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2 Sep 1991

Volume 59, Issue 10, pp. 1141-1262

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Substrate temperature measurement in a molecular beam epitaxy chamber using in situ GaAs photoluminescence monitoring

C. J. Sandroff, F. S. Turco‐Sandroff, L. T. Florez, and J. P. Harbison

Appl. Phys. Lett. 59, 1215 (1991); http://dx.doi.org/10.1063/1.105507 (3 pages) | Cited 1 time

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We use GaAs photoluminescence (PL) obtained in situ in an epitaxial growth chamber to measure substrate temperatures from 25 to 450 °C with an accuracy of ±8 °C. Since temperature is obtained directly from the measured GaAs band gap, the approach is free of the problems associated with thermal contacts and emissivity calibration, which are encountered when using thermocouples and pyrometers. The PL technique can be used for any type of sample mounting, and since absolute temperature is measured, it is unnecessary to track the thermal history of the sample.
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07.20.Dt Thermometers
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Carrier concentration determination by photoreflectance at E1 in thin film, highly doped GaAs

Ali Badakhshan, R. Glosser, S. Lambert, Mark Anthony, R. S. Sillmon, P. E. Thompson, and Kambiz Alavi

Appl. Phys. Lett. 59, 1218 (1991); http://dx.doi.org/10.1063/1.105508 (3 pages) | Cited 8 times

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Photoreflectance (PR) response at the E1 (2.9 eV) transition of GaAs doped with Si, Zn, and Be was investigated within the range of 1.5×1015 to 2×1019 cm−3. Growth technique was either metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). We find that Γ1, the broadening parameter of the E1 structure increases linearly with the logarithm of the measured carrier concentration over the range of ≊1×1017 to ≊1×1019 cm−3. A slope of 56±5 meV/decade describes all Si:GaAs samples independent of growth technique. For p‐GaAs, the slope is 30±3 meV/decade over a comparable range and is independent of doping element as well as growth technique. This linear relation could be employed as a contactless means of determining carrier concentration. The energy position of E1 shows no significant shift in the above range. We believe that the broadening is a result of the doping produced, electric field within the depletion region.
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78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Minority carrier lifetime of HgCdTe from photoconductivity decay method

Joseph Reichman

Appl. Phys. Lett. 59, 1221 (1991); http://dx.doi.org/10.1063/1.105509 (3 pages) | Cited 4 times

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The results of an analytical study of the photoconductivity decay (PCD) method for measuring carrier lifetimes of n‐type HgCdTe show that the measurements give much higher values than the minority carrier lifetimes when trapping is significant. In contrast, for p‐type HgCdTe, the PCD method gives results equal to or less than the minority carrier lifetime under the same trapping conditions. The difference in results between n‐type and p‐type HgCdTe is due to the different recombination properties of excess electrons when they are majority carriers or minority carriers, respectively.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.61.Ga II-VI semiconductors

Diffusion of manganese in GaAs and its effect on layer disordering in AlxGa1−xAs‐GaAs superlattices

C. H. Wu, K. C. Hsieh, G. E. Höfler, N. EL‐Zein, and N. Holonyak

Appl. Phys. Lett. 59, 1224 (1991); http://dx.doi.org/10.1063/1.105510 (3 pages) | Cited 4 times

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Several diffusion runs of Mn in GaAs are performed in sealed quartz ampoules with four different Mn‐containing sources: (a) solid crystal granules of Mn, (b) Mn3As, (c) MnAs, and (d) Mn thin films coated on GaAs substrates. Among these, only MnAs results in a smooth GaAs surface and uniform doping distributions. For the others interactions between the source materials and GaAs substrates give rise to poor surface morphologies and inhomogeneous distributions of new‐phase (Mn,Ga) crystals. For diffusion at 800 °C, surface p‐type carrier concentrations as high as 1020/cm3 are obtained. Diffusion profiles determined by C‐V techniques resemble those obtained for Zn diffusions. A substitutional‐interstitial mechanism is suggested as the primary diffusion mechanism for Mn in GaAs. Data are also presented showing that layer disordering in AlGaAs‐GaAs superlattices can be induced by Mn impurities.
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66.30.J- Diffusion of impurities
68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Thermal acceptor formation in nitrogen‐doped silicon

Deren Yang, Jun Lu, Liben Li, Hongnian Yao, and Duanling Que

Appl. Phys. Lett. 59, 1227 (1991); http://dx.doi.org/10.1063/1.105511 (3 pages) | Cited 4 times

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The nitrogen‐doped Czochralski (CZ) silicon crystals were grown in a nitrogen atmosphere under reduced pressure. The results show that the resistivity of n‐type N‐doped silicon increases rapidly with annealing time above 700 °C, but that of p‐type N‐doped CZ silicon decreases rapidly under the same conditions. It is suggested that thermal acceptors (TA) are formed in N‐doped silicon. The concentration of thermal acceptor can reach to 1×1014 atom/cm3. The higher the annealing temperature, the longer the time for the maximum thermal acceptor concentration to appear. Nitrogen and oxygen impurities play important roles for generating the thermal acceptor. It is postulated that the thermal acceptor is a kind of Si‐O‐N complex.
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72.80.Cw Elemental semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
71.55.Ht Other nonmetals

Cooperative quantum confinement of excitons bound to isoelectronic impurity complexes in Si1−xGex/Si superlattices

R. A. Modavis, D. G. Hall, J. Bevk, and B. S. Freer

Appl. Phys. Lett. 59, 1230 (1991); http://dx.doi.org/10.1063/1.105512 (3 pages) | Cited 8 times

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Excitons bound to isoelectronic impurity complexes in strained Si1−xGex/Si superlattices (SLs) grown on Si(100) substrates exhibit a novel type of cooperative quantum confinement. The small conduction‐band and much larger valence‐band offsets in this material system confine an electron much less effectively than a hole. The short‐range potential associated with isoelectronic electron traps located within the alloy layers of the SL provides an additional mechanism for localizing electrons within the wells of the SL. We use Be isoelectronic complexes to demonstrate and explore this cooperative confinement of excitons in Si1−xGex/Si superlattices.
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71.35.-y Excitons and related phenomena
73.20.Fz Weak or Anderson localization
73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.66.-w Optical properties of specific thin films

Submicron YBa2Cu3O7−δ‐Ag‐YBa2Cu3O7−δ superconducting proximity junctions

M. A. M. Gijs, J. B. Giesbers, F. C. M. J. M. van Delft, C. E. Timmering, A. M. Gerrits, and A. Slob

Appl. Phys. Lett. 59, 1233 (1991); http://dx.doi.org/10.1063/1.105513 (3 pages) | Cited 8 times

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Using a deep submicron structuring process for oxide superconducting films, we have fabricated planar YBa2Cu3O7−δ‐Ag‐YBa2Cu3O7–δ proximity junctions operating in the liquid nitrogen temperature region. Under microwave radiation Shapiro steps are generated in the current‐voltage characteristic, in accordance with the resistively shunted junction model.
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74.50.+r Tunneling phenomena; Josephson effects
71.20.-b Electron density of states and band structure of crystalline solids
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures

Flux pinning and critical current density of a Y1Ba2Cu3O7−x superconducting thin film

Takashi Matsuura and Hideo Itozaki

Appl. Phys. Lett. 59, 1236 (1991); http://dx.doi.org/10.1063/1.105514 (3 pages) | Cited 10 times

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The relation between the critical current density and the pinning potential of an epitaxial Y1Ba2Cu3O7−X thin film was investigated. The pinning potential was evaluated from the temperature dependence of the resistivity in various values of a magnetic field. The pinning potential was inversely proportional to the applied magnetic field and had the anisotropy in the direction of the magnetic field. Critical current density of the thin film was calculated using the obtained pinning potential. This calculated result was consistent with the critical current density measured by a four‐probe method. 
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74.70.-b Superconducting materials other than cuprates
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures

Enhanced flux pinning by combined atomic substitution and phase decomposition in cuprate superconductors

J. L. Tallon, D. M. Pooke, R. G. Buckley, M. R. Presland, N. E. Flower, S. Gibson, and P. W. Gilberd

Appl. Phys. Lett. 59, 1239 (1991); http://dx.doi.org/10.1063/1.105515 (3 pages) | Cited 6 times

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The use of combined atomic substitution and phase decomposition is shown to achieve substantial enhancement of flux pinning in Y–Ba‐Cu–O ceramics. The substituent is chosen to provide a high density of nucleation sites for decomposition and at the same time enhancing Tc in the resulting composite superconductor. Bulk YBa2Cu4O8 (124) with 2.5% La substituted for Ba is decomposed by a short anneal beyond the stability boundary for YBa2Cu3O7 (123) at low oxygen pressure. The product, principally La‐substituted 123 <m1;37p>with stacking faults and precipitates of CuO in the grain boundaries, exhibits a 17‐fold enhancement in intragrain Jc at 77 K and 0.75 Tesla over unprocessed 123, rising to 50‐fold at 85 K. Magnetization Jc exceeds 104 A/cm2 at 0.75 Tesla for temperatures up to 87 K, the highest so far observed for a superconductor.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.70.-b Superconducting materials other than cuprates
74.25.Bt Thermodynamic properties

Transistor characteristics in a three‐terminal structure having YBa2Cu3O7−x electrodes on an insulating SrTiO3 substrate

Akira Yoshida, Hirotaka Tamura, Hideki Takauchi, and Shinya Hasuo

Appl. Phys. Lett. 59, 1242 (1991); http://dx.doi.org/10.1063/1.106390 (3 pages) | Cited 2 times

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Transistor characteristics in which both voltage and current gains exceeded one, were observed at 4.2 K in a three‐terminal superconducting structure. A high critical‐temperature superconducting YBa2Cu3O7−x emitter and collector were fabricated on a high‐permittivity insulating SrTiO3 dielectric with a back‐contact base electrode. The three‐terminal structures were constructed on 500‐μm‐thick (100) single‐crystal SrTiO3 substrates with a relative permittivity of 2×104 at 4.2 K. YBa2Cu3O7−x films were deposited on chemically cleaned substrates by laser ablation and base leads were constructed of silver paste.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
85.30.Tv Field effect devices

New buffer layer for high‐temperature superconducting ceramics on sapphire: LaBa2Cu3Oy/Ag bilayers

O. Nakamura, I. N. Chan, J. Guimpel, and Ivan K. Schuller

Appl. Phys. Lett. 59, 1245 (1991); http://dx.doi.org/10.1063/1.105516 (3 pages) | Cited 7 times

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We have grown highly oriented LaBa2Cu3Oy (110)/Ag (111) bilayers on sapphire (1120). This structure constitutes a potentially excellent buffer layer for the growth of 1‐2‐3 ceramic oxides on sapphire substrates. This bilayer does not show superconductivity in resistive measurements. A DyBa2Cu3Oy film grown on this bilayer also exhibited (110) orientation.
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74.70.-b Superconducting materials other than cuprates
74.78.Fk Multilayers, superlattices, heterostructures
74.78.-w Superconducting films and low-dimensional structures
68.35.B- Structure of clean surfaces (and surface reconstruction)

High‐quality Y1Ba2Cu3O7−x thin films on polycrystalline MgO by temperature‐controlled chemical vapor deposition

Aiguo Feng, Ling Chen, Timothy W. Piazza, Hongwen Li, Alain E. Kaloyeros, Drew W. Hazelton, Li Luo, and Robert C. Dye

Appl. Phys. Lett. 59, 1248 (1991); http://dx.doi.org/10.1063/1.105517 (3 pages) | Cited 9 times

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Y1Ba2Cu3O7−x superconducting thin films were grown in situ on polycrystalline MgO substrates by a chemical vapor deposition process that closely couples the sublimation temperatures of the elemental sources to that of the substrate during deposition. It was found that the best quality films were achieved with a controlled ramping of the substrate temperature from 850  °C, at the onset of deposition, down to 750 °C at the end of deposition. The films were analyzed by Rutherford backscattering (RBS), scanning electron microscopy (SEM), x‐ray diffractometry (XRD), and four‐point resistivity probe. The results of these studies showed that the films were highly c‐axis oriented, had near‐stoichiometric composition, and exhibited Tc,onset=90 K, Tco=85 K, and had a Jc=2×105 A/cm2 at 77 K in zero magnetic field. A model is proposed for the effect of such temperature control on the CVD growth mechanism of high‐quality YBCO films.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.25.Ha Magnetic properties including vortex structures and related phenomena
79.20.Hx Electron impact: secondary emission

High temperature superconductivity in air quenched YBa2Cu3O7−δ doped with Sb2O3

K. V. Paulose, J. Koshy, P. Uma Devi, and A. D. Damodaran

Appl. Phys. Lett. 59, 1251 (1991); http://dx.doi.org/10.1063/1.105518 (3 pages) | Cited 5 times

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The superconducting properties of YBa2Cu3O7−δ compounds doped with Sb2O3 have been studied by x‐ray diffraction and electrical and magnetic measurements. It is found that the widely accepted procedure of slow cooling or annealing at 600 °C for several hours for oxygenation is not essential to obtain superconductivity in these doped samples. Superconducting transition (92 K) was obtained by directly quenching the doped specimen from the sintering temperature of 950 °C. Tetragonal to orthorhombic transformation has taken place within this short period, indicating that the rate of oxygen absorption has been increased tremendously by Sb2O3 addition in the YBa2Cu3O7−δ compound. Undoped samples quenched in air were always tetragonal and nonsuperconducting.
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74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
81.40.Rs Electrical and magnetic properties related to treatment conditions
64.70.K- Solid-solid transitions

High‐quality YBa2Cu3O7−x thin films by plasma‐enhanced metalorganic chemical vapor deposition at low temperature

J. Zhao, Y. Q. Li, C. S. Chern, P. Lu, P. Norris, B. Gallois, B. Kear, F. Cosandey, X. D. Wu, R. E. Muenchausen, and S. M. Garrison

Appl. Phys. Lett. 59, 1254 (1991); http://dx.doi.org/10.1063/1.105468 (3 pages) | Cited 23 times

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Single‐crystalline epitaxial YBa2Cu3O7‐x thin films with a sharp superconducting transition temperature of 90 K and a critical current density of 3.3×106 A/cm2 at 77 K were prepared by a plasma‐enhanced metalorganic chemical vapor deposition (PE‐MOCVD) process. The films were formed in situ on (100) LaAlO3 substrates at a temperature of 670 °C in 2 Torr partial pressure of N2O. X‐ray analysis indicated that films grew epitaxially with the c‐axis perpendicular to the substrate and the a and b axes uniformly aligned along the LaAlO3 [100] directions. High‐resolution transmission electron microscopy along with electron diffraction revealed that the films grew epitaxially with atomically abrupt film‐substrate interfaces. The high degree of epitaxial crystallinity of the films was also confirmed by Rutherford backscattering spectroscopy which gave a minimum channeling yield of 9%.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Wet etch process for patterning insulators suitable for epitaxial high Tc superconducting thin film multilevel electronic circuits

W. Eidelloth, W. J. Gallagher, R. P. Robertazzi, R. H. Koch, B. Oh, and R. L. Sandstrom

Appl. Phys. Lett. 59, 1257 (1991); http://dx.doi.org/10.1063/1.105469 (3 pages) | Cited 20 times

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We describe a wet etch process for patterning insulators suitable for multilayer epitaxial highTc superconductor‐insulator‐superconductor structures down to micronmeter‐scale dimensions. A solution of 7% HF in water gives convenient etch rates for SrTiO3 and MgO insulators (about 1500 Å/min for single crystals), and easily stops on thin high Tc superconducting layers, due to the high selectivity of this etchant between these insulators and the cuprate superconductors. Using entirely wet etching patterning processes, we have fabricated 5‐turn (20‐turn) coils with zero resistance at 89 K (79 K) and critical currents at 77 K of 2.5 mA (6 μA).
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.40.Hp Lithography, masks and pattern transfer
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates

Fabrication of thin‐film LiMn2O4 cathodes for rechargeable microbatteries

F. K. Shokoohi, J. M. Tarascon, and B. J. Wilkens

Appl. Phys. Lett. 59, 1260 (1991); http://dx.doi.org/10.1063/1.105470 (3 pages) | Cited 53 times

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We have fabricated thin‐film cathodes of lithiated manganese oxide (LixMn2O4, where x≤1), which can reversibly intercalate nearly one Li atom per unit formula, at a steady potential of 4.1 V. This results in a theoretical energy density of about 600 Wh/kg. The polycrystalline films (thickness of 0.5–2 μm) show electrochemical performance exceeding that of bulk materials. This is attributed to the small grain size and the porosity within these LixMn2O4 three‐dimensional spinel films, reducing the diffusion path length for Li+ ions. The films are tested as the cathodes in about 70 charging/discharging cycles, in a secondary lithium cell, at current rates of 10–100 μA cm−2. No measurable self‐discharge over 12 h periods is observed. These thin‐film cathodes with above electrochemical properties are very promising for a new generation thin‐film secondary batteries.
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81.10.Bk Growth from vapor
82.45.-h Electrochemistry and electrophoresis
82.47.-a Applied electrochemistry
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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