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Applied Physics Letters

Issue 26 • Date Jun 1987

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Displaying Results 1 - 24 of 24
  • Recrystallization solvent effects on second‐order nonlinear optical organic materials

    Page(s): 1855 - 1857
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    Recrystallization solvent effects on second harmonic generation (SHG) of acetylene derivatives are reported. SHG intensities of substituted diphenylacetylene recrystallized from strong polar solvents are enhanced in crystalline states. View full abstract»

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  • Optical nonlinearity in mercury telluride

    Page(s): 1858 - 1860
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    Mercury telluride is shown to have the largest known third‐order nonlinear optic susceptibility with response time in the picosecond range. At 10.6 μm and T=300 K, χ(3)=1.6×10-4 esu. The response time, estimated from the dispersion of χ(3), is 5 ps. The effect is attributed to interband population modulation. It does not saturate below 1 MW/cm2. View full abstract»

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  • Simulation studies of the dynamic behavior of semiconductor lasers with Auger recombination

    Page(s): 1861 - 1863
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    We apply the phase portrait analysis to semiconductor lasers with Auger recombination and extend the analysis to high modulation frequency ωm. On the two‐dimensional bifurcation diagram of modulation depth and modulation frequency, there are seven regions: digital pulsing regions, analog modulation region, period doubling regions, chaos regions, and one multiloop region. It is found that Auger recombination tends to suppress chaos for ωm≪ωr, the relaxation frequency. However, for ωm≫ωr, chaotic behavior becomes prominent. Furthermore, in the pulsing region, the maximum pulsation frequency is limited to a value around ωr even though ωm may be twice or three times ωr. A normalized two‐dimensional bifurcation diagram defining the digital pulse region and the analog modulation region is presented for the purpose of locating the suitable region for analog and digital operation of semiconductor lasers. View full abstract»

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  • Low‐energy ion extraction with small dispersion from an electron cyclotron resonance microwave plasma stream

    Page(s): 1864 - 1866
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    The effects of a magnetic field gradient on the energy profiles of ions extracted from an electron cyclotron resonance (ECR) microwave plasma stream are studied. The mean energy and energy dispersion of the ions strongly depend on the spatial distribution of the magnetic field strength. Ions with an energy dispersion of several eV are extracted from the plasma by the mirror field gradient application. Consequently, the magnetic field gradient, i.e., the magnetic flux profile, is one of the most important parameters in ECR microwave plasma processes. View full abstract»

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  • Pulse‐laser‐irradiated high‐brightness photoelectron source

    Page(s): 1867 - 1869
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    Linac‐driven free‐electron lasers, new powerful synchrotron radiation sources, and advanced high‐power microwave devices will require very bright emitters of electrons to operate efficiently. By irradiating a Cs3Sb photocathode with a frequency‐doubled, Nd:glass laser, we have obtained a very high normalized electron beam brightness of over 1011 A/m2/rad2. Peak currents emitted from the 1 cm2 surface in 50 ns pulses ranged up to 80 A. Measured normalized emittances were between 5 and 9 π mm mrad. View full abstract»

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  • Subsurface molecule formation in hydrogen‐implanted graphite

    Page(s): 1870 - 1872
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    A saturated bilayer of hydrogen isotopes has been formed in graphite by implanting protons and deuterons at different energies. Residual gas analysis during thermal desorption strongly suggests that hydrogen atoms recombine locally in the bulk of the damaged material and diffuse to the surface in molecular form. This model of local recombination and molecular diffusion is consistent with the predictions of the local saturation model. It also explains recent data of the low‐energy chemical erosion during hydrogen bombardment at room temperature. View full abstract»

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  • Spontaneously vitrifying crystalline alloys

    Page(s): 1873 - 1875
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    Certain metastable metallic crystals spontaneously vitrify upon low‐temperature annealing, as recently demonstrated for the high‐temperature solid solution of Cr and Ti. The driving force for the vitrification process can be accounted for by the concomitant decrease in lattice strain energy. Predictions for a number of binary phases are made and compared with preliminary experimental results. Spontaneous vitrification is found in the systems Co‐Nb, Cr‐Ti, Cu‐Ti, Fe‐Ti, Mn‐Ti, and Nb‐Ni. View full abstract»

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  • Cascade‐driven migration of structural interfaces: A new type of irradiation‐induced phase transformation

    Page(s): 1876 - 1878
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    In Ti‐Cr alloys containing both the Laves phase (ordered TiCr2) and the β phase (bcc solid solution), 1 MeV Kr+ irradiation at temperatures ≪250 K amorphizes the Laves phase but not the β phase. The irradiation‐induced amorphous material transforms into polycrystalline β upon warming to room temperature. In contrast, irradiation at room temperature causes the β phase to grow by migration of the β/Laves interface; no change in local composition across the migrating interface is observed. The β phase also grows during prolonged irradiation at 100 K, but the velocity of the β/amorphous interface per unit calculated atomic displacement rate is more than three orders of magnitude lower than that of the β/Laves interface at room temperature. An interpretation of this new type of irradiation‐induced phase transformation is presented in terms of displacement cascade formation and dynamic recovery at the structural interface that exists between the two phases. View full abstract»

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  • Characterization of reactively sputtered ruthenium dioxide for very large scale integrated metallization

    Page(s): 1879 - 1881
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    We have investigated reactively sputtered films of RuO2 for possible application in very large scale integrated circuits. Sputtering yields stoichiometric ruthenium dioxide in a large window of oxygen pressures and the films are reasonably low stressed in the 10-9 dyn cm-2 range. The resistivity of as deposited films is 40 μΩ cm. The films are excellent barriers against interdiffusion of Si and Al. View full abstract»

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  • Improved quality Si‐on‐Si3N4 structures by ion beam synthesis and lamp annealing

    Page(s): 1882 - 1884
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    Silicon wafers were implanted with 200 keV 14N+ ions to a dose of 0.95×1018 14N+ cm-2 at a temperature of 520 °C. These wafers were then annealed at 1405 °C for 30 min, a temperature significantly higher than that normally used (1200 °C) for annealing buried nitride, silicon‐on‐insulator (SOI) structures. Annealing leads to the formation of a well defined layer of essentially single‐crystal Si3N4 containing a few low angle grain boundaries. The Si/Si3N4 interfaces are abrupt, the lower one being almost planar while the upper one shows some irregularities due to fingerlike protrusions of Si3N4 and has an associated region of defective silicon. The silicon overlay is single crystal with no resolvable defects making the wafers good candidates for SOI substrates. View full abstract»

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  • Free‐carrier effects on luminescence linewidths in quantum wells

    Page(s): 1885 - 1887
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    The effects of free‐carrier broadening on luminescence linewidths in InGaAs‐InP quantum wells (QW’s) are demonstrated using Schottky barrier depletion and magnetic field quantization of the conduction‐band‐energy levels. After removal of free‐carrier broadening, linewidths of 5 meV for 100‐Å, and 3.5 meV for 150‐Å QW’s grown by metalorganic chemical vapor deposition are obtained. Widths of 3.4 meV for a 110‐Å QW grown by molecular beam epitaxy (MBE) on an n+ substrate, and only 2.0 meV at 6.2 T for a similar MBE sample grown on a semi‐insulating substrate are also reported. View full abstract»

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  • Antiphase‐domain‐free growth of cubic SiC on Si(100)

    Page(s): 1888 - 1890
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    Single crystals of cubic SiC that are free of antiphase domains were successfully grown by chemical vapor deposition on Si substrates inclined at 2° from (100) towards (011). The relationship between the generation of antiphase domains and the inclination of a surface was investigated by using spherically polished Si substrates. Inclination, except towards (011), resulted in the generation of antiphase domains. Elimination of antiphase domains was confirmed by molten KOH etching of the grown layer. View full abstract»

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  • Chemically enhanced focused ion beam etching of deep grooves and laser‐mirror facets in GaAs under Cl2 gas irradiation using a fine nozzle

    Page(s): 1891 - 1893
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    Chlorine‐enhanced GaAs maskless etching has been performed with a novel focused ion beam etching (FIBE) system. The system is composed of an air‐locked ultrahigh vacuum chamber, a 30‐keV Ga+ FIB column, and a fine nozzle. The nozzle irradiates a high‐density Cl2 flux on a desired, small area of the sample while retaining a sufficiently low surrounding gas pressure for stable Ga+ FIB emission. Condensed Ga residues, appearing on the etched surface with no Cl2 gas, could be suppressed under Cl2 gas irradiation. Highly chemically enhanced sputtering yields (up to 50 GaAs molecules per incident ion) were obtained by selecting the optimum relationship between scanning time and Cl2 gas pressure. At the maximum yield, a deep groove (about 6 μm) with a smooth surface was obtained by line‐scanning FIBE. The etching was applied to laser‐mirror formation of an AlGaAs laser. A vertical mirror facet, fabricated in advance by a reactive ion beam etching, was trimmed about one micron thick by line‐scanning FIBE. Light output versus current characteristics did not change before and after FIBE and the etching has been shown to be useful for laser‐mirror formation. View full abstract»

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  • High‐performance thin‐film transistors from optimized polycrystalline silicon films

    Page(s): 1894 - 1896
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    The performance of thin‐film transistors fabricated in unrecrystallized (small‐grain) polcrystalline silicon is shown to be greatly improved by depositing the films at much lower pressures than normally used in the low‐pressure chemical vapor deposition process. Electronic measurements on completed devices are presented and related to the film structure by transmission electron microscopy examination. View full abstract»

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  • Physics of the enhancement of impact ionization in multiquantum well structures

    Page(s): 1897 - 1899
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    We present an analytical theory of the experimentally observed enhanced impact ionization rate in multiquantum well structures, which is based on a modification of Schockley’s [Solid State Electron. 2, 35 (1961)] lucky electron theory. The general expression always predicts an enhancement in the ionization rate over the corresponding bulk value. The model is compared to both Monte Carlo calculations and recent experimental results. It is concluded that owing to the nonlinear aspects of impact ionization, the ionization rate can be significantly enhanced by the superposition of a uniform electric field and any spatially periodic electric field. View full abstract»

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  • Nondestructive analysis of silicon‐on‐insulator wafers

    Page(s): 1900 - 1902
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    Silicon‐on‐insulator structures have been fabricated using implantation of 160 keV oxygen ions at a dose of 1.9×1018 atoms/cm2 with a wafer temperature of 500 °C and no oxide cap. Both the as‐implanted and annealed wafers were examined with optical reflectometry to determine the resultant interference pattern produced by the presence of the buried layer of SiO2. The optical data are compared to the predictions of a calculation which simulated the geometry using a detailed multilayer optical model. Parameters of the model were adjusted to provide a best fit to the data. The optical prediction closely matches data from destructive measurements. It is demonstrated that the redistribution of oxygen due to annealing can be monitored with this technique. View full abstract»

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  • Dominance of surface recombination current in planar, Be‐implanted GaAs p‐n junctions prepared by rapid thermal annealing

    Page(s): 1903 - 1905
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    Rapid thermal annealing with incoherent light was used to fabricate planar, Be‐implanted p‐n junctions in GaAs. Diodes of varying diameter were used to determine if the residual implant damage would cause the space‐charge recombination current to dominate the surface recombination current. Unpassivated diodes are dominated by surface recombination over the 20–150 μm range of diameters investigated. Passivation of diode structures with a surface layer of high‐resistivity Al0.4Ga0.6As grown by metalorganic chemical vapor deposition resulted in a significant reduction of surface recombination current and permitted the measurement of the space‐charge recombination current. The space‐charge recombination current for these diodes was found to be similar in value to that previously reported for Zn‐diffused GaAs junctions. View full abstract»

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  • Capacitance spectroscopy of Si‐TaSi2 eutectic composite structures

    Page(s): 1906 - 1908
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    The Si matrix phase of directionally solidified Si‐TaSi2 composite structures has been characterized by deep level capacitance transient spectroscopy, using the grown‐in metal‐semiconductor junctions. The Si is found to be of high quality. No electrically active Ta was detected with a minimum experimental sensitivity of ∼6×1011 cm-3. Some samples exhibited one of two defect states having electron emission activation energies of 0.36 and 0.65 eV. These states appear to be associated with dislocations. View full abstract»

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  • Specular beam intensity behavior in reflection high‐energy electron diffraction during molecular beam epitaxial growth of Al0.3Ga0.7As on GaAs(100) and implications for inverted interfaces

    Page(s): 1909 - 1911
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    Results on the specular beam intensity behavior in reflection high‐energy electron diffraciton during molecular beam epitaxial growth of Al0.3Ga0.7As on GaAs(100) are reported. The behavior of steady‐state intensity as a function of substrate temperature exhibits irreversible character. The results indicate that the Al reactivity with As and residual impurities is the dominant factor controlling the surface morphology and hence the nature of inverted interfaces. A critical need for choosing optimal growth conditions prior to initiation of Al0.3Ga0.7As growth thus emerges. View full abstract»

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  • Microstructural studies of reactive ion etched silicon

    Page(s): 1912 - 1914
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    The structures of Si near‐surface damage induced after the removal of a thick SiO2 layer on Si using reactive ion etching with various etching gases were studied by transmission electron microscopy. Cross‐sectional micrographs showed the presence of a fluorocarbon film on the Si surface after the SiO2 layer is etched away. No extended defects were observed in Si etched utilizing pure CF4 or CF4/20% H2 etching gas, even after a 25‐min overetch into Si. For a CF4/40% H2 etching gas, no extended lattice defects were evident for overetch times of up to 5 min. However, extensive damage was found in the Si surface layer after a 10‐min or longer overetch. This extensive damage consists of {111} planar defects distributing underneath the Si surface to a depth of 300 Å. The planar defects are highly decorated by impurities, likely H and possibly C, F. A pure H2 etching gas was found to introduce a heavily damaged layer and a high density of extended defects near the Si surface after only a 5‐min overetch. These observations indicate that H ion bombardment plays an important role in the formation of Si near‐surface damage during reactive ion etching. View full abstract»

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  • dc characterization of the AlGaAs/GaAs tunneling emitter bipolar transistor

    Page(s): 1915 - 1917
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    AlGaAs/GaAs tunneling emitter bipolar transistors (TEBT’s), grown by molecular beam epitaxy, have been fabricated. Device structures with two different tunneling barrier Al mole fractions and each for two different barrier thicknesses were characterized at room temperature. A differential current gain of 410 was achieved using a single 50 Å AlAs tunneling barrier. Devices with either thinner barriers (20 Å) or Al0.38Ga0.62As barriers had lower gains. Al0.24Ga0.76As/GaAs heterojunction bipolar transistors and GaAs homojunction bipolar transistors without tunneling barriers were also fabricated and characterized, for comparison. The performance of the homojunction devices was improved in all cases by inserting the tunneling barrier. The variations of the base and collector currents were measured for all devices and, for the TEBT’s they showed a functional dependence on the interfacial barrier Al mole fraction and thickness, which was attributed to carrier tunneling through the barrier. Furthermore, the above characteristics exhibit a clear electron‐to‐hole preferential tunneling. View full abstract»

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  • Crystallography and microstructure of Y1Ba2Cu3O9-x, a perovskite‐based superconducting oxide

    Page(s): 1918 - 1920
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    We have investigated the crystallography and microstructure of Y1Ba2Cu3O9-x with transmission electron microscopy and x‐ray diffraction. Y1Ba2Cu3O9-x is a distorted, oxygen‐defect perovskite with ordering of the yttrium and barium ions. Its unit cell is orthorhombic with space group Pmm2 and lattice parameters a=3.893 Å, b=11.688 Å, and c=3.820 Å. The structure is heavily twinned on {101} type planes, possibly due to a tetragonal‐to‐orthorhombic transition above room temperature. View full abstract»

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  • Energy‐gap spectroscopy of superconductors using a tunneling microscope

    Page(s): 1921 - 1923
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    A unique scanning tunneling microscope (STM) system has been developed for spectroscopy of the superconducting energy gap. High‐resolution control of tunnel current and voltage allows for measurement of superconducting properties at tunnel resistance levels 102–103 greater than that achieved in prior work. The previously used STM methods for superconductor spectroscopy are compared to those developed for the work reported here. Superconducting energy‐gap spectra are reported for three superconductors, Pb, PbBi, and NbN, over a range of tunnel resistance. The measured spectra are compared directly to theory. View full abstract»

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  • Laser‐induced gratings in nematic/cholesteric mixtures

    Page(s): 1924 - 1926
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    Laser‐induced gratings are produced in thin films of mixtures of nematic and cholesteric liquid crystals doped with a dye. A transient grating regime is found which decays on the order of seconds; additionally, a ‘‘persistent’’ grating with lifetimes up to 16 h has been found. Mechanisms for creation and decay are discussed. 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