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9 Feb 2004

Volume 84, Issue 6, pp. 837-1024

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 975 (2004); http://dx.doi.org/10.1063/1.1646453 (3 pages)

Xiang Yang Kong and Zhong Lin Wang
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Degradation in blue-emitting conjugated polymer diodes due to loss of ohmic hole injection

Rizwan U. A. Khan, Donal D. C. Bradley, Matthew A. Webster, James L. Auld, and Alison B. Walker

Appl. Phys. Lett. 84, 921 (2004); http://dx.doi.org/10.1063/1.1645982 (3 pages) | Cited 25 times

Online Publication Date: 4 February 2004

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We report studies of the evolution of the hole injection and transport characteristics of fluorene-based polymer diodes subjected to electrical stressing. Dark injection (DI) transient measurements show that the polyethylenedioxythiophene/polystyrenesulphonate (PEDOT:PSS)-topolymer contact is initially ohmic, but as stressing proceeds, the transients shift to longer times and lose their characteristic temporal profile. A comparison with time-of-flight transient photocurrent measurements led us to conclude that the DI transient is modified by a loss of ohmic injection. Electroabsorption measurements show a drastic reduction in the built-in potential from 1.4 V to 0.6 V. Device simulation shows this to be consistent with a change in the PEDOT:PSS work function, and the introduction of an interfacial resistance at the PEDOT:PSS-to-polymer contact. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
72.40.+w Photoconduction and photovoltaic effects
78.20.Jq Electro-optical effects
73.40.Cg Contact resistance, contact potential

Effects of pressure on the band structure of highly mismatched Zn1−yMnyOxTe1−x alloys

W. Shan, K. M. Yu, W. Walukiewicz, J. W. Beeman, J. Wu, J. W. Ager, M. A. Scarpulla, O. D. Dubon, and E. E. Haller

Appl. Phys. Lett. 84, 924 (2004); http://dx.doi.org/10.1063/1.1646457 (3 pages) | Cited 3 times

Online Publication Date: 4 February 2004

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We report photomodulation spectroscopy measurements of the pressure dependence of the optical transition in Zn1−yMnyOxTe1−x alloys that is associated with the lowest Γ conduction band (termed E− subband). The pressure-induced energy shift of the E− transition is nonlinear and much weaker as compared to the change of the direct band gap of Zn0.88Mn0.12Te. The weak pressure dependence of the E− transition can be fully understood based on the band anticrossing model in which the E− subband results from an interaction between the extended ZnMnTe conduction-band states and the localized O electronic states. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.23.An Theories and models; localized states
62.50.-p High-pressure effects in solids and liquids
78.20.-e Optical properties of bulk materials and thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Electrical measurements on praseodymium metal to 179 GPa using designer diamond anvils

Nenad Velisavljevic, Kirkland M. MacMinn, Yogesh K. Vohra, and Samuel T. Weir

Appl. Phys. Lett. 84, 927 (2004); http://dx.doi.org/10.1063/1.1645986 (3 pages) | Cited 17 times

Online Publication Date: 4 February 2004

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The electrical and magnetic properties of light rare-earth metals and trans-plutonium actinide metals are of interest to study the f-shell delocalization phenomenon under high compressions. Using designer diamond anvil technology, sensitive electrical four-probe measurements were performed on light rare-earth metal praseodymium to pressures of 179 GPa at room temperature. We document an average drop in resistivity of 53% at a pressure of 20 GPa in a series of high-pressure experiments. This large drop in resistivity provides the strongest experimental evidence yet for the view that the 20 GPa phase transition is indeed associated with f-electron delocalization. Our results show that the precise electrical measurements are ideally suited for f-delocalization studies, especially where structural data do not provide clear evidence of this transition. © 2004 American Institute of Physics.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Rn Localization effects (Anderson or weak localization)
64.70.K- Solid-solid transitions

Organic field effect transistors based on modified oligo-p-phenylevinylenes

T. C. Gorjanc, I. Lévesque, and M. D’Iorio

Appl. Phys. Lett. 84, 930 (2004); http://dx.doi.org/10.1063/1.1639513 (3 pages) | Cited 23 times

Online Publication Date: 4 February 2004

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We report on an organic field effect transistor device based on a modified oligomer oligo-p-phenylevinylene, 1,4-bis[4-(4-octylphenyl)styryl]-benzene. The effect of growth temperature on the morphology of the organic films and their electrical properties was investigated. Substrates coated with hexamethyldisilazane prior to organic film deposition showed improved electrical characteristics, but a negligible difference with respect to film morphology. A maximum hole mobility of μ = 0.12 cm2/V s with an on–off current ratio Ion/off>106 were measured in films deposited at a substrate temperature of 150 °C.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds

Energetic of nitrogen incorporation reactions in SiO2

Walter Orellana

Appl. Phys. Lett. 84, 933 (2004); http://dx.doi.org/10.1063/1.1646466 (3 pages) | Cited 3 times

Online Publication Date: 4 February 2004

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We study using first-principles calculations the energetic, structural and electronic properties of nitrogen incorporation in SiO2. We consider NO, NH, N2 and atomic N as the nitriding species interacting with a Si–Si bond of an otherwise perfect SiO2 network in order to simulate the nitrogen incorporation near Si–SiO2 interface regions. We find that all the species react with the Si–Si bond forming bridge structures with the Si atoms without dissociating, where NH and atomic N form the most stable structures. Concerning the electronic properties, our results show that incorporated NH is the only structure which does not introduce trapping center at the interface. The structures involving NO and atomic N are acceptors, whereas that involving N2 may be either a donor or an acceptor. The hydrogen passivation of the electrically active centers is also discussed. © 2004 American Institute of Physics.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.Rv Passivation
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
68.35.Ct Interface structure and roughness
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