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5 Jan 2004

Volume 84, Issue 1, pp. 1-157

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Appl. Phys. Lett. 84, 151 (2004); http://dx.doi.org/10.1063/1.1637950 (3 pages)

M. Feng, N. Holonyak, and W. Hafez
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Effect of acidic and basic surface dipoles on the depletion layer of indium tin oxide as measured by in-plane conductance

A. L. Swint and P. W. Bohn

Appl. Phys. Lett. 84, 61 (2004); http://dx.doi.org/10.1063/1.1638630 (3 pages) | Cited 7 times

Online Publication Date: 30 December 2003

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Four-point probe measurements of indium tin oxide (ITO) films demonstrate the ability to decrease or increase in-plane resistance by surface treatment with acids or bases, respectively. Treatment of ITO surfaces with solutions of varying pH indicates that the degree of protonation or hydroxylation of basic or acidic surface sites, respectively, alters the n-type depletion layer depth and consequently affects the in-plane conductance. Modifying the ITO surface with a series of nearly constant-pH tetraalkylammonium hydroxide species reveals that the in-plane conductance is also modulated by the size of the adsorbed surface dipole layer. The overall change in in-plane conductance upon acid or base treatment is attributed to the net effect of surface charge and adsorbed dipole layer magnitude. Due to the intrinsically high signal–to–noise ratio of the in-plane resistance, these observations have implications for the use of ITO in condensed phase sensing applications. © 2004 American Institute of Physics.
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82.30.Nr Association, addition, insertion, cluster formation
73.61.Ng Insulators

Pulse-induced quantum interference of intersubband transitions in coupled quantum wells

T. Müller, W. Parz, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 84, 64 (2004); http://dx.doi.org/10.1063/1.1638881 (3 pages) | Cited 22 times

Online Publication Date: 30 December 2003

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We report the measurement of the transient intersubband absorption in a coupled quantum well semiconductor structure. Pulsed interband excitation is used to prepare a coherent population in the two lowest states of a three level system of electronic subbands. The time-dependent absorption to the upper state is probed by midinfrared time-domain spectroscopy. For certain pump–probe delay times we observe in the intersubband absorption spectra typical signatures of quantum interference: regions with reduced or enhanced absorption. © 2004 American Institute of Physics.
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73.23.-b Electronic transport in mesoscopic systems
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
73.21.Fg Quantum wells
78.47.-p Spectroscopy of solid state dynamics
78.30.Fs III-V and II-VI semiconductors

Pressure dependence of the fundamental band-gap energy of CdSe

W. Shan, W. Walukiewicz, J. W. Ager, K. M. Yu, J. Wu, and E. E. Haller

Appl. Phys. Lett. 84, 67 (2004); http://dx.doi.org/10.1063/1.1638879 (3 pages) | Cited 18 times

Online Publication Date: 30 December 2003

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Pressure-dependent photomodulation spectroscopic studies of the optical transition associated with the fundamental bandgap of single-crystal bulk CdSe are presented. Photomodulated transmission (PT) measurements were performed at room temperature as a function of applied hydrostatic pressure using the diamond-anvil-cell technique. The sharp, derivative-like PT spectral features corresponding to the band-gap transition in CdSe were found to shift linearly toward higher energy with increasing pressure. By examining the pressure dependence of the PT spectra, the pressure coefficient for the direct band gap of wurtzite CdSe was determined to be 43.1 meV/GPa. The hydrostatic deformation potential of the band gap was found to be −2.3 eV. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Millimeter wave emission from GaN high electron mobility transistor

Yanqing Deng, Roland Kersting, Jingzhou Xu, Ricardo Ascazubi, Xi-Cheng Zhang, Michael S. Shur, Remis Gaska, Grigory S. Simin, M. Asif Khan, and Victor Ryzhii

Appl. Phys. Lett. 84, 70 (2004); http://dx.doi.org/10.1063/1.1638625 (3 pages) | Cited 25 times

Online Publication Date: 30 December 2003

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We report on millimeter wave electromagnetic radiation from a GaN high electron mobility transistor with the gate length of 1.5 μm at 8 K. The emission takes place at gate and drain voltages in the linear regime of operation but close to the saturation voltage with the principal emission peak at approximately 75 GHz, which is much higher than the device cut-off frequency. An explanation of this effect involves the “shallow water” plasma wave instability, with the frequency of the plasma waves decreased by the ungated regions of the device. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology
73.50.Mx High-frequency effects; plasma effects

Photoemission study of hole-injection enhancement in organic electroluminescent devices with Au/CFx anode

J. X. Tang, Y. Q. Li, L. S. Hung, and C. S. Lee

Appl. Phys. Lett. 84, 73 (2004); http://dx.doi.org/10.1063/1.1637945 (3 pages) | Cited 14 times

Online Publication Date: 30 December 2003

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We demonstrate hole-injection enhancement from Au into N,N′-bis-(1-naphyl)-N,N′diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) by inserting between them a plasma-polymerized fluorocarbon (CFx) buffer layer. Ultraviolet and x-ray photoemission spectroscopic study indicates that chemically tailoring the Au surface with CFx can reduce the hole-injection barrier to ∼1 eV with respect to bare Au. This effect is ascribed to the buildup of an interfacial electric field, arising from the molecular dipolar characteristic of CFx. The present results suggest that CFx can function as a hole-injection enhancement layer for organic optoelectronic/electronic devices which use a metallic anode. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Two-photon photoelectron spectroscopy of conjugated polymer thin films on gold

Y. Sohn, J. Richter, J. Ament, and J. Todd Stuckless

Appl. Phys. Lett. 84, 76 (2004); http://dx.doi.org/10.1063/1.1638897 (3 pages) | Cited 9 times

Online Publication Date: 30 December 2003

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We present results for two-photon photoelectron spectroscopy of thin regioregular poly-3-hexyl-thiophene films on a gold metal substrate. The photoemission quantum yields are orders of magnitude larger than that of bare gold at the same laser intensity. Furthermore, we observe a strong increase of the quantum yield with increasing film thickness accompanied by a decreasing yield slope with respect to laser power. Our findings can be understood by assuming the creation of a long-lived intermediate state excitation that couples to the metal surface. This view is further supported by the dependence of the electron kinetic energy spectra on the laser photon energy. © 2004 American Institute of Physics.
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79.60.Fr Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Lateral homogeneity of Schottky contacts on n-type ZnO

H. von Wenckstern, E. M. Kaidashev, M. Lorenz, H. Hochmuth, G. Biehne, J. Lenzner, V. Gottschalch, R. Pickenhain, and M. Grundmann

Appl. Phys. Lett. 84, 79 (2004); http://dx.doi.org/10.1063/1.1638898 (3 pages) | Cited 41 times

Online Publication Date: 30 December 2003

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The electrical properties of Schottky contacts (SCs) produced ex situ on n-type ZnO single crystals and epitaxial thin films were investigated. Electron beam induced current imaging was used to study lateral variations of the current induced in the space charge region of the SC. Further, the effective barrier height was determined by current–voltage and capacitance–voltage measurements. Pd contacts prepared on ZnO thin films that had undergone treatment in a plasma-enhanced chemical vapor deposition with nitrous oxide (N2O) as ambient gas are laterally homogeneous with an effective barrier height of (600±30) meV. © 2004 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
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