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15 May 2000

Volume 76, Issue 20, pp. 2815-2963

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Observation of electronic Raman scattering from Mg-doped wurtzite GaN

K. T. Tsen, C. Koch, Y. Chen, H. Morkoc, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 76, 2889 (2000); http://dx.doi.org/10.1063/1.126507 (3 pages) | Cited 6 times

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Electronic Raman scattering experiments have been carried out on both molecular beam epitaxy and metal-organic chemical vapor deposition-grown Mg-doped wurtzite GaN samples. Aside from the expected Raman lines, a broad structure (full width at half maximum≅15 cm−1) observed at around 841 cm−1 is attributed to the electronic Raman scattering from neutral Mg impurities in Mg-doped GaN. Our experimental results demonstrate that the energy between the ground and first excited states of Mg impurities in wurtzite GaN is about one-half of its binding energy. © 2000 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors

Evidence for a self-organized growth in granular Co/Al2O3 multilayers

D. Babonneau, F. Petroff, J.-L. Maurice, F. Fettar, A. Vaurès, and A. Naudon

Appl. Phys. Lett. 76, 2892 (2000); http://dx.doi.org/10.1063/1.126508 (3 pages) | Cited 31 times

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By sequential deposition of thin layers of cobalt and alumina by sputtering, we have fabricated granular multilayers consisting of successive planes of nanosized cobalt clusters separated by alumina along the growth direction. Combining grazing-incidence small-angle x-ray scattering and transmission electron microscopy experiments, we show that, in a given range of thickness, the vertical arrangement of clusters from plane to plane is not random but shows a topology-induced self-organization. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.70.Ck X-ray scattering
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials

An optimal quasisuperlattice design to further improve thermal stability of tantalum nitride diffusion barriers

G. S. Chen, S. C. Huang, S. T. Chen, T. J. Yang, P. Y. Lee, J. H. Jou, and T. C. Lin

Appl. Phys. Lett. 76, 2895 (2000); http://dx.doi.org/10.1063/1.126509 (3 pages) | Cited 12 times

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X-ray diffraction and transmission electron microscopy, along with electrical and film stress measurements, were used to evaluate the effectiveness of 40-nm-thick amorphous Ta2N and microcrystalline TaN diffusion barriers, both single and multilayered, against Cu penetration. Failure of the single-layered Ta2N diffusion barrier upon annealing is initialized by crystallization/grain growth, mainly helped by frozen-in compressive stress (3–4 GPa) to transform itself into a columnar structure with a comparable grain size to the thickness of the barrier. However, when subjected to annealing, the Ta2N/TaN alternately layered diffusion barrier with an optimum bilayer thickness (10 nm) remains almost stress-free (0–0.7 GPa) and transforms itself into an equiaxed structure with grain sizes of only ⩽ 3 nm. Such quasisuperlattice films can present lengthening and complex grained structures to effectively block Cu diffusion, thus acting as much more effective barriers than Ta2N (and TaN) single-layered films. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
85.40.Ls Metallization, contacts, interconnects; device isolation
68.60.Dv Thermal stability; thermal effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
68.55.-a Thin film structure and morphology
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Metallization scheme for highly low-resistance, transparent, and thermally stable Ohmic contacts to p-GaN

Ja-Soon Jang, Seong-Ju Park, and Tae-Yeon Seong

Appl. Phys. Lett. 76, 2898 (2000); http://dx.doi.org/10.1063/1.126510 (3 pages) | Cited 38 times

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We report on a promising metallization scheme for high-quality Ohmic contacts to surface-treated p-GaN:Mg (2–3×1017 cm−3). It is shown that the as-deposited Pt/Ru contact produces a specific contact resistance of 7.8(±2.2)×10−4 Ω cm2. However, annealing of the contact at 600 °C for 2 min results in a resistance of 2.2(±2.0)×10−6 Ω cm2. It is also shown that the light transmittance of the annealed contact is 87.3% at 470 nm. Furthermore, the surface of the contact annealed at 600 °C for 30 min is found to be very smooth with a rms roughness of 0.8 nm. These results strongly indicate that the Pt/Ru can be a suitable scheme for the fabrication of high-performance laser diodes or other devices. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
81.05.Ea III-V semiconductors
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Highly monodisperse polymer-capped ZnO nanoparticles: Preparation and optical properties

Lin Guo, Shihe Yang, Chunlei Yang, Ping Yu, Jiannong Wang, Weikun Ge, and George K. L. Wong

Appl. Phys. Lett. 76, 2901 (2000); http://dx.doi.org/10.1063/1.126511 (3 pages) | Cited 156 times

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We report the preparation of highly monodisperse ZnO nanoparticles using poly(vinyl pyrrolidone) (PVP) as the capping molecules. The surface-modified ZnO nanoparticles were found to be remarkably stable. The optical absorption shows distinct excitonic features. Markedly enhanced near-band-edge ultraviolet photoluminescence and significantly reduced defect-related green emission were also observed. We attribute this observation to the nearly perfect surface passivation of the ZnO nanoparticles by the PVP molecules. The third-order nonlinear optical response of these PVP-capped ZnO nanoparticles in a dilute solution was found to be significantly larger (by at least two orders of magnitude) than that of the bulk ZnO. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
81.05.Dz II-VI semiconductors
81.05.Qk Reinforced polymers and polymer-based composites
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.65.Rv Passivation
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.65.-k Nonlinear optics

Effect of the Coulomb interaction on the response time and impedance of the resonant-tunneling diodes

Michael N. Feiginov

Appl. Phys. Lett. 76, 2904 (2000); http://dx.doi.org/10.1063/1.126512 (3 pages) | Cited 9 times

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We demonstrated that the response time of the resonant-tunneling structures (τresp) can be much smaller as well as much larger than the quasibound-state lifetime. A simple analytical expression for the impedance of the resonant-tunneling diode has been derived, it takes into account the Coulomb interaction and the quasibound-state lifetime. A simple equation relating τresp to the static differential conductance has also been obtained; it allows one to get τresp in the static measurements of the current–voltage curve. © 2000 American Institute of Physics.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling

Investigation of the cleaved surface of a p–i–n laser using Kelvin probe force microscopy and two-dimensional physical simulations

F. Robin, H. Jacobs, O. Homan, A. Stemmer, and W. Bächtold

Appl. Phys. Lett. 76, 2907 (2000); http://dx.doi.org/10.1063/1.126513 (3 pages) | Cited 34 times

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We have investigated the cross-sectional electric field and potential distribution of a cleaved n+-InP/InGaAsP/p+-InP p–i–n laser diode using Kelvin probe force microscopy (KFM) with a lateral resolution reaching 50 nm. The powerful characterization capabilities of KFM were compared with two-dimensional (2D) physics-based simulations. The agreement between simulations and KFM measurements regarding the main features of the electric field and potential is very good. However, the KFM yields a voltage drop between n-and p-doped InP regions which is 0.4 times the one simulated. This discrepancy is explained in terms of surface traps due to the exposure of the sample to the air and in terms of incomplete ionization. This hypothesis is confirmed by the 2D simulations. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
42.55.Px Semiconductor lasers; laser diodes

Large and stable field-emission current from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy

Makoto Kasu and Naoki Kobayashi

Appl. Phys. Lett. 76, 2910 (2000); http://dx.doi.org/10.1063/1.126514 (3 pages) | Cited 23 times

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We report on the electron field emission (FE) from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy. We found that, as the Si-dopant density increases, the threshold electric field decreases and, consequently, the FE current from AlN increases drastically. We show that heavily Si-doped (2.5×1020 cm−3) AlN has a threshold electric field of 34 V/μm, a maximum FE current density of 4.8 mA/cm2, and stable FE current (fluctuation: 3%). © 2000 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption

Magnetic-field effects on undriven chaos in a weakly coupled GaAs/AlAs superlattice

K. J. Luo, K.-J. Friedland, H. T. Grahn, and K. H. Ploog

Appl. Phys. Lett. 76, 2913 (2000); http://dx.doi.org/10.1063/1.126515 (3 pages) | Cited 2 times

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We have investigated the effect of a perpendicular magnetic field on the spontaneous current oscillations in a weakly coupled GaAs/AlAs superlattice. At zero magnetic field, voltage regions of periodic as well as chaotic oscillations are observed. With increasing magnetic field B, the voltage regions for chaotic oscillations become larger and those for periodic oscillations smaller. At B=9 T, the whole voltage range consists of chaotic oscillations. At the same time, the time-averaged current–voltage characteristic hardly changes. The experimental observations demonstrate that the quantization by the perpendicular magnetic field results in an equalization of the sequential resonant tunneling process over the whole superlattice, suppressing scattering effects due to disorder. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
05.45.-a Nonlinear dynamics and chaos
73.23.-b Electronic transport in mesoscopic systems
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Characterization of electron trap states due to InAs quantum dots in GaAs

C. Walther, J. Bollmann, H. Kissel, H. Kirmse, W. Neumann, and W. T. Masselink

Appl. Phys. Lett. 76, 2916 (2000); http://dx.doi.org/10.1063/1.126516 (3 pages) | Cited 23 times

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InAs quantum dots grown in a GaAs matrix are investigated using capacitive transient spectroscopy and transmission electron microscopy (TEM). Two deep levels are detected which are energetically too deep to be the intrinsic electron levels of the quantum dots. Both TEM as well as the detailed non-exponential behavior of the electron capture indicate that the traps do not result from dislocations in the GaAs matrix. We propose that the measured trap levels are due to point defects in or near the quantum dots. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
61.72.J- Point defects and defect clusters

Critical size for localization of the L-like conduction states in InAs quantum dots grown on GaAs

J. A. Prieto, G. Armelles, J. M. García, L. González, A. San Paulo, and R. García

Appl. Phys. Lett. 76, 2919 (2000); http://dx.doi.org/10.1063/1.126855 (3 pages)

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The localization of the L-like conduction states is found to change from the islands to the substrate in InAs quantum dots grown on GaAs as the island-size decreases. This is due to a size-induced modification of the strain state of the islands. The critical size should correspond to dislocation formation. As a result, small InAs islands coherently strained to GaAs exhibit optical properties markedly different from those of bulk InAs. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.Ea III-V semiconductors
73.20.Fz Weak or Anderson localization
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
81.07.-b Nanoscale materials and structures: fabrication and characterization

Conductance quantization in nanoscale vertical structure silicon field-effect transistors with a wrap gate

K. Nishiguchi and S. Oda

Appl. Phys. Lett. 76, 2922 (2000); http://dx.doi.org/10.1063/1.126517 (3 pages) | Cited 13 times

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Experimental results of quantum ballistic transport in single quantum contact by using vertical structure silicon field effect transistors with a wrap gate are presented. Based on dc measurement, the conductance–voltage characteristics show quantized plateaus at multiples of 2e2/h. The devices were prepared by electron beam lithography and by combinations of various types of etching. The channel is fabricated by the chemical vapor deposition of amorphous silicon and solid-phase crystallization. The vertical structure allows a channel length as short as 30 nm, which is defined by the film thickness. The effective channel is reduced by the depletion potential, resulting in a much narrower channel width compared to the geometrical width of 60 nm. Thus, the effective size of the silicon transistor is smaller than the elastic mean free path of 40 nm, resulting in the conduction quantization at 3–5 K. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
85.35.Ds Quantum interference devices
81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
85.40.Hp Lithography, masks and pattern transfer
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Evidence for valence fluctuation of Fe in Sr2FeMoO6−w double perovskite

J. Lindén, T. Yamamoto, M. Karppinen, H. Yamauchi, and T. Pietari

Appl. Phys. Lett. 76, 2925 (2000); http://dx.doi.org/10.1063/1.126518 (3 pages) | Cited 62 times

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In this letter evidence for the formation of a valence-fluctuation state of iron, formally denoted as Fe2.5+, is presented. The system under study is the Sr2FeMoO6−w double perovskite, known for exhibiting a very large magnetoresistance. Samples of Sr2FeMoO6−w were synthesized by means of an encapsulation technique utilizing an Fe getter technique and characterized by 57Fe Mössbauer spectroscopy. From 5 K to room temperature the Mössbauer spectrum is dominated by a component with hyperfine parameter values between those expected for high-spin Fe3+ and high-spin Fe2+. © 2000 American Institute of Physics.
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71.28.+d Narrow-band systems; intermediate-valence solids
76.80.+y Mössbauer effect; other γ-ray spectroscopy
71.70.Jp Nuclear states and interactions

Magnetic moment of Mn in the ferromagnetic semiconductor (Ga0.98Mn0.02)As

H. Ohldag, V. Solinus, F. U. Hillebrecht, J. B. Goedkoop, M. Finazzi, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 76, 2928 (2000); http://dx.doi.org/10.1063/1.126519 (3 pages) | Cited 54 times

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We have studied the quasibinary ferromagnetic semiconductor (Ga0.98Mn0.02)As by magnetic circular dichroism in x-ray absorption. We find a richly structured Mn absorption spectrum typical for localized 3d electrons. An analysis of the magnetization-averaged and dichroism line shapes shows a local Mn moment of 4.6μB, which is close to the Hund’s rule moment for the half-filled 3d shell. The magnitude of the dichroism reveals that only about 1/7 of the Mn atoms participate in the ferromagnetic order. Our experiment does not show a distinction between the ferro- and paramagnetic Mn atoms. © 2000 American Institute of Physics.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic domain and domain-wall imaging of submicron Co dots by probing the magnetostrictive response using atomic force microscopy

J. Wittborn, K. V. Rao, J. Nogués, and Ivan K. Schuller

Appl. Phys. Lett. 76, 2931 (2000); http://dx.doi.org/10.1063/1.126520 (3 pages) | Cited 6 times

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An approach to image the domains and domain walls of small ferromagnetic entities using atomic force microscopy (AFM), with a nonmagnetic AFM probe, has been developed. Exciting the sample in an external ac magnetic field, the distribution of magnetostrictive response at the surface is detected. By this technique, the domains and domain walls of submicron Co dots have been imaged with a 1 nm lateral resolution. In elliptical Co dots with a 350-nm-long axis on a triangular lattice array with 400 nm periodicity, we find evidence for two domains with opposite magnetization orientation across a wall. The domain-wall width in these dots is found to be about 35 nm. Furthermore, we observe a ferromagnetic alignment of the domains in the neighboring dots, which suggests a magnetostatic interaction among the dots. © 2000 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
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Dielectric properties of layered perovskite Sr1−xAxBi2Nb2O9 ferroelectrics (A=La, Ca and x = 0,0.1)

M. J. Forbess, S. Seraji, Y. Wu, C. P. Nguyen, and G. Z. Cao

Appl. Phys. Lett. 76, 2934 (2000); http://dx.doi.org/10.1063/1.126521 (3 pages) | Cited 68 times

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In this letter, we report an experimental study on the influences of 10 at. % Ca2+ and La3+ doping on dielectric properties and dc conductivity of SrBi2Nb2O9 ferroelectric ceramics. All the samples were made by two-step solid-state reaction sintering at temperatures up to 1150 °C for 0.5–1 h in air. X-ray diffraction analysis indicated that single-phase layered perovskite ferroelectrics were obtained and no appreciable secondary phase was found. The Curie point was found to increase from 418 °C without doping to 475 °C with Ca2+ doping and to 480 °C with La3+ doping. Dielectric constants, loss tangent, and dc conductivity of SrBi2Nb2O9 ferroelectrics doped with Ca2+ and La3+ were studied and the relationships among doping, crystal structure, and dielectric properties were discussed. © 2000 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.66.Fn Inorganic compounds
77.22.Gm Dielectric loss and relaxation
77.80.B- Phase transitions and Curie point
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators

Epitaxial growth of non-c-oriented SrBi2Nb2O9 on (111) SrTiO3

J. Lettieri, M. A. Zurbuchen, Y. Jia, D. G. Schlom, S. K. Streiffer, and M. E. Hawley

Appl. Phys. Lett. 76, 2937 (2000); http://dx.doi.org/10.1063/1.126522 (3 pages) | Cited 36 times

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Epitaxial SrBi2Nb2O9 thin films have been grown with a (103) orientation on (111) SrTiO3 substrates by pulsed-laser deposition. Four-circle x-ray diffraction and transmission electron microscopy reveal nearly phase-pure epitaxial films. Epitaxial (111) SrRuO3 electrodes enabled the electrical properties of these (103)-oriented SrBi2Nb2O9 films to be measured. The low-field relative permittivity was 185, the remanent polarization was 15.7 μC/cm2, and the dielectric loss was 2.5% for a 0.5-μm-thick film. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Controlling the concentration and position of nitrogen in ultrathin oxynitride films formed by using oxygen and nitrogen radicals

K. Watanabe and T. Tatsumi

Appl. Phys. Lett. 76, 2940 (2000); http://dx.doi.org/10.1063/1.126523 (3 pages) | Cited 8 times

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The formation of oxynitride films less than 2.0 nm by using oxygen and nitrogen radicals produced by an electron cyclotron resonance plasma in an ultrahigh-vacuum system has been studied. We found that the N concentration can be controlled at values up to 15% and that, although the interface roughness tends to increase with increasing N concentration, supplying oxygen and nitrogen radicals simultaneously decreases the roughness of the film and increases its nitrogen concentration (N: 12.1%, root mean square: 0.12 nm). We also could easily control the nitrogen profile in the oxynitride less than 2.0-nm-thick by using different processing sequences. © 2000 American Institute of Physics.
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68.55.Nq Composition and phase identification
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Mq Oxidation
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
68.35.Ct Interface structure and roughness
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Direct-current characteristics of pnp AlGaN/GaN heterojunction bipolar transistors

A. P. Zhang, G. T. Dang, F. Ren, J. Han, A. G. Baca, R. J. Shul, H. Cho, C. Monier, X. A. Cao, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 76, 2943 (2000); http://dx.doi.org/10.1063/1.126524 (3 pages) | Cited 11 times

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AlGaN/GaN pnp heterojunction bipolar transistors were fabricated using a low-damage dry-etch process, and the dc characteristics measured up to 250 °C. In the common–base mode, the collector current was approximately equal to the emitter current under all conditions. Although not optimized for power operations, the devices were tested up to power densities of ∼50 kW cm−2. The dc current gain was in the range 20–25 at room temperature. The pnp configuration avoids the problem of high base sheet resistance encountered with npn-AlGaN/GaN devices. © 2000 American Institute of Physics.
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85.30.Pq Bipolar transistors

Highly polarized blue electroluminescence from homogeneously aligned films of poly(9,9-dioctylfluorene)

K. S. Whitehead, M. Grell, D. D. C. Bradley, M. Jandke, and P. Strohriegl

Appl. Phys. Lett. 76, 2946 (2000); http://dx.doi.org/10.1063/1.126525 (3 pages) | Cited 88 times

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Homogeneous alignment of poly(9,9-dioctylfluorene) films on thin layers of rubbed precursor-route poly(p-phenylenevinylene) allows the construction of light-emitting diodes that emit highly polarized blue light (λem = 458 nm). The rubbed poly(p-phenylenevinylene) acts as an effective hole-injecting alignment layer. Annealing of poly(9,9-dioctylfluorene) in its nematic phase followed by rapid quenching orients the polymer as a glassy monodomain on the alignment layer and gives devices with a polarization ratio of 25:1 and a luminance of up to 250 cd/m2. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
81.30.Fb Solidification
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The effect of chlorine on dopant activation in hydrogenated amorphous silicon

Adam M. Payne and Sigurd Wagner

Appl. Phys. Lett. 76, 2949 (2000); http://dx.doi.org/10.1063/1.126526 (3 pages) | Cited 2 times

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The dark conductivity of hydrogenated amorphous silicon (a-Si:H) films deposited from dichlorosilane (SiCl2H2) and silane (SiH4), and doped with diborane (B2H6), increases by as much as a factor of 100 over the usual a-Si:H,B films deposited without SiCl2H2. The effect is observed at gas phase concentrations of diborane ranging from 0.006 to 0.5 vol %, and for both direct current (dc) and 13.56 MHz radio frequency plasma depositions, although it is more noticeable for the dc discharge. An increase in dark conductivity is also observed in boron doped hydrogenated amorphous silicon carbon alloys (a-SiC:H) deposited with dichlorosilane, albeit coupled with a change in the Tauc gap. Chlorine reduces the conductivity of undoped and phosphorus doped a-Si:H films. A B–Cl cluster acceptor that is not passivated by H is proposed as a possible mechanism for chlorine enhanced conductivity. This increase in p-layer conductivity translates into an increase of solar cell efficiency, but surprisingly by an increase in photocurrent rather than open circuit voltage. © 2000 American Institute of Physics.
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73.61.Jc Amorphous semiconductors; glasses
73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
84.60.Jt Photoelectric conversion
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
73.50.Pz Photoconduction and photovoltaic effects

Probing deep interaction potentials with white-noise-driven atomic force microscope cantilevers

D. O. Koralek, W. F. Heinz, M. D. Antonik, A. Baik, and J. H. Hoh

Appl. Phys. Lett. 76, 2952 (2000); http://dx.doi.org/10.1063/1.126527 (3 pages) | Cited 5 times

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Perturbations to the thermally driven motion of an atomic force microscope (AFM) cantilever can be used to probe tip-sample interactions. One limitation of such thermal-noise-based measurements is that they fail for large attractive interactions with force gradients that exceed the stiffness of the cantilever. In such cases, the AFM tip jumps to the surface and is trapped there for long periods of time. Here, we describe an approach to overcome this limitation by driving the AFM cantilever with white noise, essentially simulating high temperatures. Effective temperatures of several thousand Kelvin are easily obtained. We show that this approach allows the AFM tip to “thermally” sample interactions that would otherwise capture the tip. © 2000 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Theory of electrostatic probe microscopy: A simple perturbative approach

S. Gómez-Moñivas, J. J. Sáenz, R. Carminati, and J. J. Greffet

Appl. Phys. Lett. 76, 2955 (2000); http://dx.doi.org/10.1063/1.126528 (3 pages) | Cited 33 times

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A theoretical approach to electrostatic scanning probe microscopy is presented. We show that a simple perturbation formula, originally derived in the context of scattering theory of electromagnetic waves, can be used to obtain the capacitance and the electrostatic force between a metallic tip and an inhomogeneous dielectric sample. For inhomogeneous thin dielectric films, the scanning probe signal is shown to be proportional to the convolution between an effective surface profile and a response function of the microscope. This provides a rigorous framework to address the resolution issue and the inverse problem. © 2000 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Enhanced ballistic phonon production for surface events in cryogenic silicon detector

R. M. Clarke, P. L. Brink, B. Cabrera, P. Colling, M. B. Crisler, A. K. Davies, S. Eichblatt, R. J. Gaitskell, J. Hellmig, J. M. Martinis, S. W. Nam, T. Saab, and B. A. Young

Appl. Phys. Lett. 76, 2958 (2000); http://dx.doi.org/10.1063/1.126529 (3 pages) | Cited 9 times

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We present evidence of an enhanced ballistic phonon component resulting from surface events in a 100 g silicon cryogenic dark matter detector. Surface events, calibrated using a 14C electron source, were found to have faster rise times (∼5 μs) than bulk gamma and neutron events (∼7 μs). Using this effect, we were able to discriminate bulk nuclear recoil events from a surface electron background at better than the 97% level above 25 keV recoil energy. The phonon risetime for bulk gamma events was dependent on the applied voltage, confirming that phonons produced from electron-hole emission are ballistic. © 2000 American Institute of Physics.
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63.20.-e Phonons in crystal lattices
95.35.+d Dark matter (stellar, interstellar, galactic, and cosmological)
29.40.Wk Solid-state detectors

Field emission study of diamond-like carbon films with scanned-probe field-emission force microscopy

Takahito Inoue, D. Frank Ogletree, and Miquel Salmeron

Appl. Phys. Lett. 76, 2961 (2000); http://dx.doi.org/10.1063/1.126530 (3 pages) | Cited 12 times

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Using a tip as an anode, a scanning force microscope (SFM) with an electrically conducting tip allows simultaneous measurement of both field-emitted currents and surface electronic properties with high lateral resolution. The principle of the method and its application to field emission from chemical vapor deposition diamond-like carbon films are presented. By simultaneously imaging the topography and field-emission current distribution with a 100 nm tip-surface separation, we correlated emission, topography, and dielectric properties. Subsequent contact SFM images of the same regions correlated topography and conductivity on the nanometer scale. The electrostatic force between tip and surface showed fluctuations on a millisecond time scale during field emission. This is probably due to charging and discharging of deep traps in the diamond-like carbon film. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
79.70.+q Field emission, ionization, evaporation, and desorption
73.25.+i Surface conductivity and carrier phenomena
73.20.At Surface states, band structure, electron density of states
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