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16 Sep 2002

Volume 81, Issue 12, pp. 2145-2305

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X-ray standing wave microscopy: Chemical microanalysis with atomic resolution

Michael Drakopoulos, Jörg Zegenhagen, Anatoly Snigirev, Irina Snigireva, Maik Hauser, Karl Eberl, Vitalii Aristov, Leonid Shabelnikov, and Vecheslav Yunkin

Appl. Phys. Lett. 81, 2279 (2002); http://dx.doi.org/10.1063/1.1506779 (3 pages) | Cited 12 times

Online Publication Date: 9 September 2002

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We introduce a microprobe technique based on the x-ray standing wave method (XSW) demonstrating that structural analysis can be achieved with chemical sensitivity on a microscopic scale. We apply this XSW microscopy technique to study an epitaxially grown GaAs/Al0.1Ga0.9As/GaAs(001) heterostructure in cross section. We focus the x-ray beam by a refractive lens onto the cleaved sample and analyze the constituent elements within the 4 μm thick Al0.1Ga0.9As layer resolving the substitutional location of Al. The new micro-XSW technique will permit microscopic examinations of the structure of integrated semiconductor devices or microscopic crystalline grains with chemical sensitivity and structural resolution on the pm scale. © 2002 American Institute of Physics.
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07.85.Tt X-ray microscopes
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.37.Yz X-ray microscopy
68.65.Ac Multilayers

Laser-induced surface potential transients observed in III-nitride heterostructures

G. Koley, Ho-Young Cha, C. I. Thomas, and M. G. Spencer

Appl. Phys. Lett. 81, 2282 (2002); http://dx.doi.org/10.1063/1.1506416 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2002

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We report on very long surface potential transients induced by ultraviolet laser illumination, which have been observed in nitride heterostructures. These surface potential transients correlate with current transients when measured simultaneously. Under illumination, electron–hole pairs are generated, which screen the electric field in the AlGaN barrier layer causing the surface potential to decrease. The holes move toward the surface assisted by the electric field in the AlGaN while the electrons increase the sheet charge concentration at the AlGaN/GaN interface, decreasing the net charge dipole across the barrier layer. This reduction can cause the surface potential to vary as much as 1 V between the unilluminated and illuminated states. The long transient response observed after the laser is turned off is explained by the slow recombination of the holes with the electrons thermionically emitted from the potential well at the interface. The thermionic emission is modeled by a continuously varying barrier potential, which results in a stretched exponential-type response. © 2002 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
73.20.At Surface states, band structure, electron density of states
73.25.+i Surface conductivity and carrier phenomena
79.40.+z Thermionic emission
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects

Bright electroluminescence from a conjugated dendrimer

Dongge Ma, J. M. Lupton, I. D. W. Samuel, Shi-Chun Lo, and P. L. Burn

Appl. Phys. Lett. 81, 2285 (2002); http://dx.doi.org/10.1063/1.1507826 (3 pages) | Cited 15 times

Online Publication Date: 9 September 2002

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Show Abstract
Photoluminescence and electroluminescence (EL) from a conjugated dendrimer consisting of three distyrylbenzene units linked by a central nitrogen atom as core and meta-linked biphenyl units as dendrons were investigated. The conjugated dendrimer emits green light and shows photoluminescence quantum efficiency of 9%. Bright electroluminescence was realized by using bilayer devices with blurred interface, which were fabricated by sequentially spin coating a neat dendrimer and a dendrimer doped with 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). The devices have the following structure: indium tin oxide/3,4-polyethylenedioxythiothene-polystyrenesulfonate/dendrimer/ dendrimer:PBD/Al. By optimizing the concentration of PBD, the maximum brightness and EL quantum efficiency reach 4100 cd/m2 and 0.17%, respectively. This is the best result reported so far on organic light-emitting diodes using dendrimer as an active material with an Al cathode. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
42.70.Jk Polymers and organics
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