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Applied Physics Letters

Issue 8 • Date Feb 1986

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Displaying Results 1 - 17 of 17
  • New bar cathode system for cw CO2 transversely excited lasers

    Page(s): 505 - 507
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    A new bar cathode system that is simple and easy to construct was developed. Its characteristics were investigated and compared with a conventional multipin cathode system. The result demonstrated that transversely excited CO2 lasers employing both cathode systems have similar characteristics and also gave about 10 kW output, although oscillation mode patterns of both systems differed a little from each other. The studies showed that we should be able to get a uniform gain distribution and a uniform oscillation mode with a cathode system consisting of variously shaped bars. View full abstract»

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  • Single mode magneto‐optic waveguide films

    Page(s): 508 - 510
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    A novel triple layer film is described which provides single mode propagation in a magneto‐optically active waveguide of convenient thickness. All three layers are modified yttrium iron garnet (YIG) films grown by liquid phase epitaxy on a gadolinium gallium garnet substrate. The top film is the active layer, several microns thick. The middle layer is similar but it has a slightly smaller refractive index to assure single mode operation of the top layer. The bottom layer has high optical absorption to eliminate all of the higher order modes which are propagated in the triple layer and a slightly higher refractive index to prevent the confinement of any modes to the top two low loss layers. Using a praseodymium YIG film as the absorbing layer, 17 TE modes were propagated at 1.51 μm where the Pr absorption is low but only the TE0 mode was observed at 1.48 and 1.54 μm where the Pr absorption is high. Such triple layer garnet films will be useful in all magneto‐optic waveguide devices. View full abstract»

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  • Very low current threshold GaAs/Al0.5Ga0.5As double‐heterostructure lasers grown by chemical beam epitaxy

    Page(s): 511 - 513
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    The first device performance of GaAs/AlxGa1-xAs double‐heterostructure lasers grown by chemical beam epitaxy (CBE) is reported. Very low averaged current threshold densities of ∼500 A/cm2 were obtained for wafers with active layer thicknesses of ∼500–1000 Å and confinement layers of Al0.5Ga0.5As. Such current threshold densities were similar to those obtained from the best wafers grown by other techniques. This unequivocally established that CBE is capable of producing high optical quality multilayer heterostructures. Further, extreme device uniformity was also obtained. View full abstract»

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  • Scanning tunneling potentiometry

    Page(s): 514 - 516
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    In certain problems of electrical transport through condensed matter, it is important to know the potential distribution with microscopic resolution, e.g., at interfaces (Schottky barriers) or pn junctions. Scanning tunneling potentiometry, a new application of scanning tunneling microscopy, is capable of providing this information. The tunnel current is used for simultaneously sensing probe‐to‐sample distance and local potential. The method was tested with a gold‐island metal‐insulator‐metal structure. View full abstract»

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  • Mobility of Ni versus Zr in an amorphous Ni‐Zr alloy

    Page(s): 517 - 519
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    A method for determining the dominant diffusing constituent in a binary amorphous alloy is demonstrated with the Ni‐Zr system. Nickel is the dominant moving species in an amorphous Ni‐Zr alloy near the a‐Ni50Zr50 composition at 250 °C. In comparison to the Ni, the Zr has a negligible mobility under similar thermodynamic driving forces. Rutherford backscattering spectrometry is used to measure the change in the concentration of a thin film of Ni between thick amorphous layers. Based upon the change in the Ni profile, the diffusivity of Ni in an amorphous Ni‐Zr alloy is between 1×10-17 and 1×10-16 cm2/s at 250 °C. View full abstract»

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  • Oxygen‐rich polycrystalline magnesium oxide—A high quality thin‐film dielectric

    Page(s): 520 - 522
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    Sputtering of a magnesium target with a beam of argon ions in the presence of a partial pressure of reactive oxygen gas has been found to yield smooth MgOx thin‐film dielectrics with low electrical loss, good mechanical stability, and excellent reproducibility. The films consist of polycrystalline MgO with a grain size ≲50 Å and an OH‐containing component. The thickness dependence of the areal capacitance is discussed in the context of a two‐layer model in which this oxygen‐rich phase (x≂1.4) overlays a thin (≲40 Å) stoichiometric phase (x≂1.0). Observation of superconducting tunneling characteristics in trilayer Au‐MgOx‐Pb structures confirms pinhole‐free coverage which may have possible application as artificial tunnel barriers. View full abstract»

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  • Characteristics of CdTe grown on Si by low pressure metalorganic chemical vapor deposition

    Page(s): 523 - 525
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    Specular CdTe epitaxial layers have been grown on (100) Si substrates by the low pressure metalorganic chemical vapor deposition method with dimethylcadmium (DMCd) and diethyltelluride (DETe) source materials. Auger electron spectroscopy and scanning electron microscopy have been used to demonstrate the uniform composition, good surface morphology, and abrupt interface between the CdTe layer and the silicon substrate. The dominant sharp bound exciton related emission peak at 1.593 eV and the weak defect related extrinsic band at 1.483 eV were observed in the 14 K photoluminescence spectra, demonstrating that high quality CdTe epitaxial layers can be grown on Si at 375 °C with the DMCd/DETe mole ratio at approximate unity. View full abstract»

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  • Surface plasmon enhanced quantum efficiency of metal‐insulator‐semiconductor junctions in the visible

    Page(s): 526 - 528
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    Narrowband photosignals with quantum efficiencies up to 30% are observed on Al‐SiO2‐p‐Si junctions. The frequency selective photosignals are due to surface plasmon polaritons confined to the metal‐air interface excited by grating coupling. The best results are achieved with Ag‐Al‐SiO2‐p‐Si junctions providing a 12‐nm linewidth and a signal to background ratio of 7:1 at a wavelength of 632.8 nm. The spectral sensitivity of these photodetectors is tunable over the whole visible spectrum either by a variation of the tilt angle or by a dielectric coating. View full abstract»

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  • Molecular beam epitaxial growth of high quality ZnSe on (100) Si

    Page(s): 529 - 531
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    ZnSe films have been grown by molecular beam epitaxy for the first time on argon ion sputtered and annealed (100) Si substrates, the simultaneous sputtering and annealing process being performed at a substrate temperature of 400 °C. The sputtered and annealed Si substrates were atomically clean as determined by Auger electron spectroscopy analysis, and exhibited a streaky, reconstructed (2×1) reflection high‐energy electron diffraction (RHEED) pattern. Films grown with both the constituent element (Zn and Se) fluxes set to provide a growth rate of ∼0.6 μm/h at initiation of growth were polycrystalline, the crystallites being strongly oriented in the [111] direction as determined by RHEED observations. Parallel epitaxy, i.e., (100) ZnSe‖(100) Si was achieved when the growth rate at initiation of growth was close to zero. Epitaxial ZnSe films exhibited dominant bound excitonic 4.2 K photoluminescence (PL) emission at 2.788 eV (Iz1). The Iz1 peak was also detected in the PL spectra of polycrystalline films; however, its absolute intensity was reduced by over two orders of magnitude. View full abstract»

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  • High quality Si‐on‐SiO2 films by large dose oxygen implantation and lamp annealing

    Page(s): 532 - 534
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    Ion beam synthesis of a buried SiO2 layer is an attractive silicon‐on‐insulator technology for high‐speed complementary metal‐oxide‐semiconductor circuits and radiation hardened devices. We demonstrate here a new annealing procedure at 1405 °C that produces silicon films of excellent quality, essentially free of oxygen precipitates and with sharp interfaces between the Si and the SiO2. Buried oxide layers have been formed in Si (100) wafers by implanting 400 keV molecular oxygen at 500 °C to a dose of 1.8×1018 cm-2. Annealing was performed by radiative heating of the back side of each sample to the melt temperature of silicon, TM=1412 °C, so that the buried oxide structure was at 1405 °C. The temperature control relies entirely on the change in optical properties of silicon upon melting. This ensures, without any external feedback, that the surface exposed to the photon flux will remain at TM. View full abstract»

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  • Low resistance Pd/Ge/Au and Ge/Pd/Au ohmic contacts to n‐type GaAs

    Page(s): 535 - 537
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    We have fabricated Pd/Ge/Au and Ge/Pd/Au sintered ohmic contacts on n‐type GaAs. These contacts have specific resistances similar to those of conventional Ni/Ge/Au alloyed ohmic contacts, but their surfaces are much smoother and their edges are well defined. The fabrication procedure is compatible with GaAs technology, and the sintered contacts are thermally stable. The properties of these low resistance contacts are insensitive to the sintering temperature and to the thickness of the Pd and Ge layers or their order of deposition. View full abstract»

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  • Band alignments of coherently strained GexSi1-x/Si heterostructures on 〈001〉 GeySi1-y substrates

    Page(s): 538 - 540
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    The self‐consistent ab initio pseudopotential results of C. G. Van de Walle and R. M. Martin [J. Vac. Sci. Technol. B 3, 1256 (1985)] have been combined with a phenomenological deformation potential theory to estimate the band gap and band offsets for coherently strained multilayers of GexSi1-x/Si for growth on 〈001〉 GeySi1-y substrates. It is found that ΔEc is negligible and the narrower GexSi1-x gap falls within the wider Si gap (type I band alignment) if the Si in the multilayers is cubic, whereas ΔEc can be appreciable and the GexSi1-x conduction‐band edge tends to be higher in energy than the Si conduction‐band edge(type II band alignment) if both the Si and the GexSi1-x are strained. In particular, the present results resolve the seeming paradox which arose from interpretations of modulation doping experiments using heterojunctions grown either on Si〈001〉 substrates or on an unstrained alloy buffer layer. View full abstract»

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  • Staggered band alignments in AlGaAs heterojunctions and the determination of valence‐band offsets

    Page(s): 541 - 543
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    Photoluminescence spectra from Al0.37Ga0.63As/AlAs multiple quantum well structures with staggered band alignments are presented which provide the first direct optical measure of the valence‐band offset at a semiconductor heterojunction. The experiment takes advantage of the crossover occurring at a critical aluminum concentration above which the indirect X minima in the AlAs become the lowest energy conduction bands in the system, and recombination occurs across the interface. The resulting emission fixes the valence‐band offset at ΔEv =342±4 meV for this structure. View full abstract»

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  • Morphology of hydrogenated amorphous silicon films by photochemical vapor deposition

    Page(s): 544 - 545
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    The microstructure of hydrogenated amorphous silicon films deposited by the photochemical vapor deposition method was investigated using transmission electron microscopy. The circular structures on the top surface of the amorphous silicon film corresponded to both columnar crystalline structures and the amorphous‐microcrystalline mixed structures. The growth of a single crystalline grain as large as 0.3 μm at a mere 150 °C through the photochemical vapor deposition process was also demonstrated. View full abstract»

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  • High mobility GaAs layers obtained by open tube sulfur diffusion

    Page(s): 546 - 547
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    A new technique to diffuse sulfur in GaAs has been demonstrated. The diffusion is performed on a 2‐in. liquid encapsulated Czochralski GaAs wafer in an open tube furnace under N2 flow. A graphite assembly is used to keep the diffusion source and the wafer in close proximity. Diffusion at 850 °C for 30 min gave a sheet carrier concentration of 8.2×1012 cm-2, average mobility of 4200 cm2/V s, and sheet resistance of 180 Ω/⧠. Sheet resistance uniformity is about ±5%. Transconductances as high as 200 mS/mm have been measured on metal‐semiconductor field‐effect transistors with 2 μm gate length, fabricated on layers diffused by this technique. View full abstract»

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  • Reactivity of Dy2O3 and Tb4O7 with Nd15Fe77B8 powder and the coercivity of the sintered magnets

    Page(s): 548 - 550
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    The reaction of Dy2O3 or Tb4O7 with Nd15Fe77B8 powder during the sintering increases the coercivity of the sintered magnets. These oxides are reduced to metal during the sintering process, resulting in magnets with properties similar to those prepared from the Nd13.5Dy1.5Fe77B8 alloy. View full abstract»

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  • Wavelength dependence of laser enhanced plasma etching of semiconductors

    Page(s): 551 - 553
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    Ultraviolet (350 nm) and visible (514 nm and 647 nm) laser light have been employed to enhance silicon etching and to perform in situ patterning in a plasma reactor containing CF4/O2 or NF3 reactants. The etch rate enhancement is dependent on dopant concentration and laser wavelength. This dependence has been related to the number of photogenerated carriers on the semiconductor surface. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory