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27 Jun 2005

Volume 86, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 263107 (2005); http://dx.doi.org/10.1063/1.1952585 (3 pages)

B. Yang, M. S. Marcus, D. G. Keppel, P. P. Zhang, Z. W. Li, B. J. Larson, D. E. Savage, J. M. Simmons, O. M. Castellini, M. A. Eriksson, and M. G. Lagally
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Simple layer-by-layer photonic crystal for the control of thermal emission

S. Enoch, J.-J. Simon, L. Escoubas, Z. Elalmy, F. Lemarquis, P. Torchio, and G. Albrand

Appl. Phys. Lett. 86, 261101 (2005); http://dx.doi.org/10.1063/1.1954881 (3 pages) | Cited 22 times

Online Publication Date: 20 June 2005

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We present a theoretical and experimental study of a simple layer-by-layer photonic crystal structure designed for the control of the thermal emission in the infrared wavelength domain. We show that a relatively simple structure made of alternated ZnSe homogenous layers and gold microstructured grids can act as a thermal source itself giving us the unique opportunity to tailor its emission spectra. Comparisons between computed and measured transmission and emissivity spectra illustrate the relevance of our approach.
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42.70.Qs Photonic bandgap materials
78.30.Hv Other nonmetallic inorganics

Laser terahertz emission system to investigate hydrogen gas sensors

Toshihiko Kiwa, Keiji Tsukada, Masato Suzuki, Masayoshi Tonouchi, Sonoko Migitaka, and Koichi Yokosawa

Appl. Phys. Lett. 86, 261102 (2005); http://dx.doi.org/10.1063/1.1954885 (3 pages) | Cited 9 times

Online Publication Date: 20 June 2005

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A laser terahertz emission system is proposed to investigate the catalytic metal/semiconductor interfaces of hydrogen sensors. Samples were fabricated by depositing a catalytic metal thin film on a semi-insulating silicon substrate. A femtosecond laser was used to radiate terahertz waves from the sample in a gas cell filled with a hydrogen and nitrogen gas mixture. The peak amplitude of the terahertz waves decreased with increasing hydrogen concentration. We also fabricated a metal-oxide-semiconductor field effect transistor hydrogen sensor, and compared its properties with the terahertz radiation properties. These results suggest that the laser terahertz emission system is a potential tool to investigate catalytic metal/semiconductor interfaces.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
85.30.Tv Field effect devices
78.47.-p Spectroscopy of solid state dynamics

Absorption cross section and signal enhancement in Er-doped Si nanocluster rib-loaded waveguides

N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato

Appl. Phys. Lett. 86, 261103 (2005); http://dx.doi.org/10.1063/1.1957112 (3 pages) | Cited 31 times

Online Publication Date: 20 June 2005

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Pump and probe experiments on Er3+ ions coupled to Si nanoclusters have been performed in rib-loaded waveguides to investigate optical amplification at 1.5 μm. Rib-loaded waveguides were obtained by photolithographic and reactive ion etching of Er-doped silica layers containing Si nanoclusters grown by reactive sputtering. Insertion losses measurements in the infrared erbium absorption region allowed to gauge an Er3+ absorption cross section of about 5×10−21 cm2 at 1534 nm. Signal transmission under optical pumping at 1310 nm shows confined carrier absorption of the Si nanoclusters. Amplification experiments at 1535 nm evidence two pump power regimes: Losses due to confined carrier absorption in the Si nanoclusters at low pump powers and signal enhancement at high pump powers. For strong optical pumping, signal enhancement of about 1.2 dB/cm was obtained.
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42.79.Gn Optical waveguides and couplers
81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Am Elemental semiconductors and insulators
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Amplified spontaneous emission from a conjugated polymer undergone a high-temperature lithography cycle

Dario Pisignano, Elisa Mele, Luana Persano, Giovanni Paladini, and Roberto Cingolani

Appl. Phys. Lett. 86, 261104 (2005); http://dx.doi.org/10.1063/1.1946189 (3 pages) | Cited 8 times

Online Publication Date: 20 June 2005

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We investigated the amplified spontaneous emission (ASE) and waveguiding properties of a conjugated polymer film after a heating cycle typical of soft lithography procedures. We found a maximum gain coefficient of 8 cm−1, with excitation density and length thresholds for ASE-induced line narrowing of 200 μJ cm−2 and 0.9 mm, respectively. Importantly, we found a loss coefficient of the organic slab as low as 5.4 cm−1, which is among the best results reported for organic waveguide amplifiers. These results are important in view of the application of polymer films as active layers for laser devices realized by patterning with high-temperature mechanical lithographies.
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78.45.+h Stimulated emission
78.66.Qn Polymers; organic compounds
42.79.Wc Optical coatings
42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
81.40.Gh Other heat and thermomechanical treatments
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Isolation effect in ferromagnetic-metal/semiconductor hybrid optical waveguide

V. Zayets and K. Ando

Appl. Phys. Lett. 86, 261105 (2005); http://dx.doi.org/10.1063/1.1953878 (3 pages) | Cited 11 times

Online Publication Date: 20 June 2005

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The isolation effect in a ferromagnetic-metal/semiconductor hybrid optical waveguide was experimentally studied. Optical transmission in a Ga1−xAlxAs waveguide covered by Co was found to depend on the magnetization of the Co. The isolation direction was different for a waveguide with a SiO2 buffer layer and for a waveguide with a Ga1−xAlxAs buffer layer used between the waveguide core layer and Co layer. The physical origin of the isolation in this isolator structure was clarified.
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42.79.Gn Optical waveguides and couplers
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Fano resonance in a multimode tapered fiber coupled with a microspherical cavity

Akito Chiba, Hideki Fujiwara, Jun-ichi Hotta, Shigeki Takeuchi, and Keiji Sasaki

Appl. Phys. Lett. 86, 261106 (2005); http://dx.doi.org/10.1063/1.1951049 (3 pages) | Cited 22 times

Online Publication Date: 21 June 2005

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Fano resonance in a tapered optical fiber in contact with a high-Q microsphere is demonstrated. Multimode waves propagating in a 2.3 μm diameter taper were coupled with a single whispering gallery mode of a 220 μm sphere, and their coherent interaction resulted in Fano resonance. The asymmetric line shapes of the transmission spectra changed periodically with scanning of the coupling position along the taper. The observed 24 μm period was due to modal dispersion in the tapered fiber.
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42.81.Dp Propagation, scattering, and losses; solitons
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.81.Qb Fiber waveguides, couplers, and arrays

Monolithic Fabry-Perot resonator for the measurement of optical constants in the terahertz range

Adrian Dobroiu, René Beigang, Chiko Otani, and Kodo Kawase

Appl. Phys. Lett. 86, 261107 (2005); http://dx.doi.org/10.1063/1.1968423 (3 pages) | Cited 4 times

Online Publication Date: 21 June 2005

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A prism-shaped monolithic Fabry-Perot resonator is shown to allow absorption measurements of liquid samples in the terahertz wave range. As the radiation source a backward-wave oscillator was chosen for its tunable, highly monochromatic, continuous wave. The resonator is made of high-resistivity silicon, with two surfaces acting as partial mirrors and forming the cavity, while a third one contributes with a total internal reflection. When a liquid sample is placed on this latter surface the total reflection is attenuated and the finesse of the resonator decreases, providing absorption information about the sample. The measurement method relying on Fourier processing of the signal, as well as experimental data are presented.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.Rd Visible and ultraviolet spectrometers
42.30.Kq Fourier optics

Effect of n+-GaN subcontact layer on 4H–SiC high-power photoconductive switch

K. Zhu, S. Doğan, Y. T. Moon, J. Leach, F. Yun, D. Johnstone, H. Morkoç, G. Li, and B. Ganguly

Appl. Phys. Lett. 86, 261108 (2005); http://dx.doi.org/10.1063/1.1951056 (3 pages) | Cited 4 times

Online Publication Date: 22 June 2005

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High-power photoconductive semiconductor switching devices were fabricated on 4H–SiC. In order to prevent current crowding, reduce the contact resistance, and avoid contact degradation, a highly n-doped GaN subcontact layer was inserted between the contact metal and the high resistivity SiC bulk. This method led to a two orders of magnitude reduction in the on-state resistance and, similarly, the photocurrent efficiency was increased by two orders of magnitude with the GaN subcontact layer following the initial high current operation. Both dry etching and wet etching were used to remove the GaN subcontact layer in the channel area. Wet etching was found to be more suitable than dry etching.
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85.60.-q Optoelectronic devices
72.40.+w Photoconduction and photovoltaic effects
73.40.Cg Contact resistance, contact potential
81.65.Cf Surface cleaning, etching, patterning

Evolution of poling-assisted bleaching of metal-doped nanocomposite glass with poling conditions

Olivier Deparis, Peter G. Kazansky, Alexander Podlipensky, Amin Abdolvand, Gerhard Seifert, and Heinrich Graener

Appl. Phys. Lett. 86, 261109 (2005); http://dx.doi.org/10.1063/1.1977205 (3 pages) | Cited 7 times

Online Publication Date: 23 June 2005

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Poling-assisted bleaching was studied with respect to poling time, voltage, and temperature in glass samples having a gradient of silver nanoparticles across the depth. The optical extinction band due to the particles’ surface plasmon resonance (around 415 nm) was measured and the Maxwell–Garnett effective medium theory was used to fit extinction spectra. Fitting allowed us to determine the evolution of the thickness of the near-surface layer where the particles’ volume filling factor has dropped to zero as a result of the bleaching process. At 280 °C, bleaching started with a voltage as low as 200 V and saturated with time after about 1 h. Tight glass-electrode contact, voltage of at least 1 kV, and temperature higher than 200 °C were required in order to obtain significant and uniform bleaching in the poled area. The results were discussed in terms of the underlying electric-field-assisted dissolution of embedded metal nanoparticles.
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77.22.Ej Polarization and depolarization
64.75.-g Phase equilibria
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.68.+m Optical properties of surfaces

Voltage tunable superlattice infrared detector for mid- and long-wavelength detection

Amlan Majumdar, K. K. Choi, J. L. Reno, and D. C. Tsui

Appl. Phys. Lett. 86, 261110 (2005); http://dx.doi.org/10.1063/1.1977206 (3 pages) | Cited 6 times

Online Publication Date: 23 June 2005

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We have designed and fabricated a voltage tunable superlattice (SL) infrared photodetector where the detection wavelength switches from the 3–5 μm midwavelength infrared (MWIR) range under negative bias to the 8–12 μm long-wavelength infrared (LWIR) range under large positive bias. The structure consists of multiple periods of two different SLs that are separated by undoped blocking barriers on one side and heavily doped layers on the other side. The background-limited temperature with F/1.2 optics is 110 and 70 K for mid- and long-wavelength detection, respectively. This voltage tunable MWIR/LWIR detector has a performance comparable to those of one-color quantum-well infrared detectors designed for the respective wavelength ranges.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Strain dependence of lasing mechanisms in ZnO epilayers

H. D. Li, S. F. Yu, A. P. Abiyasa, Clement Yuen, S. P. Lau, H. Y. Yang, and Eunice S. P. Leong

Appl. Phys. Lett. 86, 261111 (2005); http://dx.doi.org/10.1063/1.1968418 (3 pages) | Cited 16 times

Online Publication Date: 23 June 2005

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The lasing characteristics of highly disordered ZnO thin films deposited on SiO2/Si substrates with and without a MgO buffer layer have been investigated. We observed that the emission spectra of the ZnO epilayers with and without a MgO buffer are associated with the radiative recombination of free-exciton ( ∼ 380 nm) and electron-hole plasma ( ∼ 395 nm), respectively. The difference in the lasing wavelength is due to the induced compressive (tensile) strain along the c axis of the ZnO epilayers as a result of the presence (absence) of the MgO buffer layer. It is demonstrated that the strain-induced variation of Mott density inside the ZnO epilayers is responsible for the observed lasing characteristics.
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81.05.Hd Other semiconductors
42.55.Px Semiconductor lasers; laser diodes
78.66.Li Other semiconductors
68.60.Bs Mechanical and acoustical properties
78.55.Hx Other solid inorganic materials
71.35.-y Excitons and related phenomena
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Complex ion-focusing effect by the sheath above the wafer in plasma immersion ion implantation

E. Stamate, N. Holtzer, and H. Sugai

Appl. Phys. Lett. 86, 261501 (2005); http://dx.doi.org/10.1063/1.1951045 (3 pages) | Cited 9 times

Online Publication Date: 20 June 2005

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The ion flux on the wafer surface during plasma immersion ion implantation is investigated by three-dimensional simulations and experiments. Due to the finite size of the wafer and its stage, the evolving sheath acts as a lens that focuses the positive ions to distinct regions on the wafer surface. Depending on the sheath profile, two focusing effects are identified. Discrete focusing involves ions entering the sheath from its frontal side and leads to the formation of a passive surface near the wafer edge, while the modal focusing affects ions entering the sheath from the lateral side of the stage and are eventually directed to the wafer center.
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81.05.Cy Elemental semiconductors
52.77.Dq Plasma-based ion implantation and deposition
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.40.Kh Plasma sheaths
81.65.Cf Surface cleaning, etching, patterning
61.72.uf Ge and Si

Laser wavelength and spot diameter dependence of extreme ultraviolet conversion efficiency in ω, 2ω, and 3ω Nd:YAG laser-produced plasmas

Shuji Miyamoto, Atushi Shimoura, Sho Amano, Keisuke Fukugaki, Hiroaki Kinugasa, Takahiro Inoue, and Takayasu Mochizuki

Appl. Phys. Lett. 86, 261502 (2005); http://dx.doi.org/10.1063/1.1968415 (3 pages) | Cited 10 times

Online Publication Date: 21 June 2005

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Conversion efficiency and spectra of extreme ultraviolet radiations from a cryogenic planar solid xenon target were investigated as a function of laser wavelength (ω, 2ω, and 3ω Nd:YAG) and the laser focus spot size (50–700 μm) at the intensity 1010–5×1012 W/cm2. The conversion efficiency increased with laser intensity and reached the maximum value at about 1011 W/cm2 for all colors. It was found that an edge effect appears more strongly at the ω-laser case, indicating more lateral energy loss, while it appears only weakly for higher harmonics. Shorter-wavelength lasers generated significant conversion efficiencies even at lower laser energies; that is, with smaller laser spots. As the wavelength decreased from ω, 2ω, and 3ω, a spectral hump appeared in the extreme ultraviolet band around 13.5 nm region, while the spectral intensity at 10.8 nm drastically decreased. High-energy photon generation in the tail of 10.8 nm peak was found to be strongly suppressed at shorter-wavelength laser (3ω), while the conversion efficiency at 13.5 nm was as large as that at ω. This indicates that a Xe[XI] ion-rich plasma have been efficiently produced in the ablation plasma by using 3ω laser without overheating the underdense plasma responsible for extreme ultraviolet emission.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Mf Laser ablation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Magnetoelasticity of chain-structured ferromagnetic composites

H. M. Yin and L. Z. Sun

Appl. Phys. Lett. 86, 261901 (2005); http://dx.doi.org/10.1063/1.1954895 (3 pages) | Cited 4 times

Online Publication Date: 20 June 2005

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A micromechanics-based model with particle interaction has been developed to study the effective elastic properties of chain-structured ferromagnetic composites subject to both magnetic and mechanical loading. Magnetomechanical coupled behavior is numerically simulated and magnetic-field-dependent elasticity is calculated using the Green’s function technique in a manner such that microstructure evolution is considered. Due to the magnetic angular momentum, the effective shear modulus of the composites increases much faster than the effective Young’s modulus as the magnetic field increases. Two mechanisms resulting in magnetic-field-dependent elasticity are demonstrated.
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75.80.+q Magnetomechanical effects, magnetostriction
75.40.Mg Numerical simulation studies
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Unintentionally doped n-type Al0.67Ga0.33N epilayers

M. L. Nakarmi, N. Nepal, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 86, 261902 (2005); http://dx.doi.org/10.1063/1.1954875 (3 pages) | Cited 14 times

Online Publication Date: 20 June 2005

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Unintentionally doped Al0.67Ga0.33N epilayers were grown on AlN∕sapphire templates by metalorganic chemical vapor deposition. Optimized undoped Al0.67Ga0.33N epilayers exhibited an n-type conductivity as confirmed by Hall-effect measurement with a room-temperature resistivity of about 85 Ω cm. Variable temperature Hall-effect measurement revealed the existence of a shallow donor level with activation energy of about 90 meV. The photoluminescence (PL) spectra exhibited an emission peak at 4.13 eV (4.06 eV) related to an impurity transition at 10 K (300 K). Temperature dependent PL measurement also confirmed the existence of a shallow donor with comparable activation energy as that obtained by Hall-effect measurement. Isolated oxygen impurities are believed to be a strong candidate of the donor that remains as a shallow state in AlxGa1−xN up to x ∼ 0.7. Compensating defects and the nature of the O donor in Al0.67Ga0.33N epilayers are also discussed.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors

Fine-structure N-polarity InN/InGaN multiple quantum wells grown on GaN underlayer by molecular-beam epitaxy

Song-Bek Che, Wataru Terashima, Yoshihiro Ishitani, Akihiko Yoshikawa, Takeyoshi Matsuda, Hirotatsu Ishii, and Seikoh Yoshida

Appl. Phys. Lett. 86, 261903 (2005); http://dx.doi.org/10.1063/1.1954877 (3 pages) | Cited 15 times

Online Publication Date: 20 June 2005

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We have succeeded in the growth of very-fine-structure InN/InGaN (3–16 nm/9 nm) multi-quantum wells (MQWs) on GaN underlayer and characterized them by transmission electron microscopy (TEM), high-resolution x-ray diffraction (XRD), and photoluminescence (PL) at 13 K. Clear satellite diffraction peaks and sharp heterointerfaces were observed by XRD and TEM, respectively. A single PL-emission peak at 1.75 μm was observed in the ten-periods InN(16.1 nm)/In0.67Ga0.33N(9.2 nm) MQWs. The use of the InGaN as a barrier layer instead of GaN resulted in remarkable reduction of lattice mismatch between the well and barrier, which was essential for the fabrication of MQWs with superior interface quality. This successful growth of fine-structure InN/InGaN MQWs would be an important step for the application of InN in optical communication devices.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.De Quantum wells
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Band alignment in GaInNP/GaAs heterostructures grown by gas-source molecular-beam epitaxy

M. Izadifard, T. Mtchedlidze, I. Vorona, W. M. Chen, I. A. Buyanova, Y. G. Hong, and C. W. Tu

Appl. Phys. Lett. 86, 261904 (2005); http://dx.doi.org/10.1063/1.1952586 (3 pages) | Cited 6 times

Online Publication Date: 20 June 2005

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Low-temperature photoluminescence (PL), PL excitation, and optically detected cyclotron resonance measurements are employed to determine band alignment in GaInNP/GaAs heterostructures grown by gas-source molecular-beam epitaxy. The type II band alignment at the Ga0.46In0.54NxP1−x/GaAs interface is concluded for the alloys with x ≥ 0.5% based on (i) highly efficient PL upconversion observed in the N containing samples and (ii) appearance of a near-infrared PL emission attributed to the spatially indirect type II transitions. Compositional dependence of the conduction band offset at the Ga1−yInyNxP1−x/GaAs interface is also estimated.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
71.20.Nr Semiconductor compounds
76.40.+b Diamagnetic and cyclotron resonances

Spectrally enhanced light emission from aperiodic photonic structures

L. Dal Negro, J. H. Yi, V. Nguyen, Y. Yi, J. Michel, and L. C. Kimerling

Appl. Phys. Lett. 86, 261905 (2005); http://dx.doi.org/10.1063/1.1954897 (3 pages) | Cited 36 times

Online Publication Date: 21 June 2005

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Light-emitting silicon-rich, SiNx/SiO2 Thue-Morse (T-M) multilayer structures have been fabricated in order to investigate the generation and transmission of light in strongly aperiodic deterministic dielectrics. Photoluminescence and optical transmission data experimentally demonstrate the presence of emission enhancement effects occurring at wavelengths corresponding to multiple T-M resonance states. Emission enhancement effects by a factor of almost 6 with respect to homogeneous SiNx dielectrics have been experimentally measured, in good agreement with transfer matrix simulations. The unprecedented degree of structural flexibility of T-M systems can provide alternative routes towards the fabrication of optically active multiwavelength photonic devices.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
68.65.Ac Multilayers
78.55.Hx Other solid inorganic materials

Radiation-induced electron traps in Al0.14Ga0.86N by 1 MeV electron radiation

Michael R. Hogsed, Yung Kee Yeo, Mo Ahoujja, Mee-Yi Ryu, James C. Petrosky, and Robert L. Hengehold

Appl. Phys. Lett. 86, 261906 (2005); http://dx.doi.org/10.1063/1.1977185 (3 pages) | Cited 4 times

Online Publication Date: 21 June 2005

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Electrical properties of defects induced in n-type molecular-beam-epitaxial-grown Al0.14Ga0.86N are studied using deep-level transient spectroscopy (DLTS) to explore the radiation tolerance of AlGaN-based electronic and optoelectronic devices. It has been found that four electron traps labeled R1 (0.15±0.02 eV), R2 (0.21±0.02 eV), R3 (0.26±0.02 eV), and R4 (0.33±0.03 eV) are created in the electron irradiated Al0.14Ga0.86N. The electron trap R4 is the most prominent radiation-induced defect in the DLTS spectrum and appears to be unique to AlGaN. Although the other radiation-induced traps anneal significantly at or below 400 K, this R4 trap is thermally stable up to 450 K, and could significantly affect the performance of AlGaN-based devices.
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71.55.Eq III-V semiconductors
61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.Cc Kinetics of defect formation and annealing

In situ observation of coalescence-related tensile stresses during metalorganic chemical vapor deposition of GaN on sapphire

Srinivasan Raghavan, Jeremy Acord, and Joan M. Redwing

Appl. Phys. Lett. 86, 261907 (2005); http://dx.doi.org/10.1063/1.1968436 (3 pages) | Cited 4 times

Online Publication Date: 22 June 2005

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Surface roughness and stress evolution were monitored in situ during the growth of GaN on sapphire substrates using low-temperature AlN buffer layers of varying thickness. A reduction in buffer layer thickness decreases the concentration of GaN nucleation sites which in turn increases the time to nuclei coalescence, thus varying the temporal evolution of surface roughness. By monitoring the accompanying changes in stress evolution, it is shown that island coalescence consisting of initial contact followed by subsequent surface roughness reduction is a source of tensile stress during growth of GaN films on sapphire. Such delayed coalescence also leads to an improvement in the structural properties of the material.
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81.05.Ea III-V semiconductors
68.60.Bs Mechanical and acoustical properties
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.47.Fg Semiconductor surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Crystallization of amorphous In2O3–10 wt % ZnO thin films annealed in air

Burag Yaglioglu, Hyo-Young Yeom, and David C. Paine

Appl. Phys. Lett. 86, 261908 (2005); http://dx.doi.org/10.1063/1.1977209 (3 pages) | Cited 27 times

Online Publication Date: 23 June 2005

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We report on the crystallization of amorphous indium zinc oxide (a-IZO) with stoichiometry of In2Zn0.38O3.38 (In2O3–10 wt % ZnO) thin films deposited by dc magnetron sputtering. Transmission electron microscopy and glancing incidence x-ray diffraction were used to show that, when annealed in air at 500 °C, the product of a-IZO thin film crystallization is a compositionally modulated crystal of high-pressure corundum In2O3 phase. The composition, microstructure, resistivity, carrier density, and mobility of this new IZO phase are reported and are compared to the bixbyite ITO (In2O3–9.8 wt % SnO2) deposited and annealed under identical conditions.
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81.05.Gc Amorphous semiconductors
64.70.K- Solid-solid transitions
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
73.61.Le Other inorganic semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
68.37.Lp Transmission electron microscopy (TEM)

Electrochemical lithium doping of a pentacene molecule semiconductor

Baizeng Fang, Haoshen Zhou, and Itaru Honma

Appl. Phys. Lett. 86, 261909 (2005); http://dx.doi.org/10.1063/1.1954873 (3 pages) | Cited 10 times

Online Publication Date: 23 June 2005

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Li-doped pentacene has been developed by using an electrochemical approach; that is, constant-potential electrolysis. Li-doped pentacene was characterized by Raman spectrometry and x-ray diffraction measurements. Lithium doping introduces a modification of the C–H vibrational modes located at the end of pentacene molecules. A low doping level has been observed for electrochemical synthesis of Li-doped pentacene, and lithium species are supposed to be intercalated between the two-dimensional pentacene layers. The lithium-doped pentacene exhibits a conductivity of ∼ 6×10−3 S cm−1.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.05.Hd Other semiconductors
61.72.up Other materials
82.45.Aa Electrochemical synthesis
82.45.Hk Electrolysis
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers
73.61.Ph Polymers; organic compounds
68.55.A- Nucleation and growth
61.72.S- Impurities in crystals

Efficiency of multiple atom doping in wide band gap semiconductors

Takehide Miyazaki and Satoshi Yamasaki

Appl. Phys. Lett. 86, 261910 (2005); http://dx.doi.org/10.1063/1.1977207 (3 pages) | Cited 10 times

Online Publication Date: 24 June 2005

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We present a thermodynamic model calculation for the efficiency of an impurity-atom-complex formation suggested for doping of wide band gap semiconductors, where the complexes with various sizes coexist at local equilibrium as suggested by Van de Walle and Neugebauer [J. Appl. Phys. 95, 3851 (2004)] . When the size of a target complex becomes large, the effect of configurational entropy of smaller complexes shows up in the energetics and may even hamper stabilization of the target. Thus one should design a target complex with the size being as small as possible and the binding energy as large as possible, in order to make the concept of multiple atom doping a real technology.
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61.72.up Other materials
65.40.G- Other thermodynamical quantities

Selective excitation of tryptophan fluorescence decay in proteins using a subnanosecond 295 nm light-emitting diode and time-correlated single-photon counting

Colin D. McGuinness, Kulwinder Sagoo, David McLoskey, and David J. S. Birch

Appl. Phys. Lett. 86, 261911 (2005); http://dx.doi.org/10.1063/1.1984088 (3 pages) | Cited 21 times

Online Publication Date: 24 June 2005

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We demonstrate an AlGaN light-emitting diode (LED) giving pulses of ∼ 600 ps full width half maximum, 0.35 μW average power, 0.6 mW peak power, and ∼ 12 nm bandwidth at 295 nm. This source is ideal for protein intrinsic tryptophan fluorescence decay research without the unwanted excitation of tyrosine and paves the way to lab-on-a-chip protein assays using fluorescence decay times. Fluorescence decay and anisotropy decay measurements of human serum albumin are reported and the usefulness of the 295 nm LED demonstrated in comparisons with a nanosecond flashlamp and LEDs with nominal wavelength emission of 280 nm.
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33.50.Dq Fluorescence and phosphorescence spectra
36.20.Kd Electronic structure and spectra
87.14.E- Proteins
87.15.M- Spectra of biomolecules
87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics
87.80.-y Biophysical techniques (research methods)
85.60.Jb Light-emitting devices
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Microwave modulation of electron heating and Shubnikov–de Haas oscillation in two-dimensional electron systems

X. L. Lei and S. Y. Liu

Appl. Phys. Lett. 86, 262101 (2005); http://dx.doi.org/10.1063/1.1949287 (3 pages) | Cited 9 times

Online Publication Date: 20 June 2005

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Recently discovered modulations of Shubnikov–de Haas oscillations in microwave-irradiated two-dimensional electron systems are shown to arise from electron heating induced by the radiation. The electron temperature, obtained by balancing the energy absorption from the microwave field and the energy dissipation to the lattice through realistic electron-phonon couplings, exhibits resonance. The modulation of the Shubnikov–de Haas oscillation and the suppression of magnetoresistance are demonstrated together with microwave-induced resistance oscillation, in agreement with experimental findings.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Ht High-field and nonlinear effects
73.63.-b Electronic transport in nanoscale materials and structures
71.38.-k Polarons and electron-phonon interactions
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