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9 Nov 1992

Volume 61, Issue 19, pp. 2257-2370

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Al/Si/AlGaAs/GaAs Schottky barriers by molecular beam epitaxy

T. J. Miller and M. I. Nathan

Appl. Phys. Lett. 61, 2332 (1992); http://dx.doi.org/10.1063/1.108234 (3 pages) | Cited 12 times

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We have grown Al/Si/AlGaAs/GaAs Schottky diode structures by molecular beam epitaxy utilizing thin Si (6 Å) and AlxGa1−xAs (1500 Å) interfacial layers with Al mole fractions of x=0, 0.15, and 0.30. The compositional dependence of the Schottky barrier height, as determined by I‐V measurement, is equal to that of the conduction band discontinuity between AlGaAs and GaAs. The barrier heights as determined by C‐V, however, show no compositional dependence. Since the C‐V characteristics depend only on the difference in the conduction band discontinuities for the Si‐AlGaAs and GaAs‐AlGaAs heterojunctions, this suggests that the change in conduction band discontinuity due to Al mole fraction is the same for both heterojunctions for the range of x studied.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Model for conductance in dry‐etch damaged n‐GaAs structures

M. Rahman, N. P. Johnson, M. A. Foad, A. R. Long, M. C. Holland, and C. D. W. Wilkinson

Appl. Phys. Lett. 61, 2335 (1992); http://dx.doi.org/10.1063/1.108235 (3 pages) | Cited 21 times

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A model for the effects of dry‐etch damage on the conductances of etched structures is developed. Expressions for defect distribution are obtained for top‐surface and sidewall damage. The expression for sidewall damage is used in the calculation of wire conductances. The model accounts accurately for changes in experimentally measured conductances of SiCl4‐etched n+‐GaAs wires with variations in material carrier concentration, epilayer thickness, and etch time/depth. The analysis indicates that defects are created at a significant rate at sidewalls as compared to top surfaces.
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81.65.-b Surface treatments
61.80.Jh Ion radiation effects
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors

Large temperature changes induced by molecular beam epitaxial growth on radiatively heated substrates

B. V. Shanabrook, J. R. Waterman, J. L. Davis, and R. J. Wagner

Appl. Phys. Lett. 61, 2338 (1992); http://dx.doi.org/10.1063/1.108236 (3 pages) | Cited 21 times

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We have performed optical transmission measurements on radiatively heated GaAs substrates as a function of molecular beam epitaxial growth of InAs, GaSb, AlSb, and GaAs films. The energy gap of the GaAs substrate is observed to decrease strongly in energy when materials with band gaps smaller than GaAs are deposited. This decrease in energy gap is a consequence of a substantial increase in growth temperature induced by the deposition of the film. We have observed increases in temperature of over 150 °C from the temperature measured before film growth. Because the thermocouple is weakly coupled to the radiatively heated substrate, conventional temperature controllers are ineffective at measuring or accounting for this change in temperature.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.20.Dt Thermometers

Auger recombination in modulated photoreflectance characterization of silicon wafers

B. C. Forget, D. Fournier, and V. E. Gusev

Appl. Phys. Lett. 61, 2341 (1992); http://dx.doi.org/10.1063/1.108237 (3 pages) | Cited 11 times

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We have used photoreflectance signal as a function of modulation frequency to characterize electronic transport properties in silicon wafers. Due to the high densities of free carriers generated in such an experiment, we propose a theoretical model which takes into account Auger recombination. This nonlinear recombination process is usually neglected in the interpretation of photothermal phenomena. Our experimental results, in good accordance with theoretical prediction, show that this nonlinear recombination process not only cannot be neglected, but can be the dominant recombination process for certain experimental configurations, particularly for modulation frequencies up to 100 kHz and pump power ranging from 1.5 kW/cm2 to 9 kW/cm2.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Ht High-field and nonlinear effects

Temperature dependence of the radiative lifetime in porous silicon

G. W. ’t Hooft, Y. A. R. R. Kessener, G. L. J. A. Rikken, and A. H. J. Venhuizen

Appl. Phys. Lett. 61, 2344 (1992); http://dx.doi.org/10.1063/1.108238 (3 pages) | Cited 47 times

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Using photoluminescence decay measurements the radiative lifetime of porous silicon is investigated between liquid helium and room temperature. The radiative recombination mechanism in porous silicon is in essence the same as in bulk silicon, viz. a phonon mediated indirect transition. The functional dependence of the lifetime on photon energy reveals the confinement character of the recombination carriers. The high external photoluminescence efficiency is well explained by the reduction of nonradiative recombination owing to low mobility, to low dimensionality, and to the extreme low surface recombination rate, and is further enhanced by the relatively small refractive index.
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78.55.Hx Other solid inorganic materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.-p Spectroscopy of solid state dynamics

Microscopic study of the surfactant‐assisted Si, Ge epitaxial growth

R. Cao, X. Yang, J. Terry, and P. Pianetta

Appl. Phys. Lett. 61, 2347 (1992); http://dx.doi.org/10.1063/1.108239 (3 pages) | Cited 25 times

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The Sb‐assisted Si, Ge epitaxial growth processes have been studied using high resolution photoemission. It is found that the initially ordered Sb monolayer on the Si(100) and Ge(100) surfaces occupies the epitaxial sites and fully saturates the surface dangling bonds. This results in a reduction of the surface energy. During the growth process, the Sb atoms and the deposited Si, Ge atoms change their positions. Sb atoms segregate to the growth front to form a new ordered layer while leaving the uniform epitaxial Si, Ge layer behind.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

New class of Si‐based superlattices: Alternating layers of crystalline Si and porous amorphous Si1−xGex alloys

R. W. Fathauer, T. George, E. W. Jones, W. T. Pike, A. Ksendzov, and R. P. Vasquez

Appl. Phys. Lett. 61, 2350 (1992); http://dx.doi.org/10.1063/1.108240 (3 pages) | Cited 5 times

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Superlattices consisting of alternating layers of crystalline Si and porous amorphous Si1−xGex have been fabricated. This is accomplished by first growing a Si/Si0.7Ge0.3 superlattice by molecular beam epitaxy, followed by Ar‐ion milling to form mesa structures, and finally by immersion in HF:HNO3:H2O. This solution creates a porous structure similar to that created by anodic etching, and a high selectivity is observed for the conversion of the alloy layers relative to the Si layers. The degree of selectivity is found to depend on alloy layer thickness and strain. Superlattices have been fabricated from 1‐μm wide mesas with Si0.7Ge0.3 layers fully converted to 5‐nm thick porous amorphous material.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.-b Surface treatments
61.43.Fs Glasses
61.43.-j Disordered solids
61.44.Br Quasicrystals

Voltage‐current characteristics of a high Tc superconducting field effect device

X. X. Xi, C. Doughty, A. Walkenhorst, S. N. Mao, Qi Li, and T. Venkatesan

Appl. Phys. Lett. 61, 2353 (1992); http://dx.doi.org/10.1063/1.108241 (3 pages) | Cited 17 times

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The source‐drain voltage‐current characteristics of a high Tc field‐effect device consisting of a YBa2Cu3O7−x/SrTiO3/Au multilayer structure are measured. Similarities of the V‐I curves to those of a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) are observed. However, we emphasize that the superconducting channel exhibits significantly lower dissipation in comparison with the inversion layer in a MOSFET. The device has a 50 Å thick YBa2Cu3O7−x channel layer (Tc=43 K) with a high critical current density Jc (5 K) over 1×105 A/cm2. A transconductance of over 0.2 mS/mm and a voltage gain of 0.9 are obtained in the device.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates

Deposition and reduction of Nd1.85Ce0.15CuO4−y superconducting thin films

S. N. Mao, X. X. Xi, S. Bhattacharya, Qi Li, T. Venkatesan, J. L. Peng, R. L. Greene, Jian Mao, Dong Ho Wu, and S. M. Anlage

Appl. Phys. Lett. 61, 2356 (1992); http://dx.doi.org/10.1063/1.108242 (3 pages) | Cited 16 times

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Superconducting thin films of Nd1.85Ce0.15CuO4−y (NCCO) were grown at 720–820 °C by pulsed laser deposition in N2O atmosphere. The reduction subsequent to the deposition was found to be critical, and was studied systematically for various temperature, atmosphere, and duration. An ac susceptibility technique was used to stringently characterize the film quality. Very high quality films were made with optimized reduction conditions which showed a Tc(R=0) of 22.4 K, with a transition width of 0.2 K and a Jc (4.2 K) of 8×105/cm2 at zero field. Microwave surface resistance Rs was measured at 9.6 GHz and a value of ∼3 mΩ was obtained at 4.2 K in a 5000 Å thick NCCO film.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
74.70.-b Superconducting materials other than cuprates

Mg2TiO4 as a novel substrate for high‐temperature superconducting thin films

H. Haefke, H. P. Lang, R. Sum, H.‐J. Güntherodt, L. Berthold, and D. Hesse

Appl. Phys. Lett. 61, 2359 (1992); http://dx.doi.org/10.1063/1.108243 (3 pages) | Cited 12 times

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Single‐crystalline Mg2TiO4 layers have been employed as a novel substrate material for superconducting YBa2Cu3O7−δ (YBCO) thin films. The Mg2TiO4 substrate layers have been grown on MgO cleavage faces by a solid‐state reaction between the MgO crystal and TiO2 vapor. The structure and morphology of laser‐deposited YBCO thin films have been studied by x‐ray diffraction, transmission electron microscopy, electron diffraction, and scanning tunneling microscopy. YBCO has been grown on Mg2TiO4(001) with the epitaxial relationship [100](001) YBCO ∥[100](001)Mg2TiO4 and (considering twins)∥[010](001)Mg2TiO4. The film morphology is characterized by growth spirals originating from screw dislocations.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
74.70.-b Superconducting materials other than cuprates

Magnetic properties and giant magnetoresistance of granular permalloy in silver

J. Samuel Jiang, John Q. Xiao, and C. L. Chien

Appl. Phys. Lett. 61, 2362 (1992); http://dx.doi.org/10.1063/1.108244 (3 pages) | Cited 35 times

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We report the first results of magnetic properties and giant magnetoresistance of granular permalloy in a metallic matrix. These new materials have resistivities comparable to those of the ferromagnetic alloys currently used in magnetoresistive devices, but yield significantly larger magnetoresistance effects that are nearly isotropic.
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75.50.Lk Spin glasses and other random magnets
72.15.Gd Galvanomagnetic and other magnetotransport effects

Ferromagnetic δ‐Mn1−xGax thin films with perpendicular anisotropy

Kannan M. Krishnan

Appl. Phys. Lett. 61, 2365 (1992); http://dx.doi.org/10.1063/1.108245 (3 pages) | Cited 58 times

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We report the structure and properties of the thermodynamically stable δ‐phase Mn1−xGax single crystal thin films grown on GaAs. X‐ray Θ–2Θ scans and grazing‐incidence scattering measurements confirmed that the unit cell of this phase is tetragonal (a=0.279 nm, c=0.351 nm) and grows with the c‐axis oriented normal to the {001} GaAs substrate surface. X‐ray emission spectroscopy confirmed the composition to be 62±2% Mn. Polar Kerr rotation, SQUID and vibrating sample magnetometer measurements with the field applied along the thin‐film normal showed nearly perfect square hysteresis loops confirming perpendicular anisotropy of the films. The film exhibits a Kerr rotation angle of ∼0.1° at 820 nm, a coercivity of 6.27 kOe and a saturation magnetization of 460 emu/cm3. The optical reflectivity of the film was 65%–70% over a broad range of wavelengths. This unique set of properties make it a very promising material for magneto‐optic recording with the additional potential of integrating semiconductor/magnetic devices by suitable patterning techniques.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.30.Gw Magnetic anisotropy
68.55.-a Thin film structure and morphology
78.20.Ls Magneto-optical effects

Observation of scattering of particles produced by laser ablation on a substrate by laser induced fluorescence

Tatsuo Okada, Yasushi Nakayama, Wanniarachchi K. A. Kumuduni, and Mitsuo Maeda

Appl. Phys. Lett. 61, 2368 (1992); http://dx.doi.org/10.1063/1.108246 (3 pages) | Cited 14 times

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The scattering of Ba atoms produced from an ArF laser ablated YBa2Cu3O7−δ target on a Si substrate was directly observed by laser induced fluorescence spectroscopy. A gated diode array determined the spatial and the time of flight (TOF) distributions of the scattered Ba atoms on the substrate. It is shown that a sticking coefficient of Ba atoms was less than unity and Ba atoms were scattered roughly isotropically. The velocity of the scattered atoms is estimated from the TOF distribution.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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