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12 Nov 1990

Volume 57, Issue 20, pp. 2045-2155

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Photoreflectance study of surface Fermi level in GaAs and GaAlAs

H. Shen, M. Dutta, L. Fotiadis, P. G. Newman, R. P. Moerkirk, W. H. Chang, and R. N. Sacks

Appl. Phys. Lett. 57, 2118 (1990); http://dx.doi.org/10.1063/1.103916 (3 pages) | Cited 85 times

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Franz–Keldysh oscillations from GaAs and AlGaAs structures have been studied and we find that the electric field obtained from the oscillations is in agreement with that derived from electrostatic calculations. Our results show that illumination from pump and probe beams in a normal photoreflectance experiment can significantly affect the measurement and thus erroneously lead to a reduced value of the electric field. The Fermi level on the bare surface of AlGaAs with different Al mole fraction has also been determined.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
73.61.Ey III-V semiconductors

n‐type doping of amorphous silicon using tertiarybutylphosphine

K. Gaughan, S. Nitta, J. M. Viner, J. Hautala, and P. C. Taylor

Appl. Phys. Lett. 57, 2121 (1990); http://dx.doi.org/10.1063/1.103917 (3 pages) | Cited 1 time

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The use of a liquid organic source for n‐type doping in hydrogenated amorphous silicon (a‐Si:H) is described. Tertiarybutylphosphine (TBP) vapor is added to silane in a rf glow discharge process to produce doped a‐Si:H thin films. Impurity levels from parts per million to about 1% phosphorus have been incorporated into the film with this method. Measurements of dark conductivity, photoconductivity, conductivity activation energy, electron spin resonance, and sub‐gap optical absorption of the TBP‐doped films are compared to those published for films doped with phosphine.
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72.80.Ng Disordered solids
73.61.Ey III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects

Nucleation rate and glide velocity of misfit dislocations in Si1−xGex/(100) Si heterostructures

D. C. Houghton

Appl. Phys. Lett. 57, 2124 (1990); http://dx.doi.org/10.1063/1.103918 (3 pages) | Cited 25 times

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Expressions are presented for the rate of strain relaxation, misfit dislocation nucleation, and propagation in strained Si1−xGex/(100)Si heterostructures. Independent measurements of misfit dislocation nucleation and 60° type a/2 〈110〉 dislocation glide velocity in the temperature range 450–1000 °C have led to a model which characterizes the kinetics of strain relaxation for 0<x<0.25. The generalized force or effective stress τeff, which drives strain relaxation, is defined for an arbitrary strain profile and strained‐layer geometry. New experimental data for misfit dislocation glide velocity (V in cm s−1) have been fitted to a semi‐empirical relation found to be appropriate for all Si1−xGex/(100)Si heterostructures, V=(4±2)⋅1013(τeff /μ)2 exp−[(2.25±0.05)/kT]. An analogous expression for the nucleation rate of new misfit dislocation segments was determined from experimental data, dN(t)/dt=BN0(τeff /μ)2.5 exp−[2.5±0.2)/kT], where N0 is the density of heterogeneous nuclei and B is a material constant ∼1018 s−1 for Si1−xGex. These expressions are combined in a kinetic model which is then used to predict the rate of strain relaxation in Si1−xGex/Si heterostructures.
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62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Gy Mechanical properties; surface strains
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

p‐type ZnSe by nitrogen atom beam doping during molecular beam epitaxial growth

R. M. Park, M. B. Troffer, C. M. Rouleau, J. M. DePuydt, and M. A. Haase

Appl. Phys. Lett. 57, 2127 (1990); http://dx.doi.org/10.1063/1.103919 (3 pages) | Cited 317 times

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A novel approach to producing p‐type ZnSe epitaxial layers is reported which involves nitrogen atom beam doping during molecular beam epitaxial growth. Net acceptor concentrations as large as 3.4×1017 cm−3 have been measured in nitrogen atom beam doped ZnSe/GaAs heteroepitaxial layers which represents the highest acceptor concentration reported to date for ZnSe:N epitaxial material grown by molecular beam epitaxy. In addition, light‐emitting diodes based on ZnSe:N/ZnSe:Cl, p‐n homojunctions have been found to exhibit dominant electroluminescence in the blue region of the visible spectrum at room temperature.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.U- Doping and impurity implantation
85.40.Hp Lithography, masks and pattern transfer
85.60.Jb Light-emitting devices

Novel superlattice in a selectively doped wide parabolic quantum well with a modulated potential

J. Jo, M. Santos, M. Shayegan, Y. W. Suen, L. W. Engel, and A‐M. Lanzillotto

Appl. Phys. Lett. 57, 2130 (1990); http://dx.doi.org/10.1063/1.103920 (3 pages) | Cited 14 times

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We report the realization of a novel superlattice which contains a high mobility (≂ 1.1×105 cm2/V s at 4 K) degenerate electron system. The structure consists of a wide, undoped AlxGa1−xAs well bounded by undoped (spacer) and doped layers of AlyGa1−yAs (y≳x) on both sides. The alloy composition in the well (x) is graded in such a way as to result in a parabolic potential with an additional sinusoidal modulation superimposed on it. Once transferred into this well, the electrons screen the parabolic potential and an electron system with a modulated charge density is obtained. We present self‐consistent quantum mechanical calculations of the electronic system, and report our characterization of the structure by secondary‐ion mass spectrometry and magnetotransport measurements.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states

Critical current enhancement in multilayered Y1Ba2Cu3O7−y/Y1Ba2(Cu1−xNix)O7−y structures

S. Witanachchi, S. Y. Lee, L. W. Song, Y. H. Kao, and D. T. Shaw

Appl. Phys. Lett. 57, 2133 (1990); http://dx.doi.org/10.1063/1.104155 (3 pages) | Cited 6 times

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Multilayers of YBaCuO superconductors and Ni‐doped YBaCuO superconductors have been grown by the laser ablation technique to study the flux pinning properties of the nonmagnetic/magnetic superconducting heterostructures. Even though Ni doping depressed the superconducting properties of the single layer films, when sandwiched between high quality YBaCuO films, the composite showed high critical temperatures. Three‐layer and five‐layer structures of the YBaCuO/YBaCuNiO system become superconducting around 87 K when the doped layer thickness was below 100 Å. Three‐layer structures grown on ZrO2(100) showed critical current densities of 3×106 A/cm2 at 77 K, which is about three times larger than the reported results in the literature. Epitaxial layer growth between the two superconductors was indicated by x‐ray diffraction measurements, which showed complete c‐axis orientation with full width at half maximum of 0.45° in a (006) line scan. Behavior of the critical current up to 0.85 T and temperatures down to 66 K has been studied. Critical current densities close to 4.5×106 A/cm2 in 0.85 T fields perpendicular to the films have been obtained at 67 K.
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74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.78.-w Superconducting films and low-dimensional structures

Metalorganic chemical vapor deposition of Tl2Ba2CaCu2Ox superconducting thin films using fluorinated β‐diketonate source reagents

N. Hamaguchi, R. Gardiner, P. S. Kirlin, R. Dye, K. M. Hubbard, and R. E. Muenchausen

Appl. Phys. Lett. 57, 2136 (1990); http://dx.doi.org/10.1063/1.104156 (3 pages) | Cited 14 times

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Superconducting Tl2Ba2CaCu2Ox films were fabricated using a three‐step process. Amorphous BaCaCuOF films were deposited on MgO(100) single‐crystal substrates by metalorganic chemical vapor deposition at 500 °C using fluorinated β‐diketonate complexes of Ba, Ca, and Cu. The fluorine was stripped in wet oxygen at 785 °C and c‐axis oriented Tl2Ba2CaCu2Ox films were then formed by annealing in dry at 870 °C in the presence of Tl2O3/Ba2Ca2CuN3Ox pellets. The best films showed onsets of superconductivity at 125 K and zero resistivity was achieved by 108 K. Critical current densities as high as 104 A/cm2 were obtained at 90 K.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.70.-b Superconducting materials other than cuprates
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Silver‐BiSrCaCuO chemical reactions

Y. Hwu, M. Marsi, Chanyong Hwang, J. Seutjens, D. C. Larbalestier, M. Onellion, and G. Margaritondo

Appl. Phys. Lett. 57, 2139 (1990); http://dx.doi.org/10.1063/1.103921 (3 pages) | Cited 11 times

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We used synchrotron‐radiation photoemission to investigate the chemical reactions that occur during the silver cladding process of BiSrCaCuO−used to increase the critical current density by over a factor of 50. We find that the Cu‐O planes are not directly affected by the chemical reaction, and that such a reaction strongly affects the Bi and Sr atoms.
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74.70.-b Superconducting materials other than cuprates
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Direct conversion of superconducting Y2Ba4Cu7O15−δ from YBa2Cu3O7−x at atmospheric pressure in an O2 ambient

J. M. Liang and L. J. Chen

Appl. Phys. Lett. 57, 2142 (1990); http://dx.doi.org/10.1063/1.104157 (3 pages)

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Direct conversion of superconducting Y2Ba4Cu7O15−δ (Y‐247) from YBa2Cu3O7−x (Y‐123) was achieved at atmospheric pressure. The Y‐247 samples were synthesized by the reactions of Y‐123 and Cu‐(NO3)2 at 860 °C in an O2 ambient. The results strongly suggest that Y‐247 is a thermodynamically more stable phase than Y‐123 at the atmospheric pressure. The conversion also provides a novel and simple route to synthesize the Y‐247 compound.
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74.70.-b Superconducting materials other than cuprates
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Pyrophoric synthesis technique for multicomponent high‐temperature superconductors

D. Bhattacharya, L. C. Pathak, S. K. Mishra, D. Sen, and K. L. Chopra

Appl. Phys. Lett. 57, 2145 (1990); http://dx.doi.org/10.1063/1.104158 (3 pages) | Cited 19 times

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A pyrophoric technique using an explosive exothermic reaction has been developed to yield calcined and microscopically homogeneous (0.3 μm size) powders of multicomponent cuprate systems. The technique has been used to synthesize superconducting materials of variable composition of the type M1M2⋅⋅⋅MnOx. The bulk materials prepared from these powders show sharp (1 K) superconducting transitions and nearly ideal Meissner effect.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
74.70.-b Superconducting materials other than cuprates
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.35.-x Polymers: properties; reactions; polymerization

Use of high Tc superconductors for far‐infrared Fabry–Perot resonators

K. F. Renk, J. Betz, J. Schützmann, A. Prückl, B. Brunner, and H. Lengfellner

Appl. Phys. Lett. 57, 2148 (1990); http://dx.doi.org/10.1063/1.103922 (2 pages) | Cited 12 times

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In this letter we report on the application of high Tc superconductors for fabrication of far‐infrared Fabry–Perot resonators. Thin films of YBa2Cu3O7−δ deposited on MgO substrates by the laser ablation technique were used as reflectors. Two films on two different MgO plates were arranged parallel at a distance determining the lowest order resonance. We demonstrate operation of a resonator in a frequency range (up to about 300 cm−1) in which MgO is transparent at low temperature.
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07.60.-j Optical instruments and equipment
42.79.-e Optical elements, devices, and systems
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
78.66.-w Optical properties of specific thin films

Observation of proposed flux pinning sites in neutron‐irradiated YBa2Cu3O7−x

J.‐W. Lee, H. S. Lessure, D. E. Laughlin, M. E. McHenry, S. G. Sankar, J. O. Willis, J. R. Cost, and M. P. Maley

Appl. Phys. Lett. 57, 2150 (1990); http://dx.doi.org/10.1063/1.104159 (3 pages) | Cited 14 times

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Microstructure and magnetic hysteresis have been compared for two samples of the YBa2Cu3O7−δ (δ∼0) high‐temperature superconductor, one unirradiated, and one irradiated with fast neutrons (E≳0.1 MeV) to a fluence of 3×1018 n/cm2. Notable changes in the microstructure include strain‐induced contrast from regions 2–7 nm in size. An intrinsic critical current density (Jc) of 4.6×106 A/cm2 in zero field at 4 K has been determined from magnetic hysteresis measurements for the irradiated sample while 1.2×106 A/cm2 is noted for the unirradiated sample. We propose that the observed defect structure in the irradiated material is responsible for increased pinning and consequently higher Jc’s.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
61.80.Hg Neutron radiation effects
74.70.-b Superconducting materials other than cuprates

Direct deposition of magnetic dots using a scanning tunneling microscope

M. A. McCord and D. D. Awschalom

Appl. Phys. Lett. 57, 2153 (1990); http://dx.doi.org/10.1063/1.103923 (3 pages) | Cited 65 times

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A scanning tunneling microscope has been used to directly deposit nanometer‐scale structures into the input coil of a planar dc superconducting quantum interference device microsusceptometer. Iron pentacarbonyl was used as the source gas for the deposits, yielding dots with diameters ranging from 10 to 30 nm and heights from 30 to 100 nm. Measurements on the particles at low temperatures show them to be magnetic and reveal macroscopic spin properties.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.40.Hp Lithography, masks and pattern transfer
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
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