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Applied Physics Letters

Issue 1 • Date Jan 1995

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Displaying Results 1 - 25 of 41
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Above room temperature near ultraviolet lasing from an optically pumped GaN film grown on sapphire

    Page(s): 1 - 3
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    Optically pumped near ultraviolet lasing from single‐crystal GaN grown by metalorganic chemical vapor deposition has been achieved over a temperature range from 10 K to over 375 K by using a side‐pumping geometry on small barlike samples. The laser emission threshold was measured as a function of temperature and the threshold was found to show weak temperature dependence: ∼500 kW/cm2 at 10 K and ∼800 kW/cm2 at room temperature (295 K) for one particular sample studied. The longitudinal lasing modes were clearly observed. The characteristics of the temperature dependence of the laser emission threshold suggests that GaN is a suitable material for the development of optoelectronic devices required to operate at high temperatures. © 1995 American Institute of Physics. View full abstract»

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  • Quantum cascade unipolar intersubband light emitting diodes in the 8–13 μm wavelength region

    Page(s): 4 - 6
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    An intersubband electroluminescent light source in the 8–13 μm spectral region is reported. The structure was grown by molecular beam epitaxy in the lattice matched AlInAs/GaInAs material system and consists of coupled‐quantum‐well active regions alternated with compositionally graded electron injecting regions. The device operates in the temperature range from 10 to 200 K with measured integrated optical powers up to 6 nW. The peak of the electroluminescent spectrum blue shifts linearly with current due to the Stark effect. From these data and straightforward electrostatic considerations we obtain the intersubband nonradiative electron lifetime, in good agreement with the calculations. © 1995 American Institute of Physics. View full abstract»

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  • Above‐threshold behavior of high‐power, single‐mode antiresonant reflecting optical waveguide diode lasers

    Page(s): 7 - 9
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    Above‐threshold analysis of antiresonant reflecting optical waveguide (ARROW) diode lasers has been performed. One key finding is that preferential pumping of the (central) low‐index core region dramatically enhances the device single‐mode power capability, as a result of defocusing and subsequent radiation‐loss increase for the first‐order spatial mode. Stable, single‐mode operation to drive levels ≳10× threshold is predicted for 6‐μm wide core devices, in excellent agreement with experiment. Similar performance is found to hold true for ARROW devices with cores as wide as 10 μm, although due to gain spatial hole burning, the far‐field beam pattern experiences mild broadening. Study of triple‐core ARROW structures of 20‐μm‐wide aperture shows stable fundamental‐mode operation to ≳10× threshold, thus raising the prospect for stable, single‐mode reliable operation to power levels as high as 1 W cw. © 1995 American Institute of Physics. View full abstract»

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  • Generation of terahertz radiation using electro‐optic crystal mosaics

    Page(s): 10 - 12
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    We describe the generation of terahertz radiation by optical rectification in an electro‐optic crystal mosaic. The mosaic is constructed from four single crystals of the organic salt dimethyl amino 4‐N‐methylstilbazolium tosylate and is approximately 1 cm2 in area. We characterize both the optical rectification efficiency and the spatial and temporal profiles of the generated terahertz beam, and find that the mosaic performs as well as a single crystal. © 1995 American Institute of Physics. View full abstract»

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  • Multiple‐crystal x‐ray topographic characterization of periodically domain‐inverted KTiOPO4 crystal

    Page(s): 13 - 15
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    A periodically domain‐inverted KTiOPO4 crystal has been characterized for the first time by multiple‐crystal multiple‐reflection x‐ray topography. The striation contrast within the domain‐ inverted regions has been revealed in high strain‐sensitivity reflection topographs. The origin of formation of the striation contrast and the mechanism of domain inversion in KTiOPO4 are discussed in terms of the structural characteristics of KTiOPO4. © 1995 American Institute of Physics. View full abstract»

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  • Generation of diamond nuclei on amorphous SiO2 by alternating‐current bias microwave plasma chemical vapor deposition

    Page(s): 16 - 18
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    The nucleation of diamond on the amorphous SiO2 mirror surface has been achieved by means of adding an ac signal to the negative dc bias in the microwave plasma chemical vapor deposition. It is found in experiment that the nucleation of diamond happens only after the frequency of the ac signal exceeds a threshold. The results also show that the diamond nucleation density depends not only on the ac frequency but also on the magnitudes of the ac signal and the dc bias. © 1995 American Institute of Physics. View full abstract»

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  • Processing and hardness of electrodeposited Ni/Al2O3 nanocomposites

    Page(s): 19 - 21
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    Nanocomposite Ni/Al2O3 films have been produced by electrochemical deposition where 50 and 300 nm Al2O3 particles are dispersed in a nickel matrix. These films exhibit considerable enhancements in their hardness in comparison to pure nickel. The strengthening mechanism is explained in terms of an Orowan bowing hardening mechanism and, hence, related to the volume fraction of the reinforcing phase. These films may have application as strong coatings that retain many of the physical properties (e.g., optical, thermal, electrical) of the metal. © 1995 American Institute of Physics. View full abstract»

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  • Quantitative measurement of the stress transfer function in nickel/polyimide thin film/copper thin film structures

    Page(s): 22 - 24
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    The stress transfer behavior in multilayer thin film structures (nickel/polyimide/copper) was measured using x‐ray stress analysis. Copper was deposited in various line lengths, and the stress/strain transferred from a loaded Ni substrate to the Cu thin film was measured as a function of line length. It was found that there is incomplete strain transfer from one layer to another, and that the shape of the stress transfer function is similar to that predicted by the shear lag model. © 1995 American Institute of Physics. View full abstract»

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  • Energy loss near‐edge structure for materials containing light elements by reflection electron energy loss spectroscopy

    Page(s): 25 - 27
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    A reflection electron energy loss spectroscopy system has been developed to investigate local surface atomic structures around light elements such as C, N, and O. Electrons scattered inelastically on a surface with a small scattering angle are energy analyzed. This system was used to measure energy loss near‐edge structures (ELNESs) for materials such as BN, graphite, and NiO. The comparison between ELNES and x‐ray absorption near edge structure suggests that the ELNES is useful for the atomic structure analyses of surfaces. © 1995 American Institute of Physics. View full abstract»

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  • Reproducible memory effect in the leakage current of epitaxial ferroelectric/conductive perovskite heterostructures

    Page(s): 28 - 30
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    Leakage currents in epitaxial ferroelectric/perovskite‐conductor heterostructures reproducibly show diode properties having hysteresis. The hysteresis appears in forward bias, which is positive for electron (n) type conductors and negative for hole (p) type conductors. The hysteresis is due to the increase of conductivity by the forward bias current, which exhibits the memory retention for more than an hour. The write and erase speeds of the diode and the origin of the effect are discussed. © 1995 American Institute of Physics. View full abstract»

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  • Effect of hydrogen ion shower doping in polycrystalline silicon thin‐film transistors

    Page(s): 31 - 33
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    We investigated the effect of hydrogen ion shower doping on polycrystalline silicon thin‐film transistors (p‐Si TFTs). Hydrogen atoms were introduced to the channel region of p‐Si TFTs by PH3/H2 ion shower doping of the source/drain contact. Hydrogen concentration in the channel region can be controlled by altering the gate metal thickness. Hydrogen atoms affect the TFT’s threshold voltage shifts until it becomes negative, in n‐type TFTs. The threshold voltage shift depends on the hydrogen content of the channel region in p‐Si TFTs. This is explained by the existence of Si-3 trap states in the grain boundaries. © 1995 American Institute of Physics. View full abstract»

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  • Cuspidal pit formation during the growth of SixGe1-x strained films

    Page(s): 34 - 36
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    We have studied the formation of cuspidal pits during the growth of strained SixGe1-x alloy layers at relatively high supersaturations. The pit formation is directly linked to strain in the alloy layer, and we propose a heterogeneous formation mechanism in which the pits develop from stress‐driven surface diffusion associated with a localized initial perturbation of the buffer layer surface. © 1995 American Institute of Physics. View full abstract»

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  • Initial stage of aluminum nitride film growth on 6H‐silicon carbide by plasma‐assisted, gas‐source molecular beam epitaxy

    Page(s): 37 - 39
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    The initial stage of AlN film growth on 6H‐SiC(0001) substrates by plasma‐assisted, gas source molecular beam epitaxy (PAGSMBE) has been investigated in terms of growth mode and interface defects. Cross‐sectional high resolution transmission electron microscopy (HRTEM) was used to observe the microstructure of the deposited films and the AlN/SiC interfaces. Surface morphologies and interface atomic structures were compared between films grown on vicinal and on‐axis surfaces. Essentially atomically flat AlN surfaces were obtained using on‐axis substrates. This is indicative of two‐dimensional growth to a thickness of ∼15 Å. Islandlike features were observed on the vicinal surface. The coalescence of these features at steps gave rise to double positioning boundaries (DPBs) as a result of the misalignment of the Si/C bilayer steps with the Al/N bilayers in the growing film. The quality of thicker AlN films is strongly influenced by the concentration of DPBs formed at the outset of growth. © 1995 American Institute of Physics. View full abstract»

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  • Effect of surface steps and nonstoichiometry on critical thickness of strained InGaAs layers grown by molecular beam epitaxy on InAlAs/InP heterostructures

    Page(s): 40 - 42
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    It is shown that critical thicknesses of In0.65Ga0.35As epilayers, grown by molecular beam epitaxy on lattice matched InAlAs/InP heterostructures, are affected by surface steps and excess arsenic, i.e., nonstoichiometry, in the overgrowth. The critical thickness is reduced in the presence of steps, but is observed to increase when the excess arsenic atoms are present in the layer. It is argued that the generation of dislocation loops required for misfit dislocations is facilitated at the step edges. The resulting misfit dislocations augment the strain relaxation produced by the glide of threading dislocations in the epilayers. On the other hand, the internal strains associated with the nonstoichiometry strengthens the lattice, thus making dislocation glide difficult which delays the relaxation process. © 1995 American Institute of Physics. View full abstract»

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  • Photoluminescence vibrational structure of Si center in chemical‐vapor deposited diamond

    Page(s): 43 - 45
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    Photoluminescence spectra from the Si impurity center in diamond films grown by chemical‐vapor deposition techniques were studied at temperatures between 9 and 300 K. Laser excitation at 514.5 nm, and resonant with the zero‐phonon absorption line at 737 nm (1.6823 eV), were used. Luminescence lines become narrowed at resonance excitation, and the vibrational structure of the Si center was observed with a major phonon replica at 767 nm (1.6165 eV). The observed vibrational energy of 515 cm-1 supports a diatomic quasi‐molecular Si2 center structure. Temperature dependencies of the linewidth of the zero‐phonon line and its phonon replica were measured and the origins of the broadening are discussed. © 1995 American Institute of Physics. View full abstract»

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  • Elastic and hardness properties of Fe–Ag (001) multilayered thin films

    Page(s): 46 - 48
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    The hardness and elastic behavior of Fe–Ag (001) multilayered thin films is presented. Significant enhancements in the hardness were observed that followed a Hall–Petch‐type dependence on bilayer thickness. A reduction in the flexural elastic modulus of 55% relative to the large bilayer thickness value was observed when the bilayer thickness was reduced to 5 nm. Concomitant with the elastic modulus reduction was a variation in the interplanar spacing perpendicular to the plane of the film. It is shown that these behaviors are generally consistent with a model based on the effects of interface stresses. Using this model, an interface stress for Fe–Ag (001) of approximately -1.8 N/m was obtained. © 1995 American Institute of Physics. View full abstract»

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  • Time‐delayed luminescence from oxidized porous silicon after ultraviolet excitation

    Page(s): 49 - 51
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    Oxidized porous silicon is known to luminesce efficiently and with a ns‐fast response in the green‐blue region of the spectrum (2.3–2.7 eV) at room temperature. For microporous Si processed by rapid thermal oxidation at 1100–1200  °C in a dry oxygen ambient, we observe that the blue light has a time‐delayed component that indicates carrier trapping. In addition to the well‐established ultrafast light (∼1 ns) a signal with a time delay of order 1 s is present under UV photoexcitation. The time‐delayed blue light exists at low temperature and has an excitation onset edge at 4.3±0.1 eV, an energy that is usually associated with a band discontinuity at the Si–SiO2 interface. © 1995 American Institute of Physics. View full abstract»

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  • Kinetic model of element III segregation during molecular beam epitaxy of III‐III’‐V semiconductor compounds

    Page(s): 52 - 54
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    Segregation of column III atoms during molecular beam epitaxy of III‐III’‐V semiconductor compounds causes nonabrupt interfaces and a surface composition different from the bulk one. To derive concentration profiles, a thermodynamical equilibrium model has been used for a long time. This model applies well to describe segregation processes at high growth temperatures, but fails in predicting concentration profile variations with substrate temperature. We have thus developed a kinetic model which correctly takes into account the evolution with the growth temperature. We apply this model to the case of indium segregation in the GaxIn1-xAs/GaAs system. The calculated indium concentration profiles are compared to those obtained with the thermodynamical equilibrium model. A kinetic limitation of segregation is shown to appear at low substrate temperatures and sufficiently high growth rates. This limitation is predicted to arise below 400 °C for a growth rate of 1 monolayer/s for In segregation in the GaxIn1-xAs/GaAs system. © 1995 American Institute of Physics. View full abstract»

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  • Substrate orientation dependence of low‐temperature GaAs grown by molecular beam epitaxy

    Page(s): 55 - 57
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    A systematic study of the substrate orientation effect on crystalline quality of GaAs grown by molecular beam epitaxy at low substrate temperature (215 °C) was performed using double‐crystal x‐ray diffractometer and transmission electron microscopy. The crystal quality was found to be strongly correlated with substrate orientations. Layers of high crystalline perfection with excess arsenic were obtained on both GaAs(100) and (311)B substrates, while columnar polycrystalline growth was observed on (211)B substrate. The transition from a single crystalline state to a polycrystalline state was clearly demonstrated by a 0.5 μm GaAs layer on (111)B surface. Surface kinetic factors are believed to play important roles during the low temperature growth. © 1995 American Institute of Physics. View full abstract»

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  • On the formation of epitaxial CoSi2 from the reaction of Si with a Co/Ti bilayer

    Page(s): 58 - 60
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    In spite of much work, the formation of epitaxial CoSi2 from Ti/Co on (100) Si remains something of a mystery. It has been proposed that epitaxy occurs via the formation of an intermediate phase of CoSi with a (311) preferred orientation. In the absence of sufficient information it is impossible to validate or to invalidate the specific original claim. However, one shows that the formation of preferably oriented CoSi is not a necessary condition for the subsequent growth of epitaxial CoSi2. Careful measurements of diffraction intensities reveal the probable, temporary formation of a metastable form of CoSi2, based on a diamond cubic rather than the usual CaF2 structure. © 1995 American Institute of Physics. View full abstract»

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  • Local mode spectroscopy of the carbon acceptor in GaAs: New experimental aspects

    Page(s): 61 - 63
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    The temperature dependence of the local mode absorption of CAs at 580 cm-1 is reexamined using high‐resolution Fourier transform spectroscopy. A new carbon‐related line is detected at room temperature on the low‐energy side of the main carbon peak at 576.6 cm-1. It follows that the integrated absorption of the whole band is independent of temperature in the temperature range between 77 and 300 K. Calibration factors are given for 77 and 300 K, providing a consistent interpretation of previous data. © 1995 American Institute of Physics. View full abstract»

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  • Three‐dimensional electron probe roughness analysis of InP sidewalls processed by reactive ion beam etching

    Page(s): 64 - 66
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    A quantitative three‐dimensional measurement of sidewall roughness of InP etched by chlorine‐based reactive ion beam etching (RIBE) is presented. An electron probe surface roughness analyzer using four secondary electron detectors was employed. The minimum value of average sidewall roughness under the optimized etching condition was as small as 1 nm, where the etching condition was an ion extraction voltage of 400 V and a Cl2 gas pressure of 1.2×10-3 Torr. It is found that the etched sidewall roughness can be reduced by lowering ion extraction voltage with a relatively higher gas pressure. © 1995 American Institute of Physics. View full abstract»

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  • Effect of barrier recombination on the high temperature performance of quaternary multiquantum well lasers

    Page(s): 67 - 69
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    We use spectrally resolved measurements of spontaneous emission to investigate the temperature characteristics of strained and lattice matched InGaAsP multiquantum well lasers. Carrier overflow into the barriers and separate confinement layers and the resulting recombination are demonstrated to be an important factor limiting high temperature performances in these devices. The barrier recombination does not saturate above threshold, instead it increases with the drive current. This effect is further enhanced with increased temperature. We show that the reduction in the barrier recombination correlates quantitatively with increased high temperature slope efficiency. © 1995 American Institute of Physics. View full abstract»

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  • Photoluminescence of strained Si1-yCy alloys grown at low temperature

    Page(s): 70 - 72
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    The photoluminescence of strained Si1-xCx alloys grown at low temperature by rapid thermal chemical vapor deposition is investigated. The photoluminescence spectra are mainly characterized by a deep level broadband at low energy which subsists up to room temperature. This low energy emission is associated with the low‐temperature growth process required for the incorporation of carbon into substitutional sites. The stability of the layers after thermal annealing is monitored using this low energy radiative recombination. A blue shift of the photoluminescence energy peak is observed and the peak intensity presents a maximum versus annealing time. The blue shift and the associated increased linewidth is explained in terms of the local strain induced band‐gap fluctuations. Infrared transmission spectra of the annealed samples suggest that silicon carbide precipitates appear during the anneal and that oxygen and carbon complexes contribute to the formation of the deep level band. © 1995 American Institute of Physics. 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