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2 Aug 2004

Volume 85, Issue 5, pp. 701-848

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 807 (2004); http://dx.doi.org/10.1063/1.1777817 (3 pages)

Henry J. Liu and Kyeongjae Cho
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Change of the electrical properties in Fe-Al2O3 granular films

M. A. S. Boff, S. R. Teixeira, J. E. Schmidt, and A. B. Antunes

Appl. Phys. Lett. 85, 757 (2004); http://dx.doi.org/10.1063/1.1775890 (2 pages) | Cited 4 times

Online Publication Date: 27 July 2004

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A systematic study of the electrical resistance as a function of the temperature was performed in Fe-Al2O3 granular thin films. Our findings revealed a nonlinear dependence of the current versus voltage in the low field regime at low temperature. The variable range hopping mechanism is the best description of the behavior of our samples. A change of the electronic properties can be observed depending on the direct current applied to the sample’s plane, and is related to different localization lengths.
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73.61.Ng Insulators
72.20.Ee Mobility edges; hopping transport

Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

T. Makino, Y. Segawa, S. Yoshida, A. Tsukazaki, A. Ohtomo, and M. Kawasaki

Appl. Phys. Lett. 85, 759 (2004); http://dx.doi.org/10.1063/1.1776630 (3 pages) | Cited 68 times

Online Publication Date: 27 July 2004

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We investigated the optical properties of epitaxial n-type ZnO films grown on lattice-matched ScAlMgO4 substrates. As the Ga doping concentration increased up to 6×1020 cm−3, the absorption edge showed a systematic blueshift, consistent with the Burstein–Moss effect. A bright near-band-edge photoluminescence (PL) could be observed even at room temperature, the intensity of which increased monotonically as the doping concentration was increased except for the highest doping level. It indicates that nonradiative transitions dominate at a low doping density. Both a Stokes shift and broadening in the PL band are monotonically increasing functions of donor concentration, which was explained in terms of potential fluctuations caused by the random distribution of donor impurities.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Removal of thick (>100 nm) InGaN layers for optical devices using band-gap-selective photoelectrochemical etching

E. D. Haberer, R. Sharma, A. R. Stonas, S. Nakamura, S. P. DenBaars, and E. L. Hu

Appl. Phys. Lett. 85, 762 (2004); http://dx.doi.org/10.1063/1.1776615 (3 pages) | Cited 24 times

Online Publication Date: 27 July 2004

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We report on band-gap-selective photoelectrochemical (PEC) etching of thick InGaN layers for use in optical devices, such as GaN microdisks, distributed Bragg reflectors, and two-dimensional photonic crystal membranes. Three InGaN sacrificial layer structures are studied: a 300 nm InGaN layer, an InGaN∕GaN superlattice, and an InGaN∕InGaN superlattice. Calculated equilibrium band diagrams of the epitaxial structures are used to explain the observed etching behavior. The strong piezoelectric-induced fields within the InGaN sacrificial layers are found to greatly affect carrier confinement and etching behavior. As a demonstration of the etching technique, a free-standing GaN microdisk on an InGaN post is fabricated.
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68.65.Cd Superlattices
81.65.Cf Surface cleaning, etching, patterning
77.65.-j Piezoelectricity and electromechanical effects
68.55.-a Thin film structure and morphology
82.45.Mp Thin layers, films, monolayers, membranes
64.60.F- Equilibrium properties near critical points, critical exponents
81.30.Dz Phase diagrams of other materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Influence of the hole injection layer on the luminescent performance of organic light-emitting diodes

Shih-Fang Chen and Ching-Wu Wang

Appl. Phys. Lett. 85, 765 (2004); http://dx.doi.org/10.1063/1.1775282 (3 pages) | Cited 39 times

Online Publication Date: 27 July 2004

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We investigate the influence of the hole injection layer (HIL) on the performance of vapor-deposited tris-(8-hydroxyquinoline) aluminum-based organic light-emitting diodes. Four different HIL materials were used: 4,4′, 4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) (m-MTDATA), 4,4′, 4″-tris{N,-(2-naphthyl)-N-phenylamino}-triphenylamine, copper phthalocyanine, and oxotitanium phthalocyanine. In all cases, Alq3 acts as the emitting layer as well as electron-transporting layers. Evidence showed that m-MTDATA exhibits a dense film structure and fine surface morphology, leading to easier hole migration at the indium tin oxide/m-MTDATA and m-MTDATA/hole-transport layer junctions. It also possesses a shallow bulk trap level, providing more detrapping holes from the bulk trap states to highest occupied molecular orbital states for transporting in m-MTDATA. We suggest that these are the main contributing factors to the superior current density–voltage and luminance-voltage performance of this device.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Background charge fluctuation in a GaAs quantum dot device

S. W. Jung, T. Fujisawa, Y. Hirayama, and Y. H. Jeong

Appl. Phys. Lett. 85, 768 (2004); http://dx.doi.org/10.1063/1.1777802 (3 pages) | Cited 25 times

Online Publication Date: 27 July 2004

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We investigate background charge fluctuation in a GaAs quantum dot device by measuring 1∕f noise in the single-electron tunneling current through the dot. The current noise is understood as fluctuations of the confinement potential and tunneling barriers. The estimated potential fluctuation increases almost linearly with temperature, which is consistent with a simple model of the 1∕f noise. We find that the fluctuation increases very slightly when electrons are injected into excited states of the quantum dot.
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85.35.Gv Single electron devices
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
72.70.+m Noise processes and phenomena

Increase of free carrier lifetime in nonpolar a-plane GaN grown by epitaxial lateral overgrowth

S. Juršènas, E. Kuokštis, S. Miasojedovas, G. Kurilčik, A. Žukauskas, C. Q. Chen, J. W. Yang, V. Adivarahan, and M. Asif Khan

Appl. Phys. Lett. 85, 771 (2004); http://dx.doi.org/10.1063/1.1777409 (3 pages) | Cited 7 times

Online Publication Date: 27 July 2004

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Carrier recombination dynamics in epitaxial a-plane GaN and fully coalesced epitaxial laterally overgrown (ELOG) a-plane GaN films has been studied by means of time-resolved photoluminescence under high photoexcitation. The results were compared with conventional c-plane GaN films grown under similar conditions. In a-plane GaN epilayers, the total efficiency of electron-hole plasma spontaneous luminescence decreases 20 times, whereas the luminescence decay time reduces from τLU=42 to τLU⩽10 ps in comparison with c-plane GaN films. Meanwhile, an essential increase in total emission efficiency (by more than two orders of magnitude) and an increase of the decay time up to τLU=430 ps have been observed for an ELOG a-plane sample in comparison with a-plane GaN films. This confirms a significant reduction of the nonradiative recombination rate for nonequilibrium carriers. Assuming a saturation of the nonradiative deep-level transitions, the room-temperature free-carrier lifetime of τ=910 ps for ELOG a-plane GaN sample was obtained, which indicates on an excellent quality of the a-plane ELOG GaN films.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Low-frequency noise in AlSb∕InAs high-electron-mobility transistor structure as a function of temperature and illumination

W. Kruppa, M. J. Yang, B. R. Bennett, and J. B. Boos

Appl. Phys. Lett. 85, 774 (2004); http://dx.doi.org/10.1063/1.1777390 (3 pages) | Cited 8 times

Online Publication Date: 27 July 2004

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Measurements of the low-frequency noise in AlSb∕InAs high-electron-mobility transistor structures over the temperature range between 60 and 300 K are reported. Without illumination, the slope of the noise level with frequency was found to be close to 1∕f with a Hooge parameter, αH, of 9×10−3 at room temperature. With broad-spectrum visible-light illumination at lower temperatures, however, the noise level increases greatly and displays a strong Lorentzian component with the characteristic 1∕f2 slope above the corner frequency. The associated sheet resistance also increases greatly, consistent with previously observed negative photoconductivity in AlSb∕InAs quantum wells.
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85.30.Tv Field effect devices
73.40.Cg Contact resistance, contact potential
72.40.+w Photoconduction and photovoltaic effects
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