy doping is necessary in high-Al-content AlGaN alloys to bring down the donor activation energy, therefore a higher conductivity.
Show PACS
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.55.Eq III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
73.61.Ey III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Electrical conduction properties of n-type Si-doped AlN with high electron mobility (>100 cm2 V−1 s−1)

Yoshitaka Taniyasu, Makoto Kasu, and Toshiki Makimoto

Appl. Phys. Lett. 85, 4672 (2004); http://dx.doi.org/10.1063/1.1824181 (3 pages) | Cited 37 times

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For n-type Si-doped AlN, we have obtained an electron mobility and concentration of 125 cm2 V−1 s−1 and 1.75×1015 cm−3 at 300 K, respectively. At 250 K, the mobility reached the maximum of 141 cm2 V−1s−1. To explain the temperature dependence of the mobility, we calculated mobilities limited by specific scattering mechanisms. We found that the mobility is limited by neutral impurity scattering rather than ionized impurity scattering or lattice scattering because of a large donor ionization energy (∼250 meV).
Show PACS
73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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