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26 Mar 2001

Volume 78, Issue 13, pp. 1805-1950

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Auger recombination in heavily carbon-doped GaAs

R. K. Ahrenkiel, R. Ellingson, W. Metzger, D. I. Lubyshev, and W. K. Liu

Appl. Phys. Lett. 78, 1879 (2001); http://dx.doi.org/10.1063/1.1357213 (3 pages) | Cited 6 times

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The recombination parameters in heavily carbon-doped GaAs are of considerable importance to current bipolar transistor technology. Here, we used time-resolved photoluminescence and quantum-efficiency techniques in parallel to measure the very short lifetimes expected at high doping. The samples were isotype double heterostructures, with the structure Al(0.4)Ga(0.6)As/GaAs/Al(0.4)Ga(0.6)As, grown by molecular-beam epitaxy. The doping level was varied from 5×1018 to 1×1020 cm−3 for the samples described here. For doping levels greater than 1×1019 cm−3, the lifetime decreased as the inverse of the cube of the hole density, indicating that phonon and impurity-assisted Auger processes are dominant. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Hot-carrier-induced oxide charge trapping and interface trap creation in metal–oxide–semiconductor devices studied by hydrogen/deuterium isotope effect

Kangguo Cheng, Jinju Lee, Karl Hess, and Joseph W. Lyding

Appl. Phys. Lett. 78, 1882 (2001); http://dx.doi.org/10.1063/1.1359143 (3 pages)

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A method based on the hydrogen/deuterium isotope effect is proposed to separate and quantify the effects of interface trap creation and oxide charge trapping on hot-carrier-induced degradation in n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs). Hydrogenated and deuterated transistors were subjected to hot-carrier stress with a fixed drain voltage Vds and various gate voltages Vgs. The threshold voltage Vt and interface trap density Nit were recorded as a function of stress time. It is found that at low Vgs stress when equal numbers of interface traps are created, the shift of Vt is larger in hydrogenated transistors than in deuterated transistors. Increasing Vgs to 1/3Vds produces no noticeable difference of Vt shift in these two kinds of transistors. However, further increasing Vgs results in larger Vt shift in deuterated transistors than in hydrogenated ones. From a quantitative analysis, the contribution of oxide charge trapping to Vt shift is separated from the contribution of interface trap creation. The results suggest that interface trap creation is the dominant mechanism for hot-carrier-induced degradation in n-channel MOSFETs. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Fq High-field and nonlinear effects
73.20.-r Electron states at surfaces and interfaces
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Anomalous transport on polymeric porous film electrodes in the dopant-induced insulator-to-conductor transition analyzed by electrochemical impedance

Germà Garcia-Belmonte, Juan Bisquert, Ernesto C. Pereira, and Francisco Fabregat-Santiago

Appl. Phys. Lett. 78, 1885 (2001); http://dx.doi.org/10.1063/1.1354671 (3 pages) | Cited 7 times

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In the present letter, we have identified anomalous transport patterns on conducting polymer thin-film electrodes [poly(thiophene-3-acetic acid)] by means of electrochemical impedance measurements. This type of electrical behavior yields conductance responses exhibiting frequency dispersion at frequencies in excess of the ac onset ωc. The study of impedance spectra under variation of the applied potential allows to determine the threshold potential at which a dopant-induced insulator-to-conductor transition takes place. Moreover, since the charge carrier concentration in the polymer matrix is directly modulated by the insertion of anions via the applied potential, some relevant aspects of the doping process, such as the dimensionality of the ion insertion, can be properly investigated. © 2001 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.35.Cd Conducting polymers
72.80.Le Polymers; organic compounds (including organic semiconductors)
82.45.Mp Thin layers, films, monolayers, membranes
72.60.+g Mixed conductivity and conductivity transitions
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Low-loss YBa2Cu3O7 films on flexible, polycrystalline-yttria-stabilized zirconia tapes for cryoelectronic applications

K. S. Harshavardhan, H. M. Christen, S. D. Silliman, V. V. Talanov, S. M. Anlage, M. Rajeswari, and J. Claassen

Appl. Phys. Lett. 78, 1888 (2001); http://dx.doi.org/10.1063/1.1358845 (3 pages) | Cited 1 time

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High-temperature superconducting films on flexible, low-thermal conductivity, low-loss substrates offer a unique base for the development of cryoelectronic digital interconnects. Using an ion-beam-assisted pulsed-laser-deposition technique, we developed biaxially textured YBa2Cu3O7 (YBCO) films on flexible polycrystalline-yttria-stabilized zirconia (YSZ) substrates with the following materials properties: (i) in-plane x-ray Φ-scan full width at half maximum of ∼7°; (ii) transition temperatures (Tc) in the range of 88–89 K with transition widths (ΔTc) of ∼0.5 K; (iii) critical current densities (Jc) in the range 1.5–2×106 A/cm2 at 77 K, zero field; (iv) magnetic penetration depth (λ) of 284 nm at 77 K; and (v) surface resistance (Rs) of 700 μΩ at 77 K, 10 GHz. The low-microwave loss, biaxilly textured YBCO films combined with the low-thermal conductivity YSZ substrate could facilitate a variety of RF cryoelectronic applications. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
84.71.Mn Superconducting wires, fibers, and tapes
81.15.Fg Pulsed laser ablation deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.N- Response to electromagnetic fields

Thermal instability near planar defects in superconductors

A. Gurevich

Appl. Phys. Lett. 78, 1891 (2001); http://dx.doi.org/10.1063/1.1358361 (3 pages) | Cited 5 times

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It is shown that the local Joule heating due to planar defects, such as grain boundaries, microcracks, etc., can cause thermal instabilities, which limit the current-carrying capability of YBa2Cu3O7-coated conductors. Explicit instability criteria are obtained for a planar defect in a film and for a grain boundary. Thermal instabilities can be triggered by low-angle grain boundaries or planar defects, which block only a small fraction of the sample cross section. Hot spots near small defects and overheating of grain boundaries are essential for interpretation of experimental data on ac losses and E–J curves of polycrystals. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.25.Bt Thermodynamic properties
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects

Inverse magnetoresistance in chromium-dioxide-based magnetic tunnel junctions

A. Gupta, X. W. Li, and Gang Xiao

Appl. Phys. Lett. 78, 1894 (2001); http://dx.doi.org/10.1063/1.1356726 (3 pages) | Cited 47 times

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Magnetic tunnel junctions have been fabricated using half-metallic chromium-dioxide (CrO2) epitaxial film with a Co counterelectrode. The native insulating layer formed on the surface of CrO2 after air exposure is used as the tunneling barrier. These junctions exhibit nonlinear current–voltage characteristics, and the changes in junction resistance with applied field correspond to the coercivities of the two magnetic layers. The maximum observed magnetoresistance (MR) is about 8% at 4.2 K and has a negative sign, i.e., the resistance of the junction with parallel alignment of the electrodes is higher than with antiparallel alignment. This is opposite of what is normally observed with transition-metal electrodes and an Al2O3 barrier. Possible reasons for the inverse MR are discussed based on previous results on manganite/Co junctions. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Low-noise flux-gate magnetic-field sensors using ring- and rod-core geometries

R. H. Koch and J. R. Rozen

Appl. Phys. Lett. 78, 1897 (2001); http://dx.doi.org/10.1063/1.1358852 (3 pages) | Cited 10 times

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We have fabricated ring-core and single-domain rod-core flux-gate magnetic field sensors with 1/f noise levels at 1 Hz of 1.4 pT/math and 3.5 pT/math, respectively. These noise sensitivities were achieved by applying an electrical current through the core of the flux gate to magnetically bias the magnetic rotation of the core perpendicular to the easy-axis direction. We also found that in the rod-core sensor, the spatial correlation lengths of the magnetic fluctuations were 25 and 40 mm with and without the biasing current. The cross-power spectrum magnitude at 1 Hz was less than 200 fT/math. © 2001 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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DC field dependent properties of Na0.5K0.5NbO3/SiO2/Si structures at millimeter-wave frequencies

S. Abadei, S. Gevorgian, C.-R. Cho, A. Grishin, J. Andreasson, and T. Lindbäck

Appl. Phys. Lett. 78, 1900 (2001); http://dx.doi.org/10.1063/1.1353838 (3 pages) | Cited 13 times

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Dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Ω cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 μm. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices. © 2001 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
81.15.Fg Pulsed laser ablation deposition
77.22.Gm Dielectric loss and relaxation
84.40.-x Radiowave and microwave (including millimeter wave) technology

Large remanent polarization of vanadium-doped Bi4Ti3O12

Yuji Noguchi and Masaru Miyayama

Appl. Phys. Lett. 78, 1903 (2001); http://dx.doi.org/10.1063/1.1357215 (3 pages) | Cited 202 times

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Effects of vanadium doping on the ferroelectric properties of Bi4Ti3O12 were investigated using dense ceramics. The incorporation of vanadium resulted in a large remanent polarization (2Pr) of over 40 μC/cm2 without sacrificing other physical properties, and the polarization characteristics were shown to be superior to SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9. In addition, dense ceramics of vanadium-doped Bi4Ti3O12 could be obtained by sintering at temperatures 100–200 °C lower than those for the SrBi2Ta2O9 system. © 2001 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Photodiode properties of epitaxial Pb(Ti, Zr)O3/SrTiO3 ferroelectric heterostructures

Yukio Watanabe and Motochika Okano

Appl. Phys. Lett. 78, 1906 (2001); http://dx.doi.org/10.1063/1.1357807 (3 pages) | Cited 20 times

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A substantial photovoltaic effect is found in heterostructures of typical ferroelectric oxides. Pb(Ti, Zr)O3/Nb-doped SrTiO3, especially, exhibits current–voltage characteristics of the photovoltaic effect of a typical pn junction (p: hole carrier type, n: electron carrier type). A preliminary nonoptimized device shows high performance such as open circuit voltage of 0.7–0.8 V, external conversion efficiency of 0.6%–0.8%, and response time faster than 20 μs for ultraviolet light at room temperature, suggesting the potential of this diode as a new class of photodiode. The results support the formation of a pn like junction by ferroelectric oxides. Additionally, the photovoltaic characteristics are tuned by the application of short pulse voltages and retained. © 2001 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects

Dielectric studies of ZnSe1−xTex epilayers

H. M. Lin, Y. F. Chen, J. L. Shen, and C. W. Chou

Appl. Phys. Lett. 78, 1909 (2001); http://dx.doi.org/10.1063/1.1355015 (3 pages) | Cited 4 times

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We present the results of experimental investigations on dielectric properties of ZnSe1−xTex epilayers by capacitance and dissipation factor at temperature 5 K<T<475 K and frequency 20 Hz<f<1 MHz. A Debye-like relaxation of dielectric behavior has been observed, which is found to be a thermally activated process. The activation energies obtained from capacitance and dissipation factor are in very good agreement. The activation energies decrease with the increase of Se content, and range from 662 to 819 meV. The results are described by means of the four-center model, in which the number of different atoms occupying the nearest-neighbor sites of defects results in a different activation energy. © 2001 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
71.55.Gs II-VI semiconductors
73.61.Ga II-VI semiconductors
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Effect of particle size on the photoluminescence from hydrogen passivated Si nanocrystals in SiO2

S. Cheylan and R. G. Elliman

Appl. Phys. Lett. 78, 1912 (2001); http://dx.doi.org/10.1063/1.1357450 (3 pages) | Cited 35 times

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The effect of hydrogen passivation on the photoluminescence from Si nanocrystals prepared in SiO2 by ion implantation and annealing is examined as a function of nanocrystal size (implant fluence). Passivation is shown to produce a significant increase in emission intensities as well as a redshift of spectra, both of which increase with increasing fluence. These results are shown to be consistent with a model in which larger nanocrystals are assumed to contain more nonradiative defects (i.e., the defect concentration is assumed to be proportional to the nanocrystal surface area or volume). Since this results in a smaller fraction of larger nanocrystals contributing to the initial luminescence, emission spectra are initially blueshifted relative to that that might be expected from the physical nanocrystal size distribution. The contribution from larger crystallites is then disproportionately increased by passivation resulting in the observed redshift. © 2001 American Institute of Physics.
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71.20.Mq Elemental semiconductors
FREE

Direct patterning of self-assembled nanocrystal monolayers by electron beams

X. M. Lin, R. Parthasarathy, and H. M. Jaeger

Appl. Phys. Lett. 78, 1915 (2001); http://dx.doi.org/10.1063/1.1358363 (3 pages) | Cited 34 times

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We demonstrate a method for laterally patterning metal nanocrystal monolayers. Extended monolayers are first self-assembled onto a solid substrate. Direct electron-beam exposure is then used to strip the dodecanethiol ligand coating from the nanocrystal cores, enabling the cores to stick to the underlying substrate. During a subsequent washing step in a solvent mixture, nanocrystals from the unexposed regions are removed and floated off, leaving behind the desired pattern. © 2001 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
81.16.Dn Self-assembly
81.07.Bc Nanocrystalline materials
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
61.46.-w Structure of nanoscale materials
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)

Effect of surface reconstruction on the structural prototypes of ultrasmall ultrabright Si29 nanoparticles

L. Mitas, J. Therrien, R. Twesten, G. Belomoin, and M. H. Nayfeh

Appl. Phys. Lett. 78, 1918 (2001); http://dx.doi.org/10.1063/1.1356447 (3 pages) | Cited 61 times

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We propose, using density functional, configuration interaction, and quantum Monte Carlo calculations, structural prototypes of ultrasmall ultrabright particles prepared by dispersion from bulk. We constructed near spherical structures (Td point group symmetry) that contain 29 Si atoms, five of which constitute a tetrahedral core and the remaining 24 constitute a hydrogen terminated reconstructed Si surface. The surface is a highly wrinkled or puckered system of hexagons and pentagons (as in a filled fullerene). We calculated, for several surface reconstruction models, the coordinates of atoms, the absorption spectrum, the absorption edge, polarizability, and the electron diffraction pattern. The Si29H24 (six reconstructed surface dimers) gives a size of 0.9 nm, an absorption spectrum and bandgap (3.5±0.3 eV), in fair agreement with measurement. The structure yields a polarizability of 830 a.u. with an effective “dielectric” constant of ∼6.0. The calculated electron diffraction of single particles shows residual crystalline coherent scattering for large but not small scattering angles. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.22.Dj Single particle states
73.20.At Surface states, band structure, electron density of states
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.40.Fy Semiconductors
78.68.+m Optical properties of surfaces

Quantitative evaluation of electron beam writing in passivated gold nanoclusters

T. R. Bedson, R. E. Palmer, T. E. Jenkins, D. J. Hayton, and J. P. Wilcoxon

Appl. Phys. Lett. 78, 1921 (2001); http://dx.doi.org/10.1063/1.1354154 (3 pages) | Cited 8 times

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We report a quantitative investigation of direct electron beam writing in monolayer films of passivated gold nanoclusters. In this process, the passivating organic ligands are (partially) removed to create gold-based nanostructures. We report the fabrication of lines with width as narrow as 26 nm, while measurements of the linewidth as a function of dose allow us to obtain a quantitative measure of the sensitivity, for comparison with established negative tone resists. © 2001 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
68.47.Jn Clusters on oxide surfaces
81.65.Rv Passivation
81.07.Lk Nanocontacts
61.46.-w Structure of nanoscale materials
85.40.Hp Lithography, masks and pattern transfer
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Electroabsorption measurements and built-in potentials in amorphous silicon–germanium solar cells

J. H. Lyou, E. A. Schiff, S. Guha, and J. Yang

Appl. Phys. Lett. 78, 1924 (2001); http://dx.doi.org/10.1063/1.1356443 (3 pages) | Cited 4 times

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We report electromodulated reflectance spectra in n-i-p solar cells with hydrogenated amorphous silicon–germanium alloy absorber layers. At lower photon energies the spectra are determined by bulk electroabsorption, and exhibit peaks near the optical gap of the absorber layers. Voltage scaling of the electroabsorption spectra indicate a built-in potential of Vbi = 1.17 V in cells with absorber layer band gaps of 1.50 eV; in conjunction with earlier work, this value argues against a systematic decline in Vbi with an absorber layer band gap. At higher photon energies the spectra are due to direct electroreflectance; the voltage scaling was consistent with model predictions for the electric field at the interface of the p-type and absorber layers. © 2001 American Institute of Physics.
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84.60.Jt Photoelectric conversion
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

External coupling efficiency in planar organic light-emitting devices

M.-H. Lu and J. C. Sturm

Appl. Phys. Lett. 78, 1927 (2001); http://dx.doi.org/10.1063/1.1357207 (3 pages) | Cited 29 times

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The external coupling efficiency in planar organic light-emitting devices is modeled based on a quantum mechanical microvavity theory and measured by examining both the far-field emission pattern and the edge emission of light trapped in the glass substrate. The external coupling efficiency is dependent upon the thickness of the indium–tin–oxide layer and the refractive index of the substrate. The coupling efficiency ranges from ∼24% to ∼52%, but in general it is much larger than the 18.9% expected from classical ray optics. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
85.60.Bt Optoelectronic device characterization, design, and modeling
85.60.Pg Display systems

Optical control of charge number in single floating quantum-dot gate in field-effect transistor structure

Masashi Shima, Yoshiki Sakuma, Yoshihiro Sugiyama, Yuji Awano, and Naoki Yokoyama

Appl. Phys. Lett. 78, 1930 (2001); http://dx.doi.org/10.1063/1.1359139 (3 pages)

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The optical characteristics of a single floating quantum-dot (QD) gate field-effect transistor memory cell were investigated at 77 K. The channel current, which can detect sensitively the charging of the QD, was saturated via some discrete levels after illuminations by light pulses, and the saturation value increased with the stronger illumination power. It was also found, by comparing the optical writing characteristics for different illumination powers at 77 K with retention characteristics at 120 K, that the discrete current levels observed in the optical characteristics corresponded to the hole number variation in the single QD. These results show that the number of holes stored in a single QD was controlled by changing the illumination power. © 2001 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Kv Quantum dots
42.79.Vb Optical storage systems, optical disks
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Pulsed liquid microjet for microsurgery

D. A. Fletcher and D. V. Palanker

Appl. Phys. Lett. 78, 1933 (2001); http://dx.doi.org/10.1063/1.1357452 (3 pages) | Cited 14 times

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The precision of soft tissue dissection with pulsed lasers in liquid media is typically limited by collateral damage from vapor bubbles created during energy deposition. We present an alternative technique for creating incisions using a pulsed liquid microjet driven by an electric discharge-induced vapor bubble generated inside a micronozzle. We use this technique to create a pulsed jet 30 μm in diameter with a peak velocity of 90 m/s and total ejected volume on the order of 100 pl. Incision tests on a polyacrylamide gel simulating soft tissue show that the width of the cut is comparable to the diameter of the micronozzle and that collateral damage is significantly less than that produced by a vapor bubble not confined by the nozzle. © 2001 American Institute of Physics.
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87.80.-y Biophysical techniques (research methods)
47.27.wg Turbulent jets
47.60.-i Flow phenomena in quasi-one-dimensional systems
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In situ x-ray microscopic observation of the electromigration in passivated Cu interconnects

G. Schneider, D. Hambach, B. Niemann, B. Kaulich, J. Susini, N. Hoffmann, and W. Hasse

Appl. Phys. Lett. 78, 1936 (2001); http://dx.doi.org/10.1063/1.1356446 (3 pages) | Cited 10 times

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X-ray imaging of electromigration in a passivated Cu interconnect was performed with 100-nm spatial resolution. A time sequence of 200 images, recorded with the European Synchrotron Radiation Facility x-ray microscope in 2.2 h at 4 keV photon energy, visualizes the mass flow of Cu at current densities up to 2×107 A/cm2. Due to the high penetration power through matter and the element specific image contrast, x-ray microscopy is a unique tool for time-resolved, quantitative mass transport measurements in interconnects. Model calculations predict that failures in operating microprocessors are detectable with 30 nm resolution by nanotomography. © 2001 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
68.37.Yz X-ray microscopy
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
07.85.Tt X-ray microscopes

Resonance frequency and Q factor mapping by ultrasonic atomic force microscopy

Kazushi Yamanaka, Yoshiki Maruyama, Toshihiro Tsuji, and Keiichi Nakamoto

Appl. Phys. Lett. 78, 1939 (2001); http://dx.doi.org/10.1063/1.1357540 (3 pages) | Cited 42 times

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We developed an improved ultrasonic atomic force microscopy (UAFM) for mapping resonance frequency and Q factor of a cantilever where the tip is in linear contact with the sample. Since the vibration amplitude at resonance is linearly proportional to the Q factor, the resonance frequency and Q factor are measured in the resonance tracking mode by scanning the sample in the constant force mode. This method enables much faster mapping of the resonance frequency and Q factor than the previous one using a network analyzer. In this letter, we describe the principle and instrumentation of the UAFM and show images of carbon-fiber-reinforced plastic composites. © 2001 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.35.Yb Ultrasonic instrumentation and measurement techniques
68.37.Tj Acoustic force microscopy
43.58.Ls Acoustical lenses and microscopes

Effect of alcohol-based sulfur treatment on Pt Ohmic contacts to p-type GaN

Chul Huh, Sang-Woo Kim, Hyun-Min Kim, Dong-Joon Kim, and Seong-Ju Park

Appl. Phys. Lett. 78, 1942 (2001); http://dx.doi.org/10.1063/1.1358356 (3 pages) | Cited 20 times

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The effects of an alcohol-based (NH4)2S solution [t-C4H9OH+(NH4)2S] treatment on Pt Ohmic contacts to p-type GaN are presented. The specific contact resistance decreased by three orders of magnitude from 2.56×10−2 to 4.71×10−5 Ω cm2 as a result of surface treatment using an alcohol-based (NH4)2S solution compared to that of the untreated sample. The O 1s and Pt 4f core-level peaks in the x-ray photoemission spectra showed that the alcohol-based (NH4)2S treatment was effective in removing of the surface oxide layer. Compared to the untreated sample, the alcohol-based (NH4)2S-treated sample showed a Ga 2p core-level peak which was shifted toward the valence-band edge by 0.25 eV, indicating that the surface Fermi level was shifted toward the valence-band edge. These results suggest that the surface barrier height for hole injection from Pt metal to p-type GaN can be lowered by the surface treatment, thus resulting in a drastic reduction in specific contact resistance. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
84.32.Dd Connectors, relays, and switches
73.40.Cg Contact resistance, contact potential
81.65.Ps Polishing, grinding, surface finishing
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states

Development of selective lateral photoelectrochemical etching of InGaN/GaN for lift-off applications

A. R. Stonas, T. Margalith, S. P. DenBaars, L. A. Coldren, and E. L. Hu

Appl. Phys. Lett. 78, 1945 (2001); http://dx.doi.org/10.1063/1.1352663 (3 pages) | Cited 18 times

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The authors have developed a wet band gap-selective photoelectrochemical etching process to produce deep undercuts (∼500 μm) into InGaN/GaN heterostructures. These undercuts were used in a lift-off process which successfully transferred device-scale (100 μm diameter, 5 μm thick) disks from their underlying sapphire substrates to another substrate. Experiments were conducted using a lamp-and-filter arrangement, employing n-type and p-type GaN pieces as filters. Polishing was conducted to smooth the resulting substrate-transferred GaN disks. © 2001 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
81.65.Ps Polishing, grinding, surface finishing
82.50.Hp Processes caused by visible and UV light
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
82.45.Mp Thin layers, films, monolayers, membranes

High-resolution imaging of surface acoustic wave scattering

T. Hesjedal and G. Behme

Appl. Phys. Lett. 78, 1948 (2001); http://dx.doi.org/10.1063/1.1357453 (3 pages) | Cited 4 times

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We examine the scattering of surface acoustic waves (SAWs) by single dots, periodic and locally damped two-dimensional dot lattices. Employing the scanning acoustic force microscope, SAW fields are imaged with nanometer resolution. We study the influence of a roughly wavelength-sized single dot on SAW diffraction. In order to distinguish between forward- and backscattered components, we insonify the dot with the pump and probe beam under 0° and 90°. We furthermore analyze the SAW diffraction by a regular dot array. The wave field appears to be localized around the dots. Adding surface distortions, the regular SAW localization pattern brakes down in the vicinity of the distortion. © 2001 American Institute of Physics.
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68.37.Tj Acoustic force microscopy
68.35.Iv Acoustical properties
07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
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