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3 Jan 1994

Volume 64, Issue 1, pp. 1-128

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Intrinsic current bistability in InAs/AlxGa1−xSb resonant tunneling devices

D. H. Chow and J. N. Schulman

Appl. Phys. Lett. 64, 76 (1994); http://dx.doi.org/10.1063/1.110873 (3 pages) | Cited 16 times

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We report the design and demonstration of a novel resonant tunneling device displaying bistability in operating current over a range of applied voltage. The device is based on a type II InAs/AlxGa1−xSb (0.4<x<0.6) double barrier heterostructure. This structure permits the simultaneous accumulation of electrons and holes in the quantum well/barrier region, resulting in a dependence of the steady‐state charge distribution on the bias history of the device. This dependence is experimentally manifested as an ‘‘S’’‐shaped negative differential resistance region under current‐controlled measurement conditions or as hysteretic I‐V behavior under voltage‐controlled conditions. Room temperature operating currents in excess of 2.5×105 A/cm2 are observed, along with peak‐to‐valley voltage ratios up to 1.5.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Thermal currents in proton isolated gallium arsenide structures at elevated temperatures

L. P. Sadwick

Appl. Phys. Lett. 64, 79 (1994); http://dx.doi.org/10.1063/1.110874 (3 pages) | Cited 1 time

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Using a new and simple technique, thermal currents between proton isolated devices fabricated on semi‐insulating gallium arsenide (GaAs) substrates have been observed for the first time at temperatures from 25 °C up to 300 °C. The thermal currents show definite Ohmic behavior with respect to the applied voltage at a fixed temperature. An Arrenhius plot of the thermal current at a fixed bias voltage level for a given test structure yields a straight line with an activation energy that can be ascribed to known deep levels in GaAs. The implications that this thermal leakage current have on the functionality of GaAs metal‐semiconductor field‐effect transistors at high temperatures are also addressed in this work.
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73.61.Ey III-V semiconductors
61.80.Jh Ion radiation effects
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Resonance effects in Raman scattering from InAs/AlSb quantum wells

J. Wagner, J. Schmitz, J. D. Ralston, and P. Koidl

Appl. Phys. Lett. 64, 82 (1994); http://dx.doi.org/10.1063/1.110876 (3 pages) | Cited 11 times

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Resonant Raman scattering has been used to study GaSb‐capped AlSb/InAs/AlSb quantum wells, grown by molecular‐beam epitaxy with a shutter sequence intended to promote the formation of an InSb‐like InAs/AlSb heterointerface. For optical excitation in resonance with the E1 band gap of InAs, scattering by one‐longitudinal‐optical (LO) phonon and by two‐LO phonons from the quantum well layer is strongly enhanced. Excitation close to the E1/E1+Δ1 gap resonance of GaSb, in contrast, enhances the one‐LO scattering from the GaSb cap over that from the InAs quantum well. Thus resonance effects in LO phonon Raman scattering allow us to distinguish between scattering from these two materials despite the near‐coincidence of the corresponding LO phonon frequencies. Scattering by an InSb‐like mode is found to resonate at approximately the InAs E1/E1+Δ1 gap energy, supporting its assignment to an interface mode.
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68.55.-a Thin film structure and morphology
78.30.Fs III-V and II-VI semiconductors
63.20.Pw Localized modes
78.66.Fd III-V semiconductors

Time‐resolved spectroscopy of visibly emitting porous silicon

S. V. Gaponenko, I. N. Germanenko, E. P. Petrov, A. P. Stupak, V. P. Bondarenko, and A. M. Dorofeev

Appl. Phys. Lett. 64, 85 (1994); http://dx.doi.org/10.1063/1.112004 (3 pages) | Cited 13 times

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Time‐resolved emission spectra and photoluminescence decay kinetics are analyzed in porous Si samples exhibiting a noticeable inhomogeneous broadening under steady‐state selective excitation. The gated emission spectra are found to be substantially narrower compared to a steady‐state one, with a pronounced redshift with time. Considerable dependence of the decay parameters upon the emission wavelength is found. The decay time distribution analysis applied leads to a model where the nonradiative decay mechanism is attributed to traps of the same type, the number of traps per Si grain obeying the Poissonian statistics.  
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78.55.Hx Other solid inorganic materials
78.47.-p Spectroscopy of solid state dynamics

Determination of band gap narrowing and hole density for heavily C‐doped GaAs by photoluminescence spectroscopy

Z. H. Lu, M. C. Hanna, and A. Majerfeld

Appl. Phys. Lett. 64, 88 (1994); http://dx.doi.org/10.1063/1.110877 (3 pages) | Cited 22 times

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The energy band gap narrowing effect in heavily C‐doped GaAs was investigated using photoluminescence spectroscopy. The band gap was determined over the hole density range 1017–4×1020 cm−3 at 10 and 300 K. The band gap data at low temperatures confirm the available theoretical calculations up to 1020 cm−3. An unexpected temperature dependence of the observed band gap at high doping levels is discussed on the basis of carrier‐phonon interactions. We present an analysis of the band gap narrowing effect that can be used for nondestructive measurement of hole densities in the range 1017–4×1020 cm−3.
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71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors

Photoluminescence properties of nitrogen‐doped ZnSe grown by molecular‐beam epitaxy

Ziqiang Zhu, Kazuhisa Takebayashi, Kiyotake Tanaka, Takashi Ebisutani, Junji Kawamata, and Takafumi Yao

Appl. Phys. Lett. 64, 91 (1994); http://dx.doi.org/10.1063/1.110878 (3 pages) | Cited 42 times

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This letter reports the photoluminescence (PL) properties of N‐doped ZnSe epilayers grown by molecular‐beam epitaxy using a microwave plasma source for N doping. The temperature dependence of PL spectra from N‐doped ZnSe epilayers with different net acceptor concentrations is described in detail. The emission due to transition from deep donors to free holes (DdF) is observed from highly N‐doped ZnSe epilayers at high temperatures, which gives a direct evidence for the formation of a deep N‐associated donor. The ionization energy for a deep N‐associated donor is estimated as 55±5 meV from comparison of the temperature dependence of the DdF emission energy with that of the free exciton energy.
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68.55.-a Thin film structure and morphology
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors

Residues, polycrystalline silicon voids, and active area damage with the polycrystalline silicon buffered local oxidation of silicon isolation process

Viju K. Mathews, Pierre C. Fazan, and Roy L. Maddox

Appl. Phys. Lett. 64, 94 (1994); http://dx.doi.org/10.1063/1.110879 (3 pages) | Cited 1 time

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The effectiveness of various post‐field oxidation mask deprocessing sequences has been investigated for the polycrystalline silicon (polysilicon) buffered local oxidation of silicon isolation process. The generation of residues is a minor issue when the gate oxide formation is preceded by the growth and removal of a sacrificial oxide. For sub‐0.5 μm ultralarge scale integration technologies, the development of stress induced voids in the buffer polysilicon film is a more severe problem. Stress concentrations that damage both the polysilicon and pad oxide films at the same location result in pitting of the active areas.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
61.72.Cc Kinetics of defect formation and annealing

Gettering and hydrogen passivation of edge‐defined film‐fed grown multicrystalline silicon solar cells by Al diffusion and forming gas anneal

Peyman Sana, Ajeet Rohatgi, Juris P. Kalejs, and Richard O. Bell

Appl. Phys. Lett. 64, 97 (1994); http://dx.doi.org/10.1063/1.110880 (3 pages) | Cited 32 times

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This study shows for the first time that a combination of Al treatment on the back, oxide passivation on the front, and 400 °C forming gas anneal in the presence of Al, raised the double‐layer antireflection‐coated edge‐defined film‐fed grown (EFG) silicon cell efficiency from 7.8% to 14.1%. Front oxide passivation contributed an ∼0.8% increase in absolute cell efficiency, Al diffusion on the back increased the efficiency by 1.4% (absolute), and the forming gas anneal (FGA) after the Al diffusion improved the cell efficiency by an additional 4.1% (absolute). A combination of the above three steps improved the EFG cell efficiency by 6.3%, indicating that the above three effects are complimentary. Oxide passivation reduced front surface recombination velocity and Al diffusion, while FGA improved diffusion length via gettering. We propose that the large increase in cell efficiency produced by the forming gas anneal results from bulk defect passivation by atomic hydrogen generated in the processing.
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84.60.Jt Photoelectric conversion
61.72.Yx Interaction between different crystal defects; gettering effect
71.55.Cn Elemental semiconductors

Eddy current microscopy using a 77‐K superconducting sensor

R. C. Black, F. C. Wellstood, E. Dantsker, A. H. Miklich, J. J. Kingston, D. T. Nemeth, and J. Clarke

Appl. Phys. Lett. 64, 100 (1994); http://dx.doi.org/10.1063/1.110906 (3 pages) | Cited 21 times

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We have used a scanning magnetic flux microscope based on a high transition temperature YBa2Cu3O7 superconducting quantum interference device (SQUID) to produce magnetic images of eddy currents in patterned Cu thin films and 11–30‐μm‐thick Cu on printed circuit boards. The fields produced by the eddy currents are imaged with a spatial resolution of about 80 μm over a 100‐mm2 sample area. With the sample and SQUID at 77 K, the microscope uses typical probing fields of 80 nT and can obtain simultaneously eddy current and static magnetic field images. At probing frequencies of 26–100 kHz, the system achieves a field sensitivity of about 7 pT Hz−1/2.
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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
81.70.-q Methods of materials testing and analysis
07.55.-w Magnetic instruments and components

Platinum‐enhanced densification of grain‐aligned YBa2Cu3O7−x films

J. A. Lewis, M. Wegmann, C. E. Platt, and M. Teepe

Appl. Phys. Lett. 64, 103 (1994); http://dx.doi.org/10.1063/1.110907 (3 pages) | Cited 7 times

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Grain‐aligned YBa2Cu3O7−x films were fabricated by vacuum filtration in an applied magnetic field (7 T). Platinum (Pt) was shown to lower the peritectic temperature of YBa2Cu3O7−x by almost 75 °C, leading to dramatic microstructural differences between films densified on MgO (single crystal) substrates and those densified on Pt foil to a maximum temperature of 1020 °C in oxygen. Superconducting quantum‐interference device hysteresis loops measured at 0–5.5 T at 5 K showed that films fired on Pt had ΔM (Happ∥c axis) values 15–60 times larger than those fired on MgO.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Local texture and percolative paths for long‐range conduction in high critical current density TlBa2Ca2Cu3O8+x deposits

D. M. Kroeger, A. Goyal, E. D. Specht, Z. L. Wang, J. E. Tkaczyk, J. A. Sutliff, and J. A. DeLuca

Appl. Phys. Lett. 64, 106 (1994); http://dx.doi.org/10.1063/1.110908 (3 pages) | Cited 20 times

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A possible microstructural origin of the high critical current densities which have been obtained in c‐axis‐aligned, polycrystalline TlBa2Ca2Cu3O8+x deposits has been identified. The results of x‐ray diffraction determinations of basal plane texture of Tl‐1223 deposits prepared by spray pyrolysis are observed to depend on the size of the x‐ray beam. Furthermore, most grain boundaries were found from transmission electron microscopy to have small misorientation angles. It is concluded that although overall the basal plane orientations are nearly random, there is a high degree of local texture indicative of colonies of similarly oriented grains. The spread in a‐axis orientation within a colony is ∼10°–15°. Intercolony conduction, it is suggested, may be enhanced by a percolative network of small‐angle grain boundaries at colony interfaces.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.78.-w Superconducting films and low-dimensional structures

Measurement of current voltage characteristics of single grain boundaries in melt textured bulk YBa2Cu3Ox

C. Sarma, G. Schindler, D. G. Haase, C. C. Koch, A. M. Saleh, and A. I. Kingon

Appl. Phys. Lett. 64, 109 (1994); http://dx.doi.org/10.1063/1.110909 (3 pages) | Cited 10 times

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We have investigated the electrical properties of small parts of single grain boundaries in melt textured YBa2Cu3Ox. Similar measurements on grain boundary networks were also made to obtain composite properties. The results of Tc measurements and current‐voltage characteristics in zero and small magnetic fields are presented. The R(T) characteristics suggest that there is second phase segregation in some parts of the grain boundary area. The current‐voltage characteristics showed three different types of behavior: Resistive, Josephson‐like, and flux flow. The Ic(B) data of Josephson junctions suggest that nonsuperconducting inclusions divide the grain boundaries into smaller single junctions.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Influence of Ag‐Au and Ag‐Cu alloys on Bi2Sr2CaCu2Ox superconductor

K. Nomura, T. Sasaoka, J. Sato, S. Kuma, H. Kumakura, K. Togano, and N. Tomita

Appl. Phys. Lett. 64, 112 (1994); http://dx.doi.org/10.1063/1.110895 (3 pages) | Cited 11 times

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The influence of Ag‐Au and Ag‐Cu alloy substrates on the microstructure and superconducting properties of Bi2Sr2CaCu2Ox (Bi‐2212) was studied. The critical current density (Jc) of Bi‐2212/(Ag‐Au) was not degraded by increasing the Au content of the Ag‐Au alloy, while the Jc of Bi‐2212/(Ag‐Cu) was drastically degraded by increasing the Cu content of the Ag‐Cu alloy. The microstructure of Bi‐2212 on the Ag‐Au alloy was uniform and no precipitates were observed. The Jc degradation of Bi‐2212 in contact with the Ag‐Cu alloy was understood by the fact that Cu absorption of Bi‐2212 from the Ag‐Cu alloys changed the composition of the oxide layer. Ag‐Au alloys are superior substrate materials for Bi‐2212 for power current leads for superconducting magnets, taking into account their low thermal conductivity.
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84.71.Mn Superconducting wires, fibers, and tapes
74.72.-h Cuprate superconductors
74.78.Fk Multilayers, superlattices, heterostructures

Enhanced Jc properties in superconducting NbTi composites by introducing Nb artificial pins with a layered structure

Kaname Matsumoto, Hirokazu Takewaki, Yasuzo Tanaka, Osuke Miura, Kaoru Yamafuji, Kazuo Funaki, Masataka Iwakuma, and Teruo Matsushita

Appl. Phys. Lett. 64, 115 (1994); http://dx.doi.org/10.1063/1.110896 (3 pages) | Cited 20 times

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High critical current densities (4250 A/mm2 at 5 T, 4.2 K, and 15 000 A/mm2 at 2 T, 4.2 K) were achieved by using an artificially designed pin structure composed of randomly oriented clusters of Nb/NbTi multilayer in a NbTi composite superconductor (with a round cross section). The maximum values were obtained when the Nb layer thickness was designed to be approximately twice the coherence length in NbTi, where the layer thickness is five to ten times thicker than that of the optimized α‐Ti ribbon thickness in a conventional NbTi system.
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74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
84.71.Mn Superconducting wires, fibers, and tapes

Lateral resonant tunneling through constrictions in a δ ‐doped GaAs layer

R. J. Blaikie, K. Nakazato, R. B. S. Oakeshott, J. R. A. Cleaver, and H. Ahmed

Appl. Phys. Lett. 64, 118 (1994); http://dx.doi.org/10.1063/1.110897 (3 pages) | Cited 3 times

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We have fabricated constrictions in δ‐doped GaAs using implanted gates to provide the lateral confinement. Large conductance oscillations are observed when the gate voltage is varied. The drain‐source current‐voltage characteristics are highly nonlinear; as many as 30 peaks are present, and peak‐to‐valley ratios greater than 100 have been measured. These results are explained in terms of resonant tunneling through the random potential distribution in the point contact. Using a simple model for the potential distribution we are able to simulate qualitatively the structure in the conductance.
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73.40.Gk Tunneling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
68.55.-a Thin film structure and morphology

Influence of steps on quantum well states in Cu/Co(100) multilayers

J. E. Ortega and F. J. Himpsel

Appl. Phys. Lett. 64, 121 (1994); http://dx.doi.org/10.1063/1.110898 (3 pages) | Cited 10 times

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Interface roughness is known to have a large effect on oscillatory magnetic coupling and giant magnetoresistance in magnetic multilayers, but the origin of this effect is still uncertain. In order to obtain a quantitative measure we have used vicinal Cu/Co(100) interfaces with well‐defined step spacing and have determined the amplitude of quantum oscillations in the density of states that are correlated with oscillatory magnetic coupling. For a step spacing of 10 Å the oscillation amplitude decreases by a factor of 1.8. This distance corresponds to the lateral extent of the quantized states in the film.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.15.Gd Galvanomagnetic and other magnetotransport effects

Scanning shearing‐stress microscope

A. Sasaki, A. Katsumata, F. Iwata, and H. Aoyama

Appl. Phys. Lett. 64, 124 (1994); http://dx.doi.org/10.1063/1.110899 (2 pages) | Cited 4 times

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A new scanning probe microscope based on a scanning tunneling microscope (STM) and a frequency shift of an AT cut quartz resonator has been developed. The quartz resonator coupled to a STM sample is oscillated at its resonance frequency. The shift of the resonance frequency corresponds to the strength of the shearing stress in the sample, and is caused by the shearing force interaction between the STM tip and the sample under the tip scanning. The preliminary images presented show simultaneously STM surface topographies and the changes of subsurface shearing stresses in gold thin films. The sensitivity of our microscope is 0.30 N/m for a 0.2‐Hz frequency shift of the quartz crystal resonance frequency.
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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

Single‐electron Coulomb exclusion on the atomic level

D. V. Averin, L. F. Register, K. K. Likharev, and K. Hess

Appl. Phys. Lett. 64, 126 (1994); http://dx.doi.org/10.1063/1.110900 (3 pages) | Cited 2 times

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The possibility of processing digital information coded by single electrons on the atomic scale is discussed by analyzing the dynamics of one and two electrons within a simple model structure. Specifically, the probability of passage of an electron within a chain of atomic sites through a potential well, either empty or already occupied by another electron, is investigated both analytically and numerically. It is demonstrated that quantum effects can significantly decrease the reliability of the control that one electron has over the propagation of another. For the structure considered, a few tens of atomic sites and a specific choice of the potential well depth are necessary for reliable control.
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72.10.-d Theory of electronic transport; scattering mechanisms
85.30.De Semiconductor-device characterization, design, and modeling
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