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3 Sep 1990

Volume 57, Issue 10, pp. 951-1069

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Subband mobility of quasi‐two‐dimensional electrons in Si atomic layer doped GaAs

Syoji Yamada and Toshiki Makimoto

Appl. Phys. Lett. 57, 1022 (1990); http://dx.doi.org/10.1063/1.103553 (3 pages) | Cited 30 times

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Subband mobility and conductivity of quasi‐two‐dimensional electrons in Si atomic layer doped GaAs are estimated for the first time. The oscillations for different subbands in low‐temperature magnetoresistance are separated from each other by using the reverse Fourier transform technique. The mobility for each subband is then determined by fitting the field dependence of the amplitudes with conventional theory. A large subband mobility difference up to 20:1 is found. This is mainly due to strong screening. Furthermore, a partial conductivity for each subband is calculated and the importance of the shallower subbands in total current transport is clarified.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
73.50.Bk General theory, scattering mechanisms

Inequivalent impurity and trap incorporation at normal and inverted interfaces of AlGaAs/GaAs quantum wells grown by molecular beam epitaxy

R. Köhrbrück, S. Munnix, D. Bimberg, D. E. Mars, and J. N. Miller

Appl. Phys. Lett. 57, 1025 (1990); http://dx.doi.org/10.1063/1.103554 (3 pages) | Cited 9 times

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The influence of growth interruption time on the incorporation of shallow impurities and traps in molecular beam epitaxy grown GaAs/AlGaAs quantum wells is studied by means of steady‐state and time‐resolved photoluminescence. With increasing interruption time, the GaAs surface becomes appreciably smoother, and increasing incorporation of shallow impurities, but not incorporation of traps is observed. At the AlGaAs surface the concentration of traps strongly increases with growth interruption time, but the surface does not become smoother. Additionally, strong accumulation of shallow impurities at the AlGaAs surface (inverted interface) is directly visualized.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Dv Composition, segregation; defects and impurities

Real‐time detection of higher hydrides on the growing surface of hydrogenated amorphous silicon by infrared reflection absorption spectroscopy

Yasutake Toyoshima, Kazuo Arai, Akihisa Matsuda, and Kazunobu Tanaka

Appl. Phys. Lett. 57, 1028 (1990); http://dx.doi.org/10.1063/1.103555 (3 pages) | Cited 34 times

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Real‐time in situ observations of the growth of a‐Si:H films have been carried out in a rf glow discharge plasma reactor by use of infrared reflection absorption spectroscopy. Deuterium substitution of an interface layer is employed so as to differentiate the higher hydride species on the growing surface from those located at the film interface on the substrate. A three‐layer model is presented to give a quantitative discussion on the absorption signal intensity in the reflection spectroscopy with respect to the normal incident transmission spectroscopy.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.30.Hv Other nonmetallic inorganics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Prediction of direct band gaps in monolayer (001) and (111) GaAs/GaP superlattices

Robert G. Dandrea and Alex Zunger

Appl. Phys. Lett. 57, 1031 (1990); http://dx.doi.org/10.1063/1.103556 (3 pages) | Cited 16 times

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The bulk GaAs0.5P0.5 alloy with lattice constant a(0.5) has an indirect band gap. First‐principles self‐consistent pseudopotential band structure calculations show that the monolayer (GaAs)1 (GaP)1 superlattice (SL) in either the (001) or the (111) layer orientation G is also indirect if constrained epitaxially on a substrate whose lattice constant is a(0.5). However, if grown coherently on a GaAs substrate we predict that both of these SLs will have a direct band gap. This is explained in terms of the deformation potentials of the underlying materials. Predicted band offsets are given for both (001) and (111) GaP/GaAs.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds

Bistable conditions for low‐temperature silicon epitaxy

Bernard S. Meyerson, Franz J. Himpsel, and Kevin J. Uram

Appl. Phys. Lett. 57, 1034 (1990); http://dx.doi.org/10.1063/1.103557 (3 pages) | Cited 112 times

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We report on the role of hydrogen surface passivation in achieving low‐temperature silicon epitaxy by chemical vapor deposition processes. Upon insertion of an HF‐etched silicon wafer into an epitaxial silicon deposition apparatus, residual contamination of the Si surface is negligible. Si 2p core level photoemission spectra demonstrate that the silicon surface is stable in air and free of SiO2 for a time period of minutes. The predominant passivating species is found to be silicon hydride. We demonstrate that hydrogen passivation by HF pretreatment leads to two divergent temperature ranges where epitaxy is successful, those being a low‐temperature range, 425≲T≲650 °C, and a high‐temperature regime, T≳750 °C. Additionally, we employ temperature‐programmed desorption techniques to elucidate the role of hydrogen in the transition to a steady‐state growth process, employing ultrahigh vacuum/chemical vapor deposition as the model system.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.Dv Composition, segregation; defects and impurities
85.40.Ls Metallization, contacts, interconnects; device isolation

Intense photoluminescence between 1.3 and 1.8 μm from strained Si1−xGex alloys

J.‐P. Noël, N. L. Rowell, D. C. Houghton, and D. D. Perovic

Appl. Phys. Lett. 57, 1037 (1990); http://dx.doi.org/10.1063/1.103558 (3 pages) | Cited 94 times

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Intense photoluminescence (PL) from strained, epitaxial Si1−xGex alloys grown by molecular beam epitaxy is reported with measured internal quantum efficiencies up to 31% from random alloy layers, single buried strained layers, and multiple quantum wells. Samples deposited at ∼400 °C exhibited low PL intensity, whereas annealing at ∼600 °C enhanced the intensity by as much as two orders of magnitude. This anneal treatment was found to be optimal for removal of grown‐in defect complexes without creating a significant density of misfit dislocations. PL peak energies at 4.2 K varied from 620 to 990 meV for Ge fractions from 0.53 to 0.06, respectively. Efficient PL was due to exciton accumulation in the strained Si1−xGex layers of single and multiple quantum wells, where the band gap was locally reduced. Optical transitions associated with the PL occurred without phonon assistance.
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78.55.Hx Other solid inorganic materials
78.66.-w Optical properties of specific thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Device quality In0.4Ga0.6As grown on GaAs by molecular beam epitaxy

P. Ribas, V. Krishnamoorthy, and R. M. Park

Appl. Phys. Lett. 57, 1040 (1990); http://dx.doi.org/10.1063/1.103559 (3 pages) | Cited 20 times

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A novel approach to growing device quality In0.4Ga0.6As epilayers on GaAs is reported which involves the controlled propagation of dislocations via a carefully designed multistage strain‐relief buffer system. Cross‐sectional transmission electron microscopy analysis revealed the In0.4Ga0.6As epilayers to be threading dislocation free in contrast to the heavily dislocated material obtained by growing In0.4Ga0.6As directly on GaAs. Hall effect measurements performed on unintentionally doped buffered In0.4Ga0.6As epilayers indicated the room‐temperature electron concentrations in the epilayers to be around 1×1015 cm−3 while electron mobilities were around 4700 cm2 V−1 s−1. In addition, strong band‐edge photoluminescence was recorded from the buffered epilayers, the luminescence peak occurring at 1304 nm having a linewidth around 7 meV at 13 K.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
85.30.De Semiconductor-device characterization, design, and modeling

Positive and negative ‘‘resistless’’ lithography of GaAs by electron beam exposure and thermal Cl2 etching

E. M. Clausen, J. P. Harbison, C. C. Chang, P. S. D. Lin, H. G. Craighead, and L. T. Florez

Appl. Phys. Lett. 57, 1043 (1990); http://dx.doi.org/10.1063/1.103560 (3 pages) | Cited 10 times

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Positive and negative lithographic patterns have been produced in epitaxial layers of GaAs, achieved by electron beam writing and subsequent etching by Cl2 gas at elevated temperatures. A latent image is formed in the native oxide which is either less resistant to thermal Cl2 etching (positive pattern) or more resistant to thermal Cl2 etching (negative pattern), depending on the electron beam dose. The pattern is stable in air for at least several weeks. The tone of the pattern also depends on the electron beam accelerating voltage, the etching conditions, and the thickness and initial state of the native oxide. Significant changes in the resulting lithography are due to changes in an oxide only a few monolayers thick. Both positive and negative patterns can be produced in adjacent areas with high contrast by variation of the electron‐beam does. Initial Auger analysis suggests that chemical rearrangement of the native oxide occurs with electron beam exposure. The discovery that the native oxide on GaAs acts as both positive and negative resists opens tremendous possibilities for in situ processing and device fabrication.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
79.20.Hx Electron impact: secondary emission

Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers

L. T. Canham

Appl. Phys. Lett. 57, 1046 (1990); http://dx.doi.org/10.1063/1.103561 (3 pages) | Cited 3760 times

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Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
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81.65.-b Surface treatments
78.55.Hx Other solid inorganic materials

Growth of untwinned Bi2Sr2Ca2Cu3Ox thin films by atomically layered epitaxy

J. N. Eckstein, I. Bozovic, D. G. Schlom, and J. S. Harris

Appl. Phys. Lett. 57, 1049 (1990); http://dx.doi.org/10.1063/1.104278 (3 pages) | Cited 38 times

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We report the growth of untwinned epitaxial thin films of Bi‐Sr‐Ca‐Cu‐O by atomically layered heteroepitaxy on SrTiO3 substrates. These films are c‐axis oriented as‐layered and do not exhibit 90° in‐plane defects, i.e., a‐b ‘‘twinning.’’ By misorienting the surface normal from {100} by approximately 4° towards 〈111〉, the cubic symmetry of the {100} surface is adequately broken to completely align the b axis of the superconducting film with respect to the substrate. Reflection high‐energy electron diffraction patterns observed during growth and post‐growth x‐ray diffraction analysis indicate that the incommensurate structural modulation occurs along the same direction as the step edges.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
74.78.Fk Multilayers, superlattices, heterostructures
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures

Multilayered structure and anisotropic electrical properties of (SiO2)100−x(Pb0.6Bi0.4)x alloys prepared by a combined technique of mechanical alloying and hot pressing

B. G. Kim, N. Kataoka, K. Matsuzaki, A. Inoue, and T. Masumoto

Appl. Phys. Lett. 57, 1052 (1990); http://dx.doi.org/10.1063/1.104279 (3 pages) | Cited 2 times

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Compacted (SiO2)100−x(Pb0.6Bi0.4)x (x=20–80 at. %) materials, prepared by mechanical alloying (MA) of amorphous SiO2, fcc Pb, and rhombohedral hexagonal Bi followed by hot pressing of the MA powder at 473 K for 1.8 ks under an applied stress of 250 MPa, were found to have a unique layered structure consisting of amorphous SiO2 and hexagonal close‐packed (hcp) ϵ(Pb‐Bi) phases which developed along the direction perpendicular to the uniaxial applied load. The thickness and interlayer distance of the layered ϵ (Pb‐Bi) phase are about 1.5 and 7 μm, respectively, for (SiO2)50Pb30Bi20. Furthermore, the multilayered compacts exhibited a strong anisotropy of electrical resistivity and superconducting properties when their properties are measured along the directions parallel or perpendicular to the layer. Electrical resistivity at 300 K, superconducting critical temperature (Tc), and upper critical magnetic field (Hc2) at 4.2 K are 10.5 μΩ m, 8.5 K, and 2.29 T, respectively, for the parallel direction and 950 μΩ m, 6.9 K, and 0.24 T, respectively, for the perpendicular direction. The strong anisotropy of electrical resistivity and superconducting properties is presumably due to a significant difference in the linkage of electrical path between the parallel and perpendicular directions.
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72.80.Sk Insulators
73.61.Ng Insulators
81.05.Bx Metals, semimetals, and alloys

THz time‐domain spectroscopy of high Tc substrates

D. Grischkowsky and Søren Keiding

Appl. Phys. Lett. 57, 1055 (1990); http://dx.doi.org/10.1063/1.104280 (3 pages) | Cited 31 times

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Using the method of time‐domain spectroscopy, we have measured the absorption and dispersion from 0.2 to 2 THz of the high Tc substrates, magnesium oxide, yttria‐stabilized zirconia (YSZ), and lanthanum aluminate. Our measurements on YSZ and LaAlO3 at both room temperature and 85 K show unacceptably large absorptions for high‐speed transmission line applications. At 85 K, MgO is shown to be an excellent material in terms of its low loss at THz frequencies.
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74.78.-w Superconducting films and low-dimensional structures
78.47.-p Spectroscopy of solid state dynamics
84.40.Az Waveguides, transmission lines, striplines

Millimeter‐wave surface resistance of laser‐ablated YBa2Cu3O7−δ superconducting films

F. A. Miranda, W. L. Gordon, K. B. Bhasin, and J. D. Warner

Appl. Phys. Lett. 57, 1058 (1990); http://dx.doi.org/10.1063/1.104281 (3 pages) | Cited 3 times

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We have measured the millimeter‐wave surface resistance of YBa2Cu3O7−δ superconducting films in a gold‐plated copper host cavity at 58.6 GHz between 25 and 300 K. High quality laser‐ablated films of 1.2 μm thickness were deposited on SrTiO3 and LaGaO3 substrates. Their transition temperatures (Tc’s) were 90.0 and 88.9 K, with a surface resistance at 70 K of 82 and 116 mΩ, respectively. These values are better than the values for the gold‐plated cavity at the same temperature and frequency.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
74.78.-w Superconducting films and low-dimensional structures
74.25.N- Response to electromagnetic fields
74.70.-b Superconducting materials other than cuprates

Flux motion in a two‐dimensional single‐crystal Nb film

J. W. P. Hsu and A. Kapitulnik

Appl. Phys. Lett. 57, 1061 (1990); http://dx.doi.org/10.1063/1.103562 (3 pages) | Cited 2 times

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We have studied thermally activated flux motion (flux creep) in the resistive transition of a single‐crystal ultrathin (20 Å) Nb film in perpendicular magnetic fields. This thermally activated resistance extends over four decades from 0.5 Rn to 10−5 Rn. Possible pinning mechanisms and the field dependence of the activation energy are discussed. Comparisons between this system and the high Tc cuprate superconductors, which are quasi‐two‐dimensional in nature, are made.
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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.)

Structural perfection of Y‐Ba‐Cu‐O thin films controlled by the growth mechanism

R. Ramesh, C. C. Chang, T. S. Ravi, D. M. Hwang, A. Inam, X. X. Xi, Q. Li, X. D. Wu, and T. Venkatesan

Appl. Phys. Lett. 57, 1064 (1990); http://dx.doi.org/10.1063/1.104282 (3 pages) | Cited 48 times

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For crystalline advanced materials, such as the high transition temperature oxide superconductors, the growth of defect‐free crystals is often the most sought after desideratum because it opens the doors to fundamental studies and the development of practical applications. We report the observation of YBa2Cu3O7−x(123) thin films having unprecedented structural perfection, at temperatures near 700 °C on [001] LaAlO3. The film’s c axis is in the surface plane, unlike films grown at higher temperatures. This orientation has important advantages for device applications and fundamental studies. The Tc,0 is only 70 K, presumably due to oxygen deficiency caused by thermal stresses; if so, it should be possible to raise the Tc,0 by relieving these stresses.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates

Magneto‐optical investigation of flux penetration in Y1Ba2Cu3O7 thin films

A. Forkl, T. Dragon, H. Kronmüller, H.‐U. Habermeier, and G. Mertens

Appl. Phys. Lett. 57, 1067 (1990); http://dx.doi.org/10.1063/1.104283 (3 pages) | Cited 4 times

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Using the magneto‐optical Faraday effect the magnetic flux penetration into high Tc superconducting Y1Ba2Cu3O7 thin films is investigated. Epitaxially grown high quality films (Tc≳88 K, jc≳106 A/cm2 at 77 K) show a flux penetration in three steps, the formation of a flux front if the acting magnetic field reaches Hc1 at the edge of the specimen, the movement of the flux front towards the center of the sample, and the increase of the flux density after the flux front reaches the center. The remanent state shows trapped magnetic flux in the film, indicating inhomogeneously distributed pinning centers.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.-b Superconducting materials other than cuprates
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