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3 Dec 1990

Volume 57, Issue 23, pp. 2393-2506

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Surface photovoltage spectroscopy of gap states at GaAs and InP metal interfaces

L. Burstein, J. Bregman, and Yoram Shapira

Appl. Phys. Lett. 57, 2466 (1990); http://dx.doi.org/10.1063/1.103853 (3 pages) | Cited 8 times

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Surface photovoltage spectroscopy has been used in order to investigate surface states at Al/n‐GaAs (110), Au/n‐GaAs (110) and Al/p‐InP (110), Au/p‐InP (110),(100) interfaces. Our results show formation of metal‐induced surface states, which can be correlated with Fermi level pinning positions. The observed energy positions are found to be in good agreement with electrically measured Schottky barrier heights. The results obtained for these metals and the different surface types are discussed and compared to published data.
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72.80.Ey III-V and II-VI semiconductors
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Effect of light on the DX centers in Si‐ and Te‐doped GaAlAs

Patrice Seguy, Peter Y. Yu, Ming‐fu Li, Rosa Leon, and K. T. Chan

Appl. Phys. Lett. 57, 2469 (1990); http://dx.doi.org/10.1063/1.103854 (3 pages) | Cited 5 times

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Deep level transient spectroscopy (DLTS) and constant temperature capacitance transient measurements have been performed on the DX centers under light illumination in GaAlAs alloys doped with Si and Te. Assuming that the effect of light is to ionize the DX centers, experimental DLTS spectra have been simulated numerically. The stimulated spectra reproduces qualitatively the spectra in Te‐doped samples only. In Si‐doped samples, the stimulated spectra cannot reproduce the light‐induced peak reported recently by Jia et al. [J. Appl. Phys. 66, 5632 (1989)]. Our results confirm that this peak may be associated with a light‐induced metastable center related to Si in GaAlAs.
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71.55.Eq III-V semiconductors
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors

Application of organometallic chemical vapor deposition mechanisms to lateral band‐gap patterning on stepped surfaces

E. Colas, E. M. Clausen, E. Kapon, D. M. Hwang, and S. Simhony

Appl. Phys. Lett. 57, 2472 (1990); http://dx.doi.org/10.1063/1.103855 (3 pages) | Cited 9 times

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We report the study of organometallic chemical vapor deposition (OMCVD) on the stepped surfaces obtained by crystal growth on nonplanar vicinal (100) GaAs substrates. Scanning and transmission electron microscopy investigations were combined to identify two distinct diffusion mechanisms in OMCVD: one mechanism involves the gas phase and allows us to selectively distribute the incoming flux of volatile reactants between two adjacent facets; the other one involves surface diffusion of nonvolatile species over distances in the hundred nm range. Spectrally and spatially resolved cathodoluminescence imaging of the light emissions from a single quantum well structure gives direct evidence that the quantum well thickness variations, which can be controlled over a wide range (up to 1:5) by growth parameters, produce effective band‐gap variations.
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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.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Effects of substrate misorientation on ordering in GaAs0.5P0.5 grown by organometallic vapor phase epitaxy

G. S. Chen, D. H. Jaw, and G. B. Stringfellow

Appl. Phys. Lett. 57, 2475 (1990); http://dx.doi.org/10.1063/1.103834 (3 pages) | Cited 12 times

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Effects of (001) GaAs substrate misorientation on the formation of the group V sublattice {111} (CuPt) ordered structure are studied for the first time for GaAs0.5P0.5. It is found that the direction of substrate misorientation has a strong effect on the determination of which variants are formed. Two of the four possible ordered variants appear for epilayers grown on exact (001) substrates. The same two variants also appear for the epilayers grown on the (001) substrates misoriented by 6° towards [110]. Only one variant appears on epilayers grown on (001) substrates misoriented by 6° towards the [110] direction. Most significantly, all the ordered‐induced diffraction spots in GaAsP are found to occur on the [110] cross section. Thus, the variants found in GaAsP are exactly the same as for GaInP, an alloy with CuPt ordering on the group III sublattice. This result is contradictory to expectations based on the bond‐length model proposed previously for GaInP alloys. In addition, for all the 6° misorientated GaAs substrates, independent of the direction of misorientation, large ordered domains with dimensions on the order of micrometers are found in the GaAsP alloys. This has not been reported for other ternary or quaternary alloy systems.
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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.)
81.65.-b Surface treatments
68.55.-a Thin film structure and morphology

Optical absorption and modulation behavior of strained InxGa1−xAs/GaAs(100)(x≤0.25) multiple quantum well structures grown via molecular beam epitaxy

Li Chen, K. C. Rajkumar, and A. Madhukar

Appl. Phys. Lett. 57, 2478 (1990); http://dx.doi.org/10.1063/1.103835 (3 pages) | Cited 13 times

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We report on the optical absorption and modulation characteristics of strained InxGa1−xAs/GaAs(0.1≤x≤0.25) multiple quantum well (MQW) structures grown on GaAs (100) substrates which also included regions of prepatterned mesas. Sharp excitonic features were realized in samples optimally grown by employing reflection high‐energy electron diffraction. High optical quality MQW structures as thick as 1.5 μm are realized. To date, the highest modulation per unit field at low fields (<50 kV/cm) in this system is achieved.
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78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Copper‐oxygen intercalation and related phase transformations in YBaCuO

M. Fendorf, C. P. Burmester, L. T. Wille, and R. Gronsky

Appl. Phys. Lett. 57, 2481 (1990); http://dx.doi.org/10.1063/1.103836 (3 pages) | Cited 10 times

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Phase transformations in the system Y2Ba4Cu6+xO14+x (0≤x≤4) are investigated by high‐resolution transmission electron microscopy (TEM) and static lattice Monte Carlo computer simulations. Micrographs reveal dislocations and stacking faults associated with the diffusion of copper and oxygen as the stoichiometric parameter x varies locally during a phase transformation, and these defects are accurately reproduced by the calculations in ‘‘snapshots’’ of the simulated structures. In addition, the simulations show the occurrence of the well known YBa2Cu3O7, YBa2Cu4O8, and Y2Ba4Cu7O15 phases and predict the formation of Y2Ba4Cu9O17 and YBa2Cu5O9 structures at higher oxygen partial pressures. Based on experimental images and Monte Carlo results, an atomic mechanism involving the intercalation and removal of extra CuO planes by partial dislocation climb is proposed for changes in the layered YBaCuO crystal structure.
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64.70.K- Solid-solid transitions
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
74.40.-n Fluctuation phenomena

a‐axis oriented epitaxial YBa2Cu3O7−x‐PrBa2Cu3O7−y heterostructures

A. Inam, C. T. Rogers, R. Ramesh, K. Remschnig, L. Farrow, D. Hart, T. Venkatesan, and B. Wilkens

Appl. Phys. Lett. 57, 2484 (1990); http://dx.doi.org/10.1063/1.104179 (3 pages) | Cited 86 times

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We have grown YBa2Cu3O7−x‐PrBa2Cu3O7−y heterostructures with the perovskite a axis normal to the surface of a variety of (001) oriented substrates using the pulsed laser deposition technique. X‐ray diffraction studies indicate little or no formation of the traditional c‐axis normal orientation usually nucleated on these substrates, while ion channeling, transmission electron microscopy (TEM), and Raman scattering studies reveal a highly ordered crystalline structure similar in quality to that obtained in the best c‐axis oriented films. Superconducting transition temperatures, for current transport in the plane of the films, consistently exceed 80 K, but are probably lower than the optimum 92 K transition expected for YBa2Cu3O7−x due to the presence of growth twin boundaries between grains with the c axis oriented along the two substrate directions.
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74.78.-w Superconducting films and low-dimensional structures
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
74.70.-b Superconducting materials other than cuprates
74.78.Fk Multilayers, superlattices, heterostructures

Quantum‐limited heterodyne detection of millimeter waves using superconducting tantalum tunnel junctions

C. A. Mears, Qing Hu, P. L. Richards, A. H. Worsham, D. E. Prober, and A. V. Räisänen

Appl. Phys. Lett. 57, 2487 (1990); http://dx.doi.org/10.1063/1.104111 (3 pages) | Cited 14 times

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We have made accurate measurements of the noise and gain of heterodyne mixers employing small‐area (1 μm2) Ta/Ta2O5/Pb0.9Bi0.1 superconductor‐insulator‐superconductor tunnel junctions. These junctions have very low subgap leakage current and an extremely sharp current rise at the sum gap. We have measured an added mixer noise of 0.61±0.31 quanta at 95.0 GHz, which is within 25% of the quantum limit of 0.5 quanta for a single‐sideband mixer. Values of the imbedding admittances are deduced from the shapes of I‐V curves pumped at the upper and lower sideband frequencies. Using these admittances, the mixer performance calculated from the quantum theory is in good agreement with the experiment.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
74.50.+r Tunneling phenomena; Josephson effects
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Preparation and critical current density of Bi2Sr2Ca2Cu3O10+x superconducting whiskers

Ichiro Matsubara, Hideo Tanigawa, Toru Ogura, Hiroshi Yamashita, Makoto Kinoshita, and Tomoji Kawai

Appl. Phys. Lett. 57, 2490 (1990); http://dx.doi.org/10.1063/1.103837 (2 pages) | Cited 15 times

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The whiskers of the Bi2Sr2Ca2Cu3O10(2223) phase have been prepared by heating the Bi2Sr2CaCu2O8(2212) whiskers inside of a calcined Bi2Sr2Ca4Cu6Pb0.5Ox powder. Temperature and magnetic field dependence of the critical current density (Jc) have been measured. The whisker yields a maximum Jc of 7.3×104 A/cm2 at 77 K, and higher than 1×104 A/cm2 below 96 K in zero applied field. At 77 K the 2223 whisker shows Jc values above 1×104 A/cm2 up to 1 T, in contrast to the 2212 whisker (1×102 A/cm2, B=1 T) which shows the steep decrease of Jc in magnetic field above 0.2 T.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.25.Ha Magnetic properties including vortex structures and related phenomena

New family of high Tc superconductors in the (Tl1−xMx)Sr2(Ca1−yYy)Cu2O7−δ system (M=IVA and VA elements)

R. S. Liu, W. Zhou, and P. P. Edwards

Appl. Phys. Lett. 57, 2492 (1990); http://dx.doi.org/10.1063/1.104180 (3 pages) | Cited 5 times

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A new family of high Tc superconductors with superconducting transition temperatures ranging from 40 to 100 K have been synthesized in the (Tl1−xMx)Sr2 (Ca1−yYy)Cu2O7−δ (M=Ti, Zr, Hf, V, Nb, and Ta) system. Here, we use as an example, vanadium and yttrium substitution into the thallium and calcium sites, respectively, in the parent compound TlSr2CaCu2O7 to demonstrate the substitutional chemistry, crystal structure, and superconductivity for these new superconductors.
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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
74.10.+v Occurrence, potential candidates
61.66.Fn Inorganic compounds

Texture growth processing of plasma‐sprayed Y‐Ba‐Cu‐O superconducting deposits

H. Wang, H. Herman, H. J. Wiesmann, Y. Zhu, Youwen Xu, R. L. Sabatini, and M. Suenaga

Appl. Phys. Lett. 57, 2495 (1990); http://dx.doi.org/10.1063/1.103838 (3 pages) | Cited 7 times

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A partial melt/texture growth process has been applied to plasma‐sprayed YBa2Cu3O7−x deposits. The length of the aligned grains is in the range 300–500 μm. Small‐angle grain boundaries with a misorientation between 3° and 5° are commonly observed. The critical current density, using a four‐probe method with continuous direct current, is in excess of 5000 A/cm2 under an applied field of 1 T at 77 K.
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81.15.Rs Spray coating techniques
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
81.10.Fq Growth from melts; zone melting and refining

In situ deposition of superconducting Bi‐Pb‐Sr‐Ca‐Cu‐O thin films on MgO(100) substrates by rf magnetron sputtering and laser ablation

J. S. Moodera, A. M. Rao, A. Kussmaul, and P. M. Tedrow

Appl. Phys. Lett. 57, 2498 (1990); http://dx.doi.org/10.1063/1.103839 (3 pages) | Cited 6 times

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Superconducting thin films of Bi‐Pb‐Sr‐Ca‐Cu‐O (BPSCCO) have been prepared in situ by magnetron sputtering and laser ablation onto heated MgO (100) substrates. Post‐deposition annealing at higher temperatures was not required to obtain superconducting BPSCCO films, and a narrow temperature window in a very similar temperature region was observed for the growth of oriented films for both the laser ablation and magnetron sputtering technique. The best films were smooth and shiny with their c axes oriented perpendicular to the substrate surface but scanning electron microscope analysis showed particulates on the film surface. Room‐temperature resistivity values of the order of 2–3 mΩ cm were obtained for these films. At 70 K and 8 T, the resistivity ratio for the H⊥ and ∥ to the plane of the film was ∼25 for an applied current density J of 0.8 A/cm2. Rutherford backscattering analysis on the laser‐ablated and sputtered films indicates that the BPSCCO films had 2223 composition while the x‐ray diffraction studies indicated mixed 2212 and 2223 phases.<lz> <lz> <lz>
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74.78.-w Superconducting films and low-dimensional structures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Cd Deposition by sputtering
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Growth of YBa2Cu3O7−δ on vicinally polished MgO substrates

S. K. Streiffer, B. M. Lairson, and J. C. Bravman

Appl. Phys. Lett. 57, 2501 (1990); http://dx.doi.org/10.1063/1.103840 (3 pages) | Cited 25 times

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YBaCu3O7−δ thin films were grown on vicinally polished MgO [001] substrates. The orientation of the films is strongly influenced by the substrate surface normal, with only very weak alignment to the substrate [001] crystallographic direction. Vicinal angles of 1°, 2.5°, and 5° toward [010] produced films with large mosaic spread parallel to the vicinal angle [as high as 4° full width half maximum (FWHM) for the 5° sample] and with critical current densities as high as films grown on on‐axis substrates (e.g., 4.4×107 A/cm2). Samples on 10° and 20° vicinal substrates showed a reduction in mosaic spread but still alignment to the surface normal, and weak and strong reductions of the critical current density, respectively.
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81.15.Cd Deposition by sputtering
74.70.-b Superconducting materials other than cuprates
68.55.-a Thin film structure and morphology
74.25.Sv Critical currents

Reaction patterning of YBa2Cu3O7−δ thin films on Si

D. K. Fork, A. Barrera, T. H. Geballe, A. M. Viano, and D. B. Fenner

Appl. Phys. Lett. 57, 2504 (1990); http://dx.doi.org/10.1063/1.104181 (3 pages) | Cited 20 times

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A novel technique exploiting the severe chemical reaction between Si and YBa2Cu3O7−δ (YBCO) has been developed for patterning epitaxial YBCO films in situ. Patterning is achieved by etching features in epitaxial YSZ on Si(100), and then depositing a final layer of YBCO; the material which grows on the exposed Si is insulating. Linewidths down to 3 μm have been demonstrated with a zero resistance critical temperature (Tc) of 86 K and a transport critical current density of 1.6×106 A/cm2 at 77 K. 45° and low‐angle twist grain boundaries occur under some circumstances but can be eliminated by regrowing 20 Å of homoepitaxial YSZ on the surface prior to YBCO growth. Si diffusion in insulating portions has been characterized by x‐ray photoemission spectroscopy, indicating vertical diffusion through the film.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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