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29 Jul 1996

Volume 69, Issue 5, pp. 593-713

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Photoluminescence study of high quality InGaN–GaN single heterojunctions

C. J. Sun, J. W. Yang, Q. Chen, B. W. Lim, M. Zubair Anwar, M. Asif Khan, H. Temkin, D. Weismann, and I. Brenner

Appl. Phys. Lett. 69, 668 (1996); http://dx.doi.org/10.1063/1.117800 (3 pages) | Cited 14 times

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In this letter we report the results of room‐temperature continuous wave and pulsed photoluminescence measurements on InGaN–GaN single heterojunctions. These InGaN–GaN heterojunctions were deposited over basal plane sapphire substrates using low pressure metalorganic chemical vapor deposition. We suggest the use of vertical cavity stimulated emission instead of spontaneous emission peak position as a good measure of the InGaN band edge. © 1996 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.45.+h Stimulated emission

Cryogenic scanning probe characterization of semiconductor nanostructures

M. A. Eriksson, R. G. Beck, M. Topinka, J. A. Katine, R. M. Westervelt, K. L. Campman, and A. C. Gossard

Appl. Phys. Lett. 69, 671 (1996); http://dx.doi.org/10.1063/1.117801 (3 pages) | Cited 64 times

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We demonstrate the use of a scanned probe microscope (SPM) at 4 Kelvin to study electron transport through a ballistic point contact in the two‐dimensional electron gas inside a GaAs/AlGaAs heterostructure. The electron gas density profile is locally perturbed by the charged SPM tip providing information about the electron flow through the point contact. As the tip is scanned, one obtains a spatial image of the ballistic electron flux as well as the topographic profile of the structure. Calculations indicate the spatial resolution is comparable to the electron gas depth. © 1996 American Institute of Physics.
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73.23.Ad Ballistic transport
07.79.-v Scanning probe microscopes and components

Formation of ultrathin, buried oxides in Si by O+ ion implantation

O. W. Holland, D. Fathy, and D. K. Sadana

Appl. Phys. Lett. 69, 674 (1996); http://dx.doi.org/10.1063/1.117802 (3 pages) | Cited 17 times

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A technique is presented for forming a silicon‐on‐insulator material with an ultrathin buried oxide by utilizing the separation by implantation of oxygen or SIMOX method. It overcomes the problem of oxide continuity encountered during standard SIMOX processing when the O+‐implanted dose is scaled down to decrease the thickness of the buried oxide below ∼0.1 μm. To promote the formation of ultrathin buried oxides (during post‐implantation annealing), the implantation process was modified to produce a microstructure which promotes coalescence of the oxygen into a continuous layer. This was accomplished by slightly modifying the standard (≳500 °C) process so that the final increment of the dose is implanted near room temperature. This dose is chosen to selectively amorphize the region near the ion’s range which will yield a high‐defective layer during subsequent annealing. It is shown that this layer, which can consist of polysilicon, provides a template or guide upon which the oxide forms. Buried oxides prepared in this way are shown to be continuous and without Si inclusions while the standard process yields a broken layer with severe discontinuities. © 1996 American Institute of Physics.
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61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology

Effect of thin HgTe layers on dislocations in HgCdTe layers on Si substrates

T. Okamoto, T. Saito, S. Murakami, H. Nishino, K. Maruyama, Y. Nishijima, H. Wada, M. Nagashima, and Y. Nogami

Appl. Phys. Lett. 69, 677 (1996); http://dx.doi.org/10.1063/1.117803 (2 pages) | Cited 2 times

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We have found the effects of HgTe layers on dislocations of (111)B HgCdTe layers grown on Si substrates by metalorganic vapor phase epitaxy. The dislocations in HgCdTe layers were reduced by inserting thin HgTe layers between HgCdTe and CdTe buffer layers. Using this method, the dislocation density of 2.3×106 cm−2 was obtained, which is less than quarter that of HgCdTe layers without HgTe. © 1996 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.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

The minority carrier lifetime of n‐type 4H‐ and 6H‐SiC epitaxial layers

O. Kordina, J. P. Bergman, C. Hallin, and E. Janzén

Appl. Phys. Lett. 69, 679 (1996); http://dx.doi.org/10.1063/1.117804 (3 pages) | Cited 29 times

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The minority carrier lifetime has been measured on n‐type 6H‐ and 4H‐SiC epitaxial layers. We observe inherently longer lifetimes in 4H layers compared to 6H‐SiC layers. A value as high as 2.1 μs has been measured at room temperature in 4H‐SiC, however, large variations may be observed over the surface. The lifetime increases with temperature and at a typical operating temperature of a device the lifetime is close to 5 μs. The lifetime appears to be correlated with the morphology of the epitaxial film showing that the lifetime limiting defect may be related to a crystalline imperfection. A strong correlation can also be seen with the thickness of the epitaxial layers. © 1996 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Measurement of the extent of strain relief in InGaAs layers grown under tensile strain on InP(100) substrates

P. Maigné, M. Gendry, T. Venet, Y. Tahri, and G. Hollinger

Appl. Phys. Lett. 69, 682 (1996); http://dx.doi.org/10.1063/1.117805 (3 pages) | Cited 4 times

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High resolution x‐ray diffraction has been used to investigate the structural properties of InxGa1−xAs epitaxial layers grown under tension on InP(100) substrates. The nominal indium composition (x=0.42) corresponds to a small lattice mismatch and a two dimensional growth mode. We have also included for comparison two samples grown under compression covering the mostly strained and the mostly relaxed regimes. Our results show that the residual strain and the asymmetry in strain relaxation along 〈011〉 directions are always larger for layers under tension. This can be explained by the difference in dislocation glide velocity induced by a different indium content, by the dissociation of perfect dislocations and partially by the difference in thermal expansion coefficients between substrate and epilayer. The larger asymmetry in strain relaxation for tensile strain layers is interpreted by the existence of microcracks aligned in the [011] direction. © 1996 American Institute of Physics.
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61.72.Dd Experimental determination of defects by diffraction and scattering
68.60.Bs Mechanical and acoustical properties

Hydrogen plasma passivation of InP: Real time ellipsometry monitoring and ex situ photoluminescence measurements

G. Bruno, M. Losurdo, P. Capezzuto, V. Capozzi, T. Trovato, G. Perna, and G. F. Lorusso

Appl. Phys. Lett. 69, 685 (1996); http://dx.doi.org/10.1063/1.117806 (3 pages) | Cited 8 times

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The remote hydrogen plasma passivation of semi‐insulating InP substrates has been investigated by in situ spectroscopic ellipsometry (SE), to characterize the changes of InP morphology, and ex situ photoluminescence (PL) to reveal the passivation effect of nonradiative centers operated by H atoms. The concurrence of the InP native oxide removal without surface damage (phosphorus ablation) and the passivation by H‐atoms results in a remarkable enhancement of the PL intensity. © 1996 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.65.Rv Passivation
68.35.Dv Composition, segregation; defects and impurities

Antenna‐coupled high‐Tc bolometers for visible and near‐infrared detection using organic dyes as light‐harvesting layers

David C. Jurbergs, Jianai Zhao, and John T. McDevitt

Appl. Phys. Lett. 69, 688 (1996); http://dx.doi.org/10.1063/1.117807 (3 pages) | Cited 3 times

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Antenna‐coupled high‐Tc bolometers fabricated from YBa2Cu3O7−δ thin films have been prepared using molecular organic dyes. Light‐harvesting layers derived from these visible and near‐infrared absorbers have been utilized to produce detectors which exhibit wavelength‐selective response characteristics in the visible and near‐infrared spectral regions. Using such hybrid structures, initial studies documenting efficient energy transfer between molecular dye layers and superconductor surfaces have been completed. © 1996 American Institute of Physics.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
74.78.-w Superconducting films and low-dimensional structures
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Coupling of terahertz radiation to a high‐Tc superconducting hot electron bolometer mixer

Yu. P. Gousev, A. D. Semenov, E. V. Pechen, A. V. Varlashkin, R. S. Nebosis, and K. F. Renk

Appl. Phys. Lett. 69, 691 (1996); http://dx.doi.org/10.1063/1.117808 (3 pages) | Cited 11 times

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We report on efficient coupling of THz radiation to a high‐Tc superconducting hot electron bolometer that is suitable for heterodyne detection. Our quasi‐optical system consisted of a planar self‐complementary spiral antenna on a dielectric substrate clamped to an extended hyperhemispherical lens. The antenna was integrated into a co‐planar line for broadband intermediate frequency matching. Measurements in the homodyne regime at a frequency of 2.5 THz showed a radiation pattern with a beam width of 1° and a coupling efficiency of ≊0.1. We measured, at an intermediate frequency of 1.5 GHz, an output noise temperature of ≊160 K and estimated for the device, operated in the heterodyne regime, a system noise temperature of ≊3×105 K. We also discuss possibilities of significant improvement of the sensitivity. © 1996 American Institute of Physics.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
74.78.-w Superconducting films and low-dimensional structures
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Error rate of a superconducting circuit

Quentin P. Herr and Marc J. Feldman

Appl. Phys. Lett. 69, 694 (1996); http://dx.doi.org/10.1063/1.117809 (2 pages) | Cited 24 times

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The bit‐error rate of the Josephson junction single‐flux‐quantum comparator was measured as a function of bias current offset, at clock rates up to 10 GHz. The bit‐error rate versus offset is a smooth curve, measured over 16 decades of incidence, which linearly extrapolates to 10−49 for optimal bias. The lowest rate actually measured was 5×10−17, corresponding to 4 errors counted in 130 h. © 1996 American Institute of Physics.
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85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
74.50.+r Tunneling phenomena; Josephson effects

Current transport across YBa2Cu3O7–Au interfaces

M. Grove, Regina Dittmann, M. Bode, M. Siegel, and A. I. Braginski

Appl. Phys. Lett. 69, 696 (1996); http://dx.doi.org/10.1063/1.117810 (3 pages) | Cited 5 times

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Current transport across each of the two YBa2Cu3O7–Au interfaces in a step‐edge superconductor–normal metal–superconductor (SNS) Josephson junction could be investigated independently, due to contacts to the Au interlayer. The I–V characteristics of each superconductor–normal metal (SN) interface showed dc and ac Josephson‐like effects fitting well to a model, which takes into account the influence of proximity effect in the normal metal layer on the transport across the SN interface, and Andreev reflection at the interface. In the investigated junctions, both SN interfaces of the step SNS junctions had similar transparencies. © 1996 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Linewidth of submillimeter wave flux‐flow oscillators

Valery P. Koshelets, Sergey V. Shitov, Alexey V. Shchukin, Lyudmila V. Filippenko, and Jesper Mygind

Appl. Phys. Lett. 69, 699 (1996); http://dx.doi.org/10.1063/1.117811 (3 pages) | Cited 16 times

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A reliable technique for wide band measurements of the spectral linewidth of superconducting oscillators integrated on‐chip with superconductor‐insulator‐superconductor (SIS) detectors has been developed. The spectral linewidth of flux‐flow oscillators (FFO) based on the unidirectional and viscous flow of magnetic vortices in a long overdamped Josephson tunnel junction was measured in the frequency range 250–580 GHz, and a linewidth as low as 200 kHz was obtained at 450 GHz. Also stable frequency locking of a FFO to very high (≤60th) harmonics of an external microwave reference source has been demonstrated. The proposed technique may improve the sensitivity, frequency resolution, and stability of the fully superconducting integrated submillimeter wave receiver. © 1996 American Institute of Physics.
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85.25.Cp Josephson devices
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
84.40.Lj Microwave integrated electronics

Molecular field theory analysis of magneto‐optic sensitivity of gallium‐substituted yttrium iron garnets

Merritt N. Deeter and Silvia Milián Bon

Appl. Phys. Lett. 69, 702 (1996); http://dx.doi.org/10.1063/1.117812 (3 pages) | Cited 1 time

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The temperature dependence of the magneto‐optic sensitivity of gallium‐substituted yttrium iron garnets was measured at 1.3 μm and compared with a model based on molecular field theory. The model incorporates results of measurements of both the saturation magnetization and saturation Faraday rotation versus temperature. These measurements were analyzed in the context of molecular field theory to extract the fundamental molecular field coefficients and the magneto‐optical coefficients as functions of gallium content. The model and direct sensitivity measurements both indicate that the magneto‐optic sensitivity of garnet compositions with gallium substitution levels near 0.8 should exhibit a vanishing first‐order temperature sensitivity.©American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.50.Dd Nonmetallic ferromagnetic materials

Field‐dependence of microscopic probes in magnetic force microscopy

K. L. Babcock, V. B. Elings, J. Shi, D. D. Awschalom, and M. Dugas

Appl. Phys. Lett. 69, 705 (1996); http://dx.doi.org/10.1063/1.117813 (3 pages) | Cited 62 times

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We present a technique for characterizing the magnetic state of a magnetic force microscopy (MFM) probe as a function of uniform external magnetic field H. A local magnetic field is generated by micron‐scale current carrying conductors and directly imaged by MFM. As H alters the magnetic state of the probe, changes in image contrast yield componentwise measures of the tip’s net magnetic moment m, tip hysteresis loops and coercivities, and possible orientations (vertical vs lateral) of remanent states mr used for most MFM imaging. Results are presented for a variety of thin‐film probes. © 1996 American Institute of Physics.
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07.79.Pk Magnetic force microscopes

Geometrically enhanced magnetoresistance in ferromagnet–insulator–ferromagnet tunnel junctions

J. S. Moodera, L. R. Kinder, J. Nowak, P. LeClair, and R. Meservey

Appl. Phys. Lett. 69, 708 (1996); http://dx.doi.org/10.1063/1.117814 (3 pages) | Cited 117 times

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Ferromagnetic–insulator–ferromagnetic trilayer tunnel junctions show magnetoresistance (JMR) effects of about 14% or greater at room temperature. Much larger values of the JMR (100% or more) are observed when the actual tunneling resistance (RT) is comparable to electrode film resistance (RL) over the junction area. This latter apparent JMR is an artifact of the nonuniform current flow over the junction in the cross geometry of the electrodes. The ferromagnetic films were CoFe and Co or Ni0.8Fe0.2, and the tunnel barrier was AlN or Al2O3. These junctions show nonvolatile memory effects. The geometrically enhanced large JMR in junctions can be effectively used as magnetic sensors and memory elements. © 1996 American Institute of Physics.
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75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Epitaxial MnGa/(Mn,Ga,As)/MnGa trilayers: Growth and magnetic properties

W. Van Roy, H. Akinaga, S. Miyanishi, K. Tanaka, and L. H. Kuo

Appl. Phys. Lett. 69, 711 (1996); http://dx.doi.org/10.1063/1.117815 (3 pages) | Cited 21 times

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Epitaxial ferromagnet/semiconductor/ferromagnet sandwiches with the nominal structure δ Mn60Ga40/GaAs/δ Mn54Ga46 have been grown on GaAs(001) by molecular beam epitaxy, with spacer layer thicknesses ranging from 2 to 19 monolayers (ML) GaAs nominally. A strong antiferromagnetic coupling field μ0Hs=−12 to −39 mT at room temperature is observed for spacer layers of 4–14 ML GaAs nominally, a weaker ferromagnetic coupling of +1 to +7 mT exists outside of this thickness region. Magnetic contamination of the spacer layer and the inclusion of antiferromagnetic Mn2As cannot be ruled out. © 1996 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.50.Cc Other ferromagnetic metals and alloys
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