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15 Dec 2002

Volume 92, Issue 12, pp. 6959-7702

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Relaxation kinetics of photoinduced surface relief grating on azopolymer films

Tatsunosuke Matsui, Shin-ichiro Yamamoto, Masanori Ozaki, Katsumi Yoshino, and Francois Kajzar

J. Appl. Phys. 92, 6959 (2002); http://dx.doi.org/10.1063/1.1516264 (7 pages) | Cited 4 times

Online Publication Date: 27 November 2002

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The relaxation kinetics of the photoinduced surface relief grating (SRG) formed on an azopolymer film after stopping laser beam writing has been systematically investigated. In addition to a photoinduced increase of the diffraction efficiency in the SRG, an anomalous further enhancement of the efficiency was observed even without light irradiation, after the recording light beam was switched off. This anomalous relaxation process consists of two components with short and long relaxation times, and strongly depends on the temperature and polarization of the probe beam used for the diffraction measurement. At lower temperatures the anomalous growth is more effective and the fast component is dominant. From the results of the polarization dependence of the diffraction efficiency and optical absorption, it has been manifested that the fast component of the relaxation originates from the cis-trans thermal isomerization of azobenzene in the side chain. The origin of the slow decay is also discussed in terms of the order parameter change of the azomolecules caused by the reorientational relaxation. © 2002 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
68.35.B- Structure of clean surfaces (and surface reconstruction)

P-type macroporous silicon for two-dimensional photonic crystals

P. Bettotti, L. Dal Negro, Z. Gaburro, L. Pavesi, A. Lui, M. Galli, M. Patrini, and F. Marabelli

J. Appl. Phys. 92, 6966 (2002); http://dx.doi.org/10.1063/1.1515127 (7 pages) | Cited 19 times

Online Publication Date: 27 November 2002

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Macroporous silicon with two-dimensional periodicity has been produced by electrochemical etching, using a p-type doped silicon substrate. The structure shows photonic energy gaps in the infrared region, as demonstrated by variable angle reflectance measurements. The agreement between measurement and band calculations confirms the high quality of the samples. The use of an optimized electrolyte allows the fabrication of very high quality samples, with high aspect ratio and low roughness both at the surface and on the pore walls. The best results are obtained with aprotic and protophilic solvents. © 2002 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
81.65.Cf Surface cleaning, etching, patterning
42.70.Qs Photonic bandgap materials
68.35.B- Structure of clean surfaces (and surface reconstruction)

Modeling of laser cleaning of metallic particulate contaminants from silicon surfaces

M. Arronte, P. Neves, and R. Vilar

J. Appl. Phys. 92, 6973 (2002); http://dx.doi.org/10.1063/1.1513190 (10 pages) | Cited 13 times

Online Publication Date: 27 November 2002

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A model for laser-assisted particle removal was developed. The model was applied to micrometer-sized particles of gold, copper, and tungsten on silicon substrates. A two-dimensional heat transfer model is used to calculate the temperature profiles and the thermal expansion for the metallic particles and the silicon substrate irradiated with ultraviolet nanosecond laser pulses. The particle/substrate system was modeled as a simple spring oscillator under the sudden thermal expansion excitation pulse and a concept of degree of coupling between the laser induced thermal expansion associated frequency and the particle/substrate system is introduced. In terms of this degree of coupling a simple method to determine the most appropriate laser pulse duration is proposed. The theoretical results were compared with previously reported experimental observations. The experimental cleaning efficiency for the different particle materials and size distributions, as well as the possibility of substrate contamination due to metal evaporation are well accounted by the theoretical model.© 2002 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
79.20.Ds Laser-beam impact phenomena
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.82.Bg Metals and alloys
61.82.Fk Semiconductors

Near-field enhanced Raman spectroscopy using side illumination optics

Norihiko Hayazawa, Alvarado Tarun, Yasushi Inouye, and Satoshi Kawata

J. Appl. Phys. 92, 6983 (2002); http://dx.doi.org/10.1063/1.1519945 (4 pages) | Cited 39 times

Online Publication Date: 27 November 2002

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We demonstrate near-field enhanced Raman spectroscopy with the use of a metallized cantilever tip and highly p-polarized light directed onto the tip with side illumination optics using a long working distance objective lens. The highly p-polarized light field excites surface plasmon polaritons localized at the tip apex, which results in the enhanced near-field Raman scattering. In this article, we achieved an enhancement factor of 4000 for Rhodamine 6G molecules adsorbed on a silver island film. The side illumination is also applicable to an opaque sample and to near-field photolithography. © 2002 American Institute of Physics.
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78.30.Jw Organic compounds, polymers
78.66.Qn Polymers; organic compounds
78.68.+m Optical properties of surfaces
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.25.Ja Polarization
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Anomalous increase of photocurrent anisotropy in a liquid crystalline binary mixture

K. L. Sandhya, Geetha G. Nair, S. Krishna Prasad, Uma S. Hiremath, and C. V. Yelamaggad

J. Appl. Phys. 92, 6987 (2002); http://dx.doi.org/10.1063/1.1522816 (3 pages) | Cited 1 time

Online Publication Date: 27 November 2002

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We report photoconductivity measurements in a binary system of naphthalene-based liquid crystals. Under ultraviolet (365 nm) illumination we observe an anomalous increase in the photocurrent for the mixtures. For a particular concentration, the photocurrent anisotropy defined as the ratio of photocurrents orthogonal to and along the director in the Crystal E phase reaches a value of 850, the highest achieved under steady-state illumination conditions from a conventional source. We argue that when using such mixtures, it is possible to reach the limiting values predicted by models based on conduction dictated by charge-carrier hopping. © 2002 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
72.20.Ee Mobility edges; hopping transport
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
64.70.M- Transitions in liquid crystals
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Calculated characteristics of radio-frequency plasma display panel cells including the influence of xenon metastables

L. C. Pitchford, J. Kang, C. Punset, and J. P. Boeuf

J. Appl. Phys. 92, 6990 (2002); http://dx.doi.org/10.1063/1.1521258 (8 pages) | Cited 8 times

Online Publication Date: 27 November 2002

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Although alternating-current plasma display panels (ac PDPs) are now produced by several companies, improvements are still necessary. In particular, the overall efficiency of the discharge in the standard configuration is low, on the order of 1 lm/W i.e., about 0.5% of the power dissipated in the discharge is transformed into useful visible photons. One way to substantially improve the efficiency of PDPs is to use radio-frequency (rf) excitation because, when compared to ac PDPs, less of the electrical energy input is dissipated by ions in the sheath and relatively more power is deposited in excitation of the xenon, which produces the ultraviolet photons used to excite the phosphors. In this article, we show calculated discharge characteristics for typical rf PDP conditions and pay particular attention to the role of the xenon metastable atoms in the ionization balance. Our discussion is limited to the sustaining regime, the “on-state,” of a PDP cell. © 2002 American Institute of Physics.
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52.75.-d Plasma devices
52.80.Pi High-frequency and RF discharges

Charged species dynamics in an inductively coupled Ar/SF6 plasma discharge

Shahid Rauf, Peter L. G. Ventzek, Ion C. Abraham, Gregory A. Hebner, and Joseph R. Woodworth

J. Appl. Phys. 92, 6998 (2002); http://dx.doi.org/10.1063/1.1519950 (10 pages) | Cited 18 times

Online Publication Date: 27 November 2002

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The chemistry of high-density SF6 plasma discharges is not well characterized. In this article, a combination of computational modeling and experimental diagnostics has been utilized to understand charged species dynamics in an inductively coupled Ar/SF6 plasma discharge. The model is based on the two-dimensional Hybrid Plasma Equipment Model with a detailed plasma chemical mechanism for Ar/SF6. In the experiments, absolute electron density and total negative ion density have been measured using microwave interferometry and laser photodetachment, respectively. In addition, we have also utilized prior measurements of mass and energy resolved ion fluxes by Goyette et al. [J. Vac. Sci. Technol. A 19, 1294 (2001)]. Computational results show that all SFx+(x=0–5) ions are present in the plasma discharge. Important negative ions include SF6−, SF5−, and F−. Electron and positive ion densities increase with coil power due to enhanced ionization. However, negative ion densities decrease with coil power as the main negative ion precursor, SF6, is lost through neutral dissociation. An increase in SF6 concentration in the Ar/SF6 gas mixture decreases electron density due to enhanced electron loss through (dissociative) attachment, which enhances negative ion densities. RF bias power does not have an appreciable impact on the ion and electron densities for the parameter range of interest. Experiments show that electron density decreases with gas pressure while the total negative ion density increases up to 25 mTorr. This is due to a decrease in electron temperature, which enhances electron loss through (dissociative) attachment. Although the model is able to capture most of the experimentally observed trends, there are discrepancies regarding the impact of gas pressure on electron density and relative flux of large positive ions. © 2002 American Institute of Physics.
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52.80.Tn Other gas discharges
52.25.Fi Transport properties
52.25.-b Plasma properties

Comparison of excessive Balmer α line broadening of glow discharge and microwave hydrogen plasmas with certain catalysts

R. L. Mills, P. C. Ray, B. Dhandapani, R. M. Mayo, and J. He

J. Appl. Phys. 92, 7008 (2002); http://dx.doi.org/10.1063/1.1522483 (14 pages) | Cited 33 times

Online Publication Date: 27 November 2002

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From the width of the 656.3 nm Balmer α line emitted from microwave and glow discharge plasmas, it was found that a strontium–hydrogen microwave plasma showed a broadening similar to that observed in the glow discharge cell of 27–33 eV; whereas, in both sources, no broadening was observed for magnesium–hydrogen. Microwave helium–hydrogen and argon–hydrogen plasmas showed extraordinary broadening corresponding to an average hydrogen atom temperature of 180–210 eV and 110–130 eV, respectively. The corresponding results from the glow discharge plasmas were 33–38 eV and 30–35 eV respectively, compared to ≈4 eV for plasmas of pure hydrogen, neon–hydrogen, krypton–hydrogen, and xenon–hydrogen maintained in either source. Similarly, the average electron temperature Te for helium–hydrogen and argon–hydrogen microwave plasmas were high, 30 500±5% K and 13 700±5% K, respectively; compared to 7400±5% K and 5700±5% K for helium and argon alone, respectively. External Stark broadening or acceleration of charged species due to high fields can not explain the microwave results since no high field was present, and the electron density was orders of magnitude too low for the corresponding Stark effect. Rather, a resonant energy transfer mechanism is proposed. © 2002 American Institute of Physics.
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52.80.Hc Glow; corona
52.80.Pi High-frequency and RF discharges
33.70.Jg Line and band widths, shapes, and shifts
33.57.+c Magneto-optical and electro-optical spectra and effects
52.25.-b Plasma properties

Mechanism of C2 hydrocarbon formation from methane in a pulsed microwave plasma

M. Heintze, M. Magureanu, and M. Kettlitz

J. Appl. Phys. 92, 7022 (2002); http://dx.doi.org/10.1063/1.1521518 (10 pages) | Cited 23 times

Online Publication Date: 27 November 2002

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Methane dissociation, followed by the formation of C2 hydrocarbons, in a pulsed microwave discharge in methane was investigated by mass spectrometry and optical emission spectroscopy (OES). Long microwave pulses (>200 μs) are characterized by a pronounced dehydrogenation, but have a disadvantage in the saturation of the methane conversion at relatively low values, due to methane depletion toward the end of the pulse. For shorter pulses, the conversion degree increases approximately linearly as a function of energy input, and a maximum conversion of 90% with 80% selectivity toward acetylene was obtained for 60 μs pulses at 1 kHz repetition frequency. A further decrease of the pulse duration (20 μs) at higher frequency, in order to ensure a similar energy input, resulted in a decrease in conversion and dehydrogenation. The explanation of the effect of the pulse duration is based on information provided by optical emission spectroscopy of active species generated in the discharge. Atomic hydrogen, formed by methane dissociation, was found to play an essential role in methane plasma chemistry. A qualitative estimation of the variation of H atom concentration with operating conditions was done by actinometry, since time-resolved OES provides evidence that atomic hydrogen is mainly formed in the ground state and dissociative excitation can be neglected. In addition to the concentration of atomic hydrogen, the second key parameter is the gas temperature. It was determined from the relative intensity distribution in the rotational structure of the (0,0) C2 Swan band and of the (2,2) H2 Fulcher-α band. Gas temperatures between 1500 and 2500 K were determined for the present discharge conditions. The hydrogen abstraction by hydrogen atoms, favored at high temperature, is responsible for the high methane conversion and low energy requirement achieved (9–10 eV/molecule) and for the distribution of the reaction products. © 2002 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.20.Hf Product distribution

Analytical model for ion angular distribution functions at rf biased surfaces with collisionless plasma sheaths

Laxminarayan L. Raja and Mark Linne

J. Appl. Phys. 92, 7032 (2002); http://dx.doi.org/10.1063/1.1524020 (9 pages) | Cited 3 times

Online Publication Date: 27 November 2002

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The article presents an analytical model for evaluation of ion angular distribution functions (IADFs) at a radio frequency (rf)-biased surface in a high-density plasma reactor. The model couples a unified rf sheath model to an assumed ion velocity distribution function-based formulation for determining the IADF under any general rf-bias condition. Under direct-current (dc) bias conditions the IADF profile shape shows a strong dependence on the bias voltage and the ion temperature is relatively independent of the plasma electron temperature, ion density, and the ion mass. The model establishes the importance of rf-bias frequency in determining the IADF. For conditions where the sheath current wave form is sinusoidal, low bias frequencies result in a large-angle tail contribution to the IADF which can potentially lead to poor anisotropic plasma etching behavior. The large-angle tail is absent at higher bias frequencies. An increase in bias power leads to a general narrowing of the IADF, but the large-angle tail for the IADF at low frequencies persists despite increasing bias powers. Therefore, plasma etch anisotropy can be improved by increasing bias powers only if the bias frequency is sufficiently high. Tangential ion drift velocities introduce azimuthal angle dependence on the IADF and a shift in the peak IADF to off-normal polar angles. While the location of the peak IADF in the azimuthal direction is dictated purely by the direction of the drift velocity, the shift in peak IADF in the polar angle depends on both the drift velocity as well as the bias frequency. © 2002 American Institute of Physics.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
52.65.-y Plasma simulation
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Stimulation of electrical conductivity in a π-conjugated polymeric conductor with infrared light

S. C. J. Meskers, J. K. J. van Duren, and R. A. J. Janssen

J. Appl. Phys. 92, 7041 (2002); http://dx.doi.org/10.1063/1.1519948 (10 pages) | Cited 5 times

Online Publication Date: 27 November 2002

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Irradiation with infrared light is found to stimulate the electrical conductivity of a film of an organic polymeric conductor [poly(3,4-ethylenedioxythiopene) with polystyrene sulfonate]. The change in conductivity is found to be linear in the intensity of the irradiation (4–400 mW/cm2). Both frequency and time domain measurements reveal that the change in resistance induced by irradiation, relaxes according to ΔR(t)∝(1/t)0.6, with t as the time after excitation. As a possible mechanism for this relaxation, we model the diffusion of heat from the polymer film to the supporting glass substrate. Assuming that the change in resistance is linear with the raise in temperature caused by the infrared irradiation, one predicts a ΔR(t)∝(1/t)0.5 dependence. The similarity between the model and experimental behavior is taken as an indication that the relaxation is limited by heat transport from the polymer film and that the thermalization of the charge carriers occurs on a shorter time scale. Electrical characterization is complemented with optical measurements. These show infrared-induced transient absorption of the polymer film with practically the same relaxation behavior as the change in resistance. This suggests that the optical transients are also due to thermal excitations. In the sub-ps time domain, measurements of the change in optical transmission (ΔT/T) induced by the infrared pulse show a very short-lived component with a lifetime close to the instrumental resolution (∼500 fs). The rapid response is followed by a slow component that decays according to (ΔT/T)(t)∝(1/t)0.65. This is interpreted in terms of cooling of the excited charge carriers limited by heat transport, indicating that the thermalization of the carriers occurs on the sub-ps time scale. © 2002 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
73.50.Pz Photoconduction and photovoltaic effects
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Optical absorption spectroscopy of Fe2+ and Fe3+ ions in LiNbO3

S. A. Basun, D. R. Evans, T. J. Bunning, S. Guha, J. O. Barnes, G. Cook, and R. S. Meltzer

J. Appl. Phys. 92, 7051 (2002); http://dx.doi.org/10.1063/1.1519951 (5 pages) | Cited 8 times

Online Publication Date: 27 November 2002

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We provide a method to measure concentrations of Fe2+ and Fe3+ ions in LiNbO3. The method, based only on optical absorption spectroscopy, provides a convenient means to determine the absorption cross sections for Fe2+ and Fe3+ ions, along with an independent measurement of the Fe2+ and Fe3+ concentrations in a given LiNbO3 crystal. The absorption cross section of the Fe2+ ions found by this method correlated well with a previously measured value. The cross section of the Fe3+ ions was obtained. It was also found that in some samples a significant fraction of Fe ions did not contribute to the absorption in the visible. © 2002 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
71.55.Ht Other nonmetals
07.60.Rd Visible and ultraviolet spectrometers

Annealing behavior of magnesium and aluminum implanted with iron ions

H. Reuther

J. Appl. Phys. 92, 7056 (2002); http://dx.doi.org/10.1063/1.1521256 (6 pages) | Cited 2 times

Online Publication Date: 27 November 2002

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Magnesium and aluminum were alloyed by implantation with iron ions. The implantation energy was 200 keV while the ion doses ranged over several decades from 1×1015 up to 9×1017 cm−2. In this way highly disordered alloyed layers with up to 90 at.% iron were obtained. To study possible ordering, stabilization, and redistribution processes samples were annealed in vacuum at subsequently increasing temperatures up to 600 °C for aluminum and up to 400 °C for magnesium. The annealing process was observed by conversion electron Mössbauer spectroscopy, Auger electron depth profiling, and x-ray diffraction. In the case of the Fe–Al system different iron aluminides are formed. In the case of the Fe–Mg system (insoluble with each other), α-iron is precipitated in small clusters in the final state. © 2002 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.82.Bg Metals and alloys
61.80.Jh Ion radiation effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.72.up Other materials
79.20.Fv Electron impact: Auger emission

Damascene process simulation using molecular dynamics

Shin-Pon Ju, Cheng-I Weng, and Chi-Chuan Hwang

J. Appl. Phys. 92, 7062 (2002); http://dx.doi.org/10.1063/1.1519947 (8 pages) | Cited 1 time

Online Publication Date: 27 November 2002

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This article uses a molecular dynamics parallel computing technique to investigate trench filling in the damascene process. The qualitative behavior of the trench filling process for different incident energies and substrate temperatures is described in terms of the filling morphology and the filling characteristics. The significance of the geometric size of the simulation model is evaluated by comparing the coverage percentage results obtained from the current large model with the results presented previously for a small model. Similar filling characteristics are identified for both simulation models. This indicates that the qualitative behavior is independent of the model size. However, a quantitative comparison shows that when the incident energy is small, or when the substrate temperature is high, the geometric dimensions of the model become significant. Finally, the results demonstrate that the nature of the relationship between coverage percentage improvement and incident energy is dependent on the model size. © 2002 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Bh Computer-aided design of microcircuits; layout and modeling
02.70.Ns Molecular dynamics and particle methods

Accounting for Auger yield energy loss for improved determination of molecular orientation using soft x-ray absorption spectroscopy

Jan Genzer, Edward J. Kramer, and Daniel A. Fischer

J. Appl. Phys. 92, 7070 (2002); http://dx.doi.org/10.1063/1.1516258 (10 pages) | Cited 17 times

Online Publication Date: 27 November 2002

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Partial (Auger) yield near edge x-ray absorption fine structure (NEXAFS) is a structural analytical technique that has been primarily used to measure the spatial orientation and chemical bonding of small molecules on solid (i.e., inorganic or semiconductor) surfaces. In this article we demonstrate that the building block (BB) scheme proposed by Outka and co-workers [Phys. Rev. Lett. 59, 1321 (1987)] for analyzing NEXAFS spectra can be applied to model the molecular orientation of larger molecules, provided one accounts properly for kinetic energy losses of the Auger electrons traversing through the sample and hence the attenuation in measured Auger yield. We test the applicability of the proposed “modified” BB (MBB) model by measuring the orientation of a self-assembled monolayer (SAM) of –O1.5Si–(CH2)2–(CF2)8F, SF–SAM (SiOx), deposited on top of SiOx-covered silicon wafer as a function of the entrance grid bias (EGB) of the channeltron photoelectron detector. Our measurements of the EGB-dependent electron escape depth reveal that a crude depth profiling within the top ≈5 nm of the sample is possible by increasing the negative EGB on the channeltron detector, at the highest bias thus selecting only the Auger electrons, which have suffered negligible energy loss. In addition, we discuss how the order parameter method introduced recently by Stöhr and Samant [J. Electron Spectrosc. Relat. Phenom. 98–99, 189 (1989)] can be used to determine the molecular orientation of large organic molecules on surfaces. We also show that by accounting for energy losses of the NEXAFS Auger electrons (attenuation of measured Auger yield), the corrected order parameter (COP) approach gives good estimates of the orientation of molecules. We present a comparison between the MBB and COP models using experimental data collected from NEXAFS experiments from semifluorinated (SF) mesogens, –(CH2)x(CF2)yF, which are attached to: (1) the isoprene backbone of polyisoprene or a styrene–isoprene diblock copolymer and (2) a SiOx-covered solid substrate. We show that on both surfaces, the SF groups are oriented and on average are tilted by an angle 〈τF-helix〉 from the sample normal. We show that at higher 〈τF-helix〉 the results from the COP approach agree almost quantitatively with those extracted using the MBB model. © 2002 American Institute of Physics.
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78.70.Dm X-ray absorption spectra

Growth of cubic-TaN thin films by plasma-enhanced atomic layer deposition

H. Kim, A. J. Kellock, and S. M. Rossnagel

J. Appl. Phys. 92, 7080 (2002); http://dx.doi.org/10.1063/1.1519949 (6 pages) | Cited 40 times

Online Publication Date: 27 November 2002

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Low resistivity cubic-TaN thin films were grown by plasma-enhanced-atomic layer deposition using TaCl5 as the metal precursor and hydrogen/nitrogen plasma. The deposition has been performed by alternate exposures of TaCl5 and the plasma of hydrogen and nitrogen mixture. X-ray diffraction analyses show that the film is composed of cubic TaN grains, in contrast to the previously reported highly resistive Ta3N5 films grown by Ta3N5 grown by TaCl5 and NH3 as precursors. The composition and thickness were measured by Rutherford backscattering and hydrogen concentrations were obtained by forward recoil elastic spectrometry as a function of growth parameters. The N content of the cubic TaN films was controlled from N/Ta=0.7 up to 1.3 by changing nitrogen partial pressure. The resistivity and growth rate increase with increasing N concentration in the film. The Cl and H content were found to be strong functions of plasma exposure time and growth temperatures, and TaN films with resistivity as low as 350 μΩ cm were obtained at a low growth temperature of 300 °C. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
85.40.Ls Metallization, contacts, interconnects; device isolation
73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Spectroscopic studies of random telegraph noise in InAs quantum dots in GaAs

N. Panev, M.-E. Pistol, S. Jeppesen, V. P. Evtikhiev, A. A. Katznelson, and E. Yu. Kotelnikov

J. Appl. Phys. 92, 7086 (2002); http://dx.doi.org/10.1063/1.1518792 (4 pages) | Cited 5 times

Online Publication Date: 27 November 2002

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We have observed and investigated random telegraph noise in the photoluminescence from InAs quantum dots in GaAs. The luminescence from a single quantum dot, exhibiting switching between two levels, has been spectrally resolved. The random telegraph noise is only observed in the presence of band filling. We find no spectral shift of the emission in the different states. It is only the intensity, mainly for higher energy peaks, that changes. The InAs quantum dots behave similarly to InP/GaInP and InGaAs/GaAs quantum dots, with respect to random telegraph noise. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Cr III-V semiconductors
72.70.+m Noise processes and phenomena

Quantitative evaluation of chemisorption processes on semiconductors

A. Rothschild, Y. Komem, and N. Ashkenasy

J. Appl. Phys. 92, 7090 (2002); http://dx.doi.org/10.1063/1.1519946 (8 pages) | Cited 19 times

Online Publication Date: 27 November 2002

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This article presents a method for numerical computation of the degree of coverage of chemisorbates and the resultant surface band bending as a function of the ambient gas pressure, temperature, and semiconductor doping level. This method enables quantitative evaluation of the effect of chemisorption on the electronic properties of semiconductor surfaces, such as the work function and surface conductivity, which is of great importance for many applications such as solid- state chemical sensors and electro-optical devices. The method is applied for simulating the chemisorption behavior of oxygen on n-type CdS, a process that has been investigated extensively due to its impact on the photoconductive properties of CdS photodetectors. The simulation demonstrates that the chemisorption of adions saturates when the Fermi level becomes aligned with the chemisorption-induced surface states, limiting their coverage to a small fraction of a monolayer. The degree of coverage of chemisorbed adions is proportional to the square root of the doping level, while neutral adsorbates are independent of the doping level. It is shown that the chemisorption of neutral adsorbates behaves according to the well-known Langmuir model, regardless of the existence of charged species on the surface, while charged adions do not obey Langmuir’s isotherm. In addition, it is found that in depletive chemisorption processes the resultant surface band bending increases by 2.3kT (where k is the Boltzmann constant and T is the temperature) when the gas pressure increases by one order of magnitude or when the doping level increases by two orders of magnitude. © 2002 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.43.Mn Adsorption kinetics
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.61.Ga II-VI semiconductors

Strain distribution of Si thin film grown on multicrystalline-SiGe with microscopic compositional distribution

Noritaka Usami, Tatsuya Takahashi, Kozo Fujiwara, Toru Ujihara, Gen Sazaki, Yoshihiro Murakami, and Kazuo Nakajima

J. Appl. Phys. 92, 7098 (2002); http://dx.doi.org/10.1063/1.1520724 (4 pages) | Cited 1 time

Online Publication Date: 27 November 2002

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We report on growth and characterizations of Si/multicrystalline-SiGe (mc-SiGe) heterostructure as a promising candidate to surpass mc-Si solar cells. Spatial distribution of the status of strain in Si was investigated using microscopic Raman spectroscopy. The strain was found to be strongly influenced by the composition and microstructure of underlying mc-SiGe. Spatial variation of the strain as well as strain relaxation was found to be suppressed by decreasing average Ge composition of underlying SiGe. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.Nq Composition and phase identification
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
78.30.Am Elemental semiconductors and insulators

X-ray photoelectron spectroscopic investigation of surface chemistry of ternary As–S–Se chalcogenide glasses

Wenyan Li, Sudipta Seal, Cedric Lopez, and Kathleen A. Richardson

J. Appl. Phys. 92, 7102 (2002); http://dx.doi.org/10.1063/1.1518134 (7 pages) | Cited 4 times

Online Publication Date: 27 November 2002

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Chalcogenide glasses belong to an important class of materials, due to their good infrared transmission, and low-phonon energy as compared to other oxide glasses. Structural and chemical variations imposed by glass processing conditions, e.g., film deposition, can lead to changes in the linear and nonlinear optical properties. X-ray photoelectron spectroscopy (XPS) has been employed to study As–S–Se glasses of differing chemical compositions, in the film and the bulk form, to understand any variations in chemical bond configuration and their electronic structure. The molecular environments of As and Se for As–S–Se samples with varying S/Se ratio (fixed As content) and As content (fixed S/Se ratio) are studied by monitoring the XPS chemical shifts. The surface chemistry of the bulk and thin-film chalcogenide glasses are also compared to determine the effect of glass processing conditions for better chalcogenides for potential waveguide applications. © 2002 American Institute of Physics.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.43.Fs Glasses
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
81.05.Kf Glasses (including metallic glasses)
42.70.Ce Glasses, quartz
68.55.-a Thin film structure and morphology
68.35.Dv Composition, segregation; defects and impurities

Phase diagram, chemical bonds, and gap bowing of cubic InxAl1−xN alloys: Ab initio calculations

L. K. Teles, L. M. R. Scolfaro, J. R. Leite, J. Furthmüller, and F. Bechstedt

J. Appl. Phys. 92, 7109 (2002); http://dx.doi.org/10.1063/1.1518136 (5 pages) | Cited 19 times

Online Publication Date: 27 November 2002

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Thermodynamic, structural, and electronic properties of cubic InxAl1−xN alloys are studied by combining first-principles total energy calculations and the generalized quasichemical approach. Results for bond-lengths, second-nearest-neighbors distances, and bond angles in the alloy are presented. The calculated phase diagram of the alloy shows a broad and asymmetric miscibility gap. The gap fluctuations in the alloy allow for the definition of a minimum gap and an average gap with different bowing parameters, that can provide an explanation for the discrepancies found in the experimental values for the bowing parameter. It is also found that lattice matched In0.2Al0.8N with GaN is suitable to form a barrier material for electronic and optoelectronic nitride based devices. © 2002 American Institute of Physics.
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71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds
71.15.Nc Total energy and cohesive energy calculations
64.70.-p Specific phase transitions
61.50.Lt Crystal binding; cohesive energy
81.30.Dz Phase diagrams of other materials
64.75.-g Phase equilibria
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Investigation of the cobalt distribution in TiO2:Co thin films

P. A. Stampe, R. J. Kennedy, Yan Xin, and J. S. Parker

J. Appl. Phys. 92, 7114 (2002); http://dx.doi.org/10.1063/1.1521259 (8 pages) | Cited 49 times

Online Publication Date: 27 November 2002

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We report a detailed study of the morphology of TiO2:Co films grown on both LaAlO3 (001) and SrTiO3 (001) substrates by pulsed laser deposition. The films are optically transparent and ferromagnetic at room temperature with a magnetic moment of 1.7±0.4 μB/Co. Plan view transmission electron microscope studies show clear evidence of cobalt segregation with the clustering more pronounced for higher cobalt concentrations. Films grown on SrTiO3 substrates show the presence of a thin surface rutile (111) layer, into which the cobalt appears to migrate. These results are supported by x-ray structure determination and resistivity measurements. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
68.35.Dv Composition, segregation; defects and impurities

Formation of misfit dislocations in thin film heterostructures

J. Narayan and S. Oktyabrsky

J. Appl. Phys. 92, 7122 (2002); http://dx.doi.org/10.1063/1.1521789 (6 pages) | Cited 12 times

Online Publication Date: 27 November 2002

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We have studied characteristics of 60° and 90° dislocations in GaAs/Si(100) thin-film heterostructures grown by metal-organic chemical-vapor deposition at 650 °C. The misfit dislocation network consists of approximately 60% of 90° dislocations, and 40% of the closely spaced pairs of 60° dislocations with intersecting glide planes. This ratio has remained essentially constant after rapid thermal annealing at 800 °C for 90 sec. It is envisaged that these 60° dislocation pairs have parallel screw components and as a result they cannot combine to form a 90° dislocation. Upon annealing, some of the 60° dislocation pairs split to form stacking faults in agreement with our earlier model. Based upon these observations, we propose a model where a first set of 60° dislocations is generated from the undulated surface above a critical thickness. The second set of 60° dislocations is nucleated at a larger thickness and at the smoother surface. The Burgers vectors of these dislocations are controlled by the dislocations from the first set, and only low-energy dislocation pairs are formed through glide towards the interface and later through short glide and climb along the interface plane. We have used a numerical analysis based on elasticity theory to evaluate the changes in the nucleation barrier for the 60° dislocations caused by the interaction with the existing misfit dislocations. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Cc Kinetics of defect formation and annealing
61.72.Lk Linear defects: dislocations, disclinations

Electrochromic properties of SnO2-incorporated Ni oxide films grown using a cosputtering system

Kwang-Soon Ahn, Yoon-Chae Nah, and Yung-Eun Sung

J. Appl. Phys. 92, 7128 (2002); http://dx.doi.org/10.1063/1.1521519 (5 pages) | Cited 7 times

Online Publication Date: 27 November 2002

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SnO2-incorporated Ni oxide (NiO:SnO2) films were grown by means of a cosputtering system, consisting of two rf sputter guns, and their electrochromic properties were compared with those of a Ni oxide film. The Ni oxide films crystallized with an increased film thickness due to a plasma heating effect, leading to a decreased maximum bleached transmittance and coloration efficiency (CE). However, the NiO:SnO2 films grown by cosputtering showed acceptable maximum bleached transmittance and CE values, which were independent of film thickness. This indicates that SnO2 adatoms generated by the side sputter gun interfere with the movement of Ni oxide adatoms deposited by the main sputter gun, preventing the crystallization of the films. This was verified by x-ray diffraction and scanning electron microscopic data. We propose that the cosputtering technique described herein has the capability of providing good maximum bleached transmittance and CE properties in thick electrochromic films with no degradation due to the plasma heating effect. © 2002 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.66.Nk Insulators
81.15.Cd Deposition by sputtering
42.79.Wc Optical coatings
52.77.Dq Plasma-based ion implantation and deposition
68.55.A- Nucleation and growth

On the frequency response of a resonant-cavity-enhanced separate absorption, grading, charge, and multiplication avalanche photodiode

N. R. Das and M. J. Deen

J. Appl. Phys. 92, 7133 (2002); http://dx.doi.org/10.1063/1.1521786 (13 pages) | Cited 2 times

Online Publication Date: 27 November 2002

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In this article the frequency response of a resonant-cavity-enhanced (RCE) separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiode (APD) has been investigated. This study on APDs includes the development of a model for the avalanche buildup of carriers including the dead-space effect. In this model, the carriers are characterized by their energy and position in the region of multiplication. The excess energy of the carriers above threshold are assumed to be equally distributed among the carriers after impact ionization. The analysis shown in this article can be used to study the frequency response of the APD for a wide range of reverse bias voltages. For low bias voltages, an analytical expression has been derived to study the emission of carriers from the interface trap. The delay due to diffusion of photogenerated carriers from the undepleted region of the absorption layer and the low velocity of carriers at low field have also been considered. The model is used to calculate gains at different biases and bandwidth at different dc gains. The results show good agreement with published experimental data on a RCE SA(G)CM APD. © 2002 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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