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Applied Physics Letters

Issue 16 • Date Apr 1996

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Displaying Results 1 - 25 of 47
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Theory of the spectral line shape and gain in quantum wells with intersubband transitions

    Page(s): 2171 - 2173
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    We investigate the spectral line shape of radiative intersubband transitions in a quantum well as determined by two factors: the electron scattering rate from states of given energy and the mass difference between the two subbands involved. The interplay between these factors leads to an essentially non‐Lorentzian form of the spectral line. We develop an analytic theory of the line shape and calculate the dependence of the intersubband optical gain in a quantum well on both the population inversion and the temperature. Under typical conditions, the effect of electron temperature on the gain is similar to that of the lattice temperature, which points to the importance of hot carrier effects in understanding the behavior of intersubband lasers. © 1996 American Institute of Physics. View full abstract»

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  • Reduction of fanning influence in two‐wave mixing coefficient measurements in thick crystals

    Page(s): 2174 - 2176
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    We propose and demonstrate a new method to measure the two‐wave mixing coefficient with slight influence of beam fanning in thick crystals with high coupling constants. The strong beam fanning was suppressed by introducing an additional erase beam. By measuring the effective two‐wave mixing coefficient with the additional erase beam, the coupling coefficient without the additional erase beam can be calculated. © 1996 American Institute of Physics. View full abstract»

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  • Room‐temperature operation of an Yb‐doped Gd3Ga5O12 buried channel waveguide laser at 1.025 μm wavelength

    Page(s): 2177 - 2179
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    An epitaxially grown ytterbium‐doped gadolinium gallium garnet (Yb:GGG) buried channel waveguide laser is prepared on an yttrium substituted GGG substrate (Y:GGG). The effective light guiding structure is obtained as a result of the difference of refractive indices of Yb:GGG and Y:GGG. The Yb:GGG waveguide exhibits single‐mode 1.025 μm lasing operation at room temperature. The incident threshold and slope efficiency of the 5‐mm‐long waveguide laser when pumped at 0.941 μm are 80 mW and 13.4%, respectively. © 1996 American Institute of Physics. View full abstract»

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  • Anomalous above‐threshold spontaneous emission in gain‐guided vertical‐cavity surface‐emitting lasers

    Page(s): 2180 - 2182
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    Anomalously large decrease in spontaneous emission is observed in gain‐guided vertical‐cavity surface‐emitting lasers after the onset of lasing. By analyzing two‐dimensional profiles of the lasing mode and carrier density, we found that this unexpected phenomenon originates from the contraction of transverse lasing mode size. Under the condition of the constant modal gain, it is explained that the above‐threshold average carrier density could decrease in contradiction to the general understanding. Unless this anomalous effect is taken into account properly, nontrivial errors could occur in determination of the external quantum efficiency. © 1996 American Institute of Physics. View full abstract»

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  • Theoretical study on intervalence band absorption in InP‐based quantum‐well laser structures

    Page(s): 2183 - 2185
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    Intervalence band absorptions of 1.5 μm light in various InGaAs/InGaAsP quantum well laser structures are investigated theoretically. The intervalence band absorption formalism based on 6×6 Luttinger‐Kohn Hamiltonian is developed. The absorption tends to decrease with the barrier height of quantum wells. The tensile strain in the well causes the absorption to reduce, while the compressive strain causes it to increase. Also is found that the absorption decreases with increase in temperature. © 1996 American Institute of Physics. View full abstract»

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  • Very high efficiency four‐wave mixing in a single semiconductor traveling‐wave amplifier

    Page(s): 2186 - 2188
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    We report on high efficiency frequency‐conversion obtained by four‐wave mixing in a single traveling‐wave semiconductor optical amplifier. Efficiency in excess of 0 dB is demonstrated for frequency conversion up to 2 THz. Measurements of the signal to the amplified spontaneous emission background ratio are also presented. © 1996 American Institute of Physics. View full abstract»

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  • Electron impact vibrational excitation cross sections of SiF4

    Page(s): 2189 - 2191
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    Electron drift velocities in mixtures of SiF4 and Ar have been measured using a pulsed‐Townsend type drift tube. A set of vibrational excitation cross sections of electron scattering in SiF4 has been subsequently determined by the swarm analyses of measured transport data in highly dilute SiF4-Ar mixtures. The derived cross sections are consistent with the electron transport properties over an order of magnitude in SiF4 concentration in gas mixtures, thus providing evidence that the main features of their near threshold behavior, and of their absolute magnitude have been captured. © 1996 American Institute of Physics. View full abstract»

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  • Ionized‐cluster‐beam deposition and electrical bistability of C60–tetracyanoquinodimethane thin films

    Page(s): 2192 - 2194
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    We report an ionized‐cluster‐beam (ICB) deposition and the electrical bistability of C60–tetracyanoquinodimethane (TCNQ) thin films. The films are fabricated by using an ionized‐cluster‐beam deposition method in a high vacuum system. The as‐deposited films were characterized by transmission electron microscopy and optical absorption spectroscopy, which verified the formation of the charge‐transfer complex system in C60–TCNQ thin films and the microstructure of these thin films. The structure and the electrical property of the ICB deposited Ag‐TCNQ thin films are also presented. The possible conductive mechanism of these ICB deposited thin films is discussed in the letter. © 1996 American Institute of Physics. View full abstract»

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  • The growth characteristics of (001) oriented diamond layers on (111) diamond face via bias‐assisted chemical vapor deposition

    Page(s): 2195 - 2197
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    A new phenomenon of diamond growth was observed. (001) oriented diamond layers can be grown on a (111) diamond face in a bias‐assisted chemical vapor deposition process. The growth characteristics were investigated by means of scanning electron microscopy and Raman spectroscopy. It was found that, due to the ion bombardment, the epitaxial growth of the (111) diamond face was interrupted and a secondary nucleation occurred. This ion‐bombardment‐induced secondary nucleation leads to the growth of a top layer with a nonparallel orientation relationship with the substrate. © 1996 American Institute of Physics. View full abstract»

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  • Growth and characterization of epitaxial Mo/NbN superlattices

    Page(s): 2198 - 2200
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    Epitaxial Mo/NbN superlattices were grown on MgO(001) substrates by reactive dc magnetron sputtering. The epitaxial relationship between the bcc metal and the NaCl (B1)‐structure compound is Mo(001) ‖NbN(001), Mo[110]‖NbN[010], and the lattice mismatch is 1.4% given the 45° rotation about the (001). Cross‐sectional transmission electron microscope images show well‐defined and relatively planar layers. High angle x‐ray diffraction results show up to 25 superlattice reflections extending over ≊30° in 2θ. Kinematical model fits to the x‐ray diffraction data suggest that the interface widths were only ≊0.3 nm, presumably because of the immiscibility of Mo and NbN. Initial nanoindentation results indicate hardness values of ≊28 GPa, about 3 times the rule‐of‐mixtures value. © 1996 American Institute of Physics. View full abstract»

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  • Magnetic field‐mediated alignment of a nematic liquid crystal at a polymer surface exposed to ultraviolet light

    Page(s): 2201 - 2203
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    A nematic liquid crystalline cell utilizing a substrate coated with polyvinylcinnamate was subjected to UV polarized light in the presence of a magnetic field. After removing the cell from the field it was found that the pretilt angle was large and both temporally and thermally robust. Irradiation in the absence of a field resulted in a rapid decay of the pretilt angle to zero, corresponding to planar alignment. © 1996 American Institute of Physics. View full abstract»

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  • Ripening‐assisted asymmetric spalling of Cu‐Sn compound spheroids in solder joints on Si wafers

    Page(s): 2204 - 2206
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    In reacting eutectic SnPb solder with Ti/Cu and Cr/Cu/Au thin film metallization on Si wafers, we have observed spalling of Cu6Sn5 spheroids when the solder consumes the Cu. The formation of the spheroids is assisted by the ripening reaction among the compound grains. In addition we have observed an asymmetric spalling phenomenon using a sandwich structure, in which two wafers were soldered face‐to‐face. The spalling occurs predominantly at the interface at the bottom of the solder joint. It suggests that gravity plays a role. © 1996 American Institute of Physics. View full abstract»

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  • Direct observation of second neighbor interactions for Cr4+ doped forsterite by resonance Raman scattering

    Page(s): 2207 - 2209
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    Fifteen Cr4+ local modes are observed using resonance Raman scattering in a Cr:Mg≪thin≫2SiO4 crystal, instead of a maximum of nine internal vibrations predicted by first neighbor interactions. The larger‐than‐predicted number of modes is explained in terms of second neighbor interactions for the Cr4+ ion. The frequency dependence of the two tetrahedral stretching modes measured at 361 and 765 cm-1 on second neighbor parameters shows a different degree of localization at the Cr≪thin≫4+ site for these modes. © 1996 American Institute of Physics. View full abstract»

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  • Selective area growth of metal nanostructures

    Page(s): 2210 - 2212
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    Nanometer‐scale metal lines are fabricated onto Si(100) substrates by scanning tunneling microscope (STM) based lithography and subsequent chemical vapor deposition. An STM tip is first used to define areas for metal layer growth by electron stimulated desorption of adsorbed hydrogen. Exposure to Fe(CO)5 at 275 °C results in preferential deposition of Fe onto Si dangling bond sites (i.e., depassivated areas defined by the STM tip), while the monohydride resist remains intact in surrounding areas. Fe metal lines with widths ∼10 nm are constructed using this selective‐area, autocatalytic growth technique. View full abstract»

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  • Surfactant‐mediated epitaxy of Ge on partially Ga‐terminated Si(111) surfaces

    Page(s): 2213 - 2215
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    Surfactant‐mediated heteroepitaxy of Ge on Si(111) with Ga as surfactant has been studied using a recently developed apparatus of scanning reflection electron microscopy combined with scanning tunneling microscopy. It has been found that Ge film formation of 4.3 ML thickness on a Ga‐terminated √3×√3 surface results in two‐dimensional island growth in contrast with pseudomorphic growth on 7×7 surface. Irregular growth of Ge clusters along the lower sides of atomic step edges also takes place on the √3×√3 surface at an elevated substrate temperature. Ge film was also grown on partially Ga‐terminated Si(111) with both Ga‐adsorbed √3×√3 and Ga‐desorbed 7×7 reconstruction areas on the surface. It has been found that self‐organized Ge clustering occurs along the Ga‐desorbed 7×7 area with stripe shape. © 1996 American Institute of Physics. View full abstract»

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  • Enhanced optical properties of in situ passivated near‐surface AlxGa1-xAs/GaAs quantum wells

    Page(s): 2216 - 2218
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    An epitaxial method for in situ passivation of epitaxial AlxGa1-xAs/GaAs surfaces is reported. The deposition of an ultrathin InP layer (about one monolayer) on the surface of AlxGa1-xAs/GaAs structures by metalorganic vapor phase epitaxy results in drastically reduced surface recombination. The effect is studied by low‐temperature photoluminescence of near‐surface Al0.22Ga0.78As/GaAs quantum wells where the top barrier thickness is varied from 0 to 50 nm. At the thicknesses of ≤5 nm, the intensity from passivated samples is more than four orders of magnitude larger than that obtained from unpassivated structures. For a passivated surface quantum well where InP is deposited directly onto the GaAs quantum well, we observe a blueshift of 15 meV and an intensity reduction of only a factor of 10 as compared to the luminescence from a quantum well placed at a depth of 50 nm from the surface. © 1996 American Institute of Physics. View full abstract»

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  • Effect of hydrogen plasma precleaning on the removal of interfacial amorphous layer in the chemical vapor deposition of microcrystalline silicon films on silicon oxide surface

    Page(s): 2219 - 2221
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    Microcrystalline silicon(μc‐Si) film deposited on silicon oxide in a remote plasma enhanced chemical vapor deposition (RPECVD) with disilane (Si2H6) and silicon tetrafluoride (SiF4) has been investigated. It was found that in situ hydrogen plasma cleaning of the substrate prior to deposition is effective to reduce the interfacial amorphous transition region. It is believed that hydrogen plasma cleaning generated adsorption and nucleation sites by breaking weak Si–O and Si–Si bonds and also removed oxygen/carbon impurity. Surface roughening was observed from the hydrogen plasma precleaning which helped nucleation and crystallization at the initial stage of the growth. © 1996 American Institute of Physics. View full abstract»

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  • Surface activated bonding of silicon wafers at room temperature

    Page(s): 2222 - 2224
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    A method to bond silicon wafers directly at room temperature was developed. In this method, surfaces of two silicon samples are activated by argon atom beam etching and brought into contact in a vacuum. By the infrared microscope and KOH etching method, no void at the bonded interface was detected in all the specimens tested. In the tensile test, fracture occurred not at the interface but mainly in the bulk of silicon. From these results, it is concluded that the method realizes strong and tight bonding at room temperature and is promising to assemble small parts made by the silicon wafer process. © 1996 American Institute of Physics. View full abstract»

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  • Ultrafast carrier trapping in high energy ion implanted gallium arsenide

    Page(s): 2225 - 2227
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    Time resolved photoluminescence and electrical measurements were made on MeV As, Ga, Si, and O ion implanted GaAs to doses in the range of 1×1014–5×1016 cm-2 and subsequently annealed at 600 °C for 20 min under arsine ambient. Carrier trapping times were found to decrease with increase in implantation dose for all species studied and can be shorter than 1 ps. Sheet resistance values were found to be independent of implantation dose and were of the order of 108 Ω/⧠ for As, Ga, and O implantation and ∼2×102 Ω/⧠ for the Si case due to its electrical activation. Conductivity activation energies of 0.67–0.69 eV were observed for As, Ga, and O ion implanted and annealed GaAs, which are close to the reported activation energy for annealed low‐temperature GaAs (0.65 eV). © 1996 American Institute of Physics. View full abstract»

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  • Assembling strained InAs islands on patterned GaAs substrates with chemical beam epitaxy

    Page(s): 2228 - 2230
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    The assembly of strained InAs islands was manipulated through growth on patterned GaAs substrates with chemical beam epitaxy. Conditions were found to selectively place the islands in patterns features but not on surrounding unpatterned fields. Chains of islands having 33 nm minimum periods were formed in trenches, and single or few islands were grown in arrays of holes. When capped with GaAs, the islands behave as quantum dots and are optically active. © 1996 American Institute of Physics. View full abstract»

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  • The effect of thermal processing on polycrystalline silicon/SiO2/6H–SiC metal‐oxide‐semiconductor devices

    Page(s): 2231 - 2233
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    Thermal processing of polycrystalline silicon (polysilicon)/SiO2/SiC metal‐oxide‐semiconductor (MOS) devices following polysilicon deposition can have an adverse effect on the electrical properties of the SiO2/SiC interface. The primary effect is a negative shift in flatband voltage caused by an increase in fixed oxide charge and interface state density. These effects can be minimized or eliminated by restricting processing temperatures to 900 °C or below following polysilicon gate deposition. © 1996 American Institute of Physics. View full abstract»

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  • Analysis of field emission characteristics of hydrogen‐adsorbed silicon surface

    Page(s): 2234 - 2236
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    It has been reported elsewhere that the intercept and the absolute value of slope of the Fowler–Nordheim plot for a hydrogen‐adsorbed silicon field emitter are smaller than those for a clean silicon field emitter. In this letter it is shown that this experimental result can be explained by taking account of the change of surface potential barrier due to the polarization of adsorbed hydrogen atom in addition to the change of work function. The amounts of decrease of the intercept and the absolute value of slope calculated for the hydrogen‐adsorbed silicon surface are in good agreement with the experimental data. © 1996 American Institute of Physics. View full abstract»

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  • Surface photoabsorption study of the effect of substrate misorientation on ordering in GaInP

    Page(s): 2237 - 2239
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    Substrate orientation strongly affects Cu–Pt ordering in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. In situ surface photoabsorption (SPA) measurements were used to measure the concentration of [1¯10]‐oriented P dimers, characteristic of the (2×4) reconstructed surface, as a function of substrate misorientation from (001). For substrates misoriented toward either [110] [or (111)A] or [1¯10] [or (111)B], the P‐dimer concentration is found to decrease systematically as the misorientation angle increases from 0° to 15.8° at 620 °C with tertiarybutylphosphine (TBP) partial pressures of 10, 50, and 200 Pa. The P‐dimer concentrations on substrates misoriented toward [110] are higher than for those misoriented toward [1¯10]. The Ga0.5In0.5P layers were found to form the Cu–Pt structure during growth. The degree of order, determined from 20 K photoluminescence measurements, shows a strong correlation with the concentration of [1¯10]‐oriented P dimers. The data also clearly show the effect of step structure on Cu–Pt ordering. They indicate that [110] steps formed by misorientation toward [1¯10] enhance ordering while [1¯10] steps formed by misorientation toward [110] retard ordering. © 1996 American Institute of Physics. View full abstract»

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  • Interface structures of InGaAs/InGaAsP/InGaP quantum well laser diodes grown by metalorganic chemical vapor deposition on GaAs substrates

    Page(s): 2240 - 2242
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    We have studied the effects of substrate misorientation on the growth of strained‐layer In0.18Ga0.82As quantum well laser structures with InGaAsP confinement layers and In0.5Ga0.5P cladding layers lattice matched to a GaAs substrate. Low‐temperature photoluminescence (PL) and atomic force microscopy (AFM) provide evidence of a strong substrate‐orientation dependence of the interface structure. The surface morphology of the InGaAs quantum well is found to be determined primarily by the underlying InGaAsP confinement layer. Structures grown on exact‐(100) oriented substrates exhibit three‐dimensional island surface morphology, whereas growths on (100) substrates oriented 2° towards [110] exhibit high surface roughness, possibly due to step bunching. These observations correlate well with previously reported device performance from strained quantum well laser diodes in the InGaAs/InGaAsP/InGaP material system, and can serve as a tool to optimize device performance. © 1996 American Institute of Physics. View full abstract»

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Aims & Scope

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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Editor
Nghi Q. Lam
Argonne National Laboratory