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21 Jan 2002

Volume 80, Issue 3, pp. 341-531

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Blue light-emitting devices from new conjugated poly(N-substituted-2,7-carbazole) derivatives

Jean-François Morin, Serge Beaupré, Mario Leclerc, Isabelle Lévesque, and Marie D’Iorio

Appl. Phys. Lett. 80, 341 (2002); http://dx.doi.org/10.1063/1.1433917 (3 pages) | Cited 44 times

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Light-emitting diodes derived from a new class of conjugated polymers, well-defined poly(N-substituted-2,7-carbazole) derivatives, are reported. Excimer-free electroluminescence in the blue range (424–432 nm) was observed. Good luminance (372 cd/m2 at 10 V) was reached in a device containing poly[N-(2-ethylhexyl)-2,7-carbazole] as the emitting material with indium tin oxide and Al as the electrodes. This high luminance value was achieved by adding ultrathin LiF layers next to the electrodes, and by using hole and electron transport molecules such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine and 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices

Growth-temperature dependence of Er-doped GaN luminescent thin films

D. S. Lee, J. Heikenfeld, and A. J. Steckl

Appl. Phys. Lett. 80, 344 (2002); http://dx.doi.org/10.1063/1.1434312 (3 pages) | Cited 6 times

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Visible photoluminescence (PL) and electroluminescence (EL) emission has been observed from Er-doped GaN thin films grown on (111) Si at various temperatures from 100 to 750 °C in a radio-frequency plasma molecular beam epitaxy system. PL and EL intensities of green emission at 537 nm from GaN:Er films exhibited strong dependence on the growth temperature, with a maximum at 600 °C. Scanning electron and atomic force microscopy showed smooth surfaces at 600 °C and rough surfaces at 100 and 750 °C. X-ray diffraction indicated that the GaN:Er film structure was oriented with the c axis perpendicular to the substrate for all growth temperatures. The crystalline quality initially improves with an increase in growth temperature, and saturates at ∼500 °C. Considering both the luminescence and structural properties of the film, ∼600 °C seems to be the optimal temperature for growth of Er-doped GaN luminescent films on Si substrates. © 2002 American Institute of Physics.
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78.60.Fi Electroluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
68.55.A- Nucleation and growth
81.05.Ea III-V semiconductors

Anisotropy in detectivity of GaN Schottky ultraviolet detectors: Comparing lateral and vertical geometry

O. Katz, V. Garber, B. Meyler, G. Bahir, and J. Salzman

Appl. Phys. Lett. 80, 347 (2002); http://dx.doi.org/10.1063/1.1433910 (3 pages) | Cited 26 times

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Vertical and lateral geometry GaN-based Schottky barrier photodetectors have been implemented, using similar quality material and the same fabrication process. The vertical detector exhibits two orders of magnitude higher responsivity. This is attributed to improved ohmic backcontacts, due to the highly doped buried layer. The vertical detectors exhibits also lower 1/f noise level, which is attributed to the reduced effect of dislocations on the carrier transport, resulting in lower mobility fluctuations. The vertical detector normalized detectivity is four orders of magnitude higher. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

High differential efficiency (>16%) quantum dot microcavity light emitting diode

H. Chen, Z. Zou, C. Cao, and D. G. Deppe

Appl. Phys. Lett. 80, 350 (2002); http://dx.doi.org/10.1063/1.1434310 (3 pages) | Cited 11 times

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Data are presented on high differential efficiency quantum dot microcavity light emitting diodes. The data show that differential efficiencies >16% can be achieved by the use of quantum dots to reduce carrier diffusion in small oxide-apertured microcavities. The measured efficiencies are sensitive to both microcavity tuning of the resonance peak to the quantum dot light emitters, and nonradiative recombination effects brought on by temperature, bias current, and edge effects. The peak efficiencies are obtained at a resonance temperature of ∼ 160 K. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.Hc Quantum dots
85.30.De Semiconductor-device characterization, design, and modeling

Laser ablation of dielectrics with temporally shaped femtosecond pulses

R. Stoian, M. Boyle, A. Thoss, A. Rosenfeld, G. Korn, I. V. Hertel, and E. E. B. Campbell

Appl. Phys. Lett. 80, 353 (2002); http://dx.doi.org/10.1063/1.1432747 (3 pages) | Cited 51 times

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A significant improvement in the quality of ultrafast laser microstructuring of dielectrics is demonstrated by using temporally shaped pulse trains with subpicosecond separation. The sequential energy delivery induces a material softening during the initial steps of excitation changing the energy coupling for the subsequent steps. This leads to lower stress, cleaner structures, and provides a material-dependent optimization process. © 2002 American Institute of Physics.
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52.38.Mf Laser ablation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
79.20.Ds Laser-beam impact phenomena

Two-photon-excited green emission and its dichroic shift of oriented thin-film CdS on glass formed by laser deposition

B. Ullrich, R. Schroeder, H. Sakai, A. Zhang, and S. Z. D. Cheng

Appl. Phys. Lett. 80, 356 (2002); http://dx.doi.org/10.1063/1.1432756 (3 pages) | Cited 4 times

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The photoluminescence of oriented thin-film CdS on glass formed by laser deposition was investigated employing 200 fs, 1.54 eV laser pulses at room temperature. The ultrafast excitation caused a two-photon absorption process, which results in purely green emission at the band gap. The spectra are fitted very well by the application of the van Roosbroeck–Shockley relation, density of states, and Urbach’s rule demonstrating the intrinsic character of the radiative recombination. It is further shown that the energy position of the emission peak depends on the polarization of the impinging laser beam due to the dichroism of the highly oriented films. © 2002 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
78.20.Fm Birefringence

Photoinduced permanent gratings inside bulk azodye-doped polymers by the coherent field of a femtosecond laser

Jinhai Si, Jianrong Qiu, Jianfeng Zhai, Yuquan Shen, and Kazuyuki Hirao

Appl. Phys. Lett. 80, 359 (2002); http://dx.doi.org/10.1063/1.1435808 (3 pages) | Cited 35 times

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Permanent holographic gratings were fabricated in bulk azodye-doped polymethylmethacrylate by the coherent field of a femtosecond laser. Optical microscopy and atomic force microscopy observations revealed that the gratings consist of two parts, surface relief gratings on both surfaces and refractive index modulated volume gratings in the interior of the polymers. The diffraction efficiency of the first-order Bragg for the gratings was estimated to be 90%. © 2002 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Jk Polymers and organics

Organic bistable light-emitting devices

Liping Ma, Jie Liu, Seungmoon Pyo, and Yang Yang

Appl. Phys. Lett. 80, 362 (2002); http://dx.doi.org/10.1063/1.1436274 (3 pages) | Cited 64 times

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An organic bistable device, with a unique trilayer structure consisting of organic/metal/organic sandwiched between two outmost metal electrodes, has been invented. [Y. Yang, L. P. Ma, and J. Liu, U.S. Patent Pending, U.S. 01/17206 (2001)]. When the device is biased with voltages beyond a critical value (for example 3 V), the device suddenly switches from a high-impedance state to a low-impedance state, with a difference in injection current of more than 6 orders of magnitude. When the device is switched to the low-impedance state, it remains in that state even when the power is off. (This is called “nonvolatile” phenomenon in memory devices.) The high-impedance state can be recovered by applying a reverse bias; therefore, this bistable device is ideal for memory applications. In order to increase the data read-out rate of this type of memory device, a regular polymer light-emitting diode has been integrated with the organic bistable device, such that it can be read out optically. These features make the organic bistable light-emitting device a promising candidate for several applications, such as digital memories, opto-electronic books, and recordable papers. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Vb Optical storage systems, optical disks
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