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31 Mar 2003

Volume 82, Issue 13, pp. 1999-2184

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Appl. Phys. Lett. 82, 2094 (2003); http://dx.doi.org/10.1063/1.1563813 (3 pages)

Y. J. Lee, J. von Boehm, M. Pesola, and R. M. Nieminen
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Atomistic simulation of strain-induced amorphization

Alan C. Lund and Christopher A. Schuh

Appl. Phys. Lett. 82, 2017 (2003); http://dx.doi.org/10.1063/1.1563831 (3 pages) | Cited 43 times

Online Publication Date: 25 March 2003

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The process of solid-state amorphization through extensive plastic straining (i.e., mechanical alloying) is studied through molecular simulation of binary Cu–Zr alloys. Without such confounding factors as impurity pick-up, or such thermal effects as melting or diffusion, we find that amorphization can be driven solely by accumulation of crystal defects and interfacial roughening between the component phases. The tendency for glass formation is also seen to depend on composition, and the results are in line with extensive prior experimental work. © 2003 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.05.Bx Metals, semimetals, and alloys

Observation of interface defects in thermally oxidized SiC using positron annihilation

James Dekker, Kimmo Saarinen, Halldór Ólafsson, and Einar Ö. Sveinbjörnsson

Appl. Phys. Lett. 82, 2020 (2003); http://dx.doi.org/10.1063/1.1564637 (3 pages) | Cited 10 times

Online Publication Date: 25 March 2003

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Positron annihilation has been applied to study thermally oxidized 4H- and 6H-SiC. The SiC/SiO2 interface is found to contain a high density of open-volume defects. The positron trapping at the interface defects correlates with the charge of the interface determined by capacitance–voltage experiments. For oxides grown on n-SiC substrates, the positron annihilation characteristics at these defects are nearly indistinguishable from those of a silicon/oxide interface, with no discernable contribution from C-related bonds or carbon clusters. These results indicate that those defects at the SiC/oxide interface, which are visible to positrons, are similar to those at the Si/oxide interface. The positron annihilation characteristics suggest that these defects are vacancies surrounded by oxygen atoms. © 2003 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.70.Bj Positron annihilation
71.55.Ht Other nonmetals
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.J- Point defects and defect clusters
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.35.Ct Interface structure and roughness
81.05.Hd Other semiconductors

Optical properties of single-crystalline ZnO nanowires on m-sapphire

Hou Tee Ng, Bin Chen, Jun Li, Jie Han, M. Meyyappan, J. Wu, S. X. Li, and E. E. Haller

Appl. Phys. Lett. 82, 2023 (2003); http://dx.doi.org/10.1063/1.1564870 (3 pages) | Cited 133 times

Online Publication Date: 25 March 2003

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ZnO nanowires have been synthesized using a catalyst-assisted heteroepitaxial carbothermal reduction approach on a m-sapphire substrate. Intricate and uniform arrays have been obtained with each nanowire forming an angle ∼30° with the substrate normal. Photoluminescence studies at room temperature for wavelengths between 335 and 620 nm reveal a strong single exciton peak at ∼ 380 nm (3.26 eV) with accompanying deep-level blueshifted emission peaks at ∼ 486, 490, and 510 nm. UV resonant Raman spectroscopy has been used to characterize the nanowires at room temperature with multiphonon scattering exhibiting phonon quantum confinement. © 2003 American Institute of Physics.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

High-electric-field photocurrent in thin-film ZnS formed by pulsed-laser deposition

S. Yano, R. Schroeder, H. Sakai, and B. Ullrich

Appl. Phys. Lett. 82, 2026 (2003); http://dx.doi.org/10.1063/1.1564287 (3 pages) | Cited 8 times

Online Publication Date: 25 March 2003

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Photocurrent spectra of thin-film ZnS on glass fabricated by pulsed-laser deposition have been studied employing electric fields up to 20 kV/cm. The spectra show a shift towards lower energy at and beyond 10 kV/cm. By modeling the film absorption with the density of states and the Urbach rule, it is shown that, without the involvement of the Franz–Keldysh effect and excitonic transitions, the slope of the Urbach tail depends on the electric field, owing to impurity ionization. © 2003 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.50.Fq High-field and nonlinear effects
71.35.-y Excitons and related phenomena

Color variation of ZnGa2O4 phosphor by reduction-oxidation processes

J. S. Kim, H. I. Kang, W. N. Kim, J. I. Kim, J. C. Choi, H. L. Park, G. C. Kim, T. W. Kim, Y. H. Hwang, S. I. Mho, M.-C. Jung, and M. Han

Appl. Phys. Lett. 82, 2029 (2003); http://dx.doi.org/10.1063/1.1564632 (3 pages) | Cited 46 times

Online Publication Date: 25 March 2003

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The color of the emission of zinc gallate (ZnGa2O4) oscillates between ultraviolet and blue by hydrogen ambient reduction and air ambient oxidation heat treatments. The photoluminescence spectra and electron paramagnetic resonance signals show that ultraviolet emission of reduced ZnGa2O4 always accompanies 680 nm emission originating from single oxygen vacancies (VO∗). The increasing difference in binding energy between Ga3+ and O2− in reduced ZnGa2O4 indicates that the configuration of octahedral sites is distorted due to VO∗ generation and it becomes more ionic which shifts the emission band from 430 to 360 nm. The x-ray diffraction patterns and Raman scattering spectra show that β-Ga2O3 from ZnGa2O4 is formed in both reduction and oxidation processes which suggests the vaporization of Zn ions. We propose a model in which the origin of 360 nm emission is the Ga–O transition at distorted octahedral sites with VO∗ in ZnGa2O4, whereas 430 nm emission originates from the Ga–O transition of regular octahedral sites without VO∗ in ZnGa2O4. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.65.Mq Oxidation
76.30.-v Electron paramagnetic resonance and relaxation
78.30.Hv Other nonmetallic inorganics
61.72.J- Point defects and defect clusters

Electromigration reliability of dual-damascene Cu/porous methylsilsesquioxane low k interconnects

Ki-Don Lee, Ennis T. Ogawa, Sean Yoon, Xia Lu, and Paul S. Ho

Appl. Phys. Lett. 82, 2032 (2003); http://dx.doi.org/10.1063/1.1564294 (3 pages) | Cited 13 times

Online Publication Date: 25 March 2003

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Electromigration (EM) reliability was investigated for Cu/porous low k interconnects. The porous low k dielectric was a methylsilsesquioxane (MSQ) based spin-on organosilicate material with k of 2.2. The activation energy for EM failure was found to be about 0.9 eV for Cu/porous MSQ between 208 and 367 °C, which is commonly associated with mass transport at the Cu/SiNx cap-layer interface. The threshold product of current density and line length (jL)c for Cu/porous MSQ was found to be 2500–3000 A/cm. The reduction in EM lifetime compared with Cu/oxide interconnect can be attributed to smaller back stress, due to less thermomechanical confinement of Cu/low k interconnects. Most interconnects failed by voiding at the cathode. Some lateral Cu extrusion followed by interfacial breakdown was also observed near the anode. © 2003 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Observation of metal–insulator transition in Al–Pd–Re quasicrystals by x-ray absorption and photoemission spectroscopy

Y. Y. Lay, J. C. Jan, J. W. Chiou, H. M. Tsai, W. F. Pong, M.-H. Tsai, T. W. Pi, J. F. Lee, C. I. Ma, K. L. Tseng, C. R. Wang, and S. T. Lin

Appl. Phys. Lett. 82, 2035 (2003); http://dx.doi.org/10.1063/1.1565183 (3 pages) | Cited 3 times

Online Publication Date: 25 March 2003

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Using x-ray absorption and valence-band photoelectron spectroscopy (PES) we investigated the electronic structures of icosahedral (i)-Al70Pd22.5Re7.5 quasicrystals (QCs) with a 4.2 K/300 K resistivity ratio, r, ranging from 8.3 to 107 obtained under various annealing conditions. Our Al K- and Pd L3-edge x-ray absorption results show that the density of states, N(E), near the Fermi level, EF, jumps to a larger value when r decreases down to below about 20.6. The valence-band PES results show that N(E) near EF is greatly reduced in i-Al70Pd22.5Re7.5 QCs relative to that of the pure metal, which confirms the existence of the pseudogap. The PES spectrum has a sharp cutoff at EF for r = 8.3 QC, while it decreases smoothly down to zero at EF for larger rs. The combined results suggest the occurrence of metal–insulator transition at an r between 13 and 20.6. © 2003 American Institute of Physics.
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71.30.+h Metal-insulator transitions and other electronic transitions
71.23.Ft Quasicrystals
72.60.+g Mixed conductivity and conductivity transitions
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Atomistic modeling of amorphization and recrystallization in silicon

Lourdes Pelaz, Luis A. Marqués, María Aboy, Juan Barbolla, and George H. Gilmer

Appl. Phys. Lett. 82, 2038 (2003); http://dx.doi.org/10.1063/1.1564296 (3 pages) | Cited 27 times

Online Publication Date: 25 March 2003

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We propose an atomistic model to describe the evolution of the damage generated by irradiation in Si, going from isolated point defects to the formation of continuous amorphous layers. The elementary units used to reproduce the defective zones are Si interstitials, vacancies and the bond defect, which is a local distortion of the Si lattice without any excess or deficit of atoms. More complex defect structures can be formed as these elementary units cluster. The amorphous pockets are treated as agglomerates of bond defects characterized by their local coordination. The model is able to reproduce the abrupt regime in the crystal-amorphous transition in Si and the epitaxial recrystallization upon annealing as observed in the experiments. The model extends the atomistic kinetic Monte Carlo simulation technique to high implant doses, adequately describing the amorphization and regrowth in Si. © 2003 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.80.Jh Ion radiation effects

Density functional theory analysis of infrared modes in carbon-incorporated SiO2

Max Petersen, Michelle T. Schulberg, and Lawrence A. Gochberg

Appl. Phys. Lett. 82, 2041 (2003); http://dx.doi.org/10.1063/1.1564874 (3 pages) | Cited 4 times

Online Publication Date: 25 March 2003

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Low dielectric constant (low k) materials become increasingly important for microelectronics as interconnect delays limit circuit performance. One of the most promising low k candidates is carbon-incorporated SiO2 (SiOC:H). Despite the technological relevance of these materials, little is known about their atomistic structure. In order to address this issue, this letter compares structures obtained from the density functional theory to experimental data. This is done by analyzing both the calculated vibrational modes and experimental Fourier-transform infrared spectra. The resulting agreement is excellent. This can allow for future modeling of mechanical and electronic properties of low k dielectrics. © 2003 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
63.50.-x Vibrational states in disordered systems
77.22.Ch Permittivity (dielectric function)
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Strain-induced band gap shrinkage in Ge grown on Si substrate

Yasuhiko Ishikawa, Kazumi Wada, Douglas D. Cannon, Jifeng Liu, Hsin-Chiao Luan, and Lionel C. Kimerling

Appl. Phys. Lett. 82, 2044 (2003); http://dx.doi.org/10.1063/1.1564868 (3 pages) | Cited 91 times

Online Publication Date: 25 March 2003

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Band gap shrinkage induced by tensile strain is shown for Ge directly grown on Si substrate. In Ge-on-Si pin diodes, photons having energy lower than the direct band gap of bulk Ge were efficiently detected. According to photoreflectance measurement, this property is due to band gap shrinkage. The origin of the shrinkage is not the Franz–Keldysh effect but rather tensile strain. It is discussed that the generation of such a tensile strain can be ascribed to the difference of thermal expansion between Ge and Si. Advantages of this tensile Ge for application to photodiode are also discussed. © 2003 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Kk Junction diodes
85.60.Dw Photodiodes; phototransistors; photoresistors
65.40.De Thermal expansion; thermomechanical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Reaction of SiO2 with hafnium oxide in low oxygen pressure

S. J. Wang, P. C. Lim, A. C. H. Huan, C. L. Liu, J. W. Chai, S. Y. Chow, J. S. Pan, Q. Li, and C. K. Ong

Appl. Phys. Lett. 82, 2047 (2003); http://dx.doi.org/10.1063/1.1565182 (3 pages) | Cited 41 times

Online Publication Date: 25 March 2003

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A dynamic process consisting of a series of reactions during deposition of HfO2 films on SiO2-covered silicon under oxygen-deficient conditions is identified. The oxygen-deficient HfOx<2 layer absorbs the oxygen in the SiO2 layer to form fully oxidized metal oxide film. As a result, there is no silicate and silicon oxide formed at the interface with silicon substrate. Thermodynamic analysis indicates that even if there is a layer of silicate forming at the initial stage of deposition, the silicate layer will be decomposed with the progress of HfOx<2 deposition. © 2003 American Institute of Physics.
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81.65.Mq Oxidation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Fg Pulsed laser ablation deposition
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Time-resolved cathodoluminescence assessment of deep-level transitions in hydride-vapor-phase-epitaxy GaN

C. Díaz-Guerra, J. Piqueras, and A. Cavallini

Appl. Phys. Lett. 82, 2050 (2003); http://dx.doi.org/10.1063/1.1565501 (3 pages) | Cited 8 times

Online Publication Date: 25 March 2003

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The temporal behavior of deep-level luminescence emissions in undoped hydride-vapor-phase-epitaxy GaN layers of different thicknesses has been investigated by time-resolved cathodoluminescence (TRCL). The complex nature of the yellow luminescence is revealed in the TRCL spectra by the presence of two bands peaked at 2.22 and 2.03 eV. A red band with a decay time of 700 μs, centered at about 1.85 eV, dominates spectra recorded for long delay times. Exponential transients with associated decay times of hundreds of μs were measured at 87 K for all the deep-level emissions found in the layers. © 2003 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.47.-p Spectroscopy of solid state dynamics
71.55.Eq III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Proton-irradiation-induced intermixing of InGaAs quantum dots

P. Lever, H. H. Tan, C. Jagadish, P. Reece, and M. Gal

Appl. Phys. Lett. 82, 2053 (2003); http://dx.doi.org/10.1063/1.1561153 (3 pages) | Cited 25 times

Online Publication Date: 25 March 2003

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Proton irradiation was used to create interdiffusion in In0.5Ga0.5As quantum dots (QDs), grown by low-pressure metalorganic chemical vapor deposition. After 25-keV proton irradiation, the QD samples were annealed at two temperatures (700 or 750 °C) for 30 s. It was found that much lower annealing temperatures were needed to recover the photoluminescence signals than in the quantum-well case. Large blueshifts (120 meV) and narrowing of the photoluminescence spectra were seen. Various doses (5×1013–1×1015 cm−2) and implant temperatures (20–200 °C) were used to study the interdiffusion processes in these samples. In QD samples, much lower doses were required to achieve similar energy shifts than reported in quantum-well samples. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.35.Fx Diffusion; interface formation
61.80.Jh Ion radiation effects
81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Buckling phenomena in Y2O3 thin films on GaAs substrates

F. Paumier, R. J. Gaboriaud, and C. Coupeau

Appl. Phys. Lett. 82, 2056 (2003); http://dx.doi.org/10.1063/1.1558971 (3 pages) | Cited 5 times

Online Publication Date: 25 March 2003

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Worm-like buckling structures have been investigated by atomic force microscopy to estimate the relevant parameters for the mechanical stability of Y2O3 thin films deposited by ion beam sputtering technique on GaAs substrates. The internal stresses involving in the observed buckling phenomena have been estimated to be around 8.5 GPa in compression. The critical thicknesses up to which the various damaging mechanisms occur have also been determined. © 2003 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.60.Bs Mechanical and acoustical properties
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.40.Lm Deformation, plasticity, and creep
68.37.Ps Atomic force microscopy (AFM)
62.20.F- Deformation and plasticity
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