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6 Dec 1993

Volume 63, Issue 23, pp. 3107-3238

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Additivity of ballistic electrons

T. Sakamoto, F. Nihey, and K. Nakamura

Appl. Phys. Lett. 63, 3182 (1993); http://dx.doi.org/10.1063/1.110192 (3 pages)

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The additivity of ballistic electron beams is confirmed in the mesoscopic regime. Two ballistic electron beams are injected simultaneously from different injectors and cross each other at a collector. The voltage drop at the collector is proven to be equivalent to the algebraic sum of those separately obtained when each electron beam is individually injected from a corresponding injector. The additivity is considered to be valid based on the fact that the mean distance between the ballistic electrons is much larger than the screening length. Confirming of additivity is essentially important in designing new functional devices such as a synapse for neural networks in the ballistic regime. The quantum interference effect is also observed in the same sample.
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72.20.-i Conductivity phenomena in semiconductors and insulators
73.40.-c Electronic transport in interface structures

Narrow current dip for the double quantum dot resonant tunneling structure with three leads: Sensitive nanometer Y‐branch switch

M. Sumetskii

Appl. Phys. Lett. 63, 3185 (1993); http://dx.doi.org/10.1063/1.110193 (3 pages) | Cited 3 times

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We propose a model of a non‐one‐dimensional nanometer resonant tunneling device consisting of two quantum dots and three leads for which a small applied voltage can switch off the current between leads 1 and 2 and simultaneously switch on the current between leads 1 and 3. The switching device proposed is based on the effect of exponentially narrow current dip discovered in the present letter.
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73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Electrical transport across oxygen‐doped‐silicon buried layers by substoichiometric oxygen ion implantation in silicon

K. Srikanth and S. Ashok

Appl. Phys. Lett. 63, 3188 (1993); http://dx.doi.org/10.1063/1.110194 (3 pages)

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The electrical and physical property changes of c‐Si after substoichiometric oxygen ion implantation have been investigated using I‐V, spreading resistance, secondary ion mass spectroscopy, spectroscopic ellipsometry and Fourier transform infrared spectroscopy. A key observation is the presence of donors in the vicinity of the implanted region, resulting in extensive counterdoping of p‐type c‐Si. Redistribution of the oxygen atoms during the high‐temperature anneal results in sharp interfaces aiding the formation of a heterojunction. Mesa‐type diodes on the implanted sample exhibit excellent rectification with a diode ideality factor n of 1.2 and a reverse saturation current density of 1×10−8 A/cm2. The near‐surface region is shown to be crucial for achieving the high rectification behavior
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61.80.Jh Ion radiation effects
71.55.Cn Elemental semiconductors
72.80.Cw Elemental semiconductors

Aharonov–Bohm effect and one‐dimensional ballistic transport through two independent parallel channels

P. J. Simpson, D. R. Mace, C. J. B. Ford, I. Zailer, M. Pepper, D. A. Ritchie, J. E. F. Frost, M. P. Grimshaw, and G. A. C. Jones

Appl. Phys. Lett. 63, 3191 (1993); http://dx.doi.org/10.1063/1.110195 (3 pages) | Cited 26 times

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We have developed a new technique to contact a submicrometer metal dot gate independently of surrounding gates. With this we have made two ballistic channels in parallel on a GaAs‐AlGaAs heterostructure. Independent control over all the gates allows unprecedented flexibility to adjust both the size of the dot and the widths of the channels. In a perpendicular magnetic field we can obtain extremely large Aharonov–Bohm oscillations and a double‐frequency oscillation indicative of edge state charging in an open system. At low magnetic fields we see no evidence for any interaction between the one‐dimensional subbands in the two channels.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Dislocation relaxation in InAsyP1−y films deposited onto (001) InP by gas‐source molecular beam epitaxy

T. Okada, R. V. Kruzelecky, G. C. Weatherly, D. A. Thompson, and B. J. Robinson

Appl. Phys. Lett. 63, 3194 (1993); http://dx.doi.org/10.1063/1.110196 (3 pages) | Cited 10 times

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The strain relaxation of InAsyP1−y layers grown on (001) InP substrates by gas‐source molecular beam epitaxy was examined using transmission electron microscopy (TEM) and cathodoluminescence (CL) imaging. InAsyP1−y films with a thickness of 190 Å were prepared, systematically varying the As content from y=0.30 and 0.77, corresponding to a lattice mismatch between 0.97% and 2.5%. Relaxation was anisotropic, with 60° misfit dislocations lying predominantly along [110], with a much lower density of dislocations along [110]. For y≳0.48, CL and plan‐view TEM observations show slip traces which make angles of about ±40° with the [110] direction. These slip traces correspond to pure‐screw dislocation segments (gliding on {111}) cross slipping to glide on planes approximately parallel to {011}.
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68.55.-a Thin film structure and morphology
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Misfit dislocation nucleation in doped and undoped ZnSe/GaAs

L. H. Kuo, L. Salamanca‐Riba, J. M. DePuydt, H. Cheng, and J. Qiu

Appl. Phys. Lett. 63, 3197 (1993); http://dx.doi.org/10.1063/1.110197 (3 pages) | Cited 19 times

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We have observed that undoped ZnSe films grown on GaAs substrates by molecular beam epitaxy show an irregular array of interfacial 60° misfit dislocations. However, N and Cl doping of the ZnSe thin films changes the interfacial dislocation structure. p‐type ZnSe with N concentrations of ∼1018/cm3 shows a regular array of interfacial 60° misfit dislocations and a lower (∼1×106/cm2) density of threading dislocations compared to undoped films. However, samples with doping levels higher than 1019/cm3 show a density of threading dislocations of ∼108/cm2. These differences are explained in terms of Frank partial dislocations observed only in doped ZnSe. The Frank partial dislocations act as nucleation sites for the misfit dislocations. Thus, different mechanisms for the formation of misfit dislocations in doped and undoped films occur in this system.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Mechanism for enhancement of electrical activation of silicon in GaAs by aluminum co‐implantation

J. P. de Souza and D. K. Sadana

Appl. Phys. Lett. 63, 3200 (1993); http://dx.doi.org/10.1063/1.110198 (3 pages)

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A pronounced enhancement in the electrical activation of implanted Si in GaAs is demonstrated by co‐implantation of Al. The maximum enhancement (×2) occurs when the Si distribution is shallow, there is a separation between the Si and Al distributions with the Al being deeper, the Si and Al are implanted at doses of ≤1×1013 cm−2, and subsequent annealing of the co‐implanted GaAs is performed under capless or proximity cap conditions. A model considering gettering of the oxygen present in the bulk Czochralski‐grown GaAs to the implanted Al is invoked to explain the observed activation enhancement.
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71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect

Direct formation of quantum‐sized dots from uniform coherent islands of InGaAs on GaAs surfaces

D. Leonard, M. Krishnamurthy, C. M. Reaves, S. P. Denbaars, and P. M. Petroff

Appl. Phys. Lett. 63, 3203 (1993); http://dx.doi.org/10.1063/1.110199 (3 pages) | Cited 813 times

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The 2D–3D growth mode transition during the initial stages of growth of highly strained InGaAs on GaAs is used to obtain quantum‐sized dot structures. Transmission electron micrographs reveal that when the growth of In0.5Ga0.5As is interrupted exactly at the onset of this 2D–3D transition, dislocation‐free islands (dots) of the InGaAs result. Size distributions indicate that these dots are ∼300 Å in diameter and remarkably uniform to within 10% of this average size. The areal dot densities can be varied between 109 and 1011 cm−2. The uniformity of the dot sizes is explained by a mechanism based on reduction in adatom attachment probabilities due to strain. We unambiguously demonstrate photoluminescence at ∼1.2 eV from these islands by comparing samples with and without dots. The luminescent intensities of the dots are greater than or equal to those of the underlying reference quantum wells.
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68.55.-a Thin film structure and morphology
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
78.55.Cr III-V semiconductors

Structure of (001) GaAs surfaces during epitaxial growth by organometallic chemical vapor deposition

Itaru Kamiya, H. Tanaka, D. E. Aspnes, M. Koza, and R. Bhat

Appl. Phys. Lett. 63, 3206 (1993); http://dx.doi.org/10.1063/1.110200 (3 pages) | Cited 7 times

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Under typical atmospheric pressure (AP) organometallic chemical vapor deposition (OMCVD) growth conditions with trimethylgallium (TMG) and arsine sources, reflectance‐difference (RD) spectra show that the (001) GaAs surface is in the d(4×4)‐like state. With sufficiently high TMG and low AsH3 exposures, we observe RD spectra similar to those obtained during atomic layer epitaxy (ALE) at lower temperatures.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Metastable and nonmetastable deep states of Ge in GaAs

C. Skierbiszewski, T. Suski, P. Wisniewski, W. Jantsch, G. Ostermayer, Z. Wilamowski, P. G. Walker, N. J. Mason, and J. Singleton

Appl. Phys. Lett. 63, 3209 (1993); http://dx.doi.org/10.1063/1.110787 (3 pages) | Cited 4 times

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We show from transport investigations that Ge doped GaAs can be either semimetallic or semiconducting depending on hydrostatic pressure and previous sample illumination. This property results from a unique crossover of two states of the Ge donor in GaAs in their energetic position under pressure. The experimental results obtained make it possible to identify the nature of these Ge‐donor states: The drastic enhancement of the electron mobility after illumination is taken as evidence of the electron transfer from the two‐electron DX− state to a neutral, localized, and unrelaxed state of the Ge donor.
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71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects

Photoluminescence excitation spectroscopy yields band gap of Ga0.5In0.5P containing relatively ordered domains

J. E. Fouquet, M. S. Minsky, and S. J. Rosner

Appl. Phys. Lett. 63, 3212 (1993); http://dx.doi.org/10.1063/1.110201 (3 pages) | Cited 22 times

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Photoluminescence excitation spectroscopy at 9 K reveals that the absorption edge of Ga0.5In0.5P containing relatively ordered domains (grown at 670 °C) is near 1.93 eV, representing the band gap of this inhomogeneous material. Photoluminescence (PL) has been observed at energies lower than this absorption edge energy by up to 70 meV. Along with the unusually slow decay times previously measured, the low energy PL indicates spatially indirect recombination. Therefore PL alone cannot reliably determine the band gap of typical ‘‘ordered’’ Ga0.5In0.5P samples. In contrast, the optical properties of relatively randomly ordered (‘‘normal’’) Ga0.5In0.5P (grown at 775 °C) are typical of a normal direct III‐V semiconductor.
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78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors

Effect of dc electric field on the effective microwave surface impedance of YBa2Cu3O7/SrTiO3/YBa2Cu3O7 trilayers

A. T. Findikoglu, C. Doughty, S. M. Anlage, Qi Li, X. X. Xi, and T. Venkatesan

Appl. Phys. Lett. 63, 3215 (1993); http://dx.doi.org/10.1063/1.110202 (3 pages) | Cited 26 times

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We have studied the effect of a dc electric field on the effective microwave surface impedance of a thin film YBa2Cu3O7/SrTiO3/YBa2Cu3O7 (YBCO/STO/YBCO) trilayer by a dielectric resonator technique. At large dc electric fields (≳105 V/cm), both the effective surface resistance and reactance of the sample decrease monotonically with increasing dc voltage applied to the to YBCO film, yielding at 25 K and 24.7 GHz ‖δRs/δVdc‖∼0.25 μΩ/V and ‖δXs/δVdc‖∼1.8 μΩ/V, respectively. A two‐fluid analysis indicates that the changes in the surface impedance can be explained in terms of field induced changes in the superconducting carrier density of the top YBCO film.
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74.25.N- Response to electromagnetic fields
74.78.Fk Multilayers, superlattices, heterostructures
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Josephson tunnel junction microwave attenuator

V. P. Koshelets, S. V. Shitov, A. V. Shchukin, A. M. Baryshev, L. V. Filippenko, G. M. Fischer, and J. Mygind

Appl. Phys. Lett. 63, 3218 (1993); http://dx.doi.org/10.1063/1.110203 (3 pages) | Cited 1 time

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A new element for superconducting electronic circuitry—a variable attenuator—has been proposed, designed, and successfully tested. The principle of operation is based on the change in the microwave impedance of a superconductor‐insulator‐superconductor (SIS) Josephson tunnel junction when dc biased at different points in the current‐voltage characteristic. Both numerical calculations based on the Tien–Gordon theory and 70‐GHz microwave experiments have confirmed the wide dynamic range (more than 15‐dB attenuation for one stage) and the low insertion loss in the ‘‘open’’ state. The performance of a fully integrated submillimeter receiver circuit which comprises a flux–flow oscillator (FFO) as local oscillator, a superconducting variable attenuator, and a microwave SIS detector with tuned‐out capacitance is also reported.
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85.25.Cp Josephson devices
74.25.N- Response to electromagnetic fields
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Josephson coupling in a‐axis YBa2Cu3O7−δ/Pr1−xYxBa2Cu3O7−δ /YBa2Cu3O7−δ sandwich‐type junctions

T. Umezawa, D. J. Lew, S. K. Streiffer, and M. R. Beasley

Appl. Phys. Lett. 63, 3221 (1993); http://dx.doi.org/10.1063/1.110204 (3 pages) | Cited 21 times

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We have studied Josephson coupling in a‐axis YBa2Cu3O7−δ/Pr1−xYxBa2Cu3O7−δ /YBa2Cu3O7−δ sandwich‐type superconductor/normal/superconductor (SNS) junctions. Growth parameters for the films were optimized for smoothness of the barrier interfaces and the films were well characterized by scanning electron microscopy, atomic force microscopy, and cross‐sectional transmission electron microscopy. Transport of the barrier material was highly dependent upon the doping: for x=0, the resistivity followed a T−1/4 behavior and was ∼105 Ω cm at 4.2 K; for x=0.45, the resistivity was nearly metallic and was 10−1 Ω cm at 4.2 K. In the small junction regime W<λj, the critical current scaled with junction area, and was modulated by a magnetic field. We have compared our results to other SNS work and found that the coupling strength of the barrier increases with the conductivity of the barrier material. Possible sources of the coupling are discussed.
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74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Incorporation of hyperfine probes into the thin‐film superconductor YBa2Cu3O7−δ during deposition

D. W. Tom, R. Platzer, John A. Gardner, and J. Tate

Appl. Phys. Lett. 63, 3224 (1993); http://dx.doi.org/10.1063/1.110205 (3 pages) | Cited 3 times

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Radioactive 111In has been incorporated into oriented thin films of YBa2Cu3O7−δ during a thermal coevaporation process. The hyperfine technique of perturbed γγ‐angular correlation spectroscopy shows that 60% of the indium substitutes at a single site in the superconductor. We obtain spectra with reasonable statistics from 2 mCi of starting material, about 1% of which is incorporated into the film. Other methods of incorporating indium into films and bulk YBa2Cu3O7−δ have often resulted in a significant amount of indium being incorporated into impurity phases.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Magnetic and magneto‐optical properties of the Co‐γFe2O3 perpendicular magnetic films

K. Tamari, T. Doi, and N. Horiishi

Appl. Phys. Lett. 63, 3227 (1993); http://dx.doi.org/10.1063/1.110206 (3 pages) | Cited 12 times

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Co‐γFe2O3 films have been prepared by annealing Fe3O4/CoO multilayers. The crystalline orientation of multilayers change with bilayer thickness Λ; the [100] axis of Fe3O4 and CoO orients perpendicular to the film plane for Λ<80 Å and the [111] axis orients for Λ≳100 Å. The Co‐γFe2O3 films obtained from multilayers of Λ<80 Å have positive perpendicular anisotropy. The magnetic coercivity and the squareness of perpendicular hysteresis curves are about 5.0 kOe and 0.8, respectively. The films show high magneto‐optical effects and the figure of merit is 5.5 deg, which is about three times larger than that of CoFe2O4.  
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects

Use of quantum‐well superlattices to obtain a high figure of merit from nonconventional thermoelectric materials

L. D. Hicks, T. C. Harman, and M. S. Dresselhaus

Appl. Phys. Lett. 63, 3230 (1993); http://dx.doi.org/10.1063/1.110207 (3 pages) | Cited 177 times

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Currently, the materials with the highest thermoelectric figure of merit (ZT) are one‐band materials. The presence of both electrons and holes lowers ZT, so two‐band materials such as semimetals are not useful thermoelectric materials. However, by preparing these materials in the form of two‐dimensional quantum‐well superlattices, it is possible to separate the two bands and transform the material to an effective one‐carrier system. We have investigated theoretically the effect of such an approach and our results indicate that a significant increase in ZT may be achieved. This result allows the possibility of using a new class of materials as thermoelectric refrigeration elements.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

High speed optoelectronic response from the edges of lead zirconate titanate thin film capacitors

Sarita Thakoor

Appl. Phys. Lett. 63, 3233 (1993); http://dx.doi.org/10.1063/1.110208 (3 pages) | Cited 7 times

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This letter reports on a high speed (∼10 ns), nondestructive, polarization‐dependent photoresponse from lead zirconate titanate (PZT) thin films, when illuminated with λ=532 nm, at ∼mW/μm2 of incident optical power. This photoresponse emerges primarily from the edges of the sandwich ferroelectric capacitors, consisting of PZT films with predominant c‐axis orientation. This response, in contrast with the thermally triggered effect, is unipolar in nature and occurs at an order of magnitude lower power level, and therefore offers a greater application potential. Its dependence on the crystal orientation and remanent polarization in the PZT film, and therefore its ability to track the built‐in E fields within the film, may offer such photoresponse as a high speed nondestructive evaluation tool.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.66.Nk Insulators
FREE

Comment on ‘‘Observation of phonon‐plasmon coupled modes at the interface between ZnSe and semi‐insulating GaAs by Raman spectroscopy’’ [Appl. Phys. Lett. 62, 1800 (1993)]

O. Pages and M. A. Renucci

Appl. Phys. Lett. 63, 3236 (1993); http://dx.doi.org/10.1063/1.110209 (2 pages) | Cited 2 times

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Abstract Unavailable
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.30.Fs III-V and II-VI semiconductors
FREE

Response to ‘‘Comment on ‘Observation of phonon‐plasmon coupled modes at the interface between ZnSe and semi‐insulating GaAs by micro‐Raman spectroscopy’ ’’ [Appl. Phys. Lett. 62, 1800 (1993)]

M. Ichimura, A. Usami, T. Wada, Sz. Fujita, and Sg. Fujita

Appl. Phys. Lett. 63, 3237 (1993); http://dx.doi.org/10.1063/1.110210 (1 page)

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Abstract Unavailable
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.30.Fs III-V and II-VI semiconductors
FREE

Erratum: ‘‘Sample current maximum at the critical angle of x‐ray total reflection’’ [Appl. Phys. Lett. 63, 269 (1993)]

Jun Kawai, Shinjiro Hayakawa, Setsuo Suzuki, Yoshinori Kitajima, Yasutaka Takata, Teruo Urai, Kuniko Maeda, Masanori Fujinami, Yoshihiro Hashiguchi, and Yohichi Gohshi

Appl. Phys. Lett. 63, 3238 (1993); http://dx.doi.org/10.1063/1.110816 (1 page)

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Abstract Unavailable
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.70.Ck X-ray scattering
99.10.Cd Errata
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