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1 Nov 1993

Volume 63, Issue 18, pp. 2455-2578

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Tunneling spectroscopy of midgap states induced by arsenic precipitates in low‐temperature‐grown GaAs

R. M. Feenstra, A. Vaterlaus, J. M. Woodall, and G. D. Pettit

Appl. Phys. Lett. 63, 2528 (1993); http://dx.doi.org/10.1063/1.110448 (3 pages) | Cited 29 times

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The scanning tunneling microscope is used to study arsenic precipitates in low‐temperature‐grown and annealed GaAs. Tunneling spectroscopy reveals a distribution of states throughout the band gap, arising from the precipitates, with the density of midgap states increasing as the precipitate size increases. The Fermi level is found to be pinned at EV+0.65 eV for 600 °C annealed material. For 800 °C annealed material the Fermi level is located at EV+1.05 eV in regions far from precipitates, and additional depletion regions are observed near the precipitates.
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71.55.Eq III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
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

Ge segregation in SiGe/Si heterostructures and its dependence on deposition technique and growth atmosphere

D. A. Grützmacher, T. O. Sedgwick, A. Powell, M. Tejwani, S. S. Iyer, J. Cotte, and F. Cardone

Appl. Phys. Lett. 63, 2531 (1993); http://dx.doi.org/10.1063/1.110449 (3 pages) | Cited 25 times

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Ge segregation at SiGe/Si heterointerfaces has been studied for films deposited by atmospheric pressure chemical vapor deposition (APCVD), ultrahigh vacuum CVD (UHV/CVD) and molecular beam epitaxy (MBE). Profiles were taken by secondary‐ion‐mass‐spectroscopy (SIMS) of samples grown with these techniques at the same growth temperatures and Ge concentrations. The MBE grown profiles are dominated by segregation of Ge into the Si top layer in the temperature range from 450 to 800 °C. SiGe/Si interfaces deposited by UHV/CVD at elevated temperatures are smeared, but at 515 °C and below the interfaces are abrupt within the resolution of the SIMS. Heterostructures grown by APCVD show abrupt interfaces and no indication of Ge segregation in the investigated temperature range from 600 to 800 °C. Surface passivation by hydrogen appears to be responsible for the suppression of the Ge segregation in CVD processes.
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68.55.-a Thin film structure and morphology

Photoluminescence of hydrogenated GaAs/AlGaAs quantum wells grown by metalorganic vapor phase epitaxy

J. R. Botha and A. W. R. Leitch

Appl. Phys. Lett. 63, 2534 (1993); http://dx.doi.org/10.1063/1.110450 (3 pages) | Cited 2 times

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The incorporation of hydrogen into an undoped GaAs/Al0.3Ga0.7As quantum well (QW) structure (containing wells of varying thickness) grown by metalorganic vapor phase epitaxy has been studied by photoluminescence (PL) in the temperature range 12–200 K. Hydrogenation is shown to reduce the PL linewidths. This is attributed to a passivation of impurities in the wells and heterointerfaces. In addition, the influence of hydrogenation on the radiative efficiency of each QW as a function of temperature is discussed in terms of a passivation of grown‐in defects as well as a depth distribution of plasma‐induced defects.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
81.65.-b Surface treatments

Oxide thickness dependence of interface trap generation in a metal‐oxide‐semiconductor structure during substrate hot‐hole injection

Quazi Deen Mohd Khosru, Naoki Yasuda, Kenji Taniguchi, and Chihiro Hamaguchi

Appl. Phys. Lett. 63, 2537 (1993); http://dx.doi.org/10.1063/1.110451 (3 pages) | Cited 6 times

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Oxide thickness dependence of interface trap generation in a metal‐oxide‐semiconductor (MOS) structure is investigated using uniform hot‐hole injection into the gate oxides of p‐channel MOS transistors with very thin oxide thicknesses. Significant dependence of interface trap generation on oxide thickness (tox) is found for very thin oxides and the dependence disappears for tox≥8 nm. A universal relationship between hole trapping in the oxide bulk and interface trap generation at the Si/SiO2 interface is observed experimentally. The experimental results suggest that interface trap generation is a process involving hole trapping in the oxide bulk, rather than a pure interfacial process. No oxide thickness dependence of interface trap generation for thicker oxides (tox≥8 nm) is in agreement with previous reports and the overall dependence can consistently be explained with the help of the spatial distribution of trapped holes in the oxide. In contrast to the reports describing delayed interface trap formation, we observed oxide field‐dependent annealing of the generated interface traps after the end of hole injection.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Ht Other nonmetals
85.30.Tv Field effect devices

Interface structure and chemical bondings in Al/S‐passivated GaAs(111)

M. Sugiyama, S. Maeyama, T. Scimeca, M. Oshima, H. Oigawa, Y. Nannichi, and H. Hashizume

Appl. Phys. Lett. 63, 2540 (1993); http://dx.doi.org/10.1063/1.110796 (3 pages) | Cited 3 times

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The position and chemical state of S atoms have been investigated for the Al/S‐passivated GaAs(111)A and (111)B samples using the soft x‐ray standing wave technique and synchrotron radiation photoemission spectroscopy. The x‐ray standing wave results indicate that the S atoms at the Al/S/GaAs(111) interface are significantly more disordered than the S atoms at the S/GaAs(111) surface. The position of the S atoms does not change upon the Al deposition. The synchrotron radiation photoemission spectra suggest that the Ga atoms bonded to S atoms before the Al deposition exchange with Al atoms upon deposition.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.B- Structure of clean surfaces (and surface reconstruction)
79.60.-i Photoemission and photoelectron spectra

Dislocation generation mechanisms for GaP on Si grown by metalorganic chemical vapor deposition

Tetsuo Soga, Takashi Jimbo, and Masayoshi Umeno

Appl. Phys. Lett. 63, 2543 (1993); http://dx.doi.org/10.1063/1.110427 (3 pages) | Cited 4 times

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Dislocation generation mechanisms for GaP on Si substrates by metalorganic chemical vapor deposition are described. Dislocations are not observed at the GaP/Si interface when the layer thickness is less than 90 nm. The presented high resolution transmission electron microscopy shows two kinds of dislocations with the extra‐half plane in the GaP layer and Si substrate. These observations predict that the misfit dislocations are formed at the growth temperature while the dislocations with the extra‐half plane in the GaP layer are formed during the cooling process, owing to the difference of the thermal expansion.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Low‐temperature rapid thermal low pressure metalorganic chemical vapor deposition of Zn‐doped InP layers using tertiarybutylphosphine

A. Katz, A. Feingold, S. J. Pearton, N. Moriya, C. J. Baiocchi, and M. Geva

Appl. Phys. Lett. 63, 2546 (1993); http://dx.doi.org/10.1063/1.110428 (3 pages)

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High purity Zn doped InP layers were grown by rapid thermal low pressure metalorganic chemical vapor deposition technique, using tertiarybutylphosphine as the phosphorus source. The best quality layer, which was grown at P:In ratio of 75, temperature as low as 525 °C, pressure of 2 Torr and growth rate of 2 nm/s, exhibited electron mobility of 80 cm2 V−1 s−1 and Hall carrier concentration of 3.5×1018 cm−3 at room temperature. The stoichiometry of the InP Zn‐doped layer was excellent, regardless of the Zn content in the reactive gas mixture. The crystallographic defect density and the surface morphological particle concentration, however, were found to be strongly dependent on the Zn concentration.
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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.)

Band offsets at the CdS/CuInSe2 heterojunction

Su‐Huai Wei and Alex Zunger

Appl. Phys. Lett. 63, 2549 (1993); http://dx.doi.org/10.1063/1.110429 (3 pages) | Cited 24 times

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The traditional explanation for the successful electron‐hole separation in CdS/CuInSe2 solar cells rests on the assumption of a type‐II band lineup: The conduction‐band minimum is assumed to be on the CdS window while the valence‐band maximum is assumed to be localized on the CuInSe2 absorber. This picture of negative conduction‐band offset ΔEc<0 was supported by the electron affinity rule, but was sharply contradicted by the more recent photoemission experiments of Nelson et al. for CdS/CuInSe2 yielding ΔEc=+1.08 eV. Our first principles calculations yield for CdS/CuInSe2 ΔEc=+0.31 eV, hence, a type‐I band alignment. We challenge the published experimental value as being in error and point to the need of revising current solar cell device models that assume ΔEc<0.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
84.60.Jt Photoelectric conversion

High quality YBa2Cu3O7 films on polyalumina

L. Ganapathi, S. Giles, Rama Rao, J. P. Zheng, and H. S. Kwok

Appl. Phys. Lett. 63, 2552 (1993); http://dx.doi.org/10.1063/1.110430 (3 pages) | Cited 4 times

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Superconducting YBCO (YBa2Cu3O7) films were deposited on polycrystalline alumina substrates with c‐normal orientation. YBCO films deposited directly on alumina exhibited a broad transition with Tc, zero=60 K. The Tc, zero increased to 86 K upon the use of a YSZ (yttria stabilized zirconia) buffer layer to stop the interface reaction. However, the Jc of these films was still below 104 A/cm2. A simple surface modification of the polycrystalline alumina substrate by way of depositing a YSZ buffer and repolishing the surface drastically improved the Jc. Values of 104 A/cm2 observed at 30 K is the best Jc reported so far for YBCO films on polycrystalline alumina. We believe further improvements in both the surface finish of the polyalumina and the YSZ buffer layer will lead to microwave quality YBCO films on polyalumina.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.55.-a Thin film structure and morphology

Elastic scattering and the current‐voltage characteristics of superconducting Nb‐InAs‐Nb junctions

Niko van der Post, Junsaku Nitta, and Hideaki Takayanagi

Appl. Phys. Lett. 63, 2555 (1993); http://dx.doi.org/10.1063/1.110431 (3 pages) | Cited 6 times

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Superconducting niobium contacts are attached to a 0.8‐μm‐long epitaxially grown InAs channel sandwiched between insulating InGaAs layers. The current‐voltage characteristics show nonlinearities at submultiples of the superconducting energy gap indicative of multiple‐Andreev reflections. We demonstrate that an increase in the elastic scattering rate in the InAs channel, caused by Ar‐ion etching, diminishes the order of Andreev reflections and explains the overall shape of the current‐voltage characteristics.
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74.78.Fk Multilayers, superlattices, heterostructures
74.50.+r Tunneling phenomena; Josephson effects
73.40.Sx Metal-semiconductor-metal structures

Processing of Bi2Sr2CaCu2Ox thick films from nitrate precursors

C. Li, S. Patel, J. Ye, E. Narumi, D. T. Shaw, and T. Sato

Appl. Phys. Lett. 63, 2558 (1993); http://dx.doi.org/10.1063/1.110432 (3 pages) | Cited 7 times

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High‐quality Bi2Sr2CaCu2Ox/Ag superconducting tapes were fabricated directly from the nitrate salts of Bi, Sr, Ca, and Cu by the partial‐melt‐growth technique. Nitrate particles were deposited electrostatically on the Ag substrate and heat treated. After process optimization of the superconducting tapes, the best samples showed typical Tc of 89 K with zero applied field critical current density of 2×104 A/cm2 (Ic=11.2 A) at 77 K and 2.6×105 A/cm2 (Ic=190 A) at 4.2 K. Unlike films grown using solid state reacted precursor powders, these films lacked the typical Bi‐free, needlelike defects and possessed a smooth morphology. X‐ray diffraction patterns showed the film to be highly c‐axis oriented. The processing of these tapes significantly reduces the overall fabrication time from precursor materials preparation to final heat treatment.
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84.71.Mn Superconducting wires, fibers, and tapes
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
74.72.-h Cuprate superconductors

Electronic states studies of alkali‐metal‐doped C60 superconductors by nuclear magnetic resonance

Mayumi Kosaka, Katsumi Tanigaki, Thomas W. Ebbesen, Yoshifumi Nakahara, and Kazuo Tateishi

Appl. Phys. Lett. 63, 2561 (1993); http://dx.doi.org/10.1063/1.110433 (3 pages) | Cited 4 times

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The density of states at the Fermi level [N(EF)] of alkali‐metal‐doped C60 superconductors having a wide range of Tc from Na2Rb1C60 (Tc=3.5 K) to Rb1Cs2C60 (Tc=33 K) is systematically studied using spin‐lattice relaxation times (T1) by NMR spectroscopy. The obtained N(EF) values suggest that the phonon modes associated with superconductivity are high and that the electron‐phonon coupling constant is responsible for the large decrease in Tc in the small lattice parameter region.
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74.70.Wz Carbon-based superconductors
74.25.Jb Electronic structure (photoemission, etc.)
76.60.-k Nuclear magnetic resonance and relaxation

Washer size and shape dependencies of current steps due to standing waves in superconducting quantum interference devices (SQUIDS)

Eriko Takeda, Toshikazu Nishino, and Kazumasa Takagi

Appl. Phys. Lett. 63, 2564 (1993); http://dx.doi.org/10.1063/1.110434 (3 pages) | Cited 3 times

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To find out the quantitative relationship between the voltages of current steps caused by standing waves and the size of the SQUID washer, experimental and numerical studies have been conducted. The wavelength of the standing wave depends on both the width and the hole size of the washer. A model treating a multiturn input coil as a plate explains the measured systematic change in the step voltages. For shortening the wavelength, a new figure of SQUID with an incision in the washer is proposed. The figure is effective for increasing the output voltage of the SQUID.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.78.Fk Multilayers, superlattices, heterostructures

Ultrafast scanning probe microscopy

S. Weiss, D. F. Ogletree, D. Botkin, M. Salmeron, and D. S. Chemla

Appl. Phys. Lett. 63, 2567 (1993); http://dx.doi.org/10.1063/1.110435 (3 pages) | Cited 51 times

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We have measured the response of the tunneling gap of a scanning tunneling microscope to excitation by a subpicosecond electrical pulse. Combining ultrashort laser pulses techniques with scanning tunneling microscopy (STM), we have obtained simultaneous 2‐ps time resolution and 50‐Å spatial resolution. This is a 9 orders of magnitude improvement in the time resolution currently attainable with STM. The potential of this powerful technique for studying ultrafast dynamical phenomena on surfaces with atomic resolution and mesoscopic electronic device physics is discussed.
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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
78.47.-p Spectroscopy of solid state dynamics
73.20.At Surface states, band structure, electron density of states
68.35.B- Structure of clean surfaces (and surface reconstruction)

Fabrication and properties of epitaxial ferroelectric heterostructures with (SrRuO3) isotropic metallic oxide electrodes

C. B. Eom, R. B. Van Dover, Julia M. Phillips, D. J. Werder, J. H. Marshall, C. H. Chen, R. J. Cava, R. M. Fleming, and D. K. Fork

Appl. Phys. Lett. 63, 2570 (1993); http://dx.doi.org/10.1063/1.110436 (3 pages) | Cited 125 times

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Epitaxial ferroelectric SrRuO3/Pb(Zr0.52Ti0.48)O3/SrRuO3 heterostructures have been fabricated employing isotropic metallic oxide electrodes on (100) SrTiO3 and (100) Si with an yttria stabilized zirconia buffer layer. The structures have been grown in situ by 90° off‐axis sputtering, which allows the growth of uniform stoichiometric films over large areas with excellent step coverage. X‐ray diffraction, Rutherford backscattering spectroscopy, and cross‐sectional transmission electron microscopy reveal high crystalline quality and coherent interfaces. They exhibit superior fatigue characteristics over those made with metal electrodes, showing little degradation over 1010 cycles, with a large remnant polarization.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.55.-g Dielectric thin films

Dynamic mode force microscopy for the detection of lateral and vertical electrostatic forces

S. Watanabe, K. Hane, M. Ito, and T. Goto

Appl. Phys. Lett. 63, 2573 (1993); http://dx.doi.org/10.1063/1.110437 (3 pages) | Cited 5 times

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In this letter, a variant of scanning force microscope for detecting attractive forces is reported. The force gradients of the attractive forces acting in two orthogonal directions were detected simultaneously from the resonant frequency shifts of a cantilever oscillating in two directions. Using the fine electrode sample, the distributions of the electrostatic forces acting in lateral and vertical directions were visualized separately.
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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.Gy Mechanical properties; surface strains
FREE

Comment on: ‘‘Direct experimental evidence for diffusion of dopants via pairs with intrinsic point defects’’

K. Maser

Appl. Phys. Lett. 63, 2576 (1993); http://dx.doi.org/10.1063/1.110438 (1 page) | Cited 3 times

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Abstract Unavailable
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61.72.uf Ge and Si
61.72.S- Impurities in crystals
66.30.J- Diffusion of impurities
FREE

Response to Comment on: ‘‘Direct experimental evidence for diffusion of dopants via pairs with intrinsic point defects’’

P. Pichler, R. Schork, T. Klauser, and H. Ryssel

Appl. Phys. Lett. 63, 2576 (1993); http://dx.doi.org/10.1063/1.110439 (2 pages)

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Abstract Unavailable
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61.72.uf Ge and Si
61.72.S- Impurities in crystals
66.30.J- Diffusion of impurities
FREE

Erratum: ‘‘Investigation of optical limiting in C60 solution’’ [Appl. Phys. Lett. 62, 1763 (1993)]

M. P. Joshi, S. R. Mishra, H. S. Rawat, S. C. Mehendale, and K. C. Rustagi

Appl. Phys. Lett. 63, 2578 (1993); http://dx.doi.org/10.1063/1.110814 (1 page) | Cited 1 time

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Abstract Unavailable
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42.65.-k Nonlinear optics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
99.10.Cd Errata
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