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27 Oct 1986

Volume 49, Issue 17, pp. 1051-1123


Room‐temperature operation of InGaAsSb/AlGaSb double heterostructure lasers near 2.2 μm prepared by molecular beam epitaxy

T. H. Chiu, W. T. Tsang, J. A. Ditzenberger, and J. P. van der Ziel

Appl. Phys. Lett. 49, 1051 (1986); http://dx.doi.org/10.1063/1.97471 (2 pages) | Cited 26 times

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In0.16Ga0.84As0.15Sb0.85/Al0.35Ga0.65Sb double heterostructure injection lasers have been grown by molecular beam epitaxy on (100) GaSb substrates. Room‐temperature operation near 2.2 μm wavelength has been achieved under pulsed conditions. Low pulsed threshold current density of 4.2 kA/cm2 and a characteristic temperature of T0∼26 K have been obtained.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Frequency‐dependent Faraday rotation in CdMnTe

M. A. Butler, S. J. Martin, and R. J. Baughman

Appl. Phys. Lett. 49, 1053 (1986); http://dx.doi.org/10.1063/1.97472 (3 pages) | Cited 18 times

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Optical Faraday rotation has been measured as a function of the frequency of an applied magnetic field in two compositions of the dilute magnetic semiconductor CdMnTe. A roll‐off in response is observed with the roll‐off frequency increasing with Mn concentration. The frequency dependence is fit well by a simple Debye relaxation model. This dependence is attributed to relaxation of the magnetization through interactions between the Zeeman and spin‐spin energy reservoirs.
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78.20.Ls Magneto-optical effects
76.70.Hb Optically detected magnetic resonance (ODMR)

Optical probing of the mechanical impulse response of a transducer

D. Royer and E. Dieulesaint

Appl. Phys. Lett. 49, 1056 (1986); http://dx.doi.org/10.1063/1.97473 (3 pages) | Cited 22 times

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The mechanical impulse response of a piezoelectric transducer has been plotted by using an optical interferometric heterodyne probe. The sensitivity of this Mach–Zehnder type probe is better than 10−4 Å/(Hz)1/2. Transient displacements of a few angstroms have been detected in a single sweep with a 20‐MHz bandwidth.
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43.38.Fx Piezoelectric and ferroelectric transducers
07.60.Ly Interferometers

Surface deformation measurements following excimer laser irradiation of insulators

R. J. von Gutfeld, F. A. McDonald, and R. W. Dreyfus

Appl. Phys. Lett. 49, 1059 (1986); http://dx.doi.org/10.1063/1.97474 (3 pages) | Cited 17 times

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We have studied the surface deformation of polyimide and Pyrex glass samples resulting from local excitation with pulsed 193 nm excimer laser radiation. The objective is to understand the primary deformation modes characterizing the surface motion. A He‐Ne probe beam was used to measure the deformation in conjunction with a fast rise time position sensitive detector. The data are compared to and found to be in agreement with a new detailed calculation. Three distinct temporal regimes are identified for the surface deformation: (1) local thermal expansion, (2) propagation of bulk and surface waves, and (3) simultaneous front and back surface motion (plate motion) for sufficiently thin samples.
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65.40.De Thermal expansion; thermomechanical effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.30.+d Mechanical and elastic waves; vibrations
68.35.Ja Surface and interface dynamics and vibrations

Ordering of oxide precipitates in oxygen implanted silicon

A. H. van Ommen, B. H. Koek, and M. P. A. Viegers

Appl. Phys. Lett. 49, 1062 (1986); http://dx.doi.org/10.1063/1.97475 (3 pages) | Cited 22 times

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An order network of oxide precipitates has been found in the monocrystalline superficial silicon layer of a silicon‐on‐insulator structure obtained by high‐dose oxygen implantation. The network consists of oxide precipitates 2 nm in size spaced about 5 nm apart. Electron diffraction patterns indicate that ordering occurs both parallel and perpendicular to the surface along the 〈100〉 directions of the silicon lattice. The precipitate network has a cubic symmetry.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
64.75.-g Phase equilibria
68.35.Dv Composition, segregation; defects and impurities
66.30.J- Diffusion of impurities

Determination of bonding in amorphous carbon films: A quantitative comparison of core‐electron energy‐loss spectroscopy and 13C nuclear magnetic resonance spectroscopy

R. H. Jarman, G. J. Ray, R. W. Standley, and G. W. Zajac

Appl. Phys. Lett. 49, 1065 (1986); http://dx.doi.org/10.1063/1.97476 (3 pages) | Cited 44 times

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The direct determination of carbon–carbon bonding in amorphous carbon thin films has been performed by core‐electron energy‐loss spectroscopy and cross‐polarization magic‐angle spinning 13C nuclear magnetic resonance (NMR) for a series of varying band‐gap amorphous carbon films (1.1–3.0 eV). The amorphous carbon films were prepared using rf plasma discharge with either capacitive or inductive coupling. The core‐electron energy‐loss spectroscopy is shown to be quantitative by measuring the relative number of unoccupied π∗ and σ∗ states available to the C 1s core electron. Determination of the percentage of sp2 and sp3 bonded carbon atoms follows from the measured ratio of π∗ and σ∗ states. If unity cross section for the C 1s to π∗ and σ∗ core losses is assumed, the agreement with high‐resolution 13C NMR determination of the sp2 and sp3 content is very encouraging. The low band‐gap material (1.1 eV) has the largest sp2 content (55–60%) which decreases with increasing band gap (3.0 eV, 12–19%). The orientation dependence of the intensities of the π∗ and σ∗ loss features is not as strong as found in highly oriented pyrolytic graphite. The observation of the orientation dependence suggests that there is a tendency for the π∗ orbitals to be parallel to the substrate.
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68.60.Wm Other nonelectronic physical properties
76.60.-k Nuclear magnetic resonance and relaxation
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
73.61.Ng Insulators

Interface width of anodic native oxide—InSb structures

Yoram Shapira, J. Bregman, and Z. Calahorra

Appl. Phys. Lett. 49, 1068 (1986); http://dx.doi.org/10.1063/1.97477 (3 pages) | Cited 2 times

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Using our improved quantitative analysis of Auger electron spectroscopy (AES) depth profiles, we have found a linear relationship between the interface width of plasma‐ and wet‐anodized InSb (111) and the oxide thickness in the range of 15–180 nm. Using a simple etching technique we have been able to ascertain that the effect was inherent to the oxidation process and not a result of the sputtering process. We have developed a theoretical model that explains the linear relationship in terms of field‐enhanced diffusion and oxidation reaction. The model is based on our earlier experiments that demonstrated the oxygen diffusion through the oxide to the interface. Application of the model to the results of over 30 different AES depth profiles yields excellent agreement with the experimental observations that show that the interface width is about 0.25 of the total oxide thickness. The results support the thermodynamic model of anodization, indicating that interface formation is the last step of the oxide growth process.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
68.55.-a Thin film structure and morphology
81.65.-b Surface treatments

X‐ray study of misfit strain relaxation in lattice‐mismatched heterojunctions

K. Kamigaki, H. Sakashita, H. Kato, M. Nakayama, N. Sano, and H. Terauchi

Appl. Phys. Lett. 49, 1071 (1986); http://dx.doi.org/10.1063/1.97478 (3 pages) | Cited 35 times

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High‐resolution x‐ray diffraction measurements have been carried out in AlxGa1−xAs and InxGa1−xAs grown by the molecular beam epitaxy method on (001) GaAs substrates. The thin epitaxial layers in these lattice‐mismatched semiconductor single heterojunctions are uniformly distorted and there is an elastic limit for large x. The epitaxial layer is affected by a thick substrate even over the elastic limit, i.e., the epitaxial layer still shows a strained state beyond the elastic limit. The relationship between the misfit strain and the lattice distortion is discussed.
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68.35.Gy Mechanical properties; surface strains
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Epitaxial growth of β‐SiC thin films on 6H α‐SiC substrates via chemical vapor deposition

H. S. Kong, J. T. Glass, and R. F. Davis

Appl. Phys. Lett. 49, 1074 (1986); http://dx.doi.org/10.1063/1.97479 (3 pages) | Cited 36 times

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Epitaxial films of cubic β‐SiC(111) have been grown via chemical vapor deposition at 1683 K on (0001) substrates of hexagonal 6H α‐SiC. Optical microscopy of the surface indicated that a decrease in the ratio of the sum of the C and Si source gases to the H2 carrier gas changed the crystallization behavior from polycrystalline to monocrystalline. Cross‐sectional transmission electron microscopy showed almost no line or planar defects at the substrate/film interface and very few defects within the bulk of the film.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Ohmic contact control in modulation‐doped gallium arsenide field‐effect transistors

A. Christou, T. Efthimiopoulos, and Z. Hatsopoulos

Appl. Phys. Lett. 49, 1077 (1986); http://dx.doi.org/10.1063/1.97480 (3 pages)

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Modulation‐doped field‐effect transistor structures grown by molecular beam epitaxy were excimer laser annealed at a wavelength of 248 nm and energy density of 75–160 mJ/cm2. A transconductance of over 100 mS/mm was obtained. Source resistance was minimized at 0.8–1.0 Ω mm. The energy density threshold for interdiffusion is 90 mJ/cm2.
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85.30.Tv Field effect devices

Optically induced far‐infrared absorption from residual acceptors in as‐grown GaAs

J. Wagner, H. Seelewind, and P. Koidl

Appl. Phys. Lett. 49, 1080 (1986); http://dx.doi.org/10.1063/1.97481 (3 pages) | Cited 22 times

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Far‐infrared Fourier transform spectroscopy has been applied to study residual shallow acceptors in as‐grown semi‐insulating GaAs. Secondary optical excitation into the EL2 absorption band has been used to create a nonequilibrium hole population to neutralize the acceptors. Optically induced absorption spectra from carbon and zinc acceptors have been observed. The dependence of these spectra on the secondary illumination is studied. A comparison is made with electronic Raman spectra recorded from the same samples.
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78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
78.30.Hv Other nonmetallic inorganics

Semiconducting/semi‐insulating reversibility in bulk GaAs

D. C. Look, P. W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, and S. S. Li

Appl. Phys. Lett. 49, 1083 (1986); http://dx.doi.org/10.1063/1.97429 (3 pages) | Cited 35 times

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Bulk, liquid‐encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ∼1 Ω cm) to semi‐insulating (ρ∼107 Ω cm) by slow or fast cooling, respectively, following a 5 h, 950 °C soak in an evacuated quartz ampoule. This effect has been studied by temperature‐dependent Hall‐effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3×1014 cm−3. Donor and acceptor concentrations, on the other hand, are in the mid 1015 cm−3 range, which means that the compensation is primarily determined by native defects, not impurities. A tentative model includes a donor at EC−0.13 eV, attributed to VAs−AsGa, and an acceptor at EV+0.07 eV, attributed to VGa−GaAs.
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72.20.My Galvanomagnetic and other magnetotransport effects
78.40.Fy Semiconductors
72.80.Ey III-V and II-VI semiconductors

Large room‐temperature effects from resonant tunneling through AlAs barriers

W. D. Goodhue, T. C. L. G. Sollner, H. Q. Le, E. R. Brown, and B. A. Vojak

Appl. Phys. Lett. 49, 1086 (1986); http://dx.doi.org/10.1063/1.97629 (3 pages) | Cited 48 times

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At room temperature, we have observed negative differential resistance in AlAs double‐barrier structures and a large hysteresis in the current‐voltage characteristic of a stack of five AlAs double‐barrier structures. The peak‐to‐valley ratio of the current was as high as 3.5:1 in a double‐barrier structure. To the best of our knowledge, this is the largest room‐temperature peak‐to‐valley ratio observed to date in a double‐barrier structure and the first report of a room‐temperature hysteresis in a stacked structure. These structures were grown by molecular beam epitaxy using thin AlAs barriers in GaAs. Both the first and second resonances were observed, and are well explained by simple tunneling theory assuming a value of 1.0±0.1 eV for the GaAs‐AlAs conduction‐band discontinuity seen by the tunneling electrons. This value is very close to the difference in conduction‐band energy at the Γ points found by using the accepted values of GaAs and AlAs band gaps with 65% of the band‐gap difference appearing in the conduction band. This suggests that negligibly few electrons relax to the lower AlAs X valley as they tunnel through the 1.5–2.5‐nm‐thick AlAs barriers. These results indicate that AlAs should be a high quality barrier material for a variety of heterojunction devices.
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73.40.Gk Tunneling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors

Amorphous silicon p‐i‐n solar cells with graded interface

R. R. Arya, A. Catalano, and R. S. Oswald

Appl. Phys. Lett. 49, 1089 (1986); http://dx.doi.org/10.1063/1.97430 (3 pages) | Cited 50 times

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The influence of inserting a thin graded interface layer at the p/i interface on the short‐wavelength response and on the overall performance of amorphous silicon p‐i‐n solar cells is discussed. This device structure has resulted in fill factor values as high as 0.771.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
72.80.Ng Disordered solids

Dangling bond electron spin‐lattice relaxation in rf‐sputtered hydrogenated amorphous silicon and silicon carbide

S. Dey, D. R. Torgeson, and R. G. Barnes

Appl. Phys. Lett. 49, 1092 (1986); http://dx.doi.org/10.1063/1.97431 (3 pages) | Cited 1 time

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Electron spin resonance methods have been used to measure the temperature dependence of the spin‐lattice relaxation time T1 of dangling bond electrons in hydrogenated amorphous silicon and silicon carbide samples prepared by radio frequency sputtering. The T1 measurements were made by a combination of continuous‐wave absorption mode saturation and periodic adiabatic passage methods over the temperature range 100–400 K, yielding T−11∝T2 behavior consistent with relaxation by two‐level systems.
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76.30.-v Electron paramagnetic resonance and relaxation
71.23.-k Electronic structure of disordered solids
33.35.+r Electron resonance and relaxation

Growth of high mobility n‐type CdTe by photoassisted molecular beam epitaxy

R. N. Bicknell, N. C. Giles, and J. F. Schetzina

Appl. Phys. Lett. 49, 1095 (1986); http://dx.doi.org/10.1063/1.97432 (3 pages) | Cited 51 times

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We report details of the successful controlled substitutional doping of CdTe films with indium. These n‐type films were prepared using a new technique, photoassisted molecular beam epitaxy, in which the substrate is illuminated during the deposition process. In the present work, an argon ion laser was used as an illumination source. The incident light was found to produce immediate and significant changes in the electrical properties of the films. In particular, highly activated n‐type CdTe:In layers resulted.
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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
73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
81.40.Rs Electrical and magnetic properties related to treatment conditions

Passivation of deep level defects in molecular beam epitaxial GaAs by hydrogen plasma exposure

W. C. Dautremont‐Smith, J. C. Nabity, V. Swaminathan, Michael Stavola, J. Chevallier, C. W. Tu, and S. J. Pearton

Appl. Phys. Lett. 49, 1098 (1986); http://dx.doi.org/10.1063/1.97433 (3 pages) | Cited 72 times

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The effect of hydrogen plasma exposure on the deep level defects present in GaAs grown by molecular beam epitaxy (MBE) has been investigated by deep level transient spectroscopy and by photoluminescence. The three commonly observed defects in MBE grown layers, the M1, M2, and M4 levels, found to be present at a total concentration of 5×1013 cm−3, are completely passivated by exposure to the hydrogen plasma. At low carrier concentration, in samples where surface recombination is suppressed by a thin GaxAl1−xAs cap, passivation of these defects increases photoluminescence efficiency by factors of 30 and 100 at 298 and 77 K, respectively. Defect passivation occurs in addition to the previously reported donor neutralization, but, whereas the latter is removed by a 400 °C, 5 min anneal, the former remains fully effective. Only upon 600 °C, 5 min annealing does the defect level passivation begin to be lost. Thus there is a wide temperature window within which it is possible to regain the carrier concentration without loss of passivation of the deep level defects.
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73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
52.40.Hf Plasma-material interactions; boundary layer effects
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.65.-b Surface treatments

Dislocation filtering in semiconductor superlattices with lattice‐matched and lattice‐mismatched layer materials

P. L. Gourley, T. J. Drummond, and B. L. Doyle

Appl. Phys. Lett. 49, 1101 (1986); http://dx.doi.org/10.1063/1.97434 (3 pages) | Cited 21 times

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We investigate the ability of semiconductor superlattices to filter or block threading dislocations by growing and studying structural properties of superlattices composed of alternating layers (∼100 Å each) of InxGa1−xAs and InyAl1−yAs. These superlattices were grown with x=y corresponding to lattice‐matched compositions such that the layers have minimal strain, and x≠y corresponding to lattice‐mismatched compositions such that the layers have large coherent strains. By correlating the number of dislocations observed in optical images of the superlattices, with the amount of layer strain determined by x‐ray double diffraction analysis, we investigate the effect of strain on the filtering ability. We find that both types of superlattices are effective in filtering dislocations.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties

New silicon‐on‐insulator technology using a two‐step oxidation technique

T. L. Lin and K. L. Wang

Appl. Phys. Lett. 49, 1104 (1986); http://dx.doi.org/10.1063/1.97435 (3 pages) | Cited 9 times

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Large silicon‐on‐insulator (SOI) structures have been obtained using a new two‐step oxidation technique on a silicon molecular epitaxial film grown onto a porous silicon sample. The first low‐temperature oxidation step oxidizes the large‐pore silicon underlayer to avoid the collapse of the porous structure and thus secure the lateral oxygen supply channels in the porous oxide. In the second step, a higher temperature is used to oxidize the remaining porous silicon and the bottom part of the Si molecular beam epitaxy overlayer with the oxygen supplied through the oxidized porous silicon underlayer. A new porous silicon structure used is composed of a top porous silicon layer which has a smaller porosity for the ease of subsequent silicon epitaxial growth, and a second layer with a larger porosity which not only gives oxygen supply channels during the SOI oxidation but also allows the volume expansion of the porous silicon oxide to be accommodated. SOI sizes of 325 μm×2 mm have been successfully fabricated. The breakdown voltage of the SOI structures is about 400 V and the leakage current densities between the SOI layer and the substrate are below 3 nA cm−2 with a 10‐V bias. n‐channel metal‐oxide‐silicon field‐effect transistors have been fabricated on the SOI structures with good characteristics, indicating that this technology may be suitable for very large scale integrated circuits applications.
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81.65.-b Surface treatments
85.30.Tv Field effect devices
68.55.-a Thin film structure and morphology
73.61.-r Electrical properties of specific thin films

Characterization of individual electron traps in amorphous Si by telegraph noise spectroscopy

C. T. Rogers, R. A. Buhrman, H. Kroger, and L. N. Smith

Appl. Phys. Lett. 49, 1107 (1986); http://dx.doi.org/10.1063/1.97436 (3 pages) | Cited 26 times

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We have used telegraph noise spectroscopy to study the properties of individual localized electron traps of a particular type in thin layers (t<∼6 nm) of rf sputtered amorphous Si and amorphous Si:H. The results indicate that these traps have bistable ionic configurations: The trapping kinetics are dominated by transitions between two different ionic configurations with an associated change in trapped charge. Above ∼20 K, configurational transitions are by thermally activated hopping; below 20 K, transitions appear to be induced by zero‐point oscillations.
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71.55.Jv Disordered structures; amorphous and glassy solids
73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Room‐temperature excitons in Ga0.47In0.53As‐InP superlattices grown by low‐pressure metalorganic chemical vapor deposition

M. Razeghi, J. Nagle, P. Maurel, F. Omnes, and J. P. Pocholle

Appl. Phys. Lett. 49, 1110 (1986); http://dx.doi.org/10.1063/1.97437 (2 pages) | Cited 12 times

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Very high quality Ga0.47In0.53As‐InP heterojunctions, quantum wells, and superlattices have been grown by low‐pressure metalorganic chemical vapor deposition. Excitation spectroscopy shows evidence of strong and well‐resolved exciton peaks in the luminescence and excitation spectra of GaInAs‐InP quantum wells. Optical absorption spectra show room‐temperature excitons in GaInAs‐InP superlattices.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
75.20.Ck Nonmetals
78.40.Fy Semiconductors
78.30.-j Infrared and Raman spectra

High gain InGaAs/InP heterostructure bipolar transistors grown by gas source molecular beam epitaxy

R. N. Nottenburg, H. Temkin, M. B. Panish, and R. A. Hamm

Appl. Phys. Lett. 49, 1112 (1986); http://dx.doi.org/10.1063/1.97438 (3 pages) | Cited 12 times

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The capability for high quality heterostructure bipolar transistors with structures in the InGaAs/InP system has been demonstrated by gas source molecular beam epitaxy. These devices are characterized by high current gain, β∼1100, only weakly dependent on the collector current. The current‐voltage characteristics of the emitter base junction exhibit an ideality factor n=1.2 over a wide bias range.
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85.30.Pq Bipolar transistors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Rotating ring fluxon oscillators: Gyroscopic effects

Fabio Marchesoni

Appl. Phys. Lett. 49, 1115 (1986); http://dx.doi.org/10.1063/1.97439 (3 pages) | Cited 1 time

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See Also: Erratum

Show Abstract
We suggest the existence of gyroscopic effects in ring fluxon oscillators, which, due to the extremely narrow oscillation linewidths, could therefore be used as sensitive rotation rate sensors. For the sake of comparison we also improve on previous analytical determinations of the thermal background intensity for oscillating Josephson lines.
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85.25.-j Superconducting devices
74.50.+r Tunneling phenomena; Josephson effects
06.30.Gv Velocity, acceleration, and rotation
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Very low noise, tightly coupled, dc SQUID amplifiers

B. Muhlfelder, J. A. Beall, M. W. Cromar, and R. H. Ono

Appl. Phys. Lett. 49, 1118 (1986); http://dx.doi.org/10.1063/1.97440 (3 pages) | Cited 8 times

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We have fabricated and tested thin film, niobium edge junction, double transformer, dc superconducting quantum interference devices (SQUID’s) that were stable under room‐temperature storage and thermal cycling and that had very good noise performance. The input inductance, approximately 1.7 μH, was large enough to facilitate good matching to many experiments. When the SQUID was operated as a small‐signal amplifier, the minimum detectable energy per unit bandwidth (Se) was 5×10−33 J/Hz at 100 kHz, referred to the SQUID loop (uncoupled). The minimum detectable energy per unit bandwidth was 1.8×10−31 J/Hz at 100 kHz, referred to the input coil. The SQUID’s had good characteristics for flux‐locked operation since the small signal Se was low over a substantial range of bias current and magnetic flux. For operation in a flux‐locked feedback circuit, Se was 6×10−32 J/Hz at 1 kHz.
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85.25.-j Superconducting devices
74.50.+r Tunneling phenomena; Josephson effects

Solid neon moderator for producing slow positrons

A. P. Mills and E. M. Gullikson

Appl. Phys. Lett. 49, 1121 (1986); http://dx.doi.org/10.1063/1.97441 (3 pages) | Cited 88 times

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Slow positrons can be obtained by moderating the energetic β+ particles from a radioactive source. We find that solid Ne makes a more efficient moderator than any other material known to date. The efficiency ϵ, defined as the number of slow positrons per β+ emitted by the source, is (0.30±0.02)% for a flat layer of Ne covering a 22Na deposit. In a cylindrical geometry, ϵ is (0.70±0.02)%, more than twice the previous best efficiency obtained with single‐crystal tungsten. The energy spectrum for Ne has a full width at half‐maximum of 0.58 eV, somewhat broader than the spectrum of positrons from a single‐crystal metal. Moderators made from the other solid rare gases have a much lower efficiency and a larger energy spread.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
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