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27 Dec 1999

Volume 75, Issue 26, pp. 4049-4210

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Impurity states are the origin of yellow-band emission in GaN structures produced by epitaxial lateral overgrowth

X. Li, P. W. Bohn, and J. J. Coleman

Appl. Phys. Lett. 75, 4049 (1999); http://dx.doi.org/10.1063/1.125532 (3 pages) | Cited 19 times

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GaN grown by selective area epitaxy and subsequent lateral overgrowth exhibits sharply peaked anisotropic structures in the form of hexagonal pyramids and ridges. Spatially resolved optical emission from these structures, using both cathodoluminescence and collection-mode near-field scanning optical microscopy, of radiation centered near 550 nm, the so-called yellow band, indicates that the emission arises predominantly from the apex regions of the pyramids and ridges. In contrast, transmission electron microscopy shows that the apex region is nearly dislocation free and that dislocations cluster at the vertical growth core region. The spatial separation of the dislocations and optical emission indicates that the yellow-band emission has no direct relationship to dislocations. The observation of yellow-band emission strongly localized in the apical regions of both types of structures and the tendency of impurity species to concentrate in these areas argues that it arises instead from impurity states, the most likely candidate of which is a complex formed between a gallium vacancy, VGa, and Si or O. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
71.55.Eq III-V semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

AlGaInP-based microcavity light-emitting diodes: Controlled on-wafer detuning and measurement of the internal quantum efficiency

P. Royo, R. P. Stanley, R. Houdré, M. Ilegems, M. Moser, R. Hövel, H. P. Schweizer, and K. H. Gulden

Appl. Phys. Lett. 75, 4052 (1999); http://dx.doi.org/10.1063/1.125533 (3 pages) | Cited 5 times

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We present results on visible red top-emission microcavity light-emitting diodes grown by metal organic chemical vapor deposition. The emission characteristics dependence with respect to the detuning between the quantum well emission and the cavity mode was experimentally investigated. The detuning was varied during growth by 60 nm across a 2 in. wafer radius according to a parabolic and reproducible dependence with respect to the position on the wafer. Numerical simulation reproduced very well the experimental results using the internal quantum efficiency ηint as a fitting parameter, resulting in a value of ηint = 56%+/−5% at a current density of 20 A/cm2. © 1999 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.)

Reduction of molecular aggregation and its application to the high-performance blue perylene-doped organic electroluminescent device

B. X. Mi, Z. Q. Gao, C. S. Lee, S. T. Lee, H. L. Kwong, and N. B. Wong

Appl. Phys. Lett. 75, 4055 (1999); http://dx.doi.org/10.1063/1.125534 (3 pages) | Cited 33 times

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A nonplanar derivative of perylene, 2,5,8,11-tetra-tertbutylperylene (TBPe), was synthesized via the Friedel–Crafts alkylation reaction. Electroluminescent (EL) devices were made using TBPe or perylene as a dopant in bis(2-methyl-8-quinolinolato)(para-phenylphenolato)aluminum(III) and their EL performance was compared. Similar to the device doped with the parent perylene molecule, the device doped with TBPe also emitted strongly in the blue. As the concentration of TBPe increased from 1% to 5%, the color coordinates in CIE 1931 chromaticity of the TBPe-doped device changed only slightly from (0.168,0.273) to (0.175,0.273), whereas the perylene-doped device exhibited a much larger shift from (0.165,0.196) to (0.178,0.252). The constancy of EL color and efficiency with respect to TBPe dopant concentration is attributable to diminishing molecular aggregation in the nonplanar perylene derivative, TBPe, due to the steric hindrance of the tert-butyl groups. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
82.30.-b Specific chemical reactions; reaction mechanisms
64.75.-g Phase equilibria

Evanescent field imaging of an optical fiber Bragg grating

J. D. Mills, C. W. J. Hillman, W. S. Brocklesby, and B. H. Blott

Appl. Phys. Lett. 75, 4058 (1999); http://dx.doi.org/10.1063/1.125535 (3 pages) | Cited 3 times

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We have investigated the evanescent field associated with an optical fiber Bragg grating using the subwavelength imaging properties of scanning near-field optical microscopy. Imaging of either the field distribution within the grating, or the periodic refractive index changes along the grating can be performed by tuning the launched light on or off the grating resonance. These measurements reveal nonuniformity in the resonant standing-wave pattern that occur due to phase errors in the refractive index profile of the grating under study. © 1999 American Institute of Physics.
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42.79.Dj Gratings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
07.79.Fc Near-field scanning optical microscopes
42.81.Cn Fiber testing and measurement of fiber parameters

Feasibility of transmission x-ray microscopy at 4 keV with spatial resolutions below 150 nm

B. Kaulich, S. Oestreich, M. Salome, R. Barrett, J. Susini, T. Wilhein, E. Di Fabrizio, M. Gentili, and P. Charalambous

Appl. Phys. Lett. 75, 4061 (1999); http://dx.doi.org/10.1063/1.125536 (3 pages) | Cited 11 times

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The feasibility of a transmission x-ray microscope operating in the 3-7 keV photon energy range using phase zone plates (ZPs) has been tested. It has been demonstrated that, at a photon energy of 4 keV, structures smaller than 150 nm can be resolved with good contrast using exposure times in the second to minute range. A large diameter gold ZP was used as condenser and a tungsten ZP with an outermost zone width of 128 nm was used as a high spatial resolution imaging objective lens. Images with a field size of 10×10 μm2 were acquired using a charge coupled device camera optically coupled to a phosphor screen. The corresponding pixel size in the object plane was 70 nm. © 1999 American Institute of Physics.
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07.85.Tt X-ray microscopes

Realization of numerical aperture 2.0 using a gallium phosphide solid immersion lens

Qiang Wu, G. D. Feke, Robert D. Grober, and L. P. Ghislain

Appl. Phys. Lett. 75, 4064 (1999); http://dx.doi.org/10.1063/1.125537 (3 pages) | Cited 41 times

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We report a study of a gallium phosphide, hemispherical, solid immersion lens through the imaging of 40-nm-diam fluorescent dye balls. A spatial resolution as small as 139 nm has been achieved at a wavelength of 560 nm, which is equivalent to a diffraction-limited system of numerical aperture 2.0. This resolution is a 33% improvement over conventional oil immersion objectives and previously reported solid immersion lenses, which typically have a numerical aperture around 1.5. © 1999 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Optical signal inversion phenomenon for 1.53 μm laser in an erbium-doped lithium niobate

Yoshinobu Maeda, Hirotoshi Nagata, Taizou Nakashima, Junichiro Ichikawa, and Kaoru Higuma

Appl. Phys. Lett. 75, 4067 (1999); http://dx.doi.org/10.1063/1.125538 (3 pages)

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Modulation characteristics of a negative nonlinear absorption effect were investigated in 3 wt % erbium-doped lithium niobate using a 1530 nm laser diode. With a decreasing incident modulation degree, a reversed-phase waveform was obtained in the transmitted laser at modulation degrees smaller than 85% for a sample length of 14 mm. The reversed-phase transmitted waveforms were observed at modulation frequencies from 1 kHz to 10 GHz. The negative nonlinear absorption effect for 1.5 μm can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion. © 1999 American Institute of Physics.
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42.65.-k Nonlinear optics
42.60.Fc Modulation, tuning, and mode locking

Carrier-induced Er3+ luminescence quenching of erbium-doped silicon-rich silicon oxide

Se-young Seo and Jung H. Shin

Appl. Phys. Lett. 75, 4070 (1999); http://dx.doi.org/10.1063/1.125539 (3 pages) | Cited 22 times

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The quenching of Er3+ luminescence induced by carriers in silicon nanoclusters of Er-doped silicon-rich silicon oxide (SRSO) is investigated. The dependence of Er3+ photoluminescence intensities and lifetimes upon the temperature, pump power, and the background illumination intensity shows that in SRSO, Auger-type interactions with carriers in the host matrix that can severely limit the Er3+ luminescence efficiency are greatly suppressed. The results also show that efficient optoelectronic devices using Er-doped SRSO may be feasible. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
71.35.Gg Exciton-mediated interactions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

The role of Er3+–Er3+ separation on the luminescence of Er–doped Al2O3 films prepared by pulsed laser deposition

R. Serna, M. Jiménez de Castro, J. A. Chaos, C. N. Afonso, and I. Vickridge

Appl. Phys. Lett. 75, 4073 (1999); http://dx.doi.org/10.1063/1.125540 (3 pages) | Cited 17 times

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Erbium-doped Al2O3 films have been deposited in a single step process by pulsed laser deposition using independent ablation of Al2O3 and Er targets. This procedure allows to control the Er3+ ions in-depth distribution. The characteristic Er3+ photoluminescence at 1.54 μm shows lifetime values which increase from 6.0 to 7.1 ms when the Er3+–Er3+ in-depth separation is increased from 3 to 9 nm. These results are discussed in terms of the ion–ion interaction and clustering for separations shorter than 6 nm. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.15.Fg Pulsed laser ablation deposition
78.66.Nk Insulators
71.55.Ht Other nonmetals

Nonuniform silicon oxidation and application for the fabrication of aperture for near-field scanning optical microscopy

Phan Ngoc Minh, Takahito Ono, and Masayoshi Esashi

Appl. Phys. Lett. 75, 4076 (1999); http://dx.doi.org/10.1063/1.125541 (3 pages) | Cited 20 times

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In this letter, a technological approach for the fabrication of a miniature aperture for near-field scanning optical microscopy using silicon micromachining technology is described. The aperture with diameter sizes from 10 to 500 nm at the apex of a SiO2 tip on a Si cantilever is fabricated using a “Low temperature Oxidation & Selective Etching” technique. The SiO2 tip is formed by nonuniform Si wet oxidation at 950 °C with a thickness of about 1 μm. The aperture is created by selective etching SiO2 in a buffered-HF (50% HF:40% NH4F, 9cc:100cc) solution at 36 °C using a thin chromium (Cr) layer deposited on the oxidized sample as a mask. Using the fabricated probe, atomic force microscopy and corresponding near-field scanning optical microscopy images of 300 nm diameter latex spheres on mica substrate are obtained. © 1999 American Institute of Physics.  
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
07.79.Fc Near-field scanning optical microscopes
81.65.Cf Surface cleaning, etching, patterning
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
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