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26 Dec 2005

Volume 87, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 263102 (2005); http://dx.doi.org/10.1063/1.2150278 (3 pages)

Z. Zhong, G. Katsaros, M. Stoffel, G. Costantini, K. Kern, O. G. Schmidt, N. Y. Jin-Phillipp, and G. Bauer
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Generation of single color centers by focused nitrogen implantation

J. Meijer, B. Burchard, M. Domhan, C. Wittmann, T. Gaebel, I. Popa, F. Jelezko, and J. Wrachtrup

Appl. Phys. Lett. 87, 261909 (2005); http://dx.doi.org/10.1063/1.2103389 (3 pages) | Cited 72 times

Online Publication Date: 21 December 2005

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Single defect centers in diamond have been generated via nitrogen implantation. The defects have been investigated by single defect center fluorescence microscopy. Optical and electron paramagnetic resonance spectra unambiguously show that the produced defect is the nitrogen-vacancy color center. An analysis of the nitrogen flux together with a determination of the number of nitrogen-vacancy centers yields that on average one 2 MeV nitrogen atom need to be implanted per defect center.
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71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters
76.30.Mi Color centers and other defects
61.72.up Other materials
78.40.Ha Other nonmetallic inorganics
61.72.Yx Interaction between different crystal defects; gettering effect

Correlating elasticity and cleavage

P. Lazar, R. Podloucky, and W. Wolf

Appl. Phys. Lett. 87, 261910 (2005); http://dx.doi.org/10.1063/1.2149988 (3 pages) | Cited 15 times

Online Publication Date: 22 December 2005

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For brittle cleavage under Load Mode I, a model for single crystals is presented which derives the critical stress in terms of the cleavage energy and the uniaxial elastic modulus. The model parameters are determined by fitting to results of ab initio density functional calculations. The crucial concept for establishing an accurate correlation between cleavage and elastic properties is based on a generalization of the traditionally applied Orowan–Gilman model by introducing a localization length Lb as a new materials parameter. By that, a precise correlation between elastic and cleavage properties is established. We propose that, with an average value of Lb ≈ 2.4 Å, the critical stress can be directly estimated from the cleavage energy and the uniaxial stress within an error of ±10%.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
62.20.M- Structural failure of materials

Atomistic analysis of the mechanism of hydrogen diffusion in plasma-deposited amorphous silicon thin films

Mayur S. Valipa and Dimitrios Maroudas

Appl. Phys. Lett. 87, 261911 (2005); http://dx.doi.org/10.1063/1.2158033 (3 pages) | Cited 5 times

Online Publication Date: 22 December 2005

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We report the mechanism and activation barrier of H diffusion on the surface and in the bulk of plasma-deposited hydrogenated amorphous silicon (a-Si:H) films during postdeposition exposure of the films to H atoms from a H2 plasma. Our study is based on molecular-dynamics simulations of repeated impingement of H atoms on surfaces of smooth a-Si:H films over the temperature range 475–800 K. The H diffusion mechanism is identical both on the a-Si:H surface and in the bulk a-Si:H film. Specifically, the H atom diffuses rapidly through a floating-bond-mediated migration process; this floating bond accompanies the H atom as it hops from one Si atom to another. The Si atoms between which the H hops during its diffusion are typically either very weakly bonded or not bonded to each other. The calculated activation barrier for H diffusion is only 0.10 eV.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
66.30.J- Diffusion of impurities
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
61.43.Dq Amorphous semiconductors, metals, and alloys

Acoustic channel drop tunneling in a phononic crystal

Y. Pennec, B. Djafari-Rouhani, J. O. Vasseur, H. Larabi, A. Khelif, A. Choujaa, S. Benchabane, and V. Laude

Appl. Phys. Lett. 87, 261912 (2005); http://dx.doi.org/10.1063/1.2158019 (3 pages) | Cited 24 times

Online Publication Date: 22 December 2005

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We study both theoretically and experimentally the possibility of resonant tunneling of acoustic waves between two parallel guides created in a phononic crystal composed of steel cylinders in water. In the absolute band gap of the phononic crystal, ranging from 250 to 325 kHz, a full transmission band exists for propagation inside a straight waveguide. We show that the transfer of a particular wavelength can occur between two parallel waveguides coupled together through an appropriate coupling structure. The latter is composed of isolated cavities interacting with stubs located at the sides of the waveguides.
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63.20.-e Phonons in crystal lattices
62.65.+k Acoustical properties of solids

Etching silicon wafer without hydrofluoric acid

Hong Liu and Zhong Lin Wang

Appl. Phys. Lett. 87, 261913 (2005); http://dx.doi.org/10.1063/1.2158021 (3 pages) | Cited 4 times

Online Publication Date: 22 December 2005

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A one-step hydrofluoric-acid-free hydrothermal-etching technique is demonstrated for the preparation of porous silicon with vertical holes. This method demonstrates a “green” chemical approach for etching a silicon wafer or the preparation of bismuth-silicon nanostructures without toxic acid or applying an external voltage. By controlling the heating temperature (<180 °C) and time, nanoscale vertically holed porous silicon has been created. A formation mechanism has been proposed on the basis of experimental observations.
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81.65.Cf Surface cleaning, etching, patterning
81.07.Bc Nanocrystalline materials

Structural and optical properties of InAs quantum dots regrown on atomic hydrogen-cleaned GaAs surface

Jong Su Kim, Mitsuo Kawabe, Nobuyki Koguchi, Dong-Yul Lee, Jin Soo Kim, and In-Ho Bae

Appl. Phys. Lett. 87, 261914 (2005); http://dx.doi.org/10.1063/1.2150582 (3 pages) | Cited 2 times

Online Publication Date: 23 December 2005

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We report the structural and optical properties of InAs quantum dots (QDs) directly regrown on air-exposed and subsequent atomic hydrogen-cleaned (AHC) GaAs (001) surface. The average size of InAs QDs on the AHC GaAs surface is 29 nm, which is larger than 22 nm for the conventionally grown InAs QDs on GaAs. The integrated photoluminescence intensity of the InAs QDs on the AHC GaAs measured at room temperature is larger than that of the reference sample by two orders, even though the cleaned GaAs surface directly faced the base of the InAs QDs. The decrease in the interface states between the wetting layer and AHC GaAs was confirmed by Franz–Keldysh oscillations of the photoreflectance spectra.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Optical characterization of GaN by N+ implantation into GaAs at elevated temperature

S. Dhara, P. Magudapathy, R. Kesavamoorthy, S. Kalavathi, K. G. M. Nair, G. M. Hsu, L. C. Chen, K. H. Chen, K. Santhakumar, and T. Soga

Appl. Phys. Lett. 87, 261915 (2005); http://dx.doi.org/10.1063/1.2099542 (3 pages) | Cited 6 times

Online Publication Date: 23 December 2005

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Both hexagonal wurtzite and cubic zinc blend GaN phases were synthesized in GaAs by 50 keV N+ implantation at 400 °C and subsequent annealing at 900 °C for 15 min in N2 ambient. The crystallographic structural and Raman scattering studies revealed that GaN phases were grown for fluence above 2×1017 cm−2. Temperature-dependent photoluminescence study showed a sharp direct band-to-band transition peak ∼ 3.32 eV at temperature ⩽ 200 K. The intermediate band-gap value, with respect to ∼ 3.4 eV for hexagonal and ∼ 3.27 eV for cubic phases of GaN, is indicative of the formation of mixed hexagonal and cubic phases.
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78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.66.Fn Inorganic compounds
61.72.Cc Kinetics of defect formation and annealing

Structural transitions in NaBH4 under pressure

Ravhi S. Kumar and Andrew L. Cornelius

Appl. Phys. Lett. 87, 261916 (2005); http://dx.doi.org/10.1063/1.2158505 (3 pages) | Cited 26 times

Online Publication Date: 27 December 2005

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The structure of the technologically important hydrogen storage compound NaBH4 has been investigated under pressures up to 30 GPa by in situ angle dispersive high pressure x-ray diffraction using synchrotron x rays and a diamond anvil cell. Our experimental results show pressure-induced structural transitions of α‐NaBH4 (cubic - Fm3m) to β‐NaBH4 (tetragonal - P421c) at 6.3 GPa and further to an orthorhombic phase (Pnma) at 8.9 GPa. The high pressure orthorhombic phase is found to be stable up to 30 GPa. The cubic phase is completely recovered on releasing the pressure back to ambient.
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64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids

Low-threshold amplified spontaneous emission in thin films of poly(tetraarylindenofluorene)

Frédéric Laquai, Panagiotis E. Keivanidis, Stanislav Baluschev, Josemon Jacob, Klaus Müllen, and Gerhard Wegner

Appl. Phys. Lett. 87, 261917 (2005); http://dx.doi.org/10.1063/1.2158508 (3 pages) | Cited 9 times

Online Publication Date: 27 December 2005

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We report on amplification of blue light (469 nm) via amplified spontaneous emission in asymmetric planar waveguides of a fully arylated polyindenofluorene derivative. A very low threshold value of about 3 μJ/cm2 ( ∼ 375 W/cm2) for amplification of light has been demonstrated by pumping the waveguides at 3.0 eV (410 nm) with a stripe shape excitation beam. Moderate gain coefficients up to 21 cm−1 and loss coefficients around 6 cm−1 have been measured. All measurements were performed under ambient conditions. No sample degradation could be observed which testifies to the excellent stability of the material against photodegradation.
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78.45.+h Stimulated emission
42.70.Jk Polymers and organics
42.70.Hj Laser materials

Mechanical properties of a bulk Cu0.5NiAlCoCrFeSi glassy alloy in 288 °C high-purity water

Y. Y. Chen, U. T. Hong, J. W. Yeh, and H. C. Shih

Appl. Phys. Lett. 87, 261918 (2005); http://dx.doi.org/10.1063/1.2159090 (3 pages) | Cited 26 times

Online Publication Date: 28 December 2005

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The tensile properties and fatigue lives of a bulk Cu0.5NiAlCoCrFeSi glassy alloy were measured in 288 °C water and compared with those obtained in air at ∼ 25 °C. The bulk glassy alloy retained good tensile properties in 288 °C water, i.e., tensile fracture strength and tensile fracture elongation were, respectively, 2660 MPa and 2.01% in air and a little lower, 2000 MPa and 1.49%, in 288 °C water. The results of fatigue tests confirmed the significant decrease in fatigue life in high-temperature water. A decrease in strain rate from 0.5 to 0.001% s−1 decreased fatigue life by a factor of ∼ 5.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
61.43.Fs Glasses
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Strain-induced ordering of small Ge islands in clusters at the surface of multilayered Si–Ge nanostructures

R. Marchetti, F. Montalenti, Leo Miglio, G. Capellini, M. De Seta, and F. Evangelisti

Appl. Phys. Lett. 87, 261919 (2005); http://dx.doi.org/10.1063/1.2151250 (3 pages) | Cited 20 times

Online Publication Date: 29 December 2005

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Classical molecular-dynamics simulations based on the Tersoff potential are used to compute at the atomic level the strain-induced potential well generated at the surface of the capping layer by a buried, three-dimensional Ge island on Si(001). A simple model is outlined in order to predict the configurational arrangement for the nucleation of small Ge islands in such a potential well. The theoretical predictions are compared with atomic force microscope images of multilayered SiGe nanostructures grown by chemical vapor deposition. The cluster configuration is shown to be strongly dependent on the capping layer thickness, and to closely mimic the behavior predicted by the model.
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68.65.Ac Multilayers
61.46.-w Structure of nanoscale materials

Kinetics of irradiation-induced Cu precipitation in nuclear reactor pressure vessel steels

Y. Nagai, T. Toyama, Y. Nishiyama, M. Suzuki, Z. Tang, and M. Hasegawa

Appl. Phys. Lett. 87, 261920 (2005); http://dx.doi.org/10.1063/1.2159091 (3 pages) | Cited 10 times

Online Publication Date: 30 December 2005

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The followup of the embrittlement of nuclear power reactor pressure vessels (RPVs) is of critical importance for the safety assessment in the nuclear industry. The prediction of their future degradation is based on the extrapolation of the past testing of surveillance materials irradiated in the power reactor and in material testing reactors with accelerated dose rates. Using positron annihilation spectroscopy, however, we here reveal a kinetics of irradiation-induced precipitation, i.e., very low dose rate can significantly enhance Cu nanoprecipitation. The mechanism results in the embrittlement in practical RPVs, occurring at a much earlier stage than that found from accelerated tests, suggesting that accelerated tests are not enough for prediction of the embrittlement from Cu nanoprecipitation.
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28.41.Qb Structural and shielding materials
28.41.Te Protection systems, safety, radiation monitoring, accidents, and dismantling
61.80.Fe Electron and positron radiation effects
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
78.70.Bj Positron annihilation

Broadband omnidirectional reflection from negative index materials

Mark Bloemer, Giuseppe D’Aguanno, Michael Scalora, and Nadia Mattiucci

Appl. Phys. Lett. 87, 261921 (2005); http://dx.doi.org/10.1063/1.2151251 (3 pages) | Cited 12 times

Online Publication Date: 30 December 2005

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We show, by using a dispersion relation with parameters taken from experimental data, that a single layer of a negative index material has omnidirectional reflection properties. In the range between the electric plasma frequency and the magnetic plasma frequency, the refractive index is close to zero and the negative index materials reflect radiation for all angles of incidence and polarization with reflectivities of ∼ 99%. In addition, with increasing angles of incidence, the reflecting band does not shift in frequency but actually widens. The operational bandwidth can be 100% or greater by increasing the separation between the electric and magnetic plasma frequencies.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Electrochemical preparation of a stable accumulation layer on Si: A synchrotron radiation photoelectron spectroscopy study

K. Skorupska, M. Lublow, M. Kanis, H. Jungblut, and H. J. Lewerenz

Appl. Phys. Lett. 87, 262101 (2005); http://dx.doi.org/10.1063/1.2150267 (3 pages) | Cited 19 times

Online Publication Date: 19 December 2005

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Chronoamperometric conditioning of float zone n-Si(111) in 2 M NaOH solution in the potential range negative from open-circuit potential is performed in a combined electrochemistry/ultrahigh-vacuum surface analysis experiment. Synchrotron Radiation Photoelectron Spectroscopy measurements at the U49/2 beamline at Bessy II using the SoLiAs facility show formation of a ultrahigh-vacuum-stable permanent accumulation layer without junction formation. Comparison of the Thomas–Fermi screening potential and the mean inelastic scattering length λesc of photoelectrons at hν = 150 eV (λesc = 4 Å) and hν = 585 eV (λesc = 15 Å) indicates a surface electron concentration of 3×1018 cm−3 for a bulk doping level of 1015 cm−3. The observed shift of the Si 2p3/2 and 2p1/2 core level with photon energy is in excellent agreement with the shifted onset of the x-ray photoelectron spectroscopy valence-band spectrum measured at hν = 150 eV.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
82.45.-h Electrochemistry and electrophoresis

Dielectric properties of ultrathin SiO2 slabs

N. Shi and R. Ramprasad

Appl. Phys. Lett. 87, 262102 (2005); http://dx.doi.org/10.1063/1.2150584 (3 pages) | Cited 6 times

Online Publication Date: 19 December 2005

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First-principles total energy calculations have been performed to determine the extent to which surfaces impact the dielectric properties of ultrathin dielectric materials. SiO2 (0001) slabs in α-quartz phase with various thicknesses were considered in this study, using a new method that allows for the partitioning of the surface and bulk contributions to the total field-induced polarization. It was found that the bulk polarization and the dielectric constant can be determined even from ultrathin films terminated with Si atoms, and that surface effects do not significantly impact the dielectric properties of (0001) α-quartz slabs.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)

Carrier dynamics in laterally strain-modulated InGaAs quantum wells

Vadim Talalaev, Jens W. Tomm, Thomas Elsaesser, Ute Zeimer, Jörg Fricke, Arne Knauer, Heiko Kissel, Markus Weyers, Georgiy G. Tarasov, J. Grenzer, and U. Pietsch

Appl. Phys. Lett. 87, 262103 (2005); http://dx.doi.org/10.1063/1.2151248 (3 pages) | Cited 2 times

Online Publication Date: 19 December 2005

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We investigate the transient recombination and transfer properties of nonequilibrium carriers in an In0.16Ga0.84As/GaAs quantum well (QW) with an additional lateral confinement implemented by a patterned stressor layer. The structure thus contains QW- and quantum-wire-like areas. At low excitation densities, photoluminescence (PL) transients from both areas are well described by a rate equation model for a three-level system with a saturable interlevel carrier transfer representing the lateral drift of carriers from the QW regions into the wires. Small-signal carrier lifetimes for QW, wires, and transfer time from QW to wire are 180, 190, and 28 ps, respectively. For high excitation densities the time constants of the observed transients increase, in agreement with the model. In addition, QW and wire PL lines merge indicating a smoothening of the potential difference, i.e., the effective carrier confinement caused by the stressor structure becomes weaker with increasing excitation.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors

Investigation of silicon-germanium fins fabricated using germanium condensation on vertical compliant structures

Tsung-Yang Liow, Kian-Ming Tan, Yee-Chia Yeo, Ajay Agarwal, Anyan Du, Chih-Hang Tung, and Narayanan Balasubramanian

Appl. Phys. Lett. 87, 262104 (2005); http://dx.doi.org/10.1063/1.2151257 (3 pages) | Cited 6 times

Online Publication Date: 19 December 2005

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We report the formation of defect-free SiGe vertical heterostructures using Ge condensation on vertical SiGe structures. To evaluate the effectiveness of substrate compliance in vertical structures, SiGe fins of various widths were subjected to Ge condensation. This formed vertical fin heterostructures comprising a SiGe core region sandwiched by Ge-rich regions. Using cross-sectional transmission electron microscopy (TEM), wide fins were found to contain more dislocations than narrower fins, in which we observed few or no dislocations. Lattice strain analysis using high-resolution TEM image analysis was used to confirm that strain relaxation has occurred. In the wide fins (noncompliant substrate), strain relaxation was dislocation mediated. In the narrow fins, substrate compliance enabled strain relaxation in the Ge-rich layer with reduced dislocation formation. Hence, we also demonstrated the formation of a strain-relaxed homogeneous SiGe fin ( ∼ 90% Ge concentration) with no observable dislocations.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.60.Bs Mechanical and acoustical properties
64.70.F- Liquid-vapor transitions

Local p-type conductivity in zinc oxide dual-doped with nitrogen and arsenic

A. Krtschil, A. Dadgar, N. Oleynik, J. Bläsing, A. Diez, and A. Krost

Appl. Phys. Lett. 87, 262105 (2005); http://dx.doi.org/10.1063/1.2149171 (3 pages) | Cited 30 times

Online Publication Date: 20 December 2005

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A doping approach for p-type ZnO is reported which is reproducible and long-time stable. For p-type doping the zinc oxide layers were doped simultaneously with nitrogen and arsenic in metal organic vapor phase epitaxy. The conductivity type of the layers was investigated by scanning capacitance microscopy, a technique based on local capacitance-voltage analysis (C-V) with submicron spatial resolution. Depending on the growth parameters, largely extended p-type domains were observed, surrounded by n-type regions. The differences in local conductivity type are directly correlated to the topography as measured with atomic force microscopy revealing p-type for smooth, two-dimensional surfaces and n-type signals in the case of three-dimensional island growth or structural defects, i.e., microcracks or surface pits.
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73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.47.Fg Semiconductor surfaces
68.37.Ps Atomic force microscopy (AFM)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
72.60.+g Mixed conductivity and conductivity transitions

Demonstration of Rashba spin splitting in GaN-based heterostructures

W. Weber, S. D. Ganichev, S. N. Danilov, D. Weiss, W. Prettl, Z. D. Kvon, V. V. Bel’kov, L. E. Golub, Hyun-Ick Cho, and Jung-Hee Lee

Appl. Phys. Lett. 87, 262106 (2005); http://dx.doi.org/10.1063/1.2158024 (3 pages) | Cited 40 times

Online Publication Date: 20 December 2005

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The circular photogalvanic effect, induced by infrared radiation, has been observed in (0001)-oriented n‐GaN low dimensional structures. The photocurrent changes sign upon reversing the radiation helicity demonstrating the existence of spin splitting of the conduction band in k space in this type of materials. The observation suggests the presence of a sizeable Rashba type of spin splitting, caused by the built-in asymmetry at the AlGaN/GaN interface.
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73.21.Fg Quantum wells
73.50.Pz Photoconduction and photovoltaic effects
73.63.Hs Quantum wells
73.20.At Surface states, band structure, electron density of states

Surface conductive layers on oxidized (111) diamonds

Sung-Gi Ri, Daisuke Takeuchi, Hiromitsu Kato, Masahiko Ogura, Toshiharu Makino, Satoshi Yamasaki, Hideyo Okushi, Bohuslav Rezek, and Christoph E. Nebel

Appl. Phys. Lett. 87, 262107 (2005); http://dx.doi.org/10.1063/1.2158020 (3 pages) | Cited 6 times

Online Publication Date: 20 December 2005

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Surface conductive layers (SCL) on oxidized (111) diamonds with smooth surfaces after exposure to air were detected and characterized by Hall effect measurements. Hall effect measurements show that the conductivity is p type with sheet hole concentrations around of 1012 cm−2 and Hall mobilities between 5 and 130 cm2/V s. The SCL vanishes by thermal annealing at a temperature higher than 460 K in He atmosphere, and recovers in air. These characteristics are similar to those generated by hydrogen termination. The experiments revealed that these SCLs are present on boron doped (111) and undoped (111) diamond films with smooth surfaces and natural IIa (111) diamonds, but not on (111) diamond films with rough surfaces and not on (100) diamonds.
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73.25.+i Surface conductivity and carrier phenomena
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.Cc Kinetics of defect formation and annealing

Fast-forming boron-oxygen-related recombination center in crystalline silicon

Karsten Bothe and Jan Schmidt

Appl. Phys. Lett. 87, 262108 (2005); http://dx.doi.org/10.1063/1.2147727 (3 pages) | Cited 5 times

Online Publication Date: 21 December 2005

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The mechanism of a fast carrier lifetime degradation effect proceeding within seconds in boron-doped Czochralski silicon is investigated. The decrease in the carrier lifetime is attributed to the formation of a deep boron-oxygen-related recombination center with a strongly asymmetric electron-to-hole capture cross section ratio of 100. The center is activated in a two-step process. In a first step, the electron quasi-Fermi level has to be shifted above an energy level at EV+0.635 eV before, in the second step, the actual activation occurs via a thermally activated process with an energy barrier of 0.23 eV. A defect model is proposed to explain the observed activation behavior.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Effect of strain on p-channel metal-oxide-semiconductor field-effect-transistor current enhancement using stress-modulated silicon nitride films

Cha-Hsin Lin, Zingway Pei, Siddheswar Maikap, Ching-Chiun Wang, Ching-Sen Lu, Lurng-Shehng Lee, Ming-Jinn Tsai, and Yi-Jen Chan

Appl. Phys. Lett. 87, 262109 (2005); http://dx.doi.org/10.1063/1.2149987 (3 pages) | Cited 1 time

Online Publication Date: 21 December 2005

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The stress in chemical-vapor-deposited silicon nitride films ( ∼ 100 nm thick) is modulated by an ion implantation technique. The tensile-strained silicon nitride film is deposited on the back and front sides of a Si wafer. After implantation of P+, As+, Sb+, or BF2+ ion species, the stress of the silicon nitride film becomes compressive on the front side. It can be explained by strain relaxation of Si–N bond on the front side and highly tensile-strained Si–N bond on the back side of wafer. The compressive stress is increased with a double-implantation process because of more atomic collisions in the silicon nitride film, as well as more strain relaxation of Si–N bond on the front side of wafer. After a thermal annealing process, the compressive stress in the silicon nitride film with P+, As+, or Sb+ implantation is reduced, while compressive stress is increased for BF2+ ion implantation due to formation of the B–N bond in silicon nitride film. To justify the stress-modulated silicon nitride film by the ion implantation technique, the p-channel metal-oxide-semiconductor field-effect transistor (p-MOSFET) is fabricated. The drive current of a p-MOSFET is improved by 7–13% for implanted silicon nitride films, due to the compressive strain-induced effective mass lowering in the channel.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing

Elliptically polarized absorption spectroscopy and observation of spin coherence in intrinsic GaAs

Tianshu Lai, Xiaodong Liu, Haihong Xu, Zhongxing Jiao, Liang Lei, Jinhui Wen, and Weizhu Lin

Appl. Phys. Lett. 87, 262110 (2005); http://dx.doi.org/10.1063/1.2150276 (3 pages) | Cited 5 times

Online Publication Date: 23 December 2005

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The elliptically polarized absorption spectroscopy is further developed to observe electron spin coherence dynamics in an intrinsic bulk GaAs in Voigt geometry. Absorption saturation quantum beats are observed and explained as spin-precession-dependent state filling. An analytical model is developed quantitatively to describe the quantum beats and used to fit experimental data to retrieve spin coherence lifetime. Comparing to the reported data reveals that the spin coherence dynamics of the real and imaginary of a complex refractive index is much different.
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78.47.-p Spectroscopy of solid state dynamics
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.20.Ls Magneto-optical effects
78.30.Fs III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Noninterfacial-nitride formation ohmic contact mechanism in Si-containing Ti/Al/Mo/Au metallizations on AlGaN/GaN heterostructures

Fitih M. Mohammed, Liang Wang, and Ilesanmi Adesida

Appl. Phys. Lett. 87, 262111 (2005); http://dx.doi.org/10.1063/1.2149968 (3 pages) | Cited 8 times

Online Publication Date: 23 December 2005

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Excellent ohmic contact formation to undoped-AlGaN/GaN heterostructures is achieved by the incorporation of silicon into Ti/Al/Mo/Au metallization. Contact resistance and specific contact resistivity as low as 0.16 Ω mm and 6.77×10−7 Ω cm2, respectively, have been obtained for the Ti/Si/Al/Si/Mo/Au scheme. Transmission electron microscopy has revealed that the ohmic contact formation mechanism depends on the competing interfacial nitride and silicide formation reactions, the latter giving rise to improved contact performance. The formation and penetration of non-nitride reaction products of Si-containing Al–Au intermetallics to depths beyond the AlGaN/GaN interface were observed. The superior ohmic performance of these schemes suggests that silicide-based low Schottky barrier contact formation may be preferable to an interfacial nitride contact mechanism in achieving improved ohmic behavior.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation
73.30.+y Surface double layers, Schottky barriers, and work functions

Impact of N-induced potential fluctuations on the electron transport in Ga(As,N)

F. Ishikawa, G. Mussler, K.-J. Friedland, H. Kostial, K. Hagenstein, L. Däweritz, and K. H. Ploog

Appl. Phys. Lett. 87, 262112 (2005); http://dx.doi.org/10.1063/1.2158511 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2005

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We investigate the electron transport in Ga(As,N) layers focusing on the influence of potential fluctuations. With increasing electron concentration, a metal-insulator transition is observed in the temperature dependence of the resistivity for a series of samples containing 0.8% of N. The observed behavior is discussed in the frame of Anderson transition. By increasing the N concentration up to 2.2%, we observe an increase of the potential fluctuations’ amplitude. Mean-square values for the intrinsic N-induced fluctuation γN are obtained from percolation theory to be larger than 30 meV. Rapid thermal annealing reduces γN significantly for samples with higher N concentration. These large potential fluctuations lead to electron localization and induce thermally activated conductivity which is observable up to 300 K.
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73.61.Ey III-V semiconductors
71.30.+h Metal-insulator transitions and other electronic transitions
61.72.Cc Kinetics of defect formation and annealing
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