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6 Apr 1992

Volume 60, Issue 14, pp. 1649-1764

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Intensity oscillations in reflection high‐energy electron diffraction during disilane gas source molecular beam epitaxy

Masayuki Hiroi, Kazuhisa Koyama, Toru Tatsumi, and Hiroyuki Hirayama

Appl. Phys. Lett. 60, 1723 (1992); http://dx.doi.org/10.1063/1.107197 (3 pages) | Cited 14 times

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Reflection high‐energy electron diffraction (RHEED) intensity oscillations during growth in disilane gas source Si molecular beam epitaxy (MBE) on Si(100) and (111) surfaces were observed under low substrate temperature and high disilane flow rate conditions. As has been observed in solid source Si MBE, these oscillations included periods corresponding to periods for monolayer and bilayer growth. On Si(100) surfaces, growth rate, which was estimated from the periods of the oscillations, was limited by a reaction process whose activation energy was 47 kcal/mol. This rate limitation is thought to stem from hydrogen desorption from monohydride phase on the Si(100). On Si(111) surfaces, oscillations in specular beam intensity were clearly observed. Although clear oscillations in the 7×7 diffraction spots could not be observed because of intensity weakness of the fractional order spots under disilane exposure. At high disilane flow rates, 7×7 diffraction spots almost disappeared and only fundamental spots were observed. The fundamental 1×1 RHEED pattern also indicated monohydride structure on Si(111) surface during the growth.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Room‐temperature recombination of point defects produced in silicon p‐n junctions by light ion irradiation

R. S. Germaná and S. U. Campisano

Appl. Phys. Lett. 60, 1726 (1992); http://dx.doi.org/10.1063/1.107198 (3 pages) | Cited 3 times

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The reverse current in a p+‐n silicon junction irradiated by high‐energy helium ions was measured as a function of time at room temperature. A rather large exponential decrease of the reverse current has been observed and the measured time constant is 3±0.2 days. Defect profiling by current‐voltage characteristics indicates that the damage recombination occurs without long‐range migration of defects. The defects responsible for the reverse current of irradiated silicon diodes after the long room‐temperature aging are characterized by an energy level 0.11 eV above Si midgap.
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61.72.-y Defects and impurities in crystals; microstructure
61.80.Jh Ion radiation effects
71.55.Ht Other nonmetals
85.30.Kk Junction diodes

Direct observation of band‐edge luminescence and alloy luminescence from ultrametastable silicon‐germanium alloy layers

J. Spitzer, K. Thonke, R. Sauer, H. Kibbel, H.‐J. Herzog, and E. Kasper

Appl. Phys. Lett. 60, 1729 (1992); http://dx.doi.org/10.1063/1.107199 (3 pages) | Cited 37 times

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Ultrametastable silicon‐germanium (Si1−xGex) layers with a Ge content x in the range from about 20% to 27% were grown by Si‐MBE at temperatures far below 550 °C (325–450 °C). The thicknesses of the layers (up to 500 nm) exceed the equilibrium thickness by a factor of up to 50. We observe in the as‐grown samples without any annealing both the excitonic Si1−xGex band‐edge luminescence and a broad alloy luminescence of unknown origin. The two peaks have an energy difference of ≊144 meV and shift linearly with the Ge content. The alloy band luminescence disappears when strain relaxation sets on upon annealing at around 600 °C.
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78.55.Hx Other solid inorganic materials
78.66.-w Optical properties of specific thin films

Spin dependent photocurrents in ribbon solar cells

C. H. Seager, E. L. Venturini, and W. K. Schubert

Appl. Phys. Lett. 60, 1732 (1992); http://dx.doi.org/10.1063/1.107200 (3 pages) | Cited 3 times

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Microwave resonance induced variations in the short circuit photocurrent of edge‐defined film‐fed growth ribbon silicon solar cells have been observed. These signals have zero‐crossing g values and linewidths which are similar to electron spin resonance and spin dependent transport (SDT) observations on silicon bicrystals, damaged silicon, and polycrystalline silicon. The SDT signals seen here depend on cell illumination levels in a way that suggests that the values of recombination velocity at electrically active linear boundaries decrease with illumination intensity. Hydrogen processed cells show markedly smaller SDT response, consistent with the passivation of Si dangling bond defects. While only dangling bond SDT response is apparent at 300 K, we suggest that similar experiments performed at low temperatures may have the resolution to identify the centers responsible for the majority of the electron‐hole recombination events in these cells.
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72.40.+w Photoconduction and photovoltaic effects
71.55.Ht Other nonmetals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
76.30.-v Electron paramagnetic resonance and relaxation

Temperature dependence of photoconductivity in buckminsterfullerene films

J. Mort, M. Machonkin, R. Ziolo, D. R. Huffman, and M. I. Ferguson

Appl. Phys. Lett. 60, 1735 (1992); http://dx.doi.org/10.1063/1.107201 (3 pages) | Cited 31 times

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We report the temperature dependence from 330 to 230 K of the photoconductivity measured in sublimed films of buckminsterfullerene, specifically, C60/70, up to 3 μm thick. In contrast to the temperature dependence of the dark conductivity, where reversible structure, associated with the onset of a phase transition to orientational ordering below 250 K, is observed, the photoconductivity shows an essentially monotonic decrease to lower temperatures. This provides additional evidence that the thermal generation rate increases as the C60/70 becomes orientationally ordered. It also suggests that the increased order below the transition temperature does not lead to significantly increased carrier mobilities.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
64.70.K- Solid-solid transitions

Molecular beam epitaxial regrowth on in situ plasma‐etched AlAs/AlGaAs heterostructures

Kent D. Choquette, M. Hong, R. S. Freund, S. N. G. Chu, J. P. Mannaerts, R. C. Wetzel, and R. E. Leibenguth

Appl. Phys. Lett. 60, 1738 (1992); http://dx.doi.org/10.1063/1.107202 (3 pages) | Cited 12 times

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Epitaxial regrowth by solid‐source molecular beam epitaxy (MBE) on dry etched heterostructures possessing exposed AlAs surfaces is accomplished for the first time using a vacuum integrated processing. Samples composed of multilayers of AlAs and AlGaAs are patterned with a SiO2 mask and are anisotropically etched using a low damage electron cyclotron resonance (ECR) SiCl4 plasma process. Etched samples are transferred in ultrahigh vacuum between the ECR and MBE chambers to avoid atmospheric exposure before regrowth. Microstructural analysis of the overgrown layers by scanning and transmission electron microscopy indicates that epitaxial regrowth on both the etched field and vertical sidewalls is achieved. The regrown material is found to contain microtwin plates, but few dislocations, indicating the good quality of the overgrowth.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.65.-b Surface treatments

Flux pinning by ordered oxygen‐deficient phases in nearly stoichiometric YBa2Cu3O7−δ single crystals

João L. Vargas and David C. Larbalestier

Appl. Phys. Lett. 60, 1741 (1992); http://dx.doi.org/10.1063/1.107203 (3 pages) | Cited 54 times

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We propose that the critical currents of nearly stoichiometric YBa2Cu3O7−δ single crystals (δ<0.1) are determined by fluxon pinning at ordered oxygen‐vacancy domains. Since these domains are also superconducting, albeit with lower Tc and Hc than the stoichiometric matrix, their pinning strength at a given temperature will increase as they are driven normal by an increasing applied field. Experimentally, the magnetization hysteresis curves display a secondary maximum, characteristic of pinning by a superconducting second phase. The ordered‐vacancy domains are assumed to result from a spinodal decomposition. The density and size of the domains were calculated on this assumption. The bulk pinning force was computed by direct summation. In the limit of low temperatures, the calculated values of critical current density Jc are in good agreement with measurements on high‐quality single crystals.
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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
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Dielectric properties of SrTiO3 thin films used in high Tc superconducting field‐effect devices

A. Walkenhorst, C. Doughty, X. X. Xi, S. N. Mao, Q. Li, T. Venkatesan, and R. Ramesh

Appl. Phys. Lett. 60, 1744 (1992); http://dx.doi.org/10.1063/1.107204 (3 pages) | Cited 41 times

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The dielectric constant ☒ of thin epitaxial SrTiO3 films used as dielectric layers in high Tc superconducting field‐effect devices has been studied. ☒ in these thin films was found to have much weaker dependence on temperature and applied electric field than the bulk material. The breakdown characteristics of gate structures containing SrTiO3 dielectric layers are strongly influenced by the metal used as the gate electrode.
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77.55.-g Dielectric thin films
85.30.Tv Field effect devices

Preparation of superconductive Y‐Ba‐Cu‐O layers formed by aggregates of released particles using laser deposition in air

Jan Wild, Pavel Engst, Svatopluk Civiš, Jiří Pochylý, and Jarmila Prachařová

Appl. Phys. Lett. 60, 1747 (1992); http://dx.doi.org/10.1063/1.107205 (3 pages) | Cited 4 times

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Superconductive Y‐Ba‐Cu‐O layers formed by aggregates of released particles were prepared by laser deposition using a nontraditional method without a vacuum apparatus, in air, at atmospheric pressure. The layers were deposited on a single‐crystal MgO (001) substrate at a temperature of 973 K. A zero‐resistance critical temperature of 69 K was attained after annealing in an oxygen stream at 1173 K. The deposited layers were analyzed by x‐ray powder diffraction, scanning electron microscopy, and energy‐dispersive x‐ray analysis.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates

Measurement of ζ potential of YBa2Cu3O7−δ from the adsorption of hydronium ions (H+, OH−)

Annie Q. Wang and Timothy R. Hart

Appl. Phys. Lett. 60, 1750 (1992); http://dx.doi.org/10.1063/1.107206 (3 pages) | Cited 2 times

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The adsorption of hydronium ions, H+ and OH−, on YBa2Cu3O7 in electrolytic solution is measured. The curve of the ζ potential (zeta potential) of YBa2Cu3O7 gives the point‐of‐zero ζ potential (pzzp). The electronegativity of YBa2Cu3O7 can be found from the pzzp. The experimental value of the electronegativity is compared with the calculated result.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
74.70.-b Superconducting materials other than cuprates

Epitaxial MgO buffer layers for YBa2Cu3O7−x thin film on GaAs

L. D. Chang, M. Z. Tseng, E. L. Hu, and D. K. Fork

Appl. Phys. Lett. 60, 1753 (1992); http://dx.doi.org/10.1063/1.107207 (3 pages) | Cited 41 times

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Epitaxial MgO thin films have been grown on GaAs using electron beam (e‐beam) evaporation. X‐ray diffraction indicates that the epitaxial relations are MgO[001]//GaAs[001] and MgO[110]//GaAs[110]. The rocking curve widths are less than 1.5°. The refractive index is 1.73 and the dielectric strength is in excess of 4×106 V/cm. The MgO epitaxial films were used as a buffer layer for the growth of in situ YBa2Cu3O7−x on GaAs. The room‐temperature resistivity of this film is 450–530 μΩ cm and Tc (R=0) is 85–87 K. The critical current density at 77 K is 4–6.7×104 and 1–3.8×106 A/cm2 at 4.2 K, in zero applied field.
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68.55.-a Thin film structure and morphology
74.70.-b Superconducting materials other than cuprates

Josephson characteristics in a‐axis oriented YBa2Cu3O7−δ/PrBa2Cu3O7−δ′/YBa2Cu3O7−δ junctions

Tatsunori Hashimoto, Masayuki Sagoi, Yoshihisa Mizutani, Jiro Yoshida, and Koichi Mizushima

Appl. Phys. Lett. 60, 1756 (1992); http://dx.doi.org/10.1063/1.107208 (3 pages) | Cited 63 times

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A sandwich‐type all‐oxide Josephson junction consisting of an a‐axis oriented YBa2Cu3O7−δ/PrBa2Cu3O7−δ′/YBa2Cu3O7−δ structure has been realized and its Josephson characteristics experimentally investigated. Almost all the fabricated junctions showed the Josephson characteristics, including a resistively shunted junction (RSJ)‐like current‐voltage characteristic and a Fraunhofer‐like magnetic‐field dependence of the critical current. The obtained maximum values of the critical‐current density jc and the IcRn value were 110 A/cm2 and 80 μV, respectively, for a 50‐nm‐thick PBCO interlayer at 3 K. Besides, the temperature dependencies of the critical current and the normal resistance were measured. Ic was proportional to exp(− aT1/2), where a is a constant.
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85.25.Cp Josephson devices
81.15.Cd Deposition by sputtering
74.50.+r Tunneling phenomena; Josephson effects
74.70.-b Superconducting materials other than cuprates

New six face lithography technique for realization of contacts on μm size Y1Ba2Cu3O7−x single crystals

Melissa Charalambous, Jacques Chaussy, and Pascal Lejay

Appl. Phys. Lett. 60, 1759 (1992); http://dx.doi.org/10.1063/1.107209 (3 pages) | Cited 4 times

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We have developed a new contact technique for use on very small Y1Ba2Cu3O7−x single crystals (typical dimensions: 100×100×20 μm). A precise contact pattern (resolution ≊2 μm) is realized on the different faces of the sample. This allows the injection of a current parallel to a single crystallographic axis, without mixing of the anisotropic conduction channels. Contact resistivities are satisfactory: 1×10−5 Ω cm2 for the ab contacts, 1×10−6 Ω cm2 for the c‐axis contacts. To date the technique has been used to directly measure the c‐axis resistivity of the Y1Ba2Cu3O7−x compound, but other applications such as anisotropic thermal conductivity and thermoelectric power are possible.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential
74.70.-b Superconducting materials other than cuprates

Short‐range order effects on copper L3,2 transitions in Cu‐Pd alloys

Kannan M. Krishnan, E. S. K. Menon, P. Huang, Prabhakar P. Singh, and D. de Fontaine

Appl. Phys. Lett. 60, 1762 (1992); http://dx.doi.org/10.1063/1.107210 (3 pages) | Cited 3 times

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The unoccupied d‐electron density of states of a range of Cu1−xPdx (x=0–0.35) alloys, based on measurements of copper L3,2 transitions in electron energy‐loss spectroscopy, is shown to be critically dependent on short‐range order. This finding is supported by band structure calculations where the d‐hole count at the Cu site for disordered alloys is found to be independent of the composition. Based on the above, a linear correlation between the degree of short‐range order, as defined by the splitting of the diffuse maxima in the diffraction patterns, and the d‐band occupancy has been established.
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61.66.Dk Alloys
68.37.-d Microscopy of surfaces, interfaces, and thin films
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