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24 Jan 2000

Volume 76, Issue 4, pp. 397-519

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Near-field optical spectroscopy using an incoherent light source

L. Aigouy, F. X. Andréani, A. C. Boccara, J. C. Rivoal, J. A. Porto, R. Carminati, J.-J. Greffet, and R. Mégy

Appl. Phys. Lett. 76, 397 (2000); http://dx.doi.org/10.1063/1.125766 (3 pages) | Cited 25 times

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We present a method to perform near-field optical spectroscopy. It consists of an apertureless near-field optical microscope combined with an incoherent light source and a monochromator. We show that the optical response of the tip depends both on the wavelength and the tip apex shape. The experimental optical response of the tips is in good agreement with the predicted theoretical one. The near-field optical spectrum obtained on a gold island in the visible spectrum range (λ = 400–600 nm) is presented and shows that the method is reliable to perform spectroscopic measurements on submicrometer-sized objects. © 2000 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
07.60.Rd Visible and ultraviolet spectrometers

Investigation of polarization-pinning mechanism in deep-line-etched vertical-cavity surface-emitting lasers

L. J. Sargent, J. M. Rorison, M. Kuball, R. V. Penty, I. H. White, S. W. Corzine, M. R. T. Tan, S. Y. Wang, and P. J. Heard

Appl. Phys. Lett. 76, 400 (2000); http://dx.doi.org/10.1063/1.125767 (3 pages) | Cited 7 times

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Recently, it has been shown that the etching of deep trenches in close proximity to GaAs vertical-cavity surface-emitting laser (VCSEL) apertures causes the linearly polarized TE emission to be pinned in a direction parallel to the line etch. In this letter, we show that etching introduces compressive strain or relaxes tensile strain through the creation of free interfaces. An anisotropic variation of strain is the origin of the polarization pinning effect. We report on the enhancement of polarization pinning by postannealing after etching. Photoluminescence and Raman measurements of the VCSEL wafer were taken before and after etching and annealing. The observed shift in the Fabry–Perot mode was used to model the strain, giving 4×108 dyn/cm2, or 0.05%, compressive strain perpendicular to the etch. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions

Solar-blind AlGaN photodiodes with very low cutoff wavelength

D. Walker, V. Kumar, K. Mi, P. Sandvik, P. Kung, X. H. Zhang, and M. Razeghi

Appl. Phys. Lett. 76, 403 (2000); http://dx.doi.org/10.1063/1.125768 (3 pages) | Cited 55 times

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We report the fabrication and characterization of AlxGa1−xN photodiodes (x ∼ 0.70) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The peak responsivity for −5 V bias is 0.11 A/W at 232 nm, corresponding to an internal quantum efficiency greater than 90%. The device response drops four orders of magnitude by 275 nm and remains at low response for the entire near-ultraviolet and visible spectrum. Improvements were made to the device design including a semitransparent Ni/Au contact layer and a GaN:Mg cap layer, which dramatically increased device response by enhancing the carrier collection efficiency. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Doubling the frequency of depleted fundamental waves in periodically poled KTiOPO4

D. Eger, M. B. Oron, A. Bruner, M. Katz, Y. Tzuk, and A. Englander

Appl. Phys. Lett. 76, 406 (2000); http://dx.doi.org/10.1063/1.125769 (3 pages) | Cited 1 time

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Frequency doubling of a diode-pumped Nd:YAG laser in 1 and 2 cm long periodically poled KTiOPO4 wafers has been investigated. Up to 60% doubling efficiency has been achieved. The good agreement obtained between measured results and those calculated by numerical integration of the coupled wave equations demonstrate that the efficiency is limited by the basic process of backconversion and dephasing rather than by thermal effects. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Absorbance spectroscopy and identification of valence subband transitions in type-II InAs/GaSb superlattices

Ron Kaspi, Charles Moeller, Andrew Ongstad, Michael L. Tilton, Donald Gianardi, Gregory Dente, and Prabhakara Gopaladasu

Appl. Phys. Lett. 76, 409 (2000); http://dx.doi.org/10.1063/1.125770 (3 pages) | Cited 23 times

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We describe the molecular-beam epitaxy growth, as well as both the structural and optical characterization of a set of InAs/GaSb type-II strained-layer superlattice samples, in which the GaSb layer thickness is systematically increased. Absorbance spectroscopy measurements show well-defined features associated with transitions from the various valence subbands to the lowest conduction subband, and also a significant blueshift of the band edge when the GaSb layers thickness is increased. Empirical pseudopotential method calculations are shown to successfully predict the blueshift and help identify the higher-energy transitions. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
78.30.Fs III-V and II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Surface treatment of indium tin oxide by SF6 plasma for organic light-emitting diodes

Beomrak Choi, Hyunsik Yoon, and Hong H. Lee

Appl. Phys. Lett. 76, 412 (2000); http://dx.doi.org/10.1063/1.125771 (3 pages) | Cited 35 times

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SF6 plasma treatment of indium tin oxide highly improves the power efficiency and the stability of the organic light-emitting diode based on poly[2-methoxy-5-(2-ethylhexyloxy)-1,4phenylenevinylene]. The treatment leads to a slight reduction in the surface roughness and a decrease in the surface content of Sn. The major effect, however, has to do with the surface incorporation of fluorine. This fluorinated surface improves the hole injection and thus the device performance. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
72.30.+q High-frequency effects; plasma effects
73.50.Mx High-frequency effects; plasma effects
68.35.B- Structure of clean surfaces (and surface reconstruction)

p-GaN surface treatments for metal contacts

Jingxi Sun, K. A. Rickert, J. M. Redwing, A. B. Ellis, F. J. Himpsel, and T. F. Kuech

Appl. Phys. Lett. 76, 415 (2000); http://dx.doi.org/10.1063/1.125772 (3 pages) | Cited 85 times

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The chemical bonding and electronic properties of wet, chemically treated p-GaN surfaces were studied using synchrotron radiation photoemission spectroscopy. Chlorine-based chemical bonding was identified on the conventional HCl-treated p-GaN surface, which is associated with a shift of the surface Fermi level toward the conduction band edge by ∼0.9 eV with respect to the thermally cleaned surface. Compared to the HCl-treated surface, the surface Fermi level on the KOH-treated surface lies about ∼1.0 eV closer to the valence band edge, resulting in a much smaller surface barrier height to p-type materials than the HCl-treated surface. The smaller surface barrier height to p-GaN after KOH treatment can lead to a lower contact resistivity and can play an important role in lowering the metal contact resistivity to p-GaN. © 2000 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
73.40.Ns Metal-nonmetal contacts
68.35.Dv Composition, segregation; defects and impurities
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
73.40.Cg Contact resistance, contact potential
73.20.At Surface states, band structure, electron density of states
79.60.Dp Adsorbed layers and thin films
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Investigations on the Stranski–Krastanow growth of CdSe quantum dots

D. Schikora, S. Schwedhelm, D. J. As, K. Lischka, D. Litvinov, A. Rosenauer, D. Gerthsen, M. Strassburg, A. Hoffmann, and D. Bimberg

Appl. Phys. Lett. 76, 418 (2000); http://dx.doi.org/10.1063/1.125773 (3 pages) | Cited 50 times

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We have investigated the growth kinetics of the self-assembled formation of coherently strained CdSe islands. We have found that two distinctly different types of islands are formed in succession. Analyzing the density distribution function of the two dominating size classes of islands, we show that islands of an average diameter of about 16 nm (type B islands) are correlated with a phase transition via a Stranski–Krastanow growth process. The other islands with a diameter of less than 10 nm (type A islands) is formed during the growth of the first 2 ML. At a coverage of about 3.1 ML CdSe stacking faults appear, indicating the beginning of the plastic relaxation of the quantum dot structure. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Desorption of positive ions from ionic crystals accompanying 248 nm laser irradiation

C. Bandis, S. C. Langford, and J. T. Dickinson

Appl. Phys. Lett. 76, 421 (2000); http://dx.doi.org/10.1063/1.125774 (3 pages) | Cited 18 times

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We present a study of the energy distributions of positive ions (Na+, Li+, Ca+, and Mg+) photodesorbed from cleaved NaCl, LiF, MgO, NaNO3, and CaCO3 surfaces during 248 nm excimer laser irradiation at fluences well below the damage thresholds. The observed ion energies are significantly higher than those predicted by already existing models that allow ion rearrangement and relaxation during the electrostatic ion repulsion by the nearby photoionized sites. In contrast to what one would expect, we find that treating the ions as fixed charges and neglecting any ion rearrangement during the emission of the adions describes best the experimentally observed ion energies from all five ionic crystals. © 2000 American Institute of Physics.
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79.20.La Photon- and electron-stimulated desorption
79.20.Ds Laser-beam impact phenomena
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Formation of Ti3+ in sapphire by co-implantation of Ti and O ions

L. D. Morpeth and J. C. McCallum

Appl. Phys. Lett. 76, 424 (2000); http://dx.doi.org/10.1063/1.125775 (3 pages) | Cited 4 times

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We have demonstrated that co-implantation of Ti and O ions into c-axis oriented α-Al2O3 substrates followed by thermal annealing can substantially increase the fraction of Ti ions present in the optically active 3+ oxidation state. Evidence for the presence of Ti3+ is given by the observation of strong luminescence over the wavelength range ∼ 600–900 nm under Ar laser excitation and by the presence of the characteristic absorption band at ∼ 450–550 nm. We have studied the luminescence intensity as a function of implantation and annealing parameters and have found that there is a strong dependence on the ratio of implanted Ti and O and on the annealing temperature. © 2000 American Institute of Physics.
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61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators
71.55.Ht Other nonmetals
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
78.55.Hx Other solid inorganic materials

A plasma process for ultrafast deposition of SiGe graded buffer layers

C. Rosenblad, H. von Känel, M. Kummer, A. Dommann, and E. Müller

Appl. Phys. Lett. 76, 427 (2000); http://dx.doi.org/10.1063/1.125776 (3 pages) | Cited 34 times

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Low energy plasma enhanced chemical vapor deposition (LEPECVD) has been applied to the synthesis of Si-modulation doped field effect transistor structures, comprising a SiGe relaxed buffer layer and a modulation doped strained Si channel. A growth rate of at least 5 nm/s for the relaxed SiGe buffer layer is well above that obtainable by any other technique. Due to the low ion energies involved in LEPECVD, ion damage is absent, despite a huge plasma density. The structural quality of the LEPECVD grown SiGe buffer layers is comparable to that of state-of-the-art material. The electronic properties of the material were evaluated by growing modulation doped Si quantum wells on the buffer layers. We obtain a low temperature (2 K) Hall mobility of μH = 2.5×104 cm2/Vs for the electrons in the Si channel at an electron sheet density of ns = 8.6×1011 cm−2. © 2000 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Hd Other semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Thermally induced stress relaxation and densification of spin-on-glass thin films

C. K. Chiang, W. E. Wallace, G. W. Lynn, D. Feiler, and W. Xia

Appl. Phys. Lett. 76, 430 (2000); http://dx.doi.org/10.1063/1.125777 (3 pages) | Cited 8 times

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The stress–temperature relationship of silica spin-on-glass thin films on silicon wafers was studied. Upon heating, the stress–temperature curves showed a dramatically increasing slope when the temperature of the film was greater than 340 °C. At 450 °C, a significant, irreversible change in the stress of the film was observed. This change in stress was correlated with an increase in film electron density and a decrease in film thickness. The observed thermally activated stress–relaxation behavior was interpreted in terms of reflow of the glassy hydrogen–silsesquioxane-based material. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Enhancement of electromechanical coupling coefficient by proton exchange in Z-cut LiNbO3

D. Čiplys, R. Rimeika, Yu. N. Korkishko, and V. A. Fedorov

Appl. Phys. Lett. 76, 433 (2000); http://dx.doi.org/10.1063/1.125778 (3 pages) | Cited 2 times

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The electromechanical coupling coefficient K for surface acoustic waves (SAWs) in proton-exchanged Z-cut X-propagation lithium niobate has been experimentally investigated by the method of evaporating a thin metal film and measuring in situ the SAW attenuation. The enhancement in K2 value by as much as two times caused by the proton exchange has been observed. It is attributed to the redistribution of electric potential of the acoustic wave due to formation of a HxLi1−xNbO3 layer at the surface. The change of electromechanical coupling coefficient in samples fabricated under different conditions depends on the acoustic wavelength–layer thickness product kd. The K2 value attains a maximum of about 0.8×10−2 at kd ≈ 0.4, whereas it is equal to 0.46×10−2 in nonexchanged lithium niobate. The increase in electromechanical coupling coefficient can be applied for enhancement of the SAW interdigital transducer efficiency. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
43.35.Pt Surface waves in solids and liquids
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
68.35.Gy Mechanical properties; surface strains

Structure and stability of ultrathin zirconium oxide layers on Si(001)

M. Copel, M. Gribelyuk, and E. Gusev

Appl. Phys. Lett. 76, 436 (2000); http://dx.doi.org/10.1063/1.125779 (3 pages) | Cited 355 times

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We have examined the structure of ultrathin ZrO2 layers on Si(001) using medium energy ion scattering and cross-sectional transmission electron microscopy. Films can be deposited on SiO2 layers with highly abrupt interfaces by atomic layer deposition. On HF stripped Si(001), nucleation was inhibited, resulting in poorer film morphology. ZrO2 showed remarkable stability against silicate formation, with no intermixing even after high temperature oxidation. The oxide is vulnerable to high temperature vacuum annealing, with silicidation occurring at temperatures above 900 °C. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Dv Thermal stability; thermal effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
68.35.Ct Interface structure and roughness

Two-photon absorption study of GaN

Chi-Kuang Sun, Jian-Chin Liang, Jiun-Cheng Wang, Fu-Jen Kao, Stacia Keller, Michael P. Mack, Umesh Mishra, and Steven P. DenBaars

Appl. Phys. Lett. 76, 439 (2000); http://dx.doi.org/10.1063/1.125780 (3 pages) | Cited 40 times

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Two-photon absorption coefficients of GaN for below band gap ultraviolet wavelength and midgap infrared wavelength were measured by using femtosecond pulsewidth autocorrelation and Z-scan techniques. Large two-photon absorption coefficients were obtained. Taking advantage of the large two-photon absorption, we have demonstrated two-photon confocal imaging of a GaN thin film. Direct correlation was found between the yellow luminescence and suppression of bandedge luminescence. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics

Self-organized propagation of dislocations in GaN films during epitaxial lateral overgrowth

Akira Sakai, Haruo Sunakawa, Akitaka Kimura, and Akira Usui

Appl. Phys. Lett. 76, 442 (2000); http://dx.doi.org/10.1063/1.125781 (3 pages) | Cited 30 times

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Dislocation propagation and defect evolution in GaN films formed by epitaxial lateral overgrowth (ELO) are examined by transmission electron microscopy. A novel effect that induces self-organized propagation of preexisting dislocations in ELO films is evaluated. This propagation forms dislocations into bundle structures along the stripes of masks used for ELO. The dislocation bundling gives rise to crystallographic tilting in the overgrown region on the mask and leads to a total reduction of threading dislocation density in the film. © 2000 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.Lw Diffusion of other defects
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Coulomb-blockade effect observed at room temperature in Ge nanocrystalline films deposited by the cluster-beam evaporation technique

Souri Banerjee, S. Nozaki, and H. Morisaki

Appl. Phys. Lett. 76, 445 (2000); http://dx.doi.org/10.1063/1.125782 (3 pages) | Cited 6 times

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The temperature-dependent current–voltage (I–V) characteristics have been studied across the thickness of Ge nanocrystalline films prepared by the cluster beam evaporation technique. It is found that a film with a thickness of 30 nm, deposited on a substrate kept at 77 K, does not exhibit any distinct step-like feature in the I–V characteristics at room temperature. However, with the lowering of the temperature, a “Coulomb gap” is observed and a pronounced step-like feature appear in the I–V characteristics suggesting the Coulomb blockade (CB) effect. It is hypothesized that the observed CB effect in these nanocrystalline thin films results from a very highly selective electron transport process where the electron transport is dominated by one local well-defined current path with the largest conductance. The result of similar measurements on a photo-oxidized sample, which shows a signature of a step-like feature in the I–V characteristics, even at room temperature, supports this hypothesis. © 2000 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.63.-b Electronic transport in nanoscale materials and structures
73.23.Hk Coulomb blockade; single-electron tunneling
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.05.Cy Elemental semiconductors

Anisotropic conduction behavior in metal-induced laterally crystallized polycrystalline silicon thin films

Mingxiang Wang, Zhiguo Meng, and Man Wong

Appl. Phys. Lett. 76, 448 (2000); http://dx.doi.org/10.1063/1.125783 (3 pages) | Cited 9 times

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The conduction behavior of metal-induced laterally crystallized (MILC) polycrystalline silicon (poly-Si) was studied and compared to that of the conventional solid-phase crystallized and low-pressure chemical vapor deposited poly-Si. MILC poly-Si was found to exhibit superior electrical properties, with significantly lower grain-boundary (GB) trap density, as well as much higher carrier mobility and conductivity. Furthermore, a unique anisotropic conduction behavior was discovered in MILC poly-Si, with the resistivity and its activation energy showing remarkable difference for conduction transverse or parallel to the MILC direction. These phenomena have been related to the fluctuation of the potential barrier associated with the longitudinal GBs separating the relatively ordered elongated grains in MILC poly-Si. © 2000 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.Mm Grain and twin boundaries

Integration and electrical properties of diffusion barrier for high density ferroelectric memory

Yoon J. Song, H. H. Kim, Sung Y. Lee, D. J. Jung, B. J. Koo, J. K. Lee, Y. S. Park, H. J. Cho, S. O. Park, and Kinam Kim

Appl. Phys. Lett. 76, 451 (2000); http://dx.doi.org/10.1063/1.125784 (3 pages) | Cited 24 times

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A reliable Ir diffusion barrier was prepared on polysilicon plugged substrate with a contact size of 0.6 μm. Using a Ti adhesion layer and stress-relief process, it was possible to integrate the Ir barrier into a high density 4 Mb ferroelectric random access memory device. After heat treating sol-gel derived Pb(Zr1−xTix)O3 (PZT) films at 700 °C, the Ir barrier contact displayed an ohmic behavior and showed a low resistance of 130 Ω per contact in 1k serial contact array. The PZT films on Pt/IrO2/Ir poly-plugged substrate exhibited excellent ferroelectric properties such as remnant polarization and coercive voltage of 25 μC/cm2 and 1.15 V, respectively. Auger depth profile and transmission electron microscopy analyses confirmed that no appreciable oxidation was formed between the Ir barrier and the polysilicon plug. © 2000 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.30.Sk Pulse and digital circuits
77.22.Ej Polarization and depolarization
68.35.Fx Diffusion; interface formation

A pump and probe study of photoinduced internal field screening dynamics in an AlGaN/GaN single-quantum-well structure

A. Shikanai, T. Deguchi, T. Sota, T. Kuroda, A. Tackeuchi, S. Chichibu, and S. Nakamura

Appl. Phys. Lett. 76, 454 (2000); http://dx.doi.org/10.1063/1.125785 (3 pages) | Cited 10 times

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Photogenerated carrier dynamics in an AlGaN/GaN single quantum well has been studied using a conventional degenerate pump and probe technique at room temperature. Photoinduced absorption at the exciton resonance has been observed. It is explained by the absorption coefficient change, through the quantum-confined Stark effect and the quantum-confined Franz–Keldish effect, caused by the photoinduced internal electric-field screening. In comparison with biased GaAs multiple quantum wells, a slower time evolution of differential transmission signals has been also found. Its origin is attributed to the longer carrier sweep-out time due to the potential profile of the sample in conjunction with the longer carrier recombination time. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Jq Electro-optical effects
78.47.-p Spectroscopy of solid state dynamics
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors

Fabrication of a single-electron transistor by current-controlled local oxidation of a two-dimensional electron system

U. F. Keyser, H. W. Schumacher, U. Zeitler, R. J. Haug, and K. Eberl

Appl. Phys. Lett. 76, 457 (2000); http://dx.doi.org/10.1063/1.125786 (3 pages) | Cited 42 times

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The surface layers of a GaAs/AlGaAs heterostructure are locally oxidized using an atomic force microscope. The local anodic oxidation depletes the underlying two-dimensional electron gas leading to the formation of tunneling barriers. The height of the barriers is determined by measuring the thermally activated current. By varying the oxidation current, the barrier heights can be tuned between a few meV and more than 100 meV. Using these barriers as tunneling elements, a side gated single-electron transistor is fabricated. © 2000 American Institute of Physics.
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85.35.Gv Single electron devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.65.Mq Oxidation
73.23.Hk Coulomb blockade; single-electron tunneling
07.79.Lh Atomic force microscopes

Electronic bistability in electrochemically self-assembled quantum dots: A potential nonvolatile random access memory

N. Kouklin, S. Bandyopadhyay, S. Tereshin, A. Varfolomeev, and D. Zaretsky

Appl. Phys. Lett. 76, 460 (2000); http://dx.doi.org/10.1063/1.125787 (3 pages) | Cited 24 times

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An electronic bistability has been observed in a two-dimensional spatially ordered array of 10 nm quantum dots self-assembled by electrodepositing CdS in nanoporous anodic alumite film. The current–voltage characteristic of the array shows switching between two stable conductance states, which can be controlled by an external bias. The bistability is observed when current flows laterally between two contacts on the top surface of the array, and also when current flows vertically between a top contact and the bottom (conducting) substrate. If the system is left in one conductance state, it remains there for at least 180 h and possibly much longer, until switched to the other state by an external bias. Such an effect may find applications in inexpensive, ultradense nonvolatile static random access memory. © 2000 American Institute of Physics.
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73.61.Ga II-VI semiconductors
72.60.+g Mixed conductivity and conductivity transitions
81.15.Pq Electrodeposition, electroplating
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
84.30.Sk Pulse and digital circuits
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Atomically resolved scanning tunneling microscopy of hydrogen-terminated Si(001) surfaces after HF cleaning

Kenta Arima, Katsuyoshi Endo, Toshihiko Kataoka, Yasushi Oshikane, Haruyuki Inoue, and Yuzo Mori

Appl. Phys. Lett. 76, 463 (2000); http://dx.doi.org/10.1063/1.125788 (3 pages) | Cited 25 times

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Atomic structures of hydrogen-terminated Si(001) surfaces after HF cleaning are investigated by scanning tunneling microscopy. It is revealed that the surface is macroscopically rough but is composed of terraces and steps. Inside a terrace, 1×1 structures are formed. This corresponds to the ideal 1×1 dihydride structure. The step edges run along the 〈110〉 direction. On the other hand, the 1×1 dihydride structure disappears when the surface is subsequently rinsed with ultrapure water, because every other dihydride row of the ideal 1×1 structure is preferentially etched in ultrapure water. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors

Direct experimental observation of the local electronic structure at threading dislocations in metalorganic vapor phase epitaxy grown wurtzite GaN thin films

Y. Xin, E. M. James, I. Arslan, S. Sivananthan, N. D. Browning, S. J. Pennycook, F. Omnès, B. Beaumont, J-P. Faurie, and P. Gibart

Appl. Phys. Lett. 76, 466 (2000); http://dx.doi.org/10.1063/1.125789 (3 pages) | Cited 40 times

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The electronic structure of pure edge threading dislocations in metalorganic vapor phase epitaxy grown wurtzite GaN thin films has been studied directly by atomic resolution Z-contrast imaging and electron energy loss spectroscopy in a scanning transmission electron microscope. Dislocation cores in n-type samples grown in N-rich conditions show no evidence for the high concentration of Ga vacancies predicted by previous theoretical calculations. Nitrogen K-edge spectra collected from edge dislocation cores show a sudden and significant increase in the intensity of the first fine-structure peak immediately above the edge onset compared to the bulk spectra. The origin of this increase is discussed. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
79.20.Kz Other electron-impact emission phenomena
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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Direct observation of subpicosecond single-flux-quantum generation in pulse-driven Y–Ba–Cu–O Josephson junctions

Roman Adam, Marc Currie, Carlo Williams, Roman Sobolewski, Oliver Harnack, and Marian Darula

Appl. Phys. Lett. 76, 469 (2000); http://dx.doi.org/10.1063/1.125790 (3 pages) | Cited 6 times

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We report our time-resolved measurements of switching dynamics of grain-boundary, 5-μm-wide Y–Ba–Cu–O (YBCO) Josephson junctions, excited by 2-ps-wide electrical pulses optically generated by a voltage-biased, 5-μm-wide, 10-μm-long YBCO microbridge. The time-resolved transients were recorded at 20 K using a subpicosecond cryogenic electro-optic sampling system. The intrinsic junction response was separated from the circuit-related feedthrough, and we observed both experimentally and in numerical simulations a 0.8-ps-wide, single-flux-quantum (SFQ) pulse, generated by the switching of the junction with the IcRn product equal to ∼2 mV. At the same time, the measured turn-on delay time was almost three times shorter than that obtained from simulations, questioning applicability of the resistively shunted tunnel junction model to nonhysteretic, high-temperature superconducting weak links. Our test structure's power consumption associated with the single SFQ pulse generation was ∼0.1 μW, leading to a (switching time)×(dissipated power) product equal to 0.08 aJ. © 2000 American Institute of Physics.
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85.25.Cp Josephson devices
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
84.30.Sk Pulse and digital circuits
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