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17 Oct 1988

Volume 53, Issue 16, pp. 1459-1568

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Threshold transport of high‐mobility two‐dimensional electron gas in GaAs/AlGaAs heterostructures

C. Jiang, D. C. Tsui, and G. Weimann

Appl. Phys. Lett. 53, 1533 (1988); http://dx.doi.org/10.1063/1.99948 (3 pages) | Cited 32 times

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We have measured the conductivity of the high‐mobility two‐dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructures at low temperatures as a function of the carrier density (n) close to the conduction threshold. We find that metallic conduction persists to n∼1.4×1010 cm−2, and that the mobility drops much faster than that expected from impurity scattering for n below a characteristic density, which decreases with increasing AlGaAs spacer thickness. This behavior is explained by the effect of the 2DEG density fluctuations at low n close to the conduction threshold, first predicted by Brews’ theory [J. Appl. Phys. 46, 2181 (1975)].
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance

Photoluminescence variations associated with the deposition of palladium electrical contacts on detector‐grade mercuric iodide

D. Wong, X. J. Bao, T. E. Schlesinger, R. B. James, A. Cheng, C. Ortale, and L. van den Berg

Appl. Phys. Lett. 53, 1536 (1988); http://dx.doi.org/10.1063/1.100433 (3 pages) | Cited 5 times

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Specimens of mercuric iodide with evaporated semitransparent palladium contacts have been studied using low‐temperature photoluminescence spectroscopy. Distinct differences were found between spectra taken from beneath the Pd contacts and those taken from regions on the HgI2 sample that were masked during the Pd deposition, indicating that contact fabrication can change the defect structure near the contact/substrate interface. Comparison of the spectra from spots beneath the contacts with spectra from bulk material specimens and HgI2 detectors graded in terms of their nuclear detection performance suggests that the processing steps used to deposit electrical contacts and the choice of contact material may have a significant influence on detector performance.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.55.Hx Other solid inorganic materials
73.40.Ns Metal-nonmetal contacts
29.40.Wk Solid-state detectors

Amplification of high repetition rate picosecond pulses using an InGaAsP traveling‐wave optical amplifier

G. Eisenstein, P. B. Hansen, J. M. Wiesenfeld, R. S. Tucker, and G. Raybon

Appl. Phys. Lett. 53, 1539 (1988); http://dx.doi.org/10.1063/1.99949 (3 pages) | Cited 11 times

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We report amplification of picosecond pulses at high repetition rates in a 1.3 μm traveling‐wave optical amplifier. At 4 GHz repetition rate, the small‐signal chip gain is 20 dB, the amplified peak output power at the facet is 400 mW (corresponding to a pulse energy of 3 pJ/pulse), and there is no measurable pulse shape distortion of 12 ps pulses for gain compression up to 1.5 dB. We also directly measure the time constant of the gain recovery to be 100 ps.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
07.60.-j Optical instruments and equipment
42.79.-e Optical elements, devices, and systems
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers

Determination of the D 0/− level in amorphous Si,Ge:H(F) by time‐of‐flight charge collection

D. S. Shen, J. P. Conde, V. Chu, J. Z. Liu, S. Aljishi, Z E. Smith, A. Maruyama, and S. Wagner

Appl. Phys. Lett. 53, 1542 (1988); http://dx.doi.org/10.1063/1.99950 (3 pages) | Cited 6 times

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We describe and demonstrate a new method for determining the density of states of the doubly occupied D0/− level in amorphous hydrogenated silicon and its alloys. The total charge collected during an electron time‐of‐flight measurement is determined as a function of T. T determines the energy E from which electrons are emitted during the measurement. Variation of T (and E) probes the local density of states. We present results for hydrogenated amorphous silicon before and after light soaking, and for amorphous silicon‐germanium (a‐Si,Ge:H,F) alloys.
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71.20.-b Electron density of states and band structure of crystalline solids
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Pseudomorphic In0.53Ga0.47As/AlAs/InAs resonant tunneling diodes with peak‐to‐valley current ratios of 30 at room temperature

Tom P. E. Broekaert, Wai Lee, and Clifton G. Fonstad

Appl. Phys. Lett. 53, 1545 (1988); http://dx.doi.org/10.1063/1.99951 (3 pages) | Cited 74 times

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Pseudomorphic In0.53 Ga0.47 As/AlAs/InAs resonant tunneling diodes have been grown on InP substrates by molecular beam epitaxy. Peak‐to‐valley current ratios as high as 30 at 300 K and 63 at 77 K are obtained on a structure with barriers of ten atomic layers AlAs, and a well consisting of three atomic layers of In0.53 Ga0.47 As, six atomic layers of InAs, and three atomic layers of In0.53 Ga0.47 As. For comparison pseudomorphic In0.53 Ga0.47 As/AlAs with In0.53 Ga0.47 As well structures have also been fabricated. For the In0.53 Ga0.47 As well structures, peak‐to‐valley current ratios as high as 23 have been obtained at 300 K, and, in other devices with lower current densities, two resonances are observed at room temperature.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Y‐Ba‐Cu‐O superconducting films prepared on SrTiO3 substrates by chemical vapor deposition

H. Yamane, H. Masumoto, T. Hirai, H. Iwasaki, K. Watanabe, N. Kobayashi, Y. Muto, and H. Kurosawa

Appl. Phys. Lett. 53, 1548 (1988); http://dx.doi.org/10.1063/1.100434 (3 pages) | Cited 64 times

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High Tc superconducting YBa2 Cu3 O7−x films were prepared by chemical vapor deposition using β‐diketonates of Y, Ba, and Cu as source materials. The films were epitaxially grown on SrTiO3 (100) substrates. The c‐axis orientation perpendicular to the plane of the substrates was observed. A sharp resistive superconducting transition with Tc (R=0) at 84 K was obtained. The maximum critical‐current density at 77 K was 2×104 A/cm2 .
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Superconductivity in thin films of Bi‐Sr‐Ca‐Cu oxide deposited via laser ablation of oxide pellets

N. K. Jaggi, M. Meskoob, S. F. Wahid, and C. J. Rollins

Appl. Phys. Lett. 53, 1551 (1988); http://dx.doi.org/10.1063/1.100474 (3 pages) | Cited 9 times

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We have grown superconducting films on the technologically important sapphire substrates by CO2 pulsed laser ablation from fully superconducting targets of Bi2Sr3−xCaxCu2Oy followed by appropriate post‐annealing. The composition of the films was found to deviate slightly from the target. Nevertheless, films with metallic resistivity decreasing between room temperature and 95 K, Tc(onset) of about 90 K and Tc(zero) of 72 K have been obtained. Magnetoresistance measurements in fields up to 12.85 T give a value of dHc2/dT of 1.6 T/K, which is intermediate between reported values of parallel and perpendicular Hc2 of fully aligned thin films. The implied partial orientation is consistent with the morphology seen by scanning electron microscopy.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Op Mixed states, critical fields, and surface sheaths
68.55.-a Thin film structure and morphology
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Friction in levitated superconductors

E. H. Brandt

Appl. Phys. Lett. 53, 1554 (1988); http://dx.doi.org/10.1063/1.100435 (3 pages) | Cited 69 times

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A type I superconductor levitated above a magnet of low symmetry has a unique equilibrium position about which it may oscillate freely. In contrast, a type II superconductor has a continuous range of stable equilibrium positions and orientations where it floats rigidly without swinging or orbiting as if it were stuck in sand. A strong internal friction conspicuously indicates the existence and unpinning of flux lines in oxide superconductors levitated above liquid nitrogen. It is shown how these effects follow from the hysteretic magnetization curves and how the energy is dissipated.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena

Epitaxial growth of YBa2Cu3O7−x thin films by a laser evaporation process

B. Roas, L. Schultz, and G. Endres

Appl. Phys. Lett. 53, 1557 (1988); http://dx.doi.org/10.1063/1.100437 (3 pages) | Cited 193 times

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Thin films of YBa2 Cu3 O7−x have been grown epitaxially in c‐axis orientation on 〈100〉 SrTiO3 by pulsed excimer laser evaporation from a stoichiometric 1‐2‐3 target. The substrate temperature was adjusted between 720 and 780 °C, and the oxygen partial pressure during the deposition was chosen in the range 0.1–0.3 mbar. Cooled to ambient temperature in situ for 1 h in flowing oxygen gas, the films showed complete diamagnetism and zero resistance at 90 K with a transition width of 2 K. Critical current densities of 2.2×106 A/cm2 in zero magnetic field and 1.5×105 A/cm2 at 2 T were measured at 77 K. The resistivity at 100 K was about 60 μΩ cm.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Kk Vapor phase epitaxy; growth from vapor phase
74.25.Sv Critical currents
74.70.-b Superconducting materials other than cuprates

Atmosphere‐sensitive 225 K feature in internal friction of YBa2Cu3O7−δ

M. P. Staines, J. L. Tallon, W. H. Robinson, and N. E. Flower

Appl. Phys. Lett. 53, 1560 (1988); http://dx.doi.org/10.1063/1.100438 (3 pages) | Cited 11 times

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The Young’s modulus and internal friction of YBa2 Cu3 O7−δ were measured from 280 to 80 K at 40 kHz using an ultrasonic composite oscillator technique. Three internal friction peaks intrinsic to the polycrystalline material which were observed at 105, 125, and 225 K disappeared when the sample was deoxygenated. Other structure in the internal friction between 220 and 280 K is ascribed to water vapor. The 225 K peak is reversibly eliminated on exposure to moist air. This is suggestive of internal friction at crystal surfaces or grain boundaries.
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62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity
74.70.-b Superconducting materials other than cuprates
74.25.N- Response to electromagnetic fields

Force microscopy of magnetization patterns in longitudinal recording media

H. J. Mamin, D. Rugar, J. E. Stern, B. D. Terris, and S. E. Lambert

Appl. Phys. Lett. 53, 1563 (1988); http://dx.doi.org/10.1063/1.99952 (3 pages) | Cited 78 times

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A force microscope with a magnetic tip has been used to examine magnetization patterns in a thin‐film cobalt‐alloy sample similar to that used in magnetic disk recording. Longitudinal magnetic bits were written on discrete tracks with a recording head flown over the surface of the sample. After minimal sample preparation, images were obtained showing strong magnetic contrast. Model calculations for the expected image contrast were found to be in excellent qualitative agreement with experimental results. By using a constant height imaging mode, enhanced contrast for fine detail was obtained.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Ak Magnetic properties of monolayers and thin films
75.60.-d Domain effects, magnetization curves, and hysteresis
75.50.Cc Other ferromagnetic metals and alloys

New fluid filter structure in silicon fabricated using a self‐aligning technique

Göran Stemme and Gjermund Kittilsland

Appl. Phys. Lett. 53, 1566 (1988); http://dx.doi.org/10.1063/1.99953 (3 pages) | Cited 6 times

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A new fluid filter structure in silicon has been designed and fabricated. The structure consists of two hole membranes of silicon displaced laterally relative to each other. The size of the largest particles which can pass through the structure is determined by the thickness of the silicon dioxide spacers separating the two hole membranes. One single‐hole pattern is used in combination with a special two‐step self‐aligning technique involving heavy boron diffusion, anisotropic silicon etching, and silicon dioxide undercut etching. Structures with membrane separation distances of 50 and 200 nm have been made. Since the structure electrically is a capacitor, other applications are possible.
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82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
81.65.-b Surface treatments
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