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Applied Physics Letters

Issue 11 • Date Sep 1994

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Displaying Results 1 - 25 of 48
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Microstructure study of a degraded pseudomorphic separate confinement heterostructure blue‐green laser diode

    Page(s): 1331 - 1333
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    The microstructure of a degraded II‐VI blue‐green laser diode based on the ZnCdSe/ZnSSe/ ZnMgSSe pseudomorphic separate confinement heterostructure has been examined by transmission electron microscopy. Triangular nonluminescent dark defects observed in the laser stripe region by electroluminescence microscopy have been identified to be dislocation networks developed at the quantum‐well region. The dislocation networks have been observed to be nucleated at threading dislocations originating from pairs of V‐shaped stacking faults which are nucleated at or near the II‐VI/GaAs interface and extending into the n‐ZnMgSSe lower cladding layer. View full abstract»

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  • Nearly degenerate four‐wave mixing in a vertical‐cavity surface‐emitting laser

    Page(s): 1334 - 1336
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    We report the measurement of the frequency response of nearly degenerate four‐wave mixing in a vertical‐cavity surface‐emitting laser. High efficiency conjugate signal generation is demonstrated. A superlinear dependence between the square of relaxation oscillation frequency and the output power is observed. The experimental observation is well described by present theories. View full abstract»

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  • High temperature pulsed and continuous‐wave operation and thermally stable threshold characteristics of vertical‐cavity surface‐emitting lasers grown by metalorganic chemical vapor deposition

    Page(s): 1337 - 1339
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    A systematic and comparative study of the temperature performance of vertical‐cavity surface‐emitting lasers (VCSELs) is presented to discuss how thermal effects govern their temperature range for cw operation. These include the temperature‐induced detuning of the lasing mode from the gain peak, thermal self‐heating, and thermal runaway. The power dissipation of the VCSELs and the resultant rise in junction temperature have been measured as a function of the mode detuning. It is shown that low power dissipation is achieved by aligning the cavity mode to the gain peak and introducing continuously graded heterointerfaces throughout the VCSEL structure. By selecting the optimal mode detuning, VCSELs have achieved excellent operating characteristics over a broad range of temperatures, including thermally stable threshold voltage and current, and a very wide temperature range for both pulsed (100–580 K) and continuous‐wave (100–400 K) operations. View full abstract»

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  • Chemically pumped visible‐wavelength laser with high optical gain

    Page(s): 1340 - 1342
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    Excitation of a mixture of FN3, B2H6, SF6, and He by a pulsed CO2 laser generates a transient gain medium capable of supporting laser oscillation at 433 nm in an optical cavity with threshold gain of 2.5%/cm. View full abstract»

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  • Reversible control of the nonlinear optical activity of one‐dimensional metal complexes

    Page(s): 1343 - 1345
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    Reversible controllability of the third‐order nonlinear optical activity has been demonstrated on a one‐dimensional metal complex. Iodine penetration to a film sample causes disappearance of the d‐p transition absorption band of the metal complex and remarkable decline of two‐odd orders in the third‐order nonlinear susceptibility. The deactivated optical nonlinearity was completely restored by removing iodine from the film with heating. The observed alterations in optical nonlinearities are mainly caused by the fluctuation of metal‐metal interaction in the linear metal chain. View full abstract»

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  • Photoluminescence of porous silicon exposed to ambient air

    Page(s): 1346 - 1348
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    The room‐temperature photoluminescence and structure were studied concerning porous silicon which was exposed to ambient air. Water vapor in ambient air gradually oxidized the surface of the porous silicon with developing Si—O—Si bonds. This room‐temperature oxidation progressively replaced an unstable H‐passivated surface with a more stable O‐passivated surface, dramatically increasing the intensity of the photoluminescence. View full abstract»

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  • Novel approach for detecting distributed surface‐breaking cracks

    Page(s): 1349 - 1351
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    A novel approach to the problem of detecting finely distributed surface cracks in a structure is proposed. The approach relies on the detection of anisotropy introduced into the surface by an oriented array of cracks and can be used for crack detection even when individual cracks in the array are below the practical threshold of detectability by conventional inspection techniques. The feasibility of detecting anisotropy associated with distributed cracking was established experimentally using: (i) a directional eddy‐current probe to detect anisotropy in the effective electrical conductivity and (ii) a line‐focused laser‐ultrasonic source to detect anisotropy in the attenuation of ultrasonic Rayleigh waves. View full abstract»

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  • Extended and localized vibrational modes in (1‐3) Penrose‐like piezocomposites

    Page(s): 1352 - 1354
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    Acoustic vibrational modes of piezocomposites with ceramic bars arranged at the vertices of both perfect Penrose tilings and random Penrose tilings have directly been observed by recording the corresponding standing vibration amplitude pattern. The random Penrose tiling exhibits similar although smoother spectrum than the perfect Penrose one. For both structures, the existence of extended and localized modes is shown. Resonances frequencies at the edges of the spectrum pseudogap correspond to localized and highly entropic modes. As expected, the modes are more localized in the random Penrose tiling case. View full abstract»

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  • Fast two‐dimensional self‐consistent kinetic modeling of low‐pressure inductively coupled RF discharges

    Page(s): 1355 - 1357
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    In this letter a two‐dimensional self‐consistent model for an inductively coupled RF plasma is presented. The model is based on the spatially resolved determination of the electron distribution function (EDF) via solution of a kinetic equation in the nonlocal approach. The static space charge potential is computed from a 2D fluid model, the RF electric field profile is calculated from the wave equation. The model can easily be treated on usual personal computers with computation times of about one hour. The theoretical results are compared to measurements presented in a previous publication [U. Kortshagen, I. Pukropski, and M. Zethoff, J. Appl. Phys. 76, 2048 (1994)]. View full abstract»

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  • Optical spectra of Si/Ge‐network copolymers: [Si(C6H13)]1-x[Ge(C6H13)]x

    Page(s): 1358 - 1360
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    Optical properties of silicon‐ and germanium‐based network copolymers, [Si(C6H13)]1-x‐ [Ge(C6H13) ]x, have been investigated for various Si/Ge compositions (x). The backbone Si/Ge atoms are coordinated by the three other Si/Ge backbone atoms in the polymers. These Si/Ge copolymers show the absorption spectra which are typical of amorphous semiconductors. Their color continuously traverses the visible range with x, which is due to the change of the band gap (Tauc gap) energy as well as to the presence of localized subgap states. The Si/Ge copolymer shows a broad band of luminescence in the visible region. The luminescence band maximum was observed to shift by ∼0.5 eV with change of the Si/Ge ratio. View full abstract»

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  • Electronic and mechanical properties of carbon nitride films prepared by laser ablation graphite under nitrogen ion beam bombardment

    Page(s): 1361 - 1363
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    Carbon nitride films have been formed on Si(100) substrates by laser ablation of graphite under a low energy nitrogen ion beam bombardment. Data of Raman shift and x‐ray photoelectron spectroscopy indicate the existence of carbon‐nitrogen bonds in the films. Time‐of‐flight measurements suggest the existence of paracyanogen‐like materials, such as C4N4, in the films. High energy backscattering spectrometry has shown that the percentage of N content in the film is 41% or so. The x‐ray diffraction and transmission electron micrograph measurements have also been taken to characterize the crystal properties of the obtained films. Qualitative tests indicate the films of high Vickers hardness Hv, and of good adhesion to the silicon substrates. View full abstract»

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  • Photocurrent multiplication in hydrogenated amorphous silicon p‐i‐n photodiode films

    Page(s): 1364 - 1366
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    The photocurrent multiplication of hydrogenated amorphous silicon p‐i‐n photodiodes was observed in photodiodes that were fabricated on a heavily doped n‐type silicon substrate using a high‐vacuum plasma enhanced chemical vapor deposition (PECVD) system. By using this improved PECVD system, the breakdown field of the photodiodes was changed from 3×105 V/cm to 1×106 V/cm. It seems that the reason for this increase of the breakdown field was a decrease of localized states in the forbidden gap that was produced by contaminants. The a‐Si:H p‐i‐n photodiodes with low residual stress were fabricated on Si substrates, and the photocurrent multiplication was observed in these photodiodes. The wavelength dependence of incident light and the a‐Si:H thickness dependence of intrinsic layer were found and these characteristics were explained by the avalanche multiplication of photogenerated electrons. View full abstract»

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  • Directional growth of copper phthalocyanine crystal by selective chemical vapor deposition method

    Page(s): 1367 - 1369
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    Novel deposition behavior was observed when 1,4‐dicyanobenzene was sublimed onto copper micropatterns on silicon wafer. On the patterns copper‐phthalocyanine whiskers and debris of similar size were formed and preferentially oriented along or perpendicular to the copper lines. The directional growth was confirmed to have nothing to do with crystal axis of the silicon, but was considered to be due to the periodic structure of the copper lines. View full abstract»

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  • Deposition of fluoropolymer thin films by vacuum‐ultraviolet laser ablation

    Page(s): 1370 - 1372
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    Crystalline thin films of polytetrafluoroethylene were deposited on Si(100) wafers by F2 laser (157 nm) ablation in 200 mTorr Ar gas atmosphere. X‐ray photoemission spectra indicated that the composition of the deposited films was similar to the source material. The surface morphology of films deposited at room temperature contained numerous fibrous structures in size of 100–400 nm, but they were smoothed out at elevated wafer temperature of ∼370 K, while the crystalline feature was still maintained. The refractive index was ∼1.35 at 633 nm. View full abstract»

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  • Metalorganic chemical vapor deposition technique for growing c‐axis oriented ZnO thin films in atmospheric pressure air

    Page(s): 1373 - 1375
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    ZnO thin films have been grown in atmospheric pressure and ambient atmospheric air using zinc 2‐ethyl hexanoate as zinc source by metalorganic chemical vapor deposition technique. The films grown on glass above 350 °C showed c‐axis orientation as seen from x‐ray diffraction studies. The films were highly transparent and free from any visual defects. The growth rate and morphology of the film was found to depend on the substrate temperature. Auger electron spectroscopy shows the presence of carbon as an impurity. View full abstract»

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  • Mechanical stength of Czochralski silicon crystals with carbon concentrations from 1014 to 1016 cm-3

    Page(s): 1376 - 1378
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    Using Czochralski‐grown silicon crystals with carbon concentrations from 1014 to 1016 cm-3, we studied the influence of oxygen precipitates on the mechanical strength of silicon crystals. Reducing carbon concentration from 1016 to 1014 cm-3 suppressed oxygen precipitation and thus, improved the strength. Carbon concentration reduction from 1015 to 1014 cm-3 did not, however, decrease oxygen precipitation as dramatically as reduction from 1016 to 1015 cm-3. Carbon impurities below 1014 cm-3 no longer affect oxygen precipitation. Therefore, we conclude that reducing carbon concentration below 1014 cm-3 no longer improves the mechanical strength of silicon crystals.   View full abstract»

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  • Scanning tunneling microscopy of diamond‐like nanocomposite films

    Page(s): 1379 - 1381
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    Scanning tunneling microscopy is used in the present investigation to study metal containing diamond‐like nanocomposites, viz. (a‐C:H)/(a‐Si:O)/Me films. By comparing images taken before and after samples were annealed at 450 °C for two hours, a formation of sp2‐rich regions is found in Pt containing samples, in contrast to the high thermal stability shown for transition‐metal containing samples. It indicates that the Pt engenders the ‘‘loosening’’ of the diamond‐like matrix with a decrease in the energy barrier. These results are further confirmed by Fourier transformation infrared spectroscopy and Raman spectroscopy. The obtained micro‐ and nanoscale surface images and observed transformation from sp3 to sp2 bonding provides new understanding of the fundamental structure of diamond‐like films. View full abstract»

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  • Interfacial microstructures of ultrathin Ge layers on Si probed by x‐ray scattering and fluorescence yield

    Page(s): 1382 - 1384
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    Angular dependence of grazing‐incidence x‐ray scattering and Ge Kα fluorescence yield were measured for buried ultrathin Ge layers grown on bulk Si by molecular beam epitaxy. Results obtained for samples with different Ge layer thickness are compared. The data reveal information on microstructures in these layered materials in terms of the average interfacial roughness, correlation lengths of height fluctuations, and Ge density profile. Structural parameters are obtained by comparison of experimental data with theoretical models.The results also indicate that the interfacial roughness at neighboring interfaces is highly correlated. Significant changes of microstructures in the Ge epilayer are found as the layer thickness approaches the critical thickness. The x‐ray scattering techniques are demonstrated to be capable of detecting a precursor of lattice relaxation in multilayers of lattice‐mismatched compound semiconductors. View full abstract»

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  • Heavily boron‐doped silicon membranes with enhanced mechanical properties for x‐ray mask substrate

    Page(s): 1385 - 1387
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    Heavily boron‐doped silicon membranes which show substantial improvement in mechanical properties have been fabricated for x‐ray mask substrate by eliminating the misfit dislocation from the membrane. The measured surface roughness, fracture strength, and residual tensile stress of the membrane are 20 Å peak to peak, 1.39×1010 and 2.7×109 dyn/cm2, while those of the conventional heavily boron‐doped silicon membrane with high density of misfit dislocations are 500 Å peak to peak, 8.27×109 and 9.3×108 dyn/cm2, respectively. The differences between the two membranes are due to misfit dislocation. Young’s modulus has been extracted as 1.45×1012 dyn/cm2 for both membranes. Also, the lattice constant of strain‐free membrane, the in‐plane lattice constant of the conventional membrane, and the density of extra‐half plane contained in the conventional membrane have been extracted as 5.424 Å, 5.426 Å, and 2.3×104/cm, respectively.   View full abstract»

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  • Selective excitation of the photoluminescence and the energy levels of ultrasmall InGaAs/GaAs quantum dots

    Page(s): 1388 - 1390
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    The energy levels of nanometer size InGaAs quantum dots epitaxially grown on GaAs by the coherent islanding effect are probed using selectively excited photoluminescence (PL), and PL excitation. A lateral‐confinement‐induced interlevel spacing of ∼30 meV between the first two states can be deduced from the spectra. View full abstract»

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  • Sharp variation in the magnetoresistance of a Si Schottky diode

    Page(s): 1391 - 1393
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    The variation of the resistance of a Si Schottky diode with magnetic field in the range 0 to 1 T was monitored at room temperature by measuring the voltage across the diode at constant current using lock‐in detection at the modulation frequency of the magnetic field. A sharp feature in the resistance was found to depend on the angle between the field and the plane of the Schottky junction. The result is explained in terms of a level‐crossing involving the magnetic sub‐levels of a triplet state recombination center in the space‐charge region of the diode. View full abstract»

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  • Spiral growth of InP by metalorganic vapor phase epitaxy

    Page(s): 1394 - 1396
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    Spirals were observed on InP grown by metalorganic vapor phase epitaxy. Atomic force microscopy is the technique used. The growth took place on a vicinal surface and the growth mechanism is according to the classical Burton–Cabrera–Frank theory. Spirals originate from screw dislocations. Successive turns of steps are sent out by the dislocations. These steps are generally of monolayer height (0.29 nm) except close to the dislocation emergence points where they are submonolayers. It is predicted that spiral growth will become the dominant mechanism if the vicinal steps are eliminated. View full abstract»

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  • Surface phosphidation of GaAs by the laser‐induced dissociation of trimethylphosphine

    Page(s): 1397 - 1399
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    The localized phosphidation of single‐crystal GaAs, by the frequency doubled argon ion laser photolysis at 257 nm of P(CH3)3, is reported. Tracks were deposited by scanning the focused laser beam at a speed of 34.6 μm s-1 and were characterized by scanning electron microscopy and laser ionization mass analysis. Evidence is presented which suggests that a photochemical reaction is initiated by band gap absorption by GaAs. View full abstract»

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  • High‐quality 4H‐SiC homoepitaxial layers grown by step‐controlled epitaxy

    Page(s): 1400 - 1402
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    4H‐SiC bulk crystals were grown controllably by means of a modified Lely method. Homoepitaxial growth of 4H‐SiC was carried out by vapor phase epitaxy utilizing step‐controlled epitaxy on 4H‐SiC substrates prepared by the modified Lely method. The physical properties (electrical and optical properties) of 4H‐SiC epilayers were characterized by Hall effects and photoluminescence (PL) measurements. The electron mobilities as high as 720 cm2/V s at 292 K, and 11 000 cm2/V s at 77 K were obtained. In the PL measurement, the epilayers with a thickness more than 20 μm showed luminescence attributed to free exciton recombination, which indicates the improvement of crystal quality by step‐controlled epitaxy. 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