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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 32 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 38 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 21 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 15 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 19 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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Greatly enhanced soft x-ray generation from femtosecond-laser-produced plasma by using a nanohole-alumina target

Tadashi Nishikawa, Hidetoshi Nakano, Naoshi Uesugi, Masashi Nakao, and Hideki Masuda

Appl. Phys. Lett. 75, 4079 (1999); http://dx.doi.org/10.1063/1.125542 (3 pages) | Cited 16 times

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By making an array of nanoholes on an alumina target, x-ray emission from laser-produced plasma can be greatly enhanced even in soft x-ray energy regions (<0.25 keV). X-ray fluence enhancement around 30 times was achieved in the 5–25 nm wavelength range. The enhancement increases as the ionization level of Al becomes higher and the x-ray wavelength becomes shorter. Over 50-fold enhancement was obtained at a soft x-ray wavelength around 6 nm, which corresponds to the emission from Al8+,9+ ions. X-ray pulse duration was 17 ps, which is much shorter than that obtained by using the prepulse technique. © 1999 American Institute of Physics.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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Nanometer-scale studies of Al–Ga interdiffusion and As precipitate coarsening in nonstoichiometric AlAs/GaAs superlattices

B. Lita, Smita Ghaisas, R. S. Goldman, and M. R. Melloch

Appl. Phys. Lett. 75, 4082 (1999); http://dx.doi.org/10.1063/1.125543 (3 pages) | Cited 5 times

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We have investigated the effects of post-growth annealing on Al–Ga interdiffusion and As precipitate coarsening in AlAs/GaAs superlattices grown by molecular-beam epitaxy at low temperatures. High-resolution x-ray diffraction spectra show a significant decrease in the number and intensity of satellite peaks for the ex situ annealed compared with the as-grown superlattices, a feature which is often attributed to a reduction in interface abruptness. However, our cross-sectional scanning tunneling microscopy images show significant variation in the apparent superlattice period of the ex situ annealed compared with the as-grown superlattices. For the as-grown superlattices, preferential As precipitation on the GaAs side of AlAs/GaAs interfaces is evident. In the ex situ annealed superlattices, a preference for As precipitates at the GaAs on AlAs interface is apparent, although the As precipitates are no longer restricted to the interface region. Thus, the apparent change in superlattice period is likely due to variations in As precipitate density, which may be influenced by AlAs–GaAs alloying at the AlAs/GaAs interfaces. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing
68.35.Ct Interface structure and roughness
66.30.Ny Chemical interdiffusion; diffusion barriers

Carbon-related defects in proton-irradiated, n-type epitaxial Si1−xGex

T. P. Leervad Pedersen, A. Nylandsted Larsen, and A. Mesli

Appl. Phys. Lett. 75, 4085 (1999); http://dx.doi.org/10.1063/1.125544 (3 pages) | Cited 12 times

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Ci and CiCs defects, created by proton irradiation of n-type, strain-relaxed, epitaxial Si1−xGex of 0.005 ⩽ x ⩽ 0.5, have been studied using deep-level transient spectroscopy (DLTS). The ionization enthalpies of the two defects relative to the conduction band edge, ΔH, are found to increase linearly with increasing Ge content. It is shown that the corresponding levels are not pinned to any of the band edges. Furthermore, it is shown that, for both defects, the slopes, δΔH/δx, as well as the full width at half maximum (FWHM) of the corresponding DLTS peaks, are similar. These observations are in agreement with conclusions deduced from previous electron-paramagnetic resonance (EPR) measurements in pure silicon, stating that, for both defects, the trapped electron is preferentially located at the Ci atom because of its larger electronegativity as compared to those of silicon and germanium. The anneal temperature of the Ci defect, and correspondingly the in-growth temperature of the CiCs complex, increase with increasing Ge content. This is equivalent to an increasing retardation of the diffusion of Ci in Si1−xGex with increasing Ge content. © 1999 American Institute of Physics.
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71.55.Ht Other nonmetals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing

Thermal stability of supersaturated MgxZn1−xO alloy films and MgxZn1−xO/ZnO heterointerfaces

A. Ohtomo, R. Shiroki, I. Ohkubo, H. Koinuma, and M. Kawasaki

Appl. Phys. Lett. 75, 4088 (1999); http://dx.doi.org/10.1063/1.125545 (3 pages) | Cited 47 times

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We have examined the thermal stability of wurtzite-phase MgxZn1−xO alloy films and ZnO/MgxZn1−xO bilayer films with x exceeding the reported solubility limit of 0.04. When a Mg0.23Zn0.78O film was annealed, the segregation of MgO started at 850 °C and the band gap was reduced to the value of that for an x = 0.15 film after annealing at 1000 °C. Mg0.15Zn0.85O films showed no change of the band gap even after annealing at 1000 °C. Therefore, we conclude that the thermodynamic solubility limit of MgO in MgxZn1−xO epitaxial film is about x = 0.15. The thermal diffusion of Mg across the MgxZn1−xO/ZnO interface was observed only after annealing above 700 °C. Unlike other II–VI semiconductors, ZnO-based alloy films and heterointerfaces are stable enough for the fabrication of high-crystallinity heterostructures. © 1999 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.35.Md Surface thermodynamics, surface energies
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing
78.40.Fy Semiconductors
78.66.Hf II-VI semiconductors
71.20.Nr Semiconductor compounds
68.55.-a Thin film structure and morphology
66.30.Ny Chemical interdiffusion; diffusion barriers

The role of particle energy and pulsed particle flux in physical vapor deposition and pulsed–laser deposition

Stefan G. Mayr, Michael Moske, Konrad Samwer, Maggie E. Taylor, and Harry A. Atwater

Appl. Phys. Lett. 75, 4091 (1999); http://dx.doi.org/10.1063/1.125546 (3 pages) | Cited 10 times

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Surface morphology evolution of thin films generated by physical and pulsed-laser deposition depending on the incident particle energy and the pulse rate is investigated using a continuum growth model. The model includes curvature-induced surface diffusion, the Schwoebel barrier and surface atom displacement as main surface processes. The numerical solution of the model is in very good agreement with the results of kinetic Monte Carlo simulations, which also serve to estimate the continuum growth parameters, and with experimental results on thin Si films. The increase of the incident particle energy, starting from thermal energy, fundamentally influences the surface topography, changing from self-affine to self-organized morphology. © 1999 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation

Strong photoluminescence from monosubstituted polyacetylenes containing biphenylyl chromophores

Yuan Ming Huang, Weikun Ge, Jacky W. Y. Lam, and Ben Zhong Tang

Appl. Phys. Lett. 75, 4094 (1999); http://dx.doi.org/10.1063/1.125547 (3 pages) | Cited 17 times

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Monosubstituted polyacetylenes are generally regarded as unlikely candidates for photoluminescent materials. We have, however, observed intense deep-blue emission in a series of photoexcited poly(1–alkynes) (PAs) containing biphenylyl pendants (–{HC=C[(CH2)m–OCO–biphenyl–OC7H15]}n–where m = 2, 3, 4, and 9). The photoluminescence (PL) is readily observable by naked eyes under normal room illumination conditions, whose integrated intensity is threefold higher than that of poly(1–phenyl–1–butyne), a well-known highly luminescent disubstituted polyacetylene. A red PL band has also been detected in the PAs. Using the extended-Hückel-tight-binding method, we have calculated the density of states of the PAs, and it is found that the functional pendants have dramatically modified the band states of polyacetylene. The strong PL of the PAs is satisfactorily explained by the engineered electronic structures. © 1999 American Institute of Physics.
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42.70.Jk Polymers and organics
78.55.Mb Porous materials
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Rv Polymers and organic compounds

Local structures of free-standing AlxGa1−xN thin films studied by extended x-ray absorption fine structure

Kin Man Yu, W. Shan, C. J. Glover, M. C. Ridgway, William S. Wong, and W. Yang

Appl. Phys. Lett. 75, 4097 (1999); http://dx.doi.org/10.1063/1.125548 (3 pages) | Cited 5 times

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Local structural information for the first two atomic shells surrounding Ga atoms in free standing AlxGa1−xN alloy films has been obtained by extended x-ray absorption fine structure spectroscopy. For an AlN mole fraction ranging from 0 to 0.6, we found that the first shell Ga–N bond length had only a weak composition dependence, roughly one quarter of that predicted by Vegard’s Law. In the second shell, the Ga–Ga bond length was significantly longer than that of Ga–Al (Δ ∼ 0.04–0.065 Å). A bond-type specific composition dependence was observed for the second shell cation–cation distances. While the composition dependence of the Ga–Ga bond length is ∼70% of that predicted by Vegard’s Law, the Ga–Al bond length was essentially composition independent. These results suggested that local strain in AlxGa1−xN was also accommodated by lattice distortion in the Al cation sublattice. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
78.70.Dm X-ray absorption spectra

Photoemission spectroscopy and velocity analysis of sputtered carbon atoms, ions, and clusters Cm0,± (m ⩽ 4)

Abdul Qayyum, M. Naeem Akhtar, Tasneem Riffat, and Shoaib Ahmad

Appl. Phys. Lett. 75, 4100 (1999); http://dx.doi.org/10.1063/1.125549 (3 pages) | Cited 4 times

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Diagnostics of the carbon atoms, ions, and clusters Cm0,± (m ⩽ 4) sputtered from a graphite surface under 10 keV Xe+ bombardment reveals the presence of neutral Cm0 and positively charged Cm+ species in the photoemission spectra. The complete absence of Cm+ in the mass spectra by a velocity analyzer is supplemented by the presence of the negatively charged Cm−. The velocity spectra are dominated by C and C2− with peaks due to C3− and C4−. These results may help us to understand the contribution of neutral and charged species in the heavy-ion sputtering of graphite and the energetics of regenerative soot. © 1999 American Institute of Physics.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
36.40.Mr Spectroscopy and geometrical structure of clusters

Size-dependent second-harmonic generation by nanocrystals prepared by plasma-enhanced chemical-vapor deposition

D. Milovzorov and T. Suzuki

Appl. Phys. Lett. 75, 4103 (1999); http://dx.doi.org/10.1063/1.125550 (3 pages) | Cited 8 times

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The second-harmonic generation (SHG) from silicon nanocrystallites in polycrystalline films prepared by low-temperature plasma-enhanced chemical-vapor deposition has been studied. We observed an increase in the SHG signal due to the quantum-size effect and shape distortion by decrease in the sizes of crystallites. It was shown that the resonant SHG spectra have a size-dependent fine structure. Also, the power dependence of the SHG response from polycrystalline silicon films was investigated. © 1999 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Vs Fine-particle systems
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
61.46.-w Structure of nanoscale materials

Strain relief and its effect on the properties of GaN using isoelectronic In doping grown by metalorganic vapor phase epitaxy

Shigeo Yamaguchi, Michihiko Kariya, Shugo Nitta, Hiroshi Amano, and Isamu Akasaki

Appl. Phys. Lett. 75, 4106 (1999); http://dx.doi.org/10.1063/1.125551 (3 pages) | Cited 25 times

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We studied the effect of isoelectronic In doping on the crystalline and optical properties of GaN grown on sapphire with H2 or N2 carrier gas by metalorganic vapor phase epitaxy. The relationship between lattice constants c and a obtained by x-ray diffraction analysis showed that with increasing trimethylindium (TMI) flow during growth, the strain in GaN decreased, and accordingly, the tilting and the twisting components of crystalline mosaicity also decreased. In addition, the Raman shift, the excitonic photoluminescence peak energy, and the its linewidth shifted in accordance with the magnitude and the sign of the strain in GaN, regardless of the carrier gas used. These results revealed that for a smaller TMI flow region, In was incorporated so that the crystallinity of GaN improved, and for a larger TMI flow region, In substituted for Ga so that alloying formation might have occurred. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.60.Bs Mechanical and acoustical properties
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.30.Fs III-V and II-VI semiconductors
71.35.-y Excitons and related phenomena

Crystal tilting in GaN grown by pendoepitaxy method on sapphire substrate

Ig-Hyeon Kim, C. Sone, Ok-Hyun Nam, Yong-Jo Park, and Taeil Kim

Appl. Phys. Lett. 75, 4109 (1999); http://dx.doi.org/10.1063/1.125552 (3 pages) | Cited 25 times

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Pendeoepitaxy of GaN on sapphire substrate with SiO2 mask is demonstrated and characterized by transmission electron microscopy and double crystal x-ray diffraction. A continuous layer of GaN with low dislocation density was achieved by this method. Parts of the GaN layer are tilted symmetrically toward [11-20] direction and have two kinds of coalesce and tilt boundaries. Each boundary was formed by a vertical array of piled up dislocations with the Burger’s vector of [11-20]. The tilting mechanism in pendeo-epitaxy is discussed in terms of surface interaction between the SiO2 mask and ELO-GaN. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Highly nonlinear photoluminescence threshold in porous silicon

M. Nayfeh, O. Akcakir, J. Therrien, Z. Yamani, N. Barry, W. Yu, and E. Gratton

Appl. Phys. Lett. 75, 4112 (1999); http://dx.doi.org/10.1063/1.125553 (3 pages) | Cited 35 times

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Porous silicon is excited using near-infrared femtosecond pulsed and continuous wave radiation at an average intensity of ∼ 106 W/cm2 (8×1010 W/cm2 peak intensity in pulsed mode). Our results demonstrate the presence of micron-size regions for which the intensity of the photoluminescence has a highly nonlinear threshold, rising by several orders of magnitude near this incident intensity for both the pulsed and continuous wave cases. These results are discussed in terms of stimulated emission from quantum confinement engineered intrinsic Si–Si radiative traps in ultrasmall nanocrystallites, populated following two-photon absorption. © 1999 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.45.+h Stimulated emission
78.47.-p Spectroscopy of solid state dynamics
42.65.-k Nonlinear optics

Transmission electron microscopy study of the nitridation of the (0001) sapphire surface

P. Vennéguès and B. Beaumont

Appl. Phys. Lett. 75, 4115 (1999); http://dx.doi.org/10.1063/1.125554 (3 pages) | Cited 15 times

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The purpose of this letter is to study, using transmission electron microscopy, the nitridation of the (0001) sapphire surface which is a key step for the fabrication of high-quality GaN materials. A nitridation conducted at 1080 °C during 7 min at atmospheric pressure with a 2 slm NH3 flow, results in the formation of a fully crystalline 10-atomic-planes-thick AlN film by the chemical transformation of the Al2O3 surface. From measurements of interplanar distances in high-resolution images, we show that this chemical transformation is incomplete, i.e., that a few Al vacancies and/or O atoms remain in the AlN structure. © 1999 American Institute of Physics.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.35.Dv Composition, segregation; defects and impurities
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters

GeSi films with reduced dislocation density grown by molecular-beam epitaxy on compliant substrates based on porous silicon

S. I. Romanov, V. I. Mashanov, L. V. Sokolov, A. Gutakovskii, and O. P. Pchelyakov

Appl. Phys. Lett. 75, 4118 (1999); http://dx.doi.org/10.1063/1.125555 (3 pages) | Cited 15 times

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To grow high-quality heteroepitaxial layers, we propose a compliant silicon substrate consisting of a thin epitaxial silicon film on a high-density porous layer as a membrane and an expansive low-density porous layer as a mechanical damper which shields the overlying layers from the massive wafer. GeSi films over the critical thickness have been grown by molecular-beam epitaxy on these substrates. Transmission electron microscopy analysis shows that Ge0.2Si0.8 films have no dislocations owing to just elastic strain relaxation whereas plastic flow in the pseudomorphic films that are being grown on conventional Si substrates occurs with generation of dislocations in a regular manner. The experimental data on porous silicon structure are presented in some detail and are briefly discussed in connection with substrate compliance. © 1999 American Institute of Physics.
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81.05.Hd Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
62.20.F- Deformation and plasticity
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Direct spectral probing of energy storage in Si:Er by a free-electron laser

T. Gregorkiewicz, D. T. X. Thao, and J. M. Langer

Appl. Phys. Lett. 75, 4121 (1999); http://dx.doi.org/10.1063/1.125556 (3 pages) | Cited 17 times

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Results of a two-color spectroscopy in the visible and the mid-infrared on erbium-doped silicon (Si:Er) are presented. In the experiments, pulsed beam provided by a free-electron laser is directed on a sample under primary above-band-gap excitation with another laser. It is shown that the powerful infrared beam can be ionize carriers localized at shallow traps. Liberation of these carriers makes them available for excitation of erbium and thereby enhances the luminescence intensity. Identification of shallow levels responsible for the effect is discussed. © 1999 American Institute of Physics.
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78.40.Fy Semiconductors
78.55.Ap Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
71.55.Cn Elemental semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
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