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5 Dec 1994

Volume 65, Issue 23, pp. 2901-3024

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Abrupt Si/Ge interface formation using atomic hydrogen in Si molecular beam epitaxy

G. Ohta, S. Fukatsu, Y. Ebuchi, T. Hattori, N. Usami, and Y. Shiraki

Appl. Phys. Lett. 65, 2975 (1994); http://dx.doi.org/10.1063/1.112481 (3 pages) | Cited 22 times

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Compositional abruptness of strained Si/Ge heterointerfaces grown by solid source Si molecular beam epitaxy under supply of atomic hydrogen (AH) was investigated using secondary ion mass spectrometry and reflection high‐energy electron diffraction. Systematic variation of growth temperature and AH exposure pressure revealed that Ge segregation length is a steadily decreasing function of AH coverage on the growth surface. © 1994 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Current induced drift mechanism in amorphous SiNx:H thin film diodes

J. M. Shannon, S. C. Deane, B. McGarvey, and J. N. Sandoe

Appl. Phys. Lett. 65, 2978 (1994); http://dx.doi.org/10.1063/1.112482 (3 pages) | Cited 22 times

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It is shown that the drift in the current–voltage characteristics of silicon‐rich amorphous silicon nitride metal–semiconductor–metal diodes can be explained by a mechanism whereby electron trapping centers are created via hole–electron recombination. A first order model which includes excitation of holes by hot electrons moving into the anode and recombination of electrons with holes trapped in the valence band tail is in good quantitative agreement with the measured dependencies between drift, device thickness, current density, time, and charge passed through the device. © 1994 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Mechanisms of implant damage annealing and transient enhanced diffusion in Si

N. E. B. Cowern, G. F. A. van de Walle, P. C. Zalm, and D. W. E. Vandenhoudt

Appl. Phys. Lett. 65, 2981 (1994); http://dx.doi.org/10.1063/1.112483 (3 pages) | Cited 56 times

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Interactions between self‐interstitials (I) and {113} interstitial defects during annealing of Si implant damage have been studied. At low damage levels diffusion is ultrafast, driven by I released direct from the ion collision cascade. At higher damage levels, free I are quenched by nucleation of {113} defects. We show that the transient enhanced diffusion seen in most previous studies arises from the subsequent dissolution of the {113} defects. © 1994 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities
61.80.Jh Ion radiation effects
61.72.uf Ge and Si

Frequency limitations of negative differential mobility in vertical conduction in superlattices

X. L. Lei, N. J. M. Horing, H. L. Cui, and K. K. Thornber

Appl. Phys. Lett. 65, 2984 (1994); http://dx.doi.org/10.1063/1.112484 (3 pages) | Cited 6 times

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The frequency‐dependence of the carrier drift velocity in superlattice miniband conduction in response to a small signal ac electric field is investigated for laterally unconfined and one‐dimensionally confined (2D) superlattices biased in the negative differential mobility regime. Numerical calculations show that in both systems there exists a mobility‐transition frequency of order of 100 GHz, above which the differential mobility becomes positive. This frequency in a 2D superlattice is about three times that in an unconfined system, owing to enhanced carrier scattering. In a domain‐driven microwave oscillator, the mobility‐transition frequency is expected to be relatively small compared to the oscillator frequency. Nonetheless, the higher mobility‐transition frequency in the 2D superlattice would render it more advantageous for use in negative differential mobility microwave oscillators. © 1994 American Institute of Physics.
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73.50.Mx High-frequency effects; plasma effects
73.50.Fq High-field and nonlinear effects
72.30.+q High-frequency effects; plasma effects
72.20.Ht High-field and nonlinear effects

Counter‐oxidation of superficial Si in single‐crystalline Si on SiO2 structure

Yasuo Takahashi, Toshihiko Ishiyama, and Michiharu Tabe

Appl. Phys. Lett. 65, 2987 (1994); http://dx.doi.org/10.1063/1.112485 (3 pages) | Cited 24 times

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This work proposes an oxidation mechanism for single‐crystalline Si overlying a buried SiO2 layer (SOI wafer). Experimental results show that not only the surface oxide but also the buried oxide layer of the SOI wafer grows during the thermal oxidation process. The oxidation behavior is analyzed with a simple model including oxygen diffusion through the superficial single crystalline Si layer, which agrees well with the experimental data. Furthermore, oxygen penetration through the superficial Si layer is verified by oxidation experiments using isotope oxygen. © 1994 American Institute of Physics.
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81.65.-b Surface treatments
66.30.J- Diffusion of impurities

Pressure dependence of optical transitions in ordered GaP/InP superlattices

Alberto Franceschetti and Alex Zunger

Appl. Phys. Lett. 65, 2990 (1994); http://dx.doi.org/10.1063/1.112486 (3 pages) | Cited 7 times

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We have calculated the pressure coefficients α of a few optical transitions in (001), (111), (110), and (201) GaP/InP ordered superlattices using ab initio methods. The equilibrium atomic geometries under hydrostatic pressure are obtained by direct minimization of the elastic enthalpy. We find that (i) the pressure coefficient of the lowest energy transition is uniformly high, due to the Γ1c character of the conduction‐band minimum; (ii) the pressure coefficient of the transition to the second lowest conduction state at Γ distinguishes the (111)‐oriented (CuPt) superlattice (α=4.0 meV/kbar) from the remaining structures (α≂−2 meV/kbar). This is so because in CuPt we have L folding, while in the other structures we have X folding; (iii) the calculated pressures for the Γ→X crossover are 45, 43, 12, and 16 kbar for the (001), (111), (110), and (201) superlattices, respectively. These trends reflect the zero‐pressure Γ1c–X1c energy separation and the Γ1c pressure coefficient of these structures. © 1994 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Relationship between radiation response and density of buried oxide in separation‐by‐implantation‐of‐oxygen material

B. J. Mrstik, P. J. McMarr, and R. K. Lawrence

Appl. Phys. Lett. 65, 2993 (1994); http://dx.doi.org/10.1063/1.112487 (3 pages) | Cited 4 times

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We show that the radiation response of separation‐by‐implantation‐of‐oxygen material is determined primarily by the density of the buried oxide. We also show that minor variations in process conditions can significantly affect the oxide density, although it is not yet clear which process parameters are most important. © 1994 American Institute of Physics.
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61.80.Cb X-ray effects
61.80.Jh Ion radiation effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Multicolor infrared detection using a voltage tunable bandpass filter

M. Z. Tidrow, K. K. Choi, C. W. Farley, and F. Chang

Appl. Phys. Lett. 65, 2996 (1994); http://dx.doi.org/10.1063/1.112488 (3 pages) | Cited 4 times

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It was demonstrated that an electron energy bandpass filter placed next to a quantum well infrared photodetector (QWIP) is not only able to suppress dark current, but also is able to select photocurrents of different energies. Since the bandpass energy of the filter changes with an applied bias across the filter, this mechanism can be used to control the detection width and the cutoff wavelength of the detector. If the photoresponse of the QWIP has more than one energy peak, the same filter can also be used to intercept a particular photoelectron peak and achieve voltage tunable multicolor infrared detection. In this work, we also show that the bandpass filter increases the background limited temperature and the detectivity of the QWIP by filtering away the lower energy dark current and the unused photocurrent. © 1994 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects

Dominant photogenerated valley current in a double‐barrier resonant‐tunneling diode

H. S. Li, L. P. Chen, Y. W. Chen, K. L. Wang, D. S. Pan, and J. M. Liu

Appl. Phys. Lett. 65, 2999 (1994); http://dx.doi.org/10.1063/1.112489 (3 pages) | Cited 4 times

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Dominant photogenerated valley current has been observed in an optically‐excited InGaAs/AlAs double‐barrier resonant‐tunneling diode. The photogenerated valley current in the resonant‐tunneling diode varies with the optical power level. Under intense illumination, the photogenerated valley current increases to such a high level that it becomes dominant over the peak current. As a consequence, the negative differential resistance of the device is removed. The observed photogenerated valley current is described by photogenerating electron‐hole pairs in the depletion region adjacent to the double‐barrier structure. Transient behavior of the photogenerated carriers is also studied. The observed dominant photogenerated valley current may have useful applications. © 1994 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
73.40.Gk Tunneling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Mechanism responsible for the semi‐insulating properties of low‐temperature‐grown GaAs

X. Liu, A. Prasad, W. M. Chen, A. Kurpiewski, A. Stoschek, Z. Liliental‐Weber, and E. R. Weber

Appl. Phys. Lett. 65, 3002 (1994); http://dx.doi.org/10.1063/1.112490 (3 pages) | Cited 92 times

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The mechanism responsible for the semi‐insulating properties of low‐temperature‐grown GaAs is investigated by determining the concentration of arsenic antisite (AsGa)‐related defects in the material. The concentrations of the defects in neutral and positively charged states, As0Ga and As+Ga, are determined by near‐infrared absorption and magnetic circular dichroism of absorption, respectively. Materials grown and annealed at different temperatures are investigated. We find that the defects are abundant in all samples studied, with the concentration of As0Ga higher than that of As+Ga defects. The results indicate that the defects can account for the pinning of the Fermi energy and consequently also the semi‐insulating properties of the material. © 1994 American Institute of Physics.
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73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors

All‐YBa2Cu3O7 trilayer tunnel junctions with Sr2AlTaO6 barrier

Q. Y. Ying and Claude Hilbert

Appl. Phys. Lett. 65, 3005 (1994); http://dx.doi.org/10.1063/1.113029 (3 pages) | Cited 5 times

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A new barrier material, Sr2AlTaO6, was employed in fabricating all‐YBa2Cu3O7 trilayer tunnel junctions using in situ coevaporation and sputtering deposition. It was found that the superior material properties of Sr2AlTaO6 allow the use of a very thin barrier layer. A dramatic increase in the quasiparticle density of states at the YBa2Cu3O7 superconductive gap was observed for the first time from thin‐film all‐YBa2Cu3O7 devices. Well‐defined gap structures were observed at temperatures up to 47 K. The tunneling characteristics are consistent with the typical superconductor‐insulator‐superconductor behavior. The temperature dependence of the superconductive gap is compared with the BCS theory. © 1994 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.78.-w Superconducting films and low-dimensional structures
85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.50.+r Tunneling phenomena; Josephson effects

Enhancement of transport critical current densities in (Bi,Pb)2Sr2Ca2Cu3O10/Ag tapes at 77 K following fast neutron irradiation

Q. Y. Hu, H. W. Weber, F. M. Sauerzopf, G. W. Schulz, R. M. Schalk, H. W. Neumüller, and S. X. Dou

Appl. Phys. Lett. 65, 3008 (1994); http://dx.doi.org/10.1063/1.112491 (3 pages) | Cited 22 times

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We report on significant enhancements of the transport critical current densities Jc in (Bi,Pb)2Sr2Ca2Cu3O10/Ag tapes at 77 K and higher magnetic fields after neutron irradiation. This enhancement is attributed to an improvement in the flux pinning capability of this material by the neutron‐induced defects. The angular dependence of Jc is still consistent with two‐dimensionality, i.e., flux pinning of pancake and/or Josephson vortices is directly confirmed by this transport measurement. Fast neutron irradiation also affects the weak links in a way which agrees with previous results on unaligned ceramics. However, there are some peculiarities which need further investigation. © 1994 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors

Postgrowth annealing of YBa2Cu3O7−x thin films in an electron cyclotron resonance oxygen plasma

I. François and G. Borghs

Appl. Phys. Lett. 65, 3011 (1994); http://dx.doi.org/10.1063/1.112492 (3 pages) | Cited 3 times

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As‐deposited epitaxial YBa2Cu3O7−x films have been prepared by laser ablation in molecular oxygen followed by a cooling procedure in an electron cyclotron resonance (ECR) plasma. We demonstrate that cooling in a plasma provides a more homogeneous oxygenation than cooling in a neutral oxygen environment. Alternating‐current susceptibility, resistivity, and x‐ray diffraction measurements have been used to compare the influence of the cooling in an ECR oxygen plasma and a neutral oxygen environment on the properties of YBa2Cu3O7−x thin films. The role of the atomic oxygen content of the plasma is discussed starting from an optical and electrical diagnosis of the plasma. © 1994 American Institute of Physics.  
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition
74.72.-h Cuprate superconductors

Growth of c‐axis in‐plane YBa2Cu4O8 thin films through in situ annealing of precursors deposited by hybrid plasma sputtering

Y. Yoshida, J. G. Wen, N. Watanabe, W. Ito, N. Koshizuka, and T. Morishita

Appl. Phys. Lett. 65, 3014 (1994); http://dx.doi.org/10.1063/1.112493 (3 pages) | Cited 3 times

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Processing for the growth of YBa2Cu4O8 (Y124) thin films has been investigated by dc 94.92 MHz hybrid plasma sputtering with in situ annealing. The amorphous precursor is found to be the best candidate for growing pure Y124 phase through in situ annealing. The Raman spectrum confirms the Y124 phase by presenting the modes at 250 and 604 cm−1 related to the double Cu‐O chains. X‐ray diffraction as well as transmission electron microscopy further show that the films are composed of grain with orthogonal c axes in the film plane. © 1994 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
74.72.-h Cuprate superconductors

Magneto‐optic Faraday effect in (La1−xCax)MnO3 films

J. F. Lawler, J. G. Lunney, and J. M. D. Coey

Appl. Phys. Lett. 65, 3017 (1994); http://dx.doi.org/10.1063/1.112494 (2 pages) | Cited 39 times

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Thin films of (La1−xCax)MnO3 prepared by laser ablation deposition are ferromagnetic when 0.2≤x≤0.5 with Tc≊250 K. These films show strong Faraday rotation both in the vicinity of the 2p(O)→3d(Mn) charge‐transfer absorption at approximately 3.0 eV (θF≳40 000°/cm), and in the vicinity of the 3d(t2g)→3d(eg) excitation at approximately 1.5 eV (θF≳10 000°/cm just below Tc). The films are moderately transparent, having values of 2θF/α of approximately 0.1 at 1.5 eV and 0.5 at 3.0 eV. © 1994 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
78.66.Nk Insulators
78.20.Ls Magneto-optical effects
81.15.Fg Pulsed laser ablation deposition

Giant magnetoresistance of nanowires of multilayers

A. Blondel, J. P. Meier, B. Doudin, and J.‐Ph. Ansermet

Appl. Phys. Lett. 65, 3019 (1994); http://dx.doi.org/10.1063/1.112495 (3 pages) | Cited 158 times

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A new technique is required which enables tailoring of the morphology of a metallic nanostructured material down to the 10 nm length scale. Using nanoporous nuclear track etched membranes as templates for electrodeposition, an assembly of wires with diameters as low as 30 nm could be obtained. Alternating the electrodeposition of two metals resulted in multilayers grown perpendicular to the wire axis. Layer thicknesses as low as 2 nm could be reached. Application is demonstrated by making wires 6 μm long, 80 nm in diameter, having a succession of either Co and Cu layers or of (Ni,Fe) and Cu layers. Wires containing layers of 5–10 nm in thickness exhibited a giant magnetoresistance. The current was naturally perpendicular to the layers. At ambient temperature, a magnetoresistance of 14% for Co/Cu and of 10% for (Fe,Ni)/Cu was observed. © 1994 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.Pq Electrodeposition, electroplating
72.15.Gd Galvanomagnetic and other magnetotransport effects

Near field emission scanning tunneling microscopy

Juan José Sáenz and Ricardo García

Appl. Phys. Lett. 65, 3022 (1994); http://dx.doi.org/10.1063/1.112496 (3 pages) | Cited 19 times

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The close proximity between probe and sample in a scanning tunneling microscope interface may produce unwanted modifications of the interface. This is particularly severe when working with soft materials, as molecular films or biomolecules. Here, we propose the operation of the scanning tunneling microscope in the near field emission regime as an effective method to overcome those problems. A theoretical description of the probe–sample interface in the near field emission regime predicts subatomic resolution in the direction normal to the surface and lateral resolution of 3 nm for tip–sample separations of 3–5 nm. Furthermore, atomic resolution is demonstrated by imaging steps of carbon atoms. © 1994 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
68.35.B- Structure of clean surfaces (and surface reconstruction)
79.70.+q Field emission, ionization, evaporation, and desorption
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