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16 Jul 1990

Volume 57, Issue 3, pp. 209-318

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Electronic energy bands and optical nonlinearity of checker‐board superlattices

L. R. Ram‐Mohan and J. Shertzer

Appl. Phys. Lett. 57, 282 (1990); http://dx.doi.org/10.1063/1.103715 (3 pages) | Cited 4 times

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We investigate the structure of the conduction minibands in a two‐dimensional periodic array of rectangular quantum wires. The finite barrier height in such a GaAs/Ga1−xAlxAs heterostructure gives rise to a ‘‘checker‐board’’ pattern of wells and barriers, i.e., a checker‐board superlattice (CBSL). The energy bands are obtained using the finite element method, in the effective mass approximation, with current continuity at interfaces. The free‐carrier‐induced optical nonlinear susceptibility χ(3) due to band nonparabolicity in the CBSL is obtained in both the rectangular directions. Our calculations predict an increase in χ(3) of about 1–2 orders of magnitude over bulk GaAs, for specific ranges of carrier concentrations.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Bh Theory, models, and numerical simulation
63.10.+a General theory

Analysis of quantum‐confined structures using the beam propagation method

Inho Kim, T. K. Gustafson, and Lars Thylén

Appl. Phys. Lett. 57, 285 (1990); http://dx.doi.org/10.1063/1.104106 (3 pages) | Cited 10 times

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The beam propagation method has been applied to find confined energy eigenvalues and eigenfunctions for a III‐V quantum well structure subjected to an external electric field. Quantum‐confined Stark shifts for both electrons and holes and excitonic states for single and double quantum wells are calculated. Excellent agreement with analytical results where available is demonstrated. A comparison with experimental data published in the literature is given.
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63.10.+a General theory
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
78.20.Bh Theory, models, and numerical simulation

Effect of patterning on defect structure in GaAs grown on Si

H. L. Tsai and Y. C. Kao

Appl. Phys. Lett. 57, 288 (1990); http://dx.doi.org/10.1063/1.103716 (3 pages) | Cited 2 times

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In this letter, we address the effectiveness of patterned growth in reducing defect density in GaAs on Si. Defect reduction is considered to be subject to the effect of edge profile and the density of defects in initial GaAs islands. Pattern edges (mask edges or large steps) are often the sites for generating microtwins/stacking faults. Mutual interaction of dislocations inhibits the gliding of dislocations to pattern edges, thus affecting the effectiveness of patterned growth in improving the epilayer quality. The study also shows that surface orientation influences the formation of misfit dislocations with a preferred Burgers vector. This observation is interpreted by considering the variation of misfit with different lattice planes across the interface between Si and ‘‘tilted’’ GaAs lattices.
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61.72.Bb Theories and models of crystal defects
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Two‐dimensional electron gas magnetic field sensors

J. Heremans, D. L. Partin, D. T. Morelli, B. K. Fuller, and C. M. Thrush

Appl. Phys. Lett. 57, 291 (1990); http://dx.doi.org/10.1063/1.103717 (3 pages) | Cited 10 times

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We describe the use of accumulation layers of electron charge in applications as magnetoresistive devices. We consider two such systems: an InGaAs/InP heterostructure in which we identify a two‐dimensional electron gas from the observation of the quantum Hall effect, and InAs films, in which a strong surface accumulation of charge is inferred from depth profiling studies of the galvanomagnetic coefficients. Magnetoresistive devices fabricated from these materials exhibit outstanding field sensitivity and temperature stability due to the existence of electrons of relatively high density and mobility in the accumulation regions. We also model the magnetosensitivity of our devices.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
07.55.-w Magnetic instruments and components
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Incorporation of carbon in heavily doped AlxGa1−xAs grown by metalorganic molecular beam epitaxy

C. R. Abernathy, S. J. Pearton, M. O. Manasreh, D. W. Fischer, and D. N. Talwar

Appl. Phys. Lett. 57, 294 (1990); http://dx.doi.org/10.1063/1.103718 (3 pages) | Cited 37 times

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Hole concentrations in excess of 1020 cm−3 have been achieved in AlxGa1−xAs using carbon doping during metalorganic molecular beam epitaxy. Hall and secondary‐ion mass spectrometry measurements show a 1:1 correspondence between the hole density and carbon concentration in as‐grown samples, although post‐growth annealing at 900 °C leads to a reduction in the net free‐carrier concentration (typically a decrease of ∼40% for 30 s anneals). The carbon‐localized vibrational modes (LVMs) show fine structure due to the presence of three different symmetries for substitutional carbon CAs, namely Td, C2v, and C3v. The experimental CAs LVM line positions are in remarkable agreement with the predictions of a rigid ion model.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.80.Ey III-V and II-VI semiconductors
61.72.U- Doping and impurity implantation

Magnetization of (100) Cu‐Ni, (100) Cu‐Co, and (100) Ni‐Co superlattices deposited on silicon using a Cu seed layer

Chin‐An Chang

Appl. Phys. Lett. 57, 297 (1990); http://dx.doi.org/10.1063/1.103719 (3 pages) | Cited 27 times

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The magnetization of (100)Cu‐Ni, (100)Cu‐Co, and (100)Ni‐Co superlattices has been studied. The structures were grown on the (100)Cu/Si substrates, with the (100)Cu epitaxially grown on the (100)Si as the seed. The (100)oriented superlattices show different magnetization curves from the (111) structures and from bulk (100)Ni and Co films. A much enhanced magnetization is observed for the (100)Cu‐Ni superlattice with the field perpendicular to the film plane. The remanence is larger than that for the field parallel to the film plane. Negative remanence and coercivity are observed for the (100)Cu‐Co and Ni‐Co structures. The magnetization curve for the (100)Ni‐Co superlattice is further shown to resemble a superposition of the Cu‐Ni and Cu‐Co ones. Upon heating the Ni‐Co structure to 400 °C to consume more Ni than Co, a magnetization curve similar to that of the Cu‐Co one is observed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

New hydrogenated amorphous silicon alloys

G. H. Lin, M. Kapur, and J. O’M. Bockris

Appl. Phys. Lett. 57, 300 (1990); http://dx.doi.org/10.1063/1.103720 (2 pages) | Cited 5 times

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New alloys of hydogenated amorphous silicon with Al, Ga, S, and Se have been prepared by the rf glow discharge method. The energy gap of these materials can be varied in the 1–2 eV range, with the Al and Ga alloys being low band‐gap semiconductors, and the S and Se alloys having higher energy gaps. The light to dark conductivity ratios of the various systems have been measured. The best photoresponse (102–103) was obtained with the Se and S alloys.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.-w Optical properties of specific thin films
72.40.+w Photoconduction and photovoltaic effects
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors

Internal stress and elasticity of synthetic diamond films

B. S. Berry, W. C. Pritchet, J. J. Cuomo, C. R. Guarnieri, and S. J. Whitehair

Appl. Phys. Lett. 57, 302 (1990); http://dx.doi.org/10.1063/1.103721 (2 pages) | Cited 41 times

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The internal tensile stress in polycrystalline diamond films deposited on silicon substrates has been measured from 100 to 700 K by a vibrating‐membrane method. The stress increases strongly with temperature, in a manner consistent with the elastic accommodation of the differential thermal strain between diamond and silicon. The results indicate that the films contain a tensile growth stress of about 500 MPa at the deposition temperature of 1123 K. Derived values of the biaxial elastic modulus fall in the range 730–850 GPa.
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62.20.D- Elasticity
65.40.De Thermal expansion; thermomechanical effects
81.40.Jj Elasticity and anelasticity, stress-strain relations

Sputter deposition of YBa2Cu3O7−x films on Si at 500 °C with conducting metallic oxide as a buffer layer

Q. X. Jia and W. A. Anderson

Appl. Phys. Lett. 57, 304 (1990); http://dx.doi.org/10.1063/1.104218 (3 pages) | Cited 32 times

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Superconducting YBa2Cu3O7−x thin films were deposited on Si substrates at 500 °C by rf magnetron sputtering from a stoichiometric oxide target. Metallic oxide RuO2, sputtered by reactive dc magnetron, was used as a buffer layer to nucleate the superconducting film and minimize the reactions between Si and superconductor. The as‐deposited thin films, without further post high‐temperature annealing, were completely superconductive at 79 K. Very smooth surface morphology was demonstrated by scanning electron microscopy. X‐ray diffraction data indicated that the films had a randomly oriented polycrystalline structure. Auger electron spectroscopy did not reveal interdiffusion of elements in the three layers.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.78.Fk Multilayers, superlattices, heterostructures
81.15.Cd Deposition by sputtering

Electronic structure of the gold/Bi2Sr2CaCu2O8 and gold/EuBa2Cu3O7−δ interfaces as studied by photoemission spectroscopy

D. S. Dessau, Z.‐X. Shen, B. O. Wells, W. E. Spicer, R. S. List, A. J. Arko, R. J. Bartlett, Z. Fisk, S‐W. Cheong, D. B. Mitzi, A. Kapitulnik, and J. E. Schirber

Appl. Phys. Lett. 57, 307 (1990); http://dx.doi.org/10.1063/1.104219 (3 pages) | Cited 12 times

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High‐resolution photoemission has been used to probe the electronic structure of the gold/Bi2Sr2CaCu2O8 and gold/EuBa2Cu3O7−δ interface formed by a low‐temperature (20 K) gold evaporation on cleaved high quality single crystals. We find that the metallicity of the EuBa2Cu3O7−δ substrate in the near surface region (∼5 Å) is essentially destroyed by the gold deposition, while the near surface region of Bi2Sr2CaCu2O8 remains metallic. This has potentially wide ranging consequences for the applicability of the different types of superconductors in real devices.
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73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
79.60.-i Photoemission and photoelectron spectra
74.50.+r Tunneling phenomena; Josephson effects

High‐resolution, tunneling‐stabilized magnetic imaging and recording

John Moreland and Paul Rice

Appl. Phys. Lett. 57, 310 (1990); http://dx.doi.org/10.1063/1.103676 (3 pages) | Cited 13 times

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We have used a scanning tunneling microscope (STM) to record and image magnetic regions on the surface of a hard disk. The usual rigid STM tip was replaced by a compliant magnetized Fe film tip. As a result, tunneling images were combinations of the surface topography and variations in the magnetic force between the Fe film tip and the disk surface. We believe that the recording process relied on maintaining the proximity of the magnetized Fe film tip near the disk surface. Apparently, the magnetic field was focused near the Fe film tip with sufficient intensity to change the surface magnetization of the disk. We have recorded spots on the disk within a 500 nm×500 nm area. These spots were subsequently imaged with the same STM tip. Our best magnetic image resolution was 20 nm. The compliance of the Fe film tips was such that image contrast due to variation of the magnetic force on the tip corresponded to z motions of the piezoelectric translator as large as 50 nm.
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07.55.-w Magnetic instruments and components
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
85.70.-w Magnetic devices

Millimeter‐wave harmonic mixing with high Tc superconducting materials at room temperature

Tomizo Kurosawa, Atsushi Onae, Etsuo Kawate, Yukinobu Miki, and Eiichi Sakuma

Appl. Phys. Lett. 57, 313 (1990); http://dx.doi.org/10.1063/1.104239 (3 pages)

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Harmonic generation and mixing in the 8∼80 GHz region has been studied in point‐contact junctions made with sharply tipped tungsten whisker and sintered polycrystalline YBa2Cu3O7−y or single‐crystal Bi2Sr2CaCu2Ox at room temperature. The signal‐to‐noise ratio (SNR) of beat notes as a function of harmonic number n is observed up to the tenth order and decreases with a slope of n−5.6 for even harmonic numbers. The dependence of the SNR of the beat note on a dc bias voltage and the current‐voltage characteristics have been measured simultaneously and theoretically analyzed using the current‐dependent mixing characteristics. The potential barrier and the insulating thickness for YBa2Cu3O7−y are estimated.
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73.40.Jn Metal-to-metal contacts
74.20.Mn Nonconventional mechanisms
74.20.Rp Pairing symmetries (other than s-wave)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Improved atomic force microscope images using microcantilevers with sharp tips

S. Akamine, R. C. Barrett, and C. F. Quate

Appl. Phys. Lett. 57, 316 (1990); http://dx.doi.org/10.1063/1.103677 (3 pages) | Cited 71 times

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Novel force‐sensing microcantilevers with sharp tips have been used to obtain atomic force microscope images of atomically flat, layered compounds as well as microfabricated samples with large‐scale topographies. When imaging atomically flat samples using cantilevers with sharp protruding tips, atomic corrugations are observed more consistently and with a higher signal‐to‐noise ratio than in the absence of tips. Some asymmetric distortions arise when tipped cantilevers are used with forces larger than 10−7 N. Side by side comparisons of images of rough samples obtained using cantilevers with and without tips reveal that the presence of a sharp tip yields superior image quality of vertical features and trenches. The cantilever assembly is a microfabricated, silicon nitride cantilever with an integral, single‐crystal silicon tip. The silicon tip is self‐aligned to the end of the cantilever and is created by a process which simultaneously fabricates and sharpens the silicon tip. Initial transmission electron microscopy studies show that the single‐crystal silicon tips have radii of curvature of 220–400 Å.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
06.60.Sx Positioning and alignment; manipulating, remote handling
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