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11 Jun 2001

Volume 78, Issue 24, pp. 3767-3908

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Traveling-wave photodetector for 1.55 μm wavelength fabricated with unitraveling-carrier photodiodes

Y. Hirota, T. Hirono, T. Ishibashi, and H. Ito

Appl. Phys. Lett. 78, 3767 (2001); http://dx.doi.org/10.1063/1.1377849 (3 pages) | Cited 5 times

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We report on a periodic traveling-wave photodetector (P-TW-PD) fabricated by unicarrier traveling photodiodes (UTC-PDs). It is comprised of three UTC-PDs periodically arranged along a coplanar waveguide transmission line. The photoresponse of the P-TW-UTC-PD is three times that of a single UTC-PD. A 3 dB bandwidth (f3dB) of 115 GHz at 1.55 μm was observed in a P-TW-UTC-PD with a terminal resistor located at the input end. This value of f3dB is almost the same as that observed in a single UTC-PD. In P-TW-UTC-PDs with no terminal resistor, the 3 dB bandwidth degrades to 56 GHz as a result of the reflection of backward-propagating microwaves at the input end. We conclude that our P-TW-UTC-PD provides velocity matching between electrical and optical waves. © 2001 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
42.82.Et Waveguides, couplers, and arrays
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Low-threshold optically pumped λ = 4.4 μm vertical-cavity surface-emitting laser with a PbSe quantum-well active region

C. L. Felix, W. W. Bewley, I. Vurgaftman, J. R. Lindle, J. R. Meyer, H. Z. Wu, G. Xu, S. Khosravani, and Z. Shi

Appl. Phys. Lett. 78, 3770 (2001); http://dx.doi.org/10.1063/1.1378808 (3 pages) | Cited 17 times

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We report pulsed emission from an optically pumped lead-salt vertical-cavity surface-emitting laser with a PbSe/PbSrSe quantum-well active region. The lasing wavelength of λ = 4.44 μm is nearly constant over the temperature range 200–280 K, and the threshold is only 10.5 kW/cm2 at 260 K, where the gain peak and cavity mode are in resonance. Over 330 mW of peak power is emitted at 260 K, into a circular beam whose divergence angle increases with pump intensity. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Catalytic role of Au in Ni/Au contact on GaN(0001)

C. C. Kim, J. K. Kim, J.-L. Lee, J. H. Je, M. S. Yi, D. Y. Noh, Y. Hwu, and P. Ruterana

Appl. Phys. Lett. 78, 3773 (2001); http://dx.doi.org/10.1063/1.1379064 (3 pages) | Cited 10 times

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We investigated the structural behavior of the Ni/Au contact on GaN(0001) and found the catalytic role of Au during annealing, using in situ x-ray scattering. The oxidation kinetics of Ni during annealing in air was greatly affected by the presence of Au. The accelerated GaN decomposition and Ni nitride formation during annealing in N2 also provide evidence of the catalytic role of Au. The results suggest that oxidized Ni/Au ohmic contact exhibit better thermal stability than that of the N2 annealed Ni/Au contacts. © 2001 American Institute of Physics.
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68.35.Ct Interface structure and roughness
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.40.Ns Metal-nonmetal contacts
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
68.60.Dv Thermal stability; thermal effects

Decay of stimulated and spontaneous emission in highly excited homoepitaxial GaN

S. Juršėnas, N. Kurilčik, G. Kurilčik, A. Žukauskas, P. Prystawko, M. Leszcynski, T. Suski, P. Perlin, I. Grzegory, and S. Porowski

Appl. Phys. Lett. 78, 3776 (2001); http://dx.doi.org/10.1063/1.1378802 (3 pages) | Cited 18 times

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The high-density effects in the recombination of electron–hole plasma in photoexcited homoepitaxial GaN epilayers were studied by means of transient photoluminescence at room temperature. Owing to the “backward” and “lateral” photoluminescence measurement geometries employed, the influence of stimulated transitions on the decay of degenerate nonthermalized plasma was revealed. The lateral stimulated emission was demonstrated to cause a remarkable increase in the recombination rate on the early stage of the luminescence transient. A delayed enhancement of the stimulated emission due to the cooling of plasma from the initial temperature of 1100 K was observed. After completion of the thermalization process and exhaustion of the stimulated emission, the spontaneous-luminescence decay exhibited an exponential slope that relates to the nonradiative recombination of the carriers. The homoepitaxially grown GaN layer featured a luminescence decay time of 445 ps that implies a room-temperature free-carrier lifetime of 890 ps (considered to be extremely high for undoped hexagonal GaN). © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.45.+h Stimulated emission
78.47.-p Spectroscopy of solid state dynamics

Instantaneous optical modulation in bulk GaAs semiconductor microcavities

S. Sanchez, C. De Matos, and M. Pugnet

Appl. Phys. Lett. 78, 3779 (2001); http://dx.doi.org/10.1063/1.1379783 (3 pages) | Cited 7 times

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Picosecond pump–probe experiments at room temperature on a bulk GaAs microcavity are presented. The microcavity device is designed to adjust the cavity mode energy 15 meV below the band gap energy of the intracavity bulk GaAs material. For low pump-energy densities (∼μJ/cm2), ultrafast modulation of the reflectivity is demonstrated due to the purely coherent refractive index change. A 5:1 contrast ratio is achieved and shows the potential of the semiconductor microcavities for implementation in ultrafast all optical switching. © 2001 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Hp Optical processors, correlators, and modulators
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Switchable diffraction gratings based on inversion of the dielectric anisotropy in nematic liquid crystals

S. W. Kang, S. Sprunt, and L. C. Chien

Appl. Phys. Lett. 78, 3782 (2001); http://dx.doi.org/10.1063/1.1377322 (3 pages) | Cited 6 times

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A switchable liquid crystal diffraction grating, responsive to both the frequency and magnitude of an applied voltage, is demonstrated. The grating is based on polymer stabilization of modulated states of the liquid crystal optic axis induced at frequencies near a sign inversion of the dielectric anisotropy. In a particular case of frequency-based switching, 70% of the transmitted intensity of a 633 nm laser beam can be shifted into or out of a ±12° forward arc by changing the frequency of an applied voltage between 10 and 16 kHz at a fixed amplitude of 27 V. © 2001 American Institute of Physics.
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42.79.Dj Gratings
42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
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Ablation plasma ion implantation experiments: Measurement of Fe implantation into Si

B. Qi, R. M. Gilgenbach, Y. Y. Lau, M. D. Johnston, J. Lian, L. M. Wang, G. L. Doll, and A. Lazarides

Appl. Phys. Lett. 78, 3785 (2001); http://dx.doi.org/10.1063/1.1379360 (3 pages) | Cited 4 times

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Experiments have been performed demonstrating the feasibility of direct implantation of laser-ablated metal ions into a substrate. Initial experiments implanted iron ions into silicon substrates at pulsed, bias voltages up to negative 10 kV. Implantation of Fe ions into Si was confirmed by cross-sectional transmission electron microscopy and x-ray photoelectron spectroscopy. The 7.6 nm depth of damage layers below the Si surface is slightly less than predicted by code calculations for a maximum, effective ion energy of about 8 keV. The ion depth of penetration is limited by the overlying Fe film as well as the slow rise and fall of the voltage. © 2001 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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Saturated defect densities of hydrogenated amorphous silicon grown by hot-wire chemical vapor deposition at rates up to 150 Å/s

A. H. Mahan, Y. Xu, B. P. Nelson, R. S. Crandall, J. D. Cohen, K. C. Palinginis, and A. C. Gallagher

Appl. Phys. Lett. 78, 3788 (2001); http://dx.doi.org/10.1063/1.1375008 (3 pages) | Cited 10 times

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Hydrogenated amorphous-silicon (a-Si:H) is grown by hot-wire chemical vapor deposition (HWCVD) at deposition rates (Rd) exceeding 140 Å/s (∼0.8 μm/min). These high rates are achieved by using multiple filaments and deposition conditions different than those used to produce our standard 20 Å/s material. With proper deposition parameter optimization, an AM1.5 photo-to-dark-conductivity ratio of 105 is maintained at an Rd up to 130 Å/s, beyond which it decreases. In addition, the first saturated defect densities of high Rd a-Si:H films are presented. These saturated defected densities are similar to those of the best HWCVD films deposited at 5–8 Å/s, and are invariant with Rd up to 130 Å/s. © 2001 American Institute of Physics.
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81.05.Gc Amorphous semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Cy Elemental semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Strong visible photoluminescence from SiO2 nanotubes at room temperature

H. J. Chang, Y. F. Chen, H. P. Lin, and C. Y. Mou

Appl. Phys. Lett. 78, 3791 (2001); http://dx.doi.org/10.1063/1.1370991 (3 pages) | Cited 49 times

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The optical studies of SiO2 mesoporous materials with hierarchical tubules-within-tubule structure have been investigated by photoluminescence and Fourier-transform infrared transmittance (FTIR). Our results suggest that the radiative intensity can be strongly enhanced by annealing the samples in N2 environment. From the FTIR spectra, we have pointed out that the origin responsible for the strong emission is Si–OH complexes located on nanotube surface. It has been observed that after turning off the pumping laser, the photoluminescence signal of SiO2 nanotubes can persist for several seconds, which is much longer than that of most materials performed under similar conditions. We have found that the decay of the photoluminescence signal is due to the quantum tunneling process. These are triplet and singlet states of Si–OH complexes that are responsible for the observed persistent photoluminescence. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
78.67.Ch Nanotubes
78.55.Mb Porous materials
78.30.Na Fullerenes and related materials

Growth, structure, and optical properties of carbon-reinforced silica fibers

Z. J. Zhang, P. M. Ajayan, G. Ramanath, J. Vacik, and Y. H. Xu

Appl. Phys. Lett. 78, 3794 (2001); http://dx.doi.org/10.1063/1.1376658 (3 pages) | Cited 2 times

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We report the synthesis of carbon-reinforced silica fibers by methane exposure of metallocene-treated oxidized-Si(001) substrates at 1100 °C. The SiO2 cap layer transforms into silica fibers reinforced by glassy carbon in the core during methane exposure. High-resolution electron microscopy and spatially resolved spectroscopy measurements of the fibers reveal an amorphous structure without a hollow, and domains of glassy carbon embedded at the fiber core. The carbon-reinforced fibers are optically transparent and have an optical band gap of ≃3.1 eV. These fibers are organized in radial patterns that vary for different metallocene species. On nickelocene-treated substrates, the fibers originate from the circumference of the circular templates and grow outwards, forming radial patterns. On ferrocene-treated substrates, randomly oriented fibers grow within as well as slightly outside the perimeter of the templates, forming wreath-like patterns. Aligned growth of such fibers could be useful for fabricating optoelectronics devices and reinforced composites. © 2001 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
78.40.Pg Disordered solids
61.43.Er Other amorphous solids

Microstructural evidence on electrical properties of Ta/Ti/Al and Ti/Ta/Al ohmic contacts to n-AlGaN/GaN

S.-H. Lim, J. Washburn, Z. Liliental-Weber, and D. Qiao

Appl. Phys. Lett. 78, 3797 (2001); http://dx.doi.org/10.1063/1.1378312 (3 pages) | Cited 27 times

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Electrical properties and microstructures of Ta/Ti/Al and Ti/Ta/Al contacts to n-AlGaN/GaN heterostructure field-effect transistor structures were investigated using the transmission line method and transmission electron microscopy. The specific resistivity (5.3×10−7 Ω cm2) of Ta/Ti/Al contacts is much lower than that (5.1×10−4 Ω cm2) of Ti/Ta/Al contacts, for the same heterostructure and similar metallization. The contact resistivity was found to depend on the thickness of the AlGaN layer, interfacial phase, and interface roughness. The formation of interfacial phases by solid-state reactions with the metal layer during annealing appears to be essential for ohmic behavior on n-III-nitrides suggesting a tunneling contact mechanism. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing
85.30.Tv Field effect devices

Alkoxy sol-gel derived Y3−xAl5O12:Tbx thin films as efficient cathodoluminescent phosphors

Jae Young Choe, D. Ravichandran, S. M. Blomquist, D. C. Morton, K. W. Kirchner, M. H. Ervin, and Unchul Lee

Appl. Phys. Lett. 78, 3800 (2001); http://dx.doi.org/10.1063/1.1378313 (3 pages) | Cited 51 times

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Thin-film Y3−xAl5O12:Tbx3+ (YAG:Tb) phosphor derived from a sol-gel chemistry is analyzed by x-ray diffraction, scanning electron microscopy, photoluminescence (PL) and cathodoluminescence (CL). The metal alkoxides organic precursors were chosen as the starting materials to form the sol-gel. This liquid sol-gel was spin coated on sapphire and silicon substrates to form the uniform thin films, then crystallized by annealing. The PL intensity of the crystallized film at 545 nm green emission was 15 times higher than that of the as-coated noncrystalline film. CL measurements show that luminance and efficiency are comparable to the films deposited by other techniques. © 2001 American Institute of Physics.
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78.66.Nk Insulators
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Hx Other solid inorganic materials
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.50.Gg Ferrimagnetics
61.72.Cc Kinetics of defect formation and annealing

Interface engineering of a ZrO2/SiO2/Si layered structure by in situ reoxidation and its oxygen-pressure-dependent thermal stability

Heiji Watanabe

Appl. Phys. Lett. 78, 3803 (2001); http://dx.doi.org/10.1063/1.1379357 (3 pages) | Cited 34 times

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Reactions at ZrO2/SiO2/Si interfaces during fabrication and postannealing have been studied in detail. The layered structures were fabricated by deposition of a thin Zr layer on a chemical oxide, followed by oxidation in an UHV chamber without air exposure (i.e., in situ reoxidation). On-line x-ray photoelectron spectroscopy was used to show that in situ reoxidation can be used for precisely designing interfacial structures. It was found that the thermal stability of ZrO2/SiO2/Si interfaces crucially depends on oxygen ambient; that is, while the interfaces are stable up to 900 °C under UHV conditions, annealing in 1×10−4 Torr oxygen results in formation of interfacial Zr silicate. Moreover, the ZrO2 overlayer was found to accelerate the interfacial oxidation reaction. © 2001 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.60.Dv Thermal stability; thermal effects
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

A yield stress scaling function for electrorheological fluids

Hyoung J. Choi, Min S. Cho, Ji W. Kim, Chul A. Kim, and Myung S. Jhon

Appl. Phys. Lett. 78, 3806 (2001); http://dx.doi.org/10.1063/1.1379058 (3 pages) | Cited 107 times

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The yield stress dependence on electric field strength for electrorheological (ER) fluids is examined. A proposed scaling function incorporates both the polarization and conductivity models. Proper scaling allows yield stress data for ER fluids to collapse onto a single curve for a broad range of electric field strengths. © 2001 American Institute of Physics.
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83.60.Np Effects of electric and magnetic fields
83.80.Gv Electro- and magnetorheological fluids
62.10.+s Mechanical properties of liquids

X-ray absorption near-edge structure in alpha-quartz and stishovite: Ab initio calculation with core–hole interaction

Shang-Di Mo and W. Y. Ching

Appl. Phys. Lett. 78, 3809 (2001); http://dx.doi.org/10.1063/1.1378311 (3 pages) | Cited 39 times

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Ab initio calculation of the XANSE/ELNES spectra for α quartz and stishovite were carried out using a large-supercell approach that includes the electron–core–hole interaction. Excellent agreements with experimental spectra were obtained for Si–K, Si–L2,3, and O–K edges. The usual interpretation using orbital-resolved local density of states in the conduction band is unsatisfactory. © 2001 American Institute of Physics.
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78.70.Dm X-ray absorption spectra
79.20.Uv Electron energy loss spectroscopy
71.15.-m Methods of electronic structure calculations
71.20.Ps Other inorganic compounds

Microscopic structure of hydrogen impurity in LiNbO3

H. H. Nahm and C. H. Park

Appl. Phys. Lett. 78, 3812 (2001); http://dx.doi.org/10.1063/1.1376667 (3 pages) | Cited 2 times

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We investigate the microscopic structures of interstitial and substitutional hydrogen impurities in LiNbO3 through the first-principles pseudopotential total-energy calculations. The interstitial hydrogen is located between two O atoms and bonds to one of the oxygen atoms. The hydrogen impurity substituting Li is significantly displaced from the Li-site and strongly bonds to an oxygen atom and is located on a biaxial axis of an O triangle. We discuss the effect of hydrogen to the ferroelectric polarization and the energetics for the trap of the interstitial hydrogen at a Li vacancy. © 2001 American Institute of Physics.
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71.55.Ht Other nonmetals
71.15.Nc Total energy and cohesive energy calculations
61.72.S- Impurities in crystals
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.J- Point defects and defect clusters
61.50.Lt Crystal binding; cohesive energy
77.22.Ej Polarization and depolarization
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Characterization of electron-irradiated n-GaN

S. A. Goodman, F. D. Auret, M. J. Legodi, B. Beaumont, and P. Gibart

Appl. Phys. Lett. 78, 3815 (2001); http://dx.doi.org/10.1063/1.1379057 (3 pages) | Cited 8 times

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Using deep level transient spectroscopy, we have investigated the electron trap defects introduced in n-GaN grown using the epitaxial lateral overgrowth technique during high energy electron irradiation from a 90Sr radionuclide source. The results indicate that the major electron-irradiation-induced defect labeled ER3 is not a single defect level but is made up of at least three defect levels (ER3b–ER3d). One of these defects, ER3d, has an activation energy and introduction rate of 0.22 eV and 0.43 cm−1, respectively. The total introduction rate of the three defects (ER3b–ER3d) is approximately 1.0 cm−1. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors

Anomalous phosphorus diffusion in Si during post-implantation annealing

Ryangsu Kim, Yoshikazu Furuta, Syunsuke Hayashi, Tetsuya Hirose, Toshihumi Shano, Hiroshi Tsuji, and Kenji Taniguchi

Appl. Phys. Lett. 78, 3818 (2001); http://dx.doi.org/10.1063/1.1379359 (3 pages) | Cited 5 times

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The transient behavior of P diffusion in Si implanted with As or Ge above the amorphizing threshold has been investigated. Annealing at 720 °C after Ge implantation induces extensive P segregation into the extended defect layer formed by implantation damage. This segregation is attributed to P trapping to end-of-range {311} defects and dislocation loops. For As implantation, P segregation was also observed only after 1 min annealing. However, in contrast to the Ge implantation, in the As-implanted samples, significant P depletion occurs in the As-tail region after further annealing. Nonequilibrium simulation that takes into account both Fermi-level and electric field effects shows the P depletion during transient enhanced diffusion. Furthermore, simulation results based on the coexistence of neutral and positively charged phosphorus-interstitial pairs agree well with the obtained experimental results. © 2001 American Institute of Physics.
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61.72.uf Ge and Si
61.82.Fk Semiconductors
66.30.J- Diffusion of impurities
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Nn Stacking faults and other planar or extended defects
81.05.Cy Elemental semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.J- Point defects and defect clusters

Charge transport through a single tetracene grain boundary

Jan Hendrik Schön and Christian Kloc

Appl. Phys. Lett. 78, 3821 (2001); http://dx.doi.org/10.1063/1.1379986 (3 pages) | Cited 8 times

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The hole transport through a single grain boundary is investigated in the temperature range from 4 to 300 K using a tetracene bicrystal. The carrier concentration is varied by the field effect. The results can be explained using the grain-boundary-trapping model. A potential barrier is formed at the grain boundary due to charged traps at the grain boundary. The barrier height depends significantly on the carrier density within the grain. At low temperatures, tunneling through the grain boundary dominates over thermionic emission over the barrier. © 2001 American Institute of Physics.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
73.40.Gk Tunneling
61.72.Mm Grain and twin boundaries
72.20.Fr Low-field transport and mobility; piezoresistance
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High throughput fabrication of transition-metal-doped epitaxial ZnO thin films: A series of oxide-diluted magnetic semiconductors and their properties

Zhengwu Jin, T. Fukumura, M. Kawasaki, K. Ando, H. Saito, T. Sekiguchi, Y. Z. Yoo, M. Murakami, Y. Matsumoto, T. Hasegawa, and H. Koinuma

Appl. Phys. Lett. 78, 3824 (2001); http://dx.doi.org/10.1063/1.1377856 (3 pages) | Cited 272 times

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Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial ZnO thin films doped with all the 3d transition metal (TM) ions in a high throughput fashion. The solubility behavior of TM ions was discussed from the viewpoints of the ionic radius and valence state. The magneto-optical responses coincident with absorption spectra were observed for Mn- and Co-doped samples. Cathodoluminescence spectra were studied for Cr-, Mn-, Fe-, and Co-doped samples, among which Cr-doped ZnO showed two sharp peaks at 2.97 eV and 3.71 eV, respectively, at the expense of the exciton emission peak of pure ZnO at 3.25 eV. Different magnetoresistance behavior was observed for the samples codoped with n-type carriers. Ferromagnetism was not observed for Cr- to Cu-doped samples down to 3 K. © 2001 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.50.Pp Magnetic semiconductors
78.66.Hf II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
78.40.Fy Semiconductors
61.72.uj III-V and II-VI semiconductors
78.20.Ls Magneto-optical effects
78.60.Hk Cathodoluminescence, ionoluminescence
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Spatially modified layer properties related to the formation of gallium droplets on GaN(0001) surfaces during plasma-assisted molecular-beam epitaxy

C. Kruse, S. Einfeldt, T. Böttcher, D. Hommel, D. Rudloff, and J. Christen

Appl. Phys. Lett. 78, 3827 (2001); http://dx.doi.org/10.1063/1.1377629 (3 pages) | Cited 7 times

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The surface morphology and the spatial distribution of defect-related luminescence of GaN(0001) layers grown by plasma-assisted molecular-beam epitaxy under gallium-rich conditions has been investigated. Droplets of liquid gallium form on the surface during growth and lead to distinct spiral hillocks under the droplet. The droplets are surrounded by extended voids which point to an incomplete gallium adlayer on the GaN surface during growth at the droplet boundary. Cathodoluminescence spectra indicate an enhanced intensity in the yellow spectral range for the GaN under the droplets which is attributed to a change in the local density of point defects in the layer. © 2001 American Institute of Physics.
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68.43.Mn Adsorption kinetics
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Dv Composition, segregation; defects and impurities
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.J- Point defects and defect clusters
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Mismatch and chemical composition analysis of vertical InxGa1−xAs quantum-dot arrays by transmission electron microscopy

Qi Zhang, Jing Zhu, Xiaowei Ren, Hongwei Li, and Taihong Wang

Appl. Phys. Lett. 78, 3830 (2001); http://dx.doi.org/10.1063/1.1378310 (3 pages) | Cited 9 times

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Vertically stacked InxGa1−xAs/GaAs quantum dots have been fabricated by molecular beam epitaxy. Cross-sectional high resolution electron microscopy analyses demonstrate that the quantum dot size increases, and the interplanar spacings of {111} for quantum dots as well as the mismatch between the quantum dots and the spacer layers, is increased with the layer number. Chemical analysis shows that, as fabrication proceeds, indium content is increased and gallium content is decreased, leading to the changes of mismatch and interplanar spacing for the quantum dots. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)
81.05.Ea III-V semiconductors

Multiplication noise of AlxGa1−xAs avalanche photodiodes with high Al concentration and thin multiplication region

X. G. Zheng, X. Sun, S. Wang, P. Yuan, G. S. Kinsey, A. L. Holmes, B. G. Streetman, and J. C. Campbell

Appl. Phys. Lett. 78, 3833 (2001); http://dx.doi.org/10.1063/1.1343851 (3 pages) | Cited 14 times

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We report that homojunction AlxGa1−xAs avalanche photodiodes (APDs) exhibit very low multiplication noise when the Al content is ⩾80%. It was also found that, due to nonlocal effects, the multiplication noise decreased as the ionization region thickness was reduced from 0.8 μm to ⩽ 0.2 μm for Al ratios (from 0 to 0.9). The excess noise factor of the thin (140 nm) Al0.9Ga0.1As APDs is the lowest reported to date for III–V compounds and is comparable to that of Si avalanche photodiodes. © 2001 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.05.Ea III-V semiconductors

Anomalous degradation of solar cells induced by carrier trapping

S. Zh. Karazhanov

Appl. Phys. Lett. 78, 3836 (2001); http://dx.doi.org/10.1063/1.1379362 (3 pages) | Cited 2 times

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A mechanism for the effect of anomalous increase of carrier lifetime and the phenomenon of anomalous degradation of solar cells has been proposed. Distinct from previously known mechanisms, based on carrier recombination, the mechanism is based on carrier trapping. It is shown that the increase of carrier lifetime and short-circuit current with increasing trap concentration is caused by the abrupt decrease of total free carrier density due to carrier trapping. Then the Fermi level will be shifted towards the middle of the band gap and the open-circuit voltage decreases. It is shown that the anomalous increase of the short-circuit current can overcome the decrease of the open-circuit voltage, resulting in the increase of the cell efficiency. However, the efficiency improvement is not the result of carrier photoemission from the defect level, but is caused by the trap-induced increase of carrier lifetime. © 2001 American Institute of Physics.
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84.60.Jt Photoelectric conversion
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.-i Impurity and defect levels

Surface hydrogenation as a method to purify and flatten a silicon surface

Shin’ichi Higai and Takahisa Ohno

Appl. Phys. Lett. 78, 3839 (2001); http://dx.doi.org/10.1063/1.1377314 (3 pages) | Cited 3 times

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We performed first-principles theoretical calculations and found that the hydrogenation of a Si surface causes the segregation of impurity metal atoms from the subsurface onto the surface top. Since the contamination by metallic impurities is a principal cause of surface defects, it is expected that, by the surface hydrogenation, a highly pure and atomically flat Si surface is realized. © 2001 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)
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