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5 Aug 1991

Volume 59, Issue 6, pp. 621-747

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High‐differential mobility of hot electrons in delta‐doped quantum wells

W. Ted Masselink

Appl. Phys. Lett. 59, 694 (1991); http://dx.doi.org/10.1063/1.105368 (3 pages) | Cited 13 times

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Although electrons in center delta‐doped AlGaAs/GaAs quantum wells have lower low‐field mobilities than do electrons in uniformly doped quantum wells, experimental results presented here show that at electric fields between 2 and 4 kV/cm the differential mobility in delta‐doped quantum wells rises dramatically. This large increase in differential mobility may be a result of the heating of the electrons out of the symmetric ground state into the antisymmetric first excited state. Because the excited state has a node at the delta doping, these hot electrons have a much smaller overlap with the ionized impurities of the doping spike in the well centers and therefore higher mobility.
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73.50.Fq High-field and nonlinear effects
73.61.Ey III-V semiconductors

Disorder‐induced transition from Gaussian to dispersive carrier transport in molecularly doped polymers

Yoshihiko Kanemitsu, Hiroshi Funada, and Yasuaki Masumoto

Appl. Phys. Lett. 59, 697 (1991); http://dx.doi.org/10.1063/1.105369 (3 pages) | Cited 8 times

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Dynamics of hopping charge transport in a polymer matrix doped with two different charge‐transport molecules was studied by means of time‐of‐flight (TOF) photoconductivity measurements. In polymers doped with two molecules of little different ionization potential, the Gaussian (near‐rectangular) TOF signal was observed over all compositions and the tail of the Gaussian TOF signal is broadened by a wide distribution of hopping time among molecules due to off‐diagonal disorder. On the other hand, in polymers doped with two molecules of different ionization potential, the transition from the Gaussian to the dispersive TOF signal was observed and this is mainly caused by diagonal disorder. It is found that the energetic and spatial distribution of hopping sites play a key role in carrier transport in molecularly doped polymers.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ng Insulators
85.60.-q Optoelectronic devices
72.80.Sk Insulators

Enhanced crystallographic selectivity in molecular beam epitaxial growth of GaAs on mesas and formation of (001)‐(111)B facet structures for edge quantum wires

Y. Nakamura, S. Koshiba, M. Tsuchiya, H. Kano, and H. Sakaki

Appl. Phys. Lett. 59, 700 (1991); http://dx.doi.org/10.1063/1.105370 (3 pages) | Cited 25 times

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The crystallographic selectivity of molecular beam epitaxial growth of GaAs on mesas consisting of a (001) surface and (111)B facets is studied systematically. It was found that the growth rate on (111)B facets can be drastically reduced to ∼1/30 of the growth rate on (001) surface by the reduction of As flux on the (111)B facets. This enhanced selectivity results from the enhanced intersurface migration, and strongly indicates a feasibility of forming microheterostructures needed for the fabrication of edge quantum wires on (001)‐(111)B mesas.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Fx Diffusion; interface formation
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Influence of hydrogen passivation on the infrared spectra of Hg0.8Cd0.2Te

Y. F. Chen and W. S. Chen

Appl. Phys. Lett. 59, 703 (1991); http://dx.doi.org/10.1063/1.106385 (3 pages) | Cited 9 times

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Hydrogen passivation has been investigated in Hg0.8Cd0 2Te using infrared transmission measurements. The ability of atomic hydrogen to passivate the activities of residual impurities or defects is demonstrated by the fact that the absorption edge is moved to the short wave direction and the absorption below the energy gap is reduced after the incorporation of atomic hydrogen using an rf glow discharge system. It is also found that Hg vacancies can be effectively passivated after hydrogenation. Hydrogen injection and passivation of residual impurities or defects are also observed in Hg0.8Cd0.2Te boiled in water.
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78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
71.55.Gs II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
81.40.Tv Optical and dielectric properties related to treatment conditions

X‐ray scattering studies of the SiO2/Si(001) interfacial structure

T. A. Rabedeau, I. M. Tidswell, P. S. Pershan, J. Bevk, and B. S. Freer

Appl. Phys. Lett. 59, 706 (1991); http://dx.doi.org/10.1063/1.105371 (3 pages) | Cited 14 times

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X‐ray scattering has been utilized in a study of the SiO2/Si(001) interfacial structure. Scattering data provide evidence for a low coverage 2×1 epitaxial structure at the SiO2/Si interface for dry oxides grown on highly ordered Si surfaces at room temperature. The observed scattering is consistent with distorted dimer models of the interfacial structure. Thermal annealing substantially reduces the order of the 2×1 structure while prolonged exposure to humid air almost eliminates the 2×1 symmetry scattering. These findings suggest that the observed 2×1 order is associated with a metastable, intermediate state of the dry oxidation process.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.-b Surface treatments

Analysis of lateral uniformity of ultrashallow junctions in polycrystalline silicon‐on‐single crystal silicon systems

Keunhyung Park, Shubneesh Batra, and Sanjay Banerjee

Appl. Phys. Lett. 59, 709 (1991); http://dx.doi.org/10.1063/1.105372 (3 pages) | Cited 3 times

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The lateral uniformity of n+‐p junctions formed by indiffusion of As or P from an amorphous or polycrystalline silicon thin‐film source into the underlying silicon substrate has been investigated using a concentration‐dependent etch and transmission electron microscopy. Grain boundaries act as fast diffusant pipelines and also possibly inject point defects into the substrate, thereby enhancing bulk diffusivities locally in the substrate. Delineated ultrashallow junctions show significant doping lateral inhomogeneities in the substrate for as‐deposited amorphous silicon diffusion sources but not for as‐deposited polycrystalline silicon diffusion sources because of a larger final grain microstructure after annealing in the former case. However, the doping inhomogeneities are gradually smeared out as impurities diffuse deeper into the substrate.
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68.35.Fx Diffusion; interface formation
61.72.uf Ge and Si
66.30.J- Diffusion of impurities

Residual strain in epitaxially grown ZnSe/GaAs studied by two‐photon absorption spectroscopy

Fujio Minami, Yukio Kato, Kouji Yoshida, Kuon Inoue, and Koh Era

Appl. Phys. Lett. 59, 712 (1991); http://dx.doi.org/10.1063/1.105373 (3 pages) | Cited 14 times

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We apply two‐photon absorption spectroscopy as a novel tool to study residual strain in ZnSe epitaxial layers grown on GaAs substrates. Taking advantage of the polarization selection rules, we find that ZnSe layers thicker than 2 μm suffer in‐plane tensile strain of the order of 10−4. Deformation potential for the ZnSe layer is determined directly from two‐photon data to high accuracy.
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71.35.-y Excitons and related phenomena
78.66.-w Optical properties of specific thin films
68.35.Gy Mechanical properties; surface strains

Novel photoacoustic spectroscopy of semiconductor thin films by a transparent transducer: Pyroelectric and piezoelectric effects

Yoshihiko Kanemitsu and Hiroyuki Nabeta

Appl. Phys. Lett. 59, 715 (1991); http://dx.doi.org/10.1063/1.105374 (3 pages) | Cited 2 times

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We have studied the generation mechanism of photoacoustic (PA) signals in semiconductor thin films by means of a transparent LiNbO3 transducer both experimentally and theoretically. In the transparent transducer method, the PA signal was detected at the light‐irradiated surface of the samples. The PA signal of the thin film directly attached to the transducer is mainly due to the pyroelectric effect, and the PA signal of the underlain substrate is the piezoelectric signal caused by sample bending. These results show that this method becomes a powerful tool for measuring optical and thermal properties of thin films on the substrate nondestructively.
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43.38.Zp Acoustooptic and photoacoustic transducers
43.38.Fx Piezoelectric and ferroelectric transducers
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Remote plasma hydrogenation of ion beam amorphized silicon

S. Kar, J. I. Pankove, and Y. S. Tsuo

Appl. Phys. Lett. 59, 718 (1991); http://dx.doi.org/10.1063/1.105375 (3 pages) | Cited 4 times

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In this investigation, the efficacy of remote plasma hydrogenation, in the passivation of bonding and other electronic defects in amorphous silicon, has been compared with those of ion beam and radio‐frequency plasma hydrogenations. The amorphous silicon film was obtained by amorphization of the subsurface of ultrapure crystalline silicon by a Si ion beam. Electrical measurements indicated remote plasma hydrogenation to be a promising low‐ temperature defect removal technique, without the damaging effect of a plasma or the etching effects of low‐energy hydrogen ions.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Femtosecond refractive‐index spectral hole burning in intrinsic and doped GaAs

T. Gong, P. Mertz, W. L. Nighan, and P. M. Fauchet

Appl. Phys. Lett. 59, 721 (1991); http://dx.doi.org/10.1063/1.105376 (3 pages) | Cited 10 times

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The temporal and spectral dependence of carrier‐induced changes of the refractive index in intrinsic, n‐type and p‐type GaAs samples is measured using femtosecond pump and continuum‐probe techniques. We observe, for the first time, a refractive‐index spectral hole burning arising from a nonthermal carrier distribution generated around the initial excited states. Such spectral hole burning is not present within our time resolution in the n‐type sample when the injected carrier density is low. The extremely fast initial scattering time in the presence of cold electrons is attributed to relaxation through the emission of phonon‐plasmon coupled modes.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling
78.55.Cr III-V semiconductors
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Oxygen tracer diffusion through BaF2 and MgO overcoats on YBa2Cu3O7−Δ

S. B. Wong, J. J. Vajo, A. T. Hunter, and C. W. Nieh

Appl. Phys. Lett. 59, 724 (1991); http://dx.doi.org/10.1063/1.105377 (3 pages) | Cited 2 times

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The movement of oxygen through MgO and BaF2 overcoats on YBa2Cu3O7−Δ has been studied using 18O tracer diffusion techniques. By analyzing the 18O and 16O signals from secondary‐ion mass spectrometry depth profiles, the motion of small concentrations of oxygen in both insulating and oxygenated hosts has been tracked. BaF2 was found to be <m1;37p>transparent to oxygen diffusion while MgO blocked its motion during 10 min 500–600 °C anneals. Uncovered YBa2Cu3O7−Δ films were also found to exchange up to 90% of their oxygen during similar anneals. These results have important ramifications for reoxygenation steps during device fabrications.
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66.30.J- Diffusion of impurities
74.78.Fk Multilayers, superlattices, heterostructures
74.78.-w Superconducting films and low-dimensional structures
66.30.Ny Chemical interdiffusion; diffusion barriers

Focused ion beam fabrication of single grain Bi2Sr2Ca1Cu2Ox submicron bridges

I. D. Zitkovsky, Qing Hu, T. P. Orlando, J. Melngailis, and Tao Tao

Appl. Phys. Lett. 59, 727 (1991); http://dx.doi.org/10.1063/1.105353 (3 pages) | Cited 2 times

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Superconducting microbridges have been patterned by direct milling of the Bi2Sr2Ca1Cu2Ox polycrystalline thin films using focused ion beam. Several single grain and multigrain bridges of sizes as small as 0.3 μm have been fabricated. Single grain microbridges exhibit a linear temperature dependence of the critical current density with Jc=106 A/cm2 at 8 K, and zero magnetic field. Larger 50–100 μm bridges show lower critical current densities of Jc=104–105 A/cm2. The current‐voltage (I‐V) and the Jc vs T characteristics show two qualitatively different types of superconducting weak links. The single grain microbridges behave as homogeneous superconductors with transport exhibiting flux creep and flux flow. The large bridges can be characterized as granular superconductors with weakly connected grains, and their I‐V and the Jc vs T characteristics are dependent on processing conditions.
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74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices

Noncontacting alternating current surface probe measurements of transport critical currents in a slab geometry

K. L. Telschow and T. K. O’Brien

Appl. Phys. Lett. 59, 730 (1991); http://dx.doi.org/10.1063/1.105354 (3 pages) | Cited 4 times

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Determination of the critical state full penetration field of a slab of YBa2Cu3O7−x by induced screening currents is described. This geometry allows spatial measurements to be made by scanning with the probe coil even though nonuniform demagnetization effects are present. The onset of transport current dissipation was observed by the reduction of diamagnetism and appearance of dissipation in the probe coil induced current. The results are compared to contact four‐point probe direct current measurements and to the critical state model.
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74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Bi‐epitaxial grain boundary junctions in YBa2Cu3O7

K. Char, M. S. Colclough, S. M. Garrison, N. Newman, and G. Zaharchuk

Appl. Phys. Lett. 59, 733 (1991); http://dx.doi.org/10.1063/1.105355 (3 pages) | Cited 134 times

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We have developed a new way of making grain boundary junctions in YBa2Cu3O7 thin films by controlling the in‐plane epitaxy of the deposited film using seed and buffer layers. We produce 45° grain boundaries along photolithographically defined lines. The typical value of the critical current density of the junctions is 103–104 A/cm2 at 4.2 K and 102–103 A/cm2 at 77 K, while the rest of the film has a critical current density of 1–3×106 A/cm2 at 77 K. The current‐voltage characteristics of the junctions show resistively shunted junction behavior and we have used them to fabricate dc superconducting quantum interference devices (SQUIDs) which show modulation at temperatures well above 77 K. This is the first planar high Tc Josephson junction technology that appears readily extendable to high Tc integrated circuits.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Critical currents and processing of wound coils of Ag‐sheathed Bi‐2223 high Tc tape: Microstructural and pinning effects

L. R. Motowidlo, E. Gregory, P. Haldar, J. A. Rice, and R. D. Blaugher

Appl. Phys. Lett. 59, 736 (1991); http://dx.doi.org/10.1063/1.105328 (3 pages) | Cited 19 times

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Using a ‘‘powder‐in‐tube’’ process long lengths of high Tc prototype tape have been fabricated with high critical currents at liquid‐nitrogen temperature and excellent high field properties at liquid‐helium temperature. A Pb‐doped bismuth‐based 2223 powder was initially prepared then packed into silver tubes. Using a combination of cold work and heat treatment, a high degree of texture and good compaction with uniform properties was achieved. Current densities exceeding 10 000 A/cm2 at 77 K and 50 000 A/cm2 at 4.2 K in zero field were measured. At the 4.2 K temperature, the material still carried approximately 14 000 A/cm2 at 8 T. Tests on spirally wound and reacted coils, 52 cm long, have also demonstrated high current carrying capability. Effects of process variations and observed microstructure on superconducting properties are described.
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84.71.Ba Superconducting magnets; magnetic levitation devices
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Characterization of Y‐Ba‐Cu‐O thin films and yttria‐stabilized zirconia intermediate layers on metal alloys grown by pulsed laser deposition

R. P. Reade, X. L. Mao, and R. E. Russo

Appl. Phys. Lett. 59, 739 (1991); http://dx.doi.org/10.1063/1.105329 (3 pages) | Cited 26 times

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The use of an intermediate layer is necessary for the growth of YBaCuO thin films on polycrystalline metallic alloys for tape conductor applications. A pulsed laser deposition process to grow controlled‐orientation yttria‐stabilized zirconia (YSZ) films as intermediate layers on Haynes Alloy No. 230 was developed and characterized. YBaCuO films deposited on these YSZ‐coated substrates are primarily c‐axis oriented and superconducting as deposited. The best YBaCuO films grow on (001) oriented YSZ intermediate layers and have Tc (R=0) = 86.0 K and Jc ∼ 3×103 A/cm2 at 77 K.
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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
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.-b Superconducting materials other than cuprates

All a‐axis oriented YBa2Cu3O7−y‐PrBa2Cu3O7−z‐YBa2Cu3O7−y Josephson devices operating at 80 K

J. B. Barner, C. T. Rogers, A. Inam, R. Ramesh, and S. Bersey

Appl. Phys. Lett. 59, 742 (1991); http://dx.doi.org/10.1063/1.105330 (3 pages) | Cited 82 times

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We have demonstrated the controllable, reproducible fabrication of nonhysteretic Josephson devices with excess‐current weak‐link characteristics at temperatures up to 80 K. The devices are patterned from in situ deposited a‐axis oriented YBa2Cu3O7−y‐PrBa2Cu3O7−z‐YBa2Cu3O7−y trilayers grown on SrTiO3(001) substrates. Control of the critical current density and resistance is achieved by varying the thickness of the PrBa2Cu3O7−z barrier layer. Critical current densities in excess of 104 A/cm2 have been reproducibly measured; good uniformity across the wafer is obtained with device parameters scaling with device area. Strong constant‐voltage current steps are observed under 11.2 GHz microwave radiation at temperatures up to and above 80 K.
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85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures
74.78.Fk Multilayers, superlattices, heterostructures
74.70.-b Superconducting materials other than cuprates

Oxidation studies of fluorine containing diamond films

K. J. Grannen, D. V. Tsu, R. J. Meilunas, and R. P. H. Chang

Appl. Phys. Lett. 59, 745 (1991); http://dx.doi.org/10.1063/1.105331 (3 pages) | Cited 1 time

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The thermogravimetric method is used to study the oxidation properties of plasma grown diamond films both with and without fluorine. The oxidation experiments occur over a temperature range of 600–800 °C in pure oxygen at atmospheric pressure. Diamond films with fluorine are found more resistant (by a factor of 4 at 700 °C) to oxidation. The activation energy for oxidation, however, is a factor of at least 2.3 lower for fluorinated diamond films. Consequently, it is postulated that oxidation mechanisms for diamond films are quite different depending upon the fluorine content. Oxidation on nonfluorinated diamond films seem to proceed as a rate‐limited reaction while the oxidation of fluorinated films seems to be a diffusion limited reaction. Oxidation rates are also found to depend weakly on film density, crystal texture, and phase composition of the diamond films.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
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