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25 Jul 2005

Volume 87, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 043111 (2005); http://dx.doi.org/10.1063/1.1996851 (3 pages)

Y. Gu, E.-S. Kwak, J. L. Lensch, J. E. Allen, T. W. Odom, and L. J. Lauhon
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Light-induced resonant transmittance through a gold film

Igor I. Smolyaninov, Yu-Ju Hung, and Christopher C. Davis

Appl. Phys. Lett. 87, 041101 (2005); http://dx.doi.org/10.1063/1.2001127 (2 pages) | Cited 2 times

Online Publication Date: 18 July 2005

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We report the experimental observation of photoinduced resonant transmission of light through a gold film deposited on a chalcogenide glass surface. This effect is caused by the formation of a photoinduced diffraction grating in the chalcogenide glass near the gold film surface by an optical pump beam. The transmittance of a probe beam is resonantly enhanced due to grating-induced coupling to surface electromagnetic excitations on the gold film surface. This observation demonstrates the feasibility of all-optical signal processing using the extraordinary light transmission of thin metal films.
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78.66.Bz Metals and metallic alloys
78.68.+m Optical properties of surfaces
42.79.Dj Gratings
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Mechanism of the temperature sensitivity of mid-infrared GaSb-based semiconductor lasers

S. Suchalkin, L. Shterengas, M. Kisin, S. Luryi, G. Belenky, R. Kaspi, A. Ongstad, J. G. Kim, and R. U. Martinelli

Appl. Phys. Lett. 87, 041102 (2005); http://dx.doi.org/10.1063/1.2001132 (3 pages) | Cited 4 times

Online Publication Date: 18 July 2005

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The sources of temperature sensitivity of the threshold current in type-I and type-II mid-infrared semiconductor lasers are investigated. Measurements of the interband optical absorption allow direct comparison of the optical matrix elements in laser structures with type-I and type-II band alignments and prove that the difference in the optical matrix elements is insignificant for these two groups of structures. We show that thermally-induced hole escape from the active quantum wells strongly deteriorates the optical emission in both type heterostructures. Experiments show that the temperature decay of PL is generally stronger for type-II samples.
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42.55.Px Semiconductor lasers; laser diodes
78.55.Cr III-V semiconductors
78.45.+h Stimulated emission
78.67.De Quantum wells
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Achieving 280 fs resolution with a streak camera by reducing the deflection dispersion

Mahendra Man Shakya and Zenghu Chang

Appl. Phys. Lett. 87, 041103 (2005); http://dx.doi.org/10.1063/1.2001732 (3 pages) | Cited 12 times

Online Publication Date: 18 July 2005

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The factors that limit the temporal resolution in a streak camera operating in an accumulative mode were studied. By controlling the timing jitter, the transit-time dispersion and the technical resolution of the camera on the order of 100 fs, the role of the deflection dispersion was investigated experimentally. It was done by changing the electron beam size in the deflection plates with a variable slit in front of the plates. The temporal resolution of the camera reached 280 fs when the slit width was a 5 μm slit.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.85.Qe Synchrotron radiation instrumentation
41.85.Gy Chromatic and geometrical aberrations

High-power, room-temperature, and continuous-wave operation of distributed-feedback quantum-cascade lasers at λ ∼ 4.8 μm

J. S. Yu, S. Slivken, S. R. Darvish, A. Evans, B. Gokden, and M. Razeghi

Appl. Phys. Lett. 87, 041104 (2005); http://dx.doi.org/10.1063/1.2000343 (3 pages) | Cited 43 times

Online Publication Date: 18 July 2005

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A high-power continuous-wave (CW) operation of distributed-feedback quantum-cascade lasers using a buried grating with epitaxial regrowth up to temperatures of above 60 °C is demonstrated. For a high-reflectivity-coated 13 μm-wide and 3 mm-long cavity, CW output powers of 135 mW at 25 °C and still 37 mW at 60 °C are obtained. The device exhibits a CW threshold current density of 1.1 kA/cm2, a maximum CW wall-plug efficiency of 1.48% at 25 °C, and a characteristic temperature of 177 K in pulsed mode. Single-mode emission near 4.8 μm with a side-mode suppression ratio of >30 dB and a tuning range of ∼ 8.1 cm−1 (i.e., tunability of 0.18 cm−1/K) in the temperature range from 15 to 60 °C is observed.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.65.Cd Superlattices
42.55.Px Semiconductor lasers; laser diodes

Infrared (3.8 μm) interband cascade light-emitting diode array with record high efficiency

Naresh C. Das, Kim Olver, F. Towner, G. Simonis, and H. Shen

Appl. Phys. Lett. 87, 041105 (2005); http://dx.doi.org/10.1063/1.2001759 (3 pages) | Cited 10 times

Online Publication Date: 20 July 2005

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We report here the light emission from IR interband-cascade (IC) type-II-superlattice light-emitting diode (LED) structures. We employed two different IC epitaxial structures consisting of 9 or 18 periods of active superlattice gain regions separated by multilayer injection regions. The light output (and the voltage drop) of the LEDs is observed to increase as expected with increase in the number of IC active regions. The 18-period LEDs are found to have 0.65% and 2.8% external efficiency at room temperature and liquid nitrogen temperature respectively. An increase of light intensity by 6 times is observed by thinning the GaSb substrates from 500 μm to 25 μm. Another 10% increase is observed using a linear grating on the top surface of the device.
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85.60.Jb Light-emitting devices
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources

Photomixers fabricated on nitrogen-ion-implanted GaAs

M. Mikulics, M. Marso, I. Cámara Mayorga, R. Güsten, S. Stanček, P. Kováč, S. Wu, Xia Li, M. Khafizov, R. Sobolewski, E. A. Michael, R. Schieder, M. Wolter, D. Buca, A. Förster, et al.

Appl. Phys. Lett. 87, 041106 (2005); http://dx.doi.org/10.1063/1.2006983 (3 pages) | Cited 11 times

Online Publication Date: 20 July 2005

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We report on fabrication and measurement of photomixers based on nitrogen-ion-implanted GaAs. We used energies of 500 keV, 700 keV, and 880 keV to implant N+ ions into GaAs substrates with an ion concentration of ∼ 3×1012 cm−2. The resulting material exhibited 110 fs carrier lifetime due to implantation-induced defects. Our photomixers were fabricated as metal-semiconductor-metal devices, placed at the feed point of a broadband antenna. Optoelectronic measurements were performed in the wavelength range between 350 nm and 950 nm. In comparison to their counterparts (photomixers fabricated on low-temperature-grown GaAs) the N+-implanted GaAs photomixers exhibit improvements on both the output power and responsivity. A maximal responsivity of above 100 mA/W was achieved and we did not observe any dependence of the mixer cut-off frequency on the bias voltage. These characteristics make N+-implanted GaAs the material of choice for efficient optoelectronic photomixers.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
61.72.uj III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Highly sensitive ultrafast all-optical light modulation by complex refractive-index changes in guided mode geometry composed of a photoresponsive polymer and a low-refractive-index polymer

Toshihiko Nagamura, Ryuji Matsumoto, Atsushi Naito, and Yasuyuki Nagai

Appl. Phys. Lett. 87, 041107 (2005); http://dx.doi.org/10.1063/1.1992654 (3 pages) | Cited 6 times

Online Publication Date: 22 July 2005

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Highly sensitive ultrafast all-optical light modulation is proposed on the basis of photoinduced complex refractive-index changes in composite guided wave mode (GWM) geometry composed of a low-refractive-index polymer and a photoresponsive polymer. Both calculated and observed results indicated that reflectance, which was unity at an extinction coefficient k = 0, decreased rapidly with increasing k until a certain value (kc), and increased again after that. The kc-value and the GWM dip width decreased with increasing the thickness of both polymer layers. The real-part changes shifted the GWM dip very sensitively. The low-refractive polymer contributed great improvements, such as high sensitivity and durability against a repeated femtosecond laser. The present device can give highly enhanced changes of probe light as compared with simple transmission-type devices or the GWM geometry on a metal thin film. A photoelectrochromic polymer was employed in this geometry to demonstrate ultrafast reflectance control upon femtosecond laser excitation.
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42.79.Hp Optical processors, correlators, and modulators
42.70.Jk Polymers and organics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Jq Electro-optical effects

Photonic crystals for biochemical sensing in the terahertz region

Hamza Kurt and D. S. Citrin

Appl. Phys. Lett. 87, 041108 (2005); http://dx.doi.org/10.1063/1.1999861 (3 pages) | Cited 21 times

Online Publication Date: 22 July 2005

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The propagation of terahertz waves in two-dimensional photonic-crystal waveguides was studied computationally to investigate the effects of introducing small quantities of molecules, such as deoxyribonucleic acid, into selected air holes for sensor applications. Comparison with bulk systems shows that photonic-crystal waveguides are promising for biochemical sensing.
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42.70.Qs Photonic bandgap materials
87.80.-y Biophysical techniques (research methods)
82.80.-d Chemical analysis and related physical methods of analysis
87.14.G- Nucleic acids
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Gn Optical waveguides and couplers

Fully-screened polarization-induced electric fields in blue∕violet InGaN/GaN light-emitting devices grown on bulk GaN

G. Franssen, T. Suski, P. Perlin, R. Bohdan, A. Bercha, W. Trzeciakowski, I. Makarowa, P. Prystawko, M. Leszczyński, I. Grzegory, S. Porowski, and S. Kokenyesi

Appl. Phys. Lett. 87, 041109 (2005); http://dx.doi.org/10.1063/1.2000331 (3 pages) | Cited 24 times

Online Publication Date: 22 July 2005

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Photocurrent spectroscopy and hydrostatic-pressure-dependent electroluminescence are used to show that heavy 1×1019 cm−3 Si doping of quantum barriers is sufficient to achieve full screening of polarization-induced electric fields (PIEFs) in nitride light emitting diodes (LEDs) and laser diodes (LDs) with InGaN quantum wells. Furthermore, it is shown that at currents close to lasing threshold in nitride LDs injected charge alone is sufficient to achieve full screening of PIEFs. In contrast, full screening at low currents can only be accomplished via Si doping of quantum barriers.
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85.60.Jb Light-emitting devices
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.uj III-V and II-VI semiconductors

Optical enhancement of diode laser-photoacoustic trace gas detection by means of external Fabry-Perot cavity

Alessandro Rossi, Roberto Buffa, Mario Scotoni, Davide Bassi, Salvatore Iannotta, and Andrea Boschetti

Appl. Phys. Lett. 87, 041110 (2005); http://dx.doi.org/10.1063/1.2000341 (3 pages) | Cited 12 times

Online Publication Date: 22 July 2005

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An optical enhancement method applied to a diode laser photoacoustic trace gas detector is presented. In order to improve the detection sensitivity, the light intensity inside the acoustic resonator is amplified using a Fabry-Perot cavity. A feedback signal stabilizes the laser frequency to the optical cavity length, in order to maintain the light amplification constant during the probe frequency scan. The usefulness of the optical amplifier is demonstrated by showing two ethylene spectra obtained at 1.624 μm with and without the optical enhancement. Tens to hundreds ppb (part per billion) sensibility for molecules absorbing in the region between 1.5–1.7 μm can be obtained.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.64.+z Acoustic instruments and equipment
43.20.Ye
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.62.Fi Laser spectroscopy
42.62.−b
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Feature of electron energy distribution in a low-pressure capacitive discharge

S. J. You, C. W. Chung, and H. Y. Chang

Appl. Phys. Lett. 87, 041501 (2005); http://dx.doi.org/10.1063/1.1928320 (3 pages)

Online Publication Date: 20 July 2005

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The evolution of the electron energy distribution function is investigated in the low-pressure capacitive discharge under the collisionless electron heating regime, where the electron mean-free path is comparable to or larger than the system length. As the gas pressure decreases from 50 to 10 mTorr, a different feature of electron energy distribution with a plateau in the low-energy electron range, indicating the strong electron heating in that energy range, is found. This observed result can be explained in terms of collisionless heating from the interaction between the electron bouncing motion and the oscillating sheath [ Y. M. Aliev, I. D. Kaganovich, and H. Schuter, Phys. Plasmas 4, 2413 (1997) ]. A simple calculation of the electron energy distribution with the energy diffusion coefficient, including the electron bounce effect, is in good agreement with the experiment.
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52.80.-s Electric discharges
52.25.Fi Transport properties
52.40.Kh Plasma sheaths
52.50.Gj Plasma heating by particle beams
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Extraction of a nearly monoenergetic ion beam using a pulsed plasma

Lin Xu, Demetre J. Economou, Vincent M. Donnelly, and Paul Ruchhoeft

Appl. Phys. Lett. 87, 041502 (2005); http://dx.doi.org/10.1063/1.2001129 (3 pages) | Cited 13 times

Online Publication Date: 20 July 2005

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A nearly monoenergetic ion beam was extracted from a capacitively coupled pulsed Ar plasma. The electron temperature decayed rapidly in the afterglow, resulting in uniform plasma potential, and minimal energy spread for ions extracted in the afterglow. Ion energy was controlled by a dc bias on a ring electrode surrounding the plasma. Langmuir probe measurements indicated that this bias simply raised the plasma potential without heating the electrons in the afterglow. A rejection grid downstream of the plasma allowed ions to pass only during a selected time window in the afterglow. The energy spread was 3.4 eV full width at half maximum for a peak ion beam energy of 102.0 eV. This energy spread is about an order of magnitude narrower than the beam extracted from the continuous plasma.
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52.50.Dg Plasma sources
52.80.Hc Glow; corona
52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties

Comparative study on emission characteristics of extreme ultraviolet radiation from CO2 and Nd:YAG laser-produced tin plasmas

Hiroki Tanaka, Atsushi Matsumoto, Kouzi Akinaga, Akihiko Takahashi, and Tatsuo Okada

Appl. Phys. Lett. 87, 041503 (2005); http://dx.doi.org/10.1063/1.1989441 (3 pages) | Cited 43 times

Online Publication Date: 22 July 2005

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The direct comparison of the emission characteristics of an extreme ultraviolet (EUV) light between the CO2 and the Nd:YAG laser-produced plasmas (LPP) with a solid tin target is reported. In the case of the Nd:YAG LPP, the conversion efficiency (C.E.) peaked at a laser intensity of about 5×1010 W/cm2 and decreased at higher laser intensity. In the case of the CO2 LPP, the C.E. monotonically increased up to 2×1010 W/cm2, where the C.E. is comparable to the maximum C.E. of the Nd:YAG LPP. The spectral efficiency of the Nd:YAG LPP within the 2% bandwidth around 13.5 nm decreased with laser intensity. The corresponding spectral efficiency of the CO2 LPP was almost constant. This observation indicates the potential of the CO2 laser-produced LPP as the EUV light source for the EUV lithographic systems.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.55.Rz Doped-insulator lasers and other solid state lasers
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Buckling properties of carbon nanotube bundles

K. M. Liew, C. H. Wong, and M. J. Tan

Appl. Phys. Lett. 87, 041901 (2005); http://dx.doi.org/10.1063/1.2001135 (3 pages) | Cited 33 times

Online Publication Date: 18 July 2005

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In the study described herein, we observed the buckling behavior of carbon nanotube (CNT) bundles under axial compression using molecular dynamics (MD) simulations. We found that the critical buckling loads of CNT bundles are much higher than that of an individual single-walled carbon nanotube (SWCNT). The addition of SWCNTs into a CNT bundle results in as much as a fivefold increase in its buckling load. The long-range van der Waals interactions also improve the overall rigidity of the CNT bundles. The larger the CNT bundle, the greater the significance of the van der Waals interactions. We also found that the buckling load of a CNT bundle is directly proportional to that of a SWCNT.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Correlation between interfacial electronic structure and mechanical properties of ZrN–Me (MeAg, Au, or Pd) nanocomposite films

S. M. Aouadi, P. K. Shreeman, Q. Ge, J. Xu, and S. R. Mishra

Appl. Phys. Lett. 87, 041902 (2005); http://dx.doi.org/10.1063/1.2001141 (3 pages) | Cited 4 times

Online Publication Date: 18 July 2005

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Nanocomposite films of ZrN–Me (MeAg, Au, or Pd) were prepared using reactive unbalanced magnetron sputtering. The hardness and elastic modulus were measured by nanoindention and were found to vary differently with composition for the three nanocomposite structures. Young’s modulus was found to decrease much more dramatically with the increase in Me content for the ZrN–Ag system. These findings were attributed to the weaker bonding mechanism at the interface between the ceramic and the metallic phases, which is more prone to grain-boundary sliding as shown using first-principles calculations of the electronic structure at the interface for the three systems.
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81.05.Mh Cermets, ceramic and refractory composites
68.35.Gy Mechanical properties; surface strains
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity
73.20.-r Electron states at surfaces and interfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Segregation of nearest-neighbor donor-pair defects to Si/SiO2 interfaces

Yong-Sung Kim and K. J. Chang

Appl. Phys. Lett. 87, 041903 (2005); http://dx.doi.org/10.1063/1.2001752 (3 pages) | Cited 4 times

Online Publication Date: 18 July 2005

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We perform first-principles density-functional calculations to study the stability of donor-pair defects at Si/SiO2 interfaces. For P dopants, individual dopant atoms energetically favor Si lattice sites in the interface region, as compared to bulk Si. When dopant atoms aggregate to the interface region at very high dopant concentrations, dopant segregation occurs in form of electrically deactivating nearest-neighbor donor pairs that comprise two threefold coordinated dopant atoms. Our defect model explains both the redistribution and deactivation of dopant atoms observed at Si/SiO2 interfaces.
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61.72.Bb Theories and models of crystal defects
61.72.J- Point defects and defect clusters
61.72.up Other materials
71.55.Ht Other nonmetals

Combined synchrotron x-ray diffraction and wafer curvature measurements during Ni–Si reactive film formation

C. Rivero, P. Gergaud, M. Gailhanou, O. Thomas, B. Froment, H. Jaouen, and V. Carron

Appl. Phys. Lett. 87, 041904 (2005); http://dx.doi.org/10.1063/1.1999021 (3 pages) | Cited 16 times

Online Publication Date: 18 July 2005

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Combined x-ray diffraction and wafer curvature measurements during annealing of Ni thin films (13 nm) deposited on Si (001) reveal distinct stages in stress development and silicide growth. Thanks to this unique experimental setup, a clear correlation is established between force extrema at distinct temperatures and the appearance of new silicides. It is shown that the transient formation of Ni3Si2 has a strong influence on the overall stress development.
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68.60.Bs Mechanical and acoustical properties
81.40.Gh Other heat and thermomechanical treatments

Raman studies of Ge-promoted stress modulation in 3C–SiC grown on Si(111)

Ch. Zgheib, L. E. McNeil, M. Kazan, P. Masri, F. M. Morales, O. Ambacher, and J. Pezoldt

Appl. Phys. Lett. 87, 041905 (2005); http://dx.doi.org/10.1063/1.1999858 (3 pages) | Cited 16 times

Online Publication Date: 18 July 2005

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We present a study of the stress state in cubic silicon carbide (3C–SiC) thin films (120 and 300 nm) grown by solid-source molecular-beam epitaxy (SSMBE) on Si(111) substrates modified by the deposition of germanium prior to the carbonization of Si. μ-Raman measurements were used to determine the residual stress existing in the 3C–SiC layers. The stress is found to decrease linearly with increasing Ge quantity but with different strength depending on the 3C–SiC thickness deposited after the introduction of Ge. Based on secondary ions mass spectroscopy (SIMS) and transmission electron microscopy (TEM) analyses it is suggested that the Ge introduced prior to the carbonization step remains in the near-interface region and reduces the Si outdiffusion, which further reduces the stress state of the 3C–SiC layers.
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68.60.Bs Mechanical and acoustical properties
78.30.Hv Other nonmetallic inorganics
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Electronic structure of wurtzite quantum dots with cylindrical symmetry

L. C. Lew Yan Voon, C. Galeriu, B. Lassen, M. Willatzen, and R. Melnik

Appl. Phys. Lett. 87, 041906 (2005); http://dx.doi.org/10.1063/1.2000329 (3 pages) | Cited 8 times

Online Publication Date: 18 July 2005

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This paper presents a six-band k∙p theory for wurtzite semiconductor nanostructures with cylindrical symmetry. Our work extends the formulation of Vahala and Sercel [Phys. Rev. Lett. 65 239 (1990) ] to the Rashba-Sheka-Pikus Hamiltonian for wurtzite semiconductors, without the need for the axial approximation. Comparisons of our formulation for studying the electronic structure of wurzite quantum dots with the conventional formulation are given.
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71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations

Cross-sectional Raman spectra of InN epifilms

J. W. Chen, Y. F. Chen, H. Lu, and W. J. Schaff

Appl. Phys. Lett. 87, 041907 (2005); http://dx.doi.org/10.1063/1.2001137 (3 pages) | Cited 17 times

Online Publication Date: 20 July 2005

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Cross-sectional Raman spectroscopy was performed on InN epifilms. We found direct evidence for the existence of residual strain along the growth direction of the InN films. This result is very useful for the understanding of the depth dependence of the physical properties. We also found that cross-sectional Raman spectroscopy can be used to study certain vibration modes that are normally not observable in the normal surface Raman configuration.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.60.Bs Mechanical and acoustical properties
63.20.-e Phonons in crystal lattices

Frequency-dependent optical constants and conductivities of hydrogen-functionalized single-walled carbon nanotubes

Chul Kang, In Hee Maeng, Seung Jae Oh, Joo-Hiuk Son, Tae-In Jeon, Kay Hyeok An, Seong Chu Lim, and Young Hee Lee

Appl. Phys. Lett. 87, 041908 (2005); http://dx.doi.org/10.1063/1.1999015 (3 pages) | Cited 12 times

Online Publication Date: 20 July 2005

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The frequency-dependent optical constants and electrical conductivities of hydrogen-functionalized single-walled carbon nanotubes (SWNTs) have been measured from the 0.2 to 1.5 THz region using a terahertz time domain spectroscopy. The indices of refraction and electrical conductivities of the sample after hydrogen functionalization were smaller than those of the sample before hydrogen functionalization. The experimental results were fitted using the Maxwell–Garnett model, and a reduction of plasma frequency was observed. This can be attributed to the fact that the hydrogen functionalization has reduced the number of free carriers with the bonding change from sp2 to sp3.
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81.07.De Nanotubes
78.67.Ch Nanotubes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
73.63.Fg Nanotubes
72.20.-i Conductivity phenomena in semiconductors and insulators

Optical properties and carrier dynamics of two-dimensional electrons in AlGaN/GaN single heterostructures

Ho-Sang Kwack, Yong-Hoon Cho, G. H. Kim, M. R. Park, D. H. Youn, S. B. Bae, K.-S. Lee, Jae-Hoon Lee, Jung-Hee Lee, T. W. Kim, T. W. Kang, and Kang L. Wang

Appl. Phys. Lett. 87, 041909 (2005); http://dx.doi.org/10.1063/1.2000334 (3 pages) | Cited 12 times

Online Publication Date: 21 July 2005

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We have investigated the optical properties and carrier dynamics of the two-dimensional electron gas (2DEG) in Al0.4Ga0.6N/GaN single heterostructures grown by metalorganic chemical vapor deposition by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. Shubnikov-de Haas oscillations were clearly observed at 1.5 K, confirming the existence of a 2DEG. An additional 2DEG PL emission appeared at about 40 meV below the GaN band-edge emission and persisted up to about 100 K, while this peak disappeared when the top Al0.4Ga0.6N layer was removed by reactive ion etching. We observed abrupt PLE absorption at GaN band edge energy and approximately 50‐ps delayed risetime compared to GaN and AlGaN emissions, indicating effective carrier transfer from the GaN flatband and AlGaN regions to the heterointerface. Even though the 2DEG emission is a spatially-indirect (slow) recombination, a fast decay component of ∼ 0.2 ns is found to be dominant in 2DEG emission because of the fast exhaustion of photogenerated holes in GaN flatband region via spatially-direct (fast) GaN recombination. From the results, we explain the carrier generation, transfer, and recombination dynamics and the relationships between 2DEG, GaN, and Al0.4Ga0.6N emissions in undoped Al0.4Ga0.6N/GaN single heterostructures.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Ab initio study of the structural stability of TiSi2 compounds

C. Colinet, W. Wolf, R. Podloucky, and A. Pasturel

Appl. Phys. Lett. 87, 041910 (2005); http://dx.doi.org/10.1063/1.2000340 (3 pages) | Cited 7 times

Online Publication Date: 21 July 2005

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In order to clarify the allotropic structural properties of TiSi2 we calculated by means of an ab initio density functional approach the total energies of the C49, C54, and C40 crystal structures of the bulk compound. We found that at T = 0 K the C49 structure of TiSi2 is its most stable phase whereas the C54 structure, which experimentally is considered to be the ground state, is less favorable. Furthermore, by calculating the vibrational properties and the corresponding temperature dependent free energies of the three structures we predict a structural transition from C49 to C54 at about 1100 K. We also demonstrate that point defects as well as stacking faults, which are known to be present in the C49 phase, have no significant influence on the structural stability.
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61.66.Fn Inorganic compounds
61.72.J- Point defects and defect clusters
61.72.Nn Stacking faults and other planar or extended defects
64.70.K- Solid-solid transitions
63.20.-e Phonons in crystal lattices
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
65.40.G- Other thermodynamical quantities

Self-forming diffusion barrier layer in Cu–Mn alloy metallization

J. Koike and M. Wada

Appl. Phys. Lett. 87, 041911 (2005); http://dx.doi.org/10.1063/1.1993759 (3 pages) | Cited 63 times

Online Publication Date: 22 July 2005

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Advancement of semiconductor devices requires the realization of an ultrathin diffusion barrier layer between Cu interconnect and insulating layers. The present work investigated the possibility of the self-forming barrier layer in Cu–Mn alloy thin films deposited directly on SiO2. After annealing at 450 °C for 30 min, a Mn containing amorphous oxide layer of 3–4 nm in thickness was formed uniformly at the interface. Residual Mn atoms were removed to form a surface oxide layer, leading to a drastic resistivity decrease of the film. No interdiffusion was detected between Cu and SiO2 within the detection limit of x-ray energy dispersive spectroscopy.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Fx Diffusion; interface formation

Zone-axis diffraction study of pressure-induced inhomogeneity in single-crystal Fe1−xO

Yang Ding, Haozhe Liu, Jian Xu, Charles T. Prewitt, Russell J. Hemley, and Ho-kwang Mao

Appl. Phys. Lett. 87, 041912 (2005); http://dx.doi.org/10.1063/1.1999016 (3 pages) | Cited 5 times

Online Publication Date: 22 July 2005

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A zone-axis synchrotron diffraction study of complex and inhomogeneous Fe1−xO thin single crystal under pressure is presented in this letter. Using this method, four phases are observed to coexist in a single crystal of Fe1−xO at 35 GPa in diamond-anvil cells. One phase has cubic symmetry, whereas the other three phases have not been reported previously and can be interpreted as either orthorhombic or monoclinic. The discovery of multiple phases existing in Fe1−xO indicates that structural inhomogeneity of the sample can be induced under high pressure, a result that has important implications for the high P-T behavior of this complex material. Such information is not available using conventional diffraction techniques.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
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