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25 Jan 1988

Volume 52, Issue 4, pp. 249-336

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Near‐field optical scanning microscopy in reflection

U. Ch. Fischer, U. T. Dürig, and D. W. Pohl

Appl. Phys. Lett. 52, 249 (1988); http://dx.doi.org/10.1063/1.99483 (3 pages) | Cited 61 times

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The resolution of near‐field optical scanning microscopy (NFOS) is determined by the dimensions of the microscopic light source rather than the diffraction limit. To demonstrate NFOS in reflection, intensity changes in the (backward) scattering from a 70–100 nm diam hole in a metal film were recorded while the sample was scanned in close proximity to this aperture. Raster‐scan images of a planar metal test pattern yield a resolution comparable to the size of the aperture.
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07.60.Pb Conventional optical microscopes
68.35.B- Structure of clean surfaces (and surface reconstruction)
42.30.-d Imaging and optical processing

Effect of group V/III flux ratio on the reliability of GaAs/Al0.3Ga0.7As laser diodes prepared by molecular beam epitaxy

T. Hayakawa, K. Takahashi, T. Suyama, M. Kondo, S. Yamamoto, and T. Hijikata

Appl. Phys. Lett. 52, 252 (1988); http://dx.doi.org/10.1063/1.99484 (3 pages) | Cited 3 times

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The effect of group V/III flux ratio γ on the reliability of GaAs/Al0.3Ga0.7As double‐heterostructure lasers grown by molecular beam epitaxy at 720 °C has been studied. The threshold current does not change with γ. By contrast, the degradation rate strongly depends on γ and it takes a minimum at γ∼3 where the photoluminescence intensity of the Al0.3Ga0.7As cladding layer is maximum. In the case of γ∼3, the degradation rate is lower than that of lasers grown by liquid phase epitaxy.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.55.Cr III-V semiconductors

cw laser action of Er3+ in double sensitized fluoroaluminate glass at room temperature

E. Heumann, M. Ledig, D. Ehrt, W. Seeber, E. W. Duczynski, H.‐J. v.d. Heide, and G. Huber

Appl. Phys. Lett. 52, 255 (1988); http://dx.doi.org/10.1063/1.99485 (2 pages) | Cited 4 times

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cw lasing at 1.6 μm was obtained for the first time in Cr, Yb, Er:fluoroaluminate glass. Double step pumping via Cr3+ and Yb3+ with a krypton laser yields a threshold pump power of 80 mW. Efficient lasing can be expected using glass samples of optimized dopant concentration and improved optical quality.
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42.55.Rz Doped-insulator lasers and other solid state lasers
78.45.+h Stimulated emission
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Gain switching of semiconductor injection lasers

K. Y. Lau

Appl. Phys. Lett. 52, 257 (1988); http://dx.doi.org/10.1063/1.99486 (3 pages) | Cited 56 times

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The limiting factors in short pulse generation by gain switching of semiconductor lasers are analyzed using an approach parallel to conventional Q switching analysis. The dependence of the gain‐switched pulse width and pulse energy on various input parameters such as drive current amplitude, bias current, and spontaneous emission factor, etc., can be predicted in a simple manner.
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42.60.Fc Modulation, tuning, and mode locking
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Mode control in broad‐area diode lasers by thermally induced lateral index tailoring

J. P. Hohimer, G. R. Hadley, and A. Owyoung

Appl. Phys. Lett. 52, 260 (1988); http://dx.doi.org/10.1063/1.99487 (3 pages) | Cited 11 times

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Broad‐area diode lasers that emit in the fundamental mode under short‐pulse excitation are observed to evolve into higher order lateral modes with increasing pulse width. Our data provide convincing evidence that the lateral refractive index profile arising from junction heating plays a dominant role in determining the lateral emission modes in these devices for long‐pulse and cw operation. Furthermore, we show that an external focused laser heat source can be used to modify the lateral index profile in a broad‐area laser and thus control the lasing mode. In particular, we demonstrate that ≲50 mW of absorbed heating power is sufficient to counteract the effects of internal junction heating and restore fundamental mode operation at cw injection currents as high as 1.5 Ithreshold. Our results suggest that fundamental mode operation of broad‐area devices at high‐power levels might be realized by incorporating a tailored lateral index profile to compensate for internal junction heating.
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42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Instability threshold resonances in directly modulated external‐cavity semiconductor lasers

A. Schremer, T. Fujita, C. F. Lin, and C. L. Tang

Appl. Phys. Lett. 52, 263 (1988); http://dx.doi.org/10.1063/1.99488 (3 pages) | Cited 7 times

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The relationship between the modulation frequency and maximum modulation depth for stable and low‐noise oscillation in external‐cavity semiconductor lasers is investigated. Sharp resonances in the threshold for the onset of instability occur when the laser is nearly synchronously modulated. A physical model is proposed to explain these observations.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Stable, single‐(array)‐mode operation from phase‐locked, interferometric arrays of index‐guided AlGaAs/GaAs diode lasers

D. Botez, L. Mawst, P. Hayashida, T. J. Roth, and E. Anderson

Appl. Phys. Lett. 52, 266 (1988); http://dx.doi.org/10.1063/1.99489 (3 pages) | Cited 5 times

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Single‐array‐mode (L=8) oscillation is achieved with virtually diffraction‐limited beams to three times above lasing threshold, and with beamwidths 1.5 times the diffraction limit at 4.7 times above lasing threshold and 130 mW output power per uncoated emitting facet. The arrays are 10/11‐element wide‐waveguide‐interferometric (WWI) AlGaAs/GaAs lasers grown by liquid‐phase epitaxy over channeled substrates. Selection of the L=8 mode is a consequence of two mode‐dependent loss mechanisms: transverse antiguiding between elements and radiation losses in the interferometer. Near‐field pattern analysis indicates that the (high‐order) array mode is self‐stabilizing with increasing drive above threshold. Simple means of achieving single‐lobe operation are discussed.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.By Design of specific laser systems

Measurement of soft x‐ray multilayer mirror reflectance at normal incidence using laser‐produced plasmas

J. A. Trail, R. L. Byer, and T. W. Barbee

Appl. Phys. Lett. 52, 269 (1988); http://dx.doi.org/10.1063/1.99490 (3 pages) | Cited 13 times

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We have used laser‐produced plasmas as a broadband source of soft x rays to measure the normal incidence reflectance of multilayer mirrors in the 10–25 nm spectral region. The measurements have a spectral resolution of 0.03 nm and a reflectance resolution of 10%. Measurements made on a Mo/Si multilayer show excellent agreement with results obtained using a synchrotron and indicate a normal incidence peak reflectance of over 50% at 15 nm. By repeating the reflectance measurement at different positions across a single 7.5 cm mirror we determined multilayer uniformity as a function of position and we relate this dependence to the geometry of the deposition process.
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07.85.-m X- and γ-ray instruments
78.66.-w Optical properties of specific thin films
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.15.Eq Optical system design
42.79.Bh Lenses, prisms and mirrors

Aluminum spiking at contact windows in Al/Ti‐W/Si

Peng‐Heng Chang, R. Hawkins, T. D. Bonifield, and L. A. Melton

Appl. Phys. Lett. 52, 272 (1988); http://dx.doi.org/10.1063/1.99491 (3 pages) | Cited 10 times

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Aluminum spike formation through a Ti‐W interdiffusion barrier layer at contact windows is studied by cross‐sectional transmission electron microscopy for Al‐1% Si and Al‐2% Cu films. For Ti‐W layers thinner than 1000 Å Al spikes form in both Al‐Si and Al‐Cu systems. The two types of Al films behave similarly in terms of the propensity for spike formation and spike morphology in the presence of a Ti‐W layer. Aluminum spikes generally have an inverted pyramidal, truncated inverted pyramidal, or parallelepipedal shape. Aluminum in a spike is generally single crystal and some of the Al spikes maintain one of the following orientation relationships with the surrounding Si substrate: [011]Al∥[123]Si and (200)Al∥(111)Si or [001]Al∥[112]Si and (200)Al is 2° off (111)Si. A mechanism for Al spike formation through Ti‐W is proposed.
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68.35.Fx Diffusion; interface formation
68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.-b Surface treatments

Amorphous SiC/Si three‐color detector

Hsiung‐Kuang Tsai and Si‐Chen Lee

Appl. Phys. Lett. 52, 275 (1988); http://dx.doi.org/10.1063/1.99492 (3 pages) | Cited 37 times

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A hydrogenated amorphous SiC/hydrogenated amorphous Si heterojunction photodetector whose peak response could be voltage adjusted to three wavelengths, i.e., 480, 530, and 575 nm, by applying a small bias within ±2 V has been successfully fabricated. The basic principle is to use two back‐to‐back p‐i‐n junction diodes (or an n‐i‐p‐i‐n transistor) in which photons with wavelength λ<500 nm (blue) are mainly collected in the front a‐SiC:H/a‐Si:H heterojunction and the rest (green and red) are absorbed in the rear a‐Si:H homojunction. To further distinguish the green from the red, two undoped a‐Si:H layers, deposited at different conditions, were used in the rear homojunction to obtain two distinct collection regions. It is found that the required voltage to select one of the collection regions is less than 2 V. This detector shows a very high rejection ratio at various responses and thus is good for distinguishing the entire color spectrum.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.80.Ng Disordered solids
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors

Direct control and characterization of a Schottky barrier by scanning tunneling microscopy

L. D. Bell, W. J. Kaiser, M. H. Hecht, and F. J. Grunthaner

Appl. Phys. Lett. 52, 278 (1988); http://dx.doi.org/10.1063/1.99493 (3 pages) | Cited 38 times

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Scanning tunneling microscopy (STM) methods are used to directly control the barrier height of a metal tunnel tip‐semiconductor tunnel junction. Barrier behavior is measured by tunnel current‐voltage spectroscopy and compared to theory. A unique surface preparation method is used to prepare a low surface state density Si surface. Control of band bending with this method enables STM investigation of semiconductor subsurface properties.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Gk Tunneling
73.20.At Surface states, band structure, electron density of states
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Electrical properties of shallow p+‐n junctions formed by BF2 ion implantation in germanium preamorphized silicon

M. C. Ozturk and J. J. Wortman

Appl. Phys. Lett. 52, 281 (1988); http://dx.doi.org/10.1063/1.99494 (3 pages) | Cited 17 times

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Shallow p+‐n junctions were formed by BF2 ion implantation into both crystalline and Ge preamorphized substrates. Rapid thermal annealing (RTA) was used for dopant activation and damage removal. Secondary ion mass spectroscopy (SIMS) was used to measure the boron and fluorine distribution profiles. Based on SIMS analysis, junction depths as shallow as 0.12 μm can be formed using 25 keV/1×1015 cm−2 BF2 ion implantation into Ge preamorphized Si. The influence of Ge implantation parameters on the leakage current of junctions was investigated. The results show that if the Ge implantation conditions are optimized, high quality p+‐n junctions can be formed in preamorphized substrates using RTA temperatures as low as 950 °C.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.80.Jh Ion radiation effects
61.72.uf Ge and Si
85.30.Tv Field effect devices

Kinetics of structural relaxation and hydrogen evolution from plasma deposited silicon nitride

R. C. Budhani, R. F. Bunshah, and P. A. Flinn

Appl. Phys. Lett. 52, 284 (1988); http://dx.doi.org/10.1063/1.99495 (3 pages) | Cited 22 times

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Infrared absorption measurements and the temperature dependence of stress have been used to establish the kinetics of structural relaxation and hydrogen evolution from plasma deposited a‐SixNy :H films. The Arrhenius rate law describes the dissociation of N–H and Si–H bonds which occurs on annealing the films above 600 °C. The activation energies deduced from the infrared data are lower than the respective bond dissociation energies. The films undergo a rapid stress relaxation in the temperature range 400–650 °C. The discussion of the experimental results highlights possible mechanisms for the evolution of hydrogen from a‐SixNy@B:H networks.
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78.66.-w Optical properties of specific thin films
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Reflectance line shapes from GaAs/Ga1−xAlxAs quantum well structures

X. L. Zheng, D. Heiman, B. Lax, and F. A. Chambers

Appl. Phys. Lett. 52, 287 (1988); http://dx.doi.org/10.1063/1.99496 (3 pages) | Cited 67 times

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Reflectance experiments on GaAs/Ga1−xAlxAs single quantum well structures were performed at 4.2 K, with different thicknesses of the front GaAlAs barrier layer (100–1000 Å). The observed exciton reflectance line shapes depend strongly on the thickness of the front barrier layer due to the interferences between the reflected waves from the front surface and the quantum well interfaces. Calculations of the reflectance line shapes show good agreement with the observations. The absorption coefficient for the electron heavy‐hole exciton transition in a single quantum well sample is determined. Our study also provides a new understanding of the line shapes measured in photoreflectance experiments.
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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

Atomic steps at GaInAs/InP interfaces grown by organometallic vapor phase epitaxy

T. Y. Wang, K. L. Fry, A. Persson, E. H. Reihlen, and G. B. Stringfellow

Appl. Phys. Lett. 52, 290 (1988); http://dx.doi.org/10.1063/1.99652 (3 pages) | Cited 19 times

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InP/GaInAs/InP quantum well structures have been grown using atmospheric pressure organometallic vapor phase epitaxy (OMVPE). For thin wells the 10 K photoluminescence spectra show a clearly resolved doublet (or in some cases a triplet). The energy separation of the two peaks increase with decreasing well width down to a nominal width of approximately two to three atomic monolayers. For thinner wells the energy separation decreases with decreasing well width. The doublet is interpreted as being due to the photoluminescence from two wells differing in thickness by a single monolayer. A simple calculation for a finite quantum well describes the general features of the energy splitting versus well width. The half‐widths of the two photoluminescence peaks for the thin wells, where the two peaks are resolved, are extremely narrow. The value of <15 meV for the thinnest well is much better than observed previously for low‐pressure or atmospheric‐pressure OMVPE and matches the results obtained by chemical beam epitaxy.
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78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Pseudomorphic GaAs/InGaAs single quantum wells by atmospheric pressure organometallic chemical vapor deposition

Daniel C. Bertolet, Jung‐Kuei Hsu, Stephen H. Jones, and Kei May Lau

Appl. Phys. Lett. 52, 293 (1988); http://dx.doi.org/10.1063/1.99497 (3 pages) | Cited 23 times

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High‐quality pseudomorphic GaAs/In0.12Ga0.88As single quantum wells (QW’s) were prepared by atmospheric‐pressure organometallic chemical vapor deposition. Photoluminesence spectra measured at 2.5 and 78 K exhibit intense, sharp peaks [full width at half‐maximum (FWHM)=2.6 meV for a 17‐Å well at 78 K] from the quantized energy transitions of the QW’s. Peak positions agree well with a square well calculation that includes the strain‐induced band‐gap shift in the In0.12Ga0.88As. Quite unlike previous work with QW’s in which the FWHM was found to exponentially increase with decreasing well width, we observed a narrowing of the QW signals as the well width went below ∼30 Å. In larger well samples (300 Å), the onset of surface crosshatch patterns was observed, which is expected from critical thickness theory.
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78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Impact ionization in AlxGa1−xAs for x=0.1–0.4

V. M. Robbins, S. C. Smith, and G. E. Stillman

Appl. Phys. Lett. 52, 296 (1988); http://dx.doi.org/10.1063/1.99498 (3 pages) | Cited 32 times

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The impact ionization coefficients in AlxGa1−xAs have been experimentally determined for compositions x≤0.4. These data are necessary for accurate device design and modeling. Both α, the electron ionization coefficient, and β, the hole ionization coefficient, decrease with increasing x, and there is no appreciable change in the ratio α/β over the range of compositions and electric fields studied.
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79.20.Kz Other electron-impact emission phenomena
85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors

Rapid thermal annealing of elevated‐temperature silicon implants in InP

B. Tell, K. F. Brown‐Goebeler, and C. L. Cheng

Appl. Phys. Lett. 52, 299 (1988); http://dx.doi.org/10.1063/1.99499 (3 pages) | Cited 22 times

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Rapid thermal annealing of elevated‐temperature Si implants in InP is shown to result in higher donor activation and electron mobility with lower‐temperature–shorter‐anneal cycles than for room‐temperature implants. The reduced cycles (temperature below 800 °C with times of ∼10 s) also result in process simplification with negligible thermal surface degradation and insignificant Si diffusion. The results are demonstrated with a dual‐energy implant scheme applicable to field‐effect transistors and with a single‐energy heavy‐dose implant useful for achieving low‐resistance ohmic contacts.
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81.40.Rs Electrical and magnetic properties related to treatment conditions
61.72.U- Doping and impurity implantation
72.20.Fr Low-field transport and mobility; piezoresistance
71.55.Eq III-V semiconductors

Optical investigations of the band structure of strained InAs/AlInAs quantum wells

M.‐H. Meynadier, J.‐L. de Miguel, M. C. Tamargo, and R. E. Nahory

Appl. Phys. Lett. 52, 302 (1988); http://dx.doi.org/10.1063/1.99500 (3 pages) | Cited 16 times

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We report photoluminescence and photoconductivity measurements on single InAs quantum wells under a 3.4% biaxial compression. The photoluminescence line, which is in the 1.2–1.6 μm wavelength range depending on well thickness, is interpreted as recombination between electrons and holes distributed over a range of confined energy states associated with quantum well width fluctuations. Photoconductivity is found to provide spectroscopic measurements of the optical transitions even for single, extremely thin quantum wells. We find excellent agreement between the measured transition energies and the result of an envelope function calculation taking into account the effect of both strain and quantum confinement.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors

Slope resistance characteristics of GaAs‐(Al,Ga)As‐GaAs single barrier structures

D. E. Lacklison, G. Duggan, J. J. Harris, C. T. B. Foxon, D. Hilton, C. Roberts, and C. M. Hellon

Appl. Phys. Lett. 52, 305 (1988); http://dx.doi.org/10.1063/1.99501 (3 pages) | Cited 2 times

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Measurements of the incremental slope resistance of a GaAs‐(Al,Ga)As‐GaAs single barrier structure have been made at temperatures between 70 and 230 K. In contrast with other work we deliberately concentrate on the region close to zero applied bias. The deficiencies in the often‐used Wentzel–Kramers–Brillouin analysis of the electrical characteristics are exposed in this regime, and an exact, Airy function approach is found to be essential to describe our observations.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
73.50.-h Electronic transport phenomena in thin films
73.61.Ey III-V semiconductors

Effect of strain on the band structure of GaAs and In0.2Ga0.8As

J. Hwang, C. K. Shih, P. Pianetta, G. D. Kubiak, R. H. Stulen, L. R. Dawson, Y.‐C. Pao, and J. S. Harris

Appl. Phys. Lett. 52, 308 (1988); http://dx.doi.org/10.1063/1.99502 (3 pages) | Cited 8 times

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The valence‐band structures of 50‐Å‐thick layers of GaAs(001) in tension and In0.2Ga0.8As(001) in compression have been determined using angle‐resolved photoemission spectroscopy. Our studies show that the Δ3+Δ4 bands and the Δ1 band respond differently to the strain perturbation. For strained GaAs(001), the Δ3+Δ4 bands (Px+Py‐like) are shifted up in energy by a maximum amount of 0.3 eV, while in contrast, the Δ1 band (Pz‐like) is shifted down by about 0.1 eV. For strained In0.2Ga0.8As(001), the band shifts are in the opposite direction, consistent with the opposite strain conditions. For both materials, the strain‐induced changes cannot be characterized simply by rigid band shifts, but rather exhibit significant wave vector dependence. This results in a reduction of the effective mass of the Δ3+Δ4 bands for both GaAs and In0.2Ga0.8As.
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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
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.60.Bs Mechanical and acoustical properties

Ordering‐induced changes in the optical spectra of semiconductor alloys

J. E. Bernard, S.‐H. Wei, D. M. Wood, and Alex Zunger

Appl. Phys. Lett. 52, 311 (1988); http://dx.doi.org/10.1063/1.99503 (3 pages) | Cited 25 times

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It is shown how the recently predicted and subsequently observed spontaneous long‐range ordering of pseudobinary A0.5B0.5C isovalent semiconductor alloys into the (AC)1(BC)1 superlattice structure (a CuAuI‐type crystal) gives rise to characteristic changes in the optical and photoemission spectra. We predict new direct transitions and substantial splittings of transitions absent in the disordered alloy.
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78.40.Fy Semiconductors
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
81.65.-b Surface treatments
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Current‐voltage characteristics of In0.53Ga0.47As/In0.52Al0.48As resonant tunneling barrier structures grown by molecular beam epitaxy

Yoshihiro Sugiyama, Tsuguo Inata, Shunichi Muto, Yoshiaki Nakata, and Satoshi Hiyamizu

Appl. Phys. Lett. 52, 314 (1988); http://dx.doi.org/10.1063/1.99504 (3 pages) | Cited 12 times

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Well width dependence and temperature dependence of negative differential resistance characteristics of InGaAs/InAlAs resonant tunneling barrier diodes were investigated. Peak current density was almost independent of temperature, while the valley current density increased with increasing temperature above 100 K. At room temperature, a peak‐to‐valley current ratio of 5.5 with a peak current density of 4.8×104 A/cm2 was obtained by reducing the quantum well width to a narrow 32.2 Å. This is the largest peak‐to‐valley current ratio ever reported for resonant tunneling barrier diodes at room temperature.
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73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors

Growth of the superconducting phase in ceramic Y1.2Ba0.8CuOy samples

R. Wördenweber, H. U. Krebs, F. Gelsdorf, K. Heinemann, G. V. S. Sastry, H. C. Freyhardt, and K. Winzer

Appl. Phys. Lett. 52, 317 (1988); http://dx.doi.org/10.1063/1.99505 (3 pages) | Cited 4 times

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Differently prepared samples with the nominal composition Y1.2Ba0.8CuOy are examined via microscopy, energy dispersive x‐ray analysis, x‐ray diffraction, and measurements of resistivity and susceptibility. Various phases are identified directly. Essentially these are Y2BaCuO5, which forms a matrix with semiconducting and antiferromagnetic properties and YBa2Cu3O7−x, which is present in a dendritic morphology. The dendritic appearance indicates that YBa2Cu3O7−x is formed by nucleation and growth during sintering. Despite the particular growth mechanism of sintered materials a strong analogy exists with dendritic growth during solid‐state transformations in metallic alloys.
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74.70.-b Superconducting materials other than cuprates
74.10.+v Occurrence, potential candidates
74.25.Ha Magnetic properties including vortex structures and related phenomena
64.70.K- Solid-solid transitions

Superconducting thin films of Y‐Ba‐Cu‐O produced by neodymium:yttrium aluminum garnet laser ablation

L. Lynds, B. R. Weinberger, G. G. Peterson, and H. A. Krasinski

Appl. Phys. Lett. 52, 320 (1988); http://dx.doi.org/10.1063/1.99480 (3 pages) | Cited 44 times

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Superconducting thin films of Y‐Ba‐Cu‐O produced by laser ablation of nonsuperconducting targets by 1064 nm neodymium:yttrium aluminum garnet radiation in an oxygen ambient are described. Deposition rates of 100 Å/s were achieved for 1 J pulses at 30 Hz. Scanning Auger microscopy indicates phase segregated films. Optical probing of ablated flux suggests it consists of atomic and molecular fragments.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
79.20.Ds Laser-beam impact phenomena
81.15.Jj Ion and electron beam-assisted deposition; ion plating
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