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Journal of Applied Physics

Issue 6 • Date Sep 1989

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Displaying Results 1 - 25 of 89
  • Oxygen complexes in III‐V compounds as determined by secondary‐ion mass spectrometry under cesium bombardment

    Page(s): 2241 - 2247
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    Recent studies related to the p‐type doping of GaInAs epilayers, grown by molecular‐beam epitaxy, mentioned erratic results concerning the electrical activity of beryllium (Be). This work reports on the secondary‐ion mass spectrometry analysis of moderately Be‐doped (between 5×1017 and 5×1018 cm-3 ) GaInAs/InP layers. Two of them were n type while they should have been p type. The comparison of Be depth profiles, obtained under either oxygen or cesium primary‐ion bombardment, and detailed study of the secondary‐ion mass spectra reveals that Be+ secondary‐ion useful yields are largely enhanced in n‐type samples when using cesium primary ions. Such behavior is attributed to the presence of varying oxygen contents in the samples, as confirmed by quantitative analyses. Comparison of Be and O concentrations indicates that the two elements probably form complexes inside the GaInAs matrix, providing a mechanism for the observed Be electrical inactivity. The use of positive secondary‐ion yield enhancement under cesium bombardment is generalized to other elements (magnesium) in other semiconductor materials, in particular to the case of Au‐Mn/GaAs ohmic contacts. Once again such ions reveal the presence of oxygen. Paradoxically, BeCs+ or MgCs+ molecular ions are not sensitive to the presence of oxygen. It is hypothesized that MCs+ species are more stable than MO+ . Such a differential effect is very helpful in characterizing the presence of oxygen in semiconductor materials. View full abstract»

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  • Laser gain on 3p‐3d and 3s‐3p transitions and x‐ray line ratios for the nitrogen isoelectronic sequence

    Page(s): 2248 - 2252
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    The populations of the 72 levels belonging to the 2s22p3, 2s2p4, 2p5, 2s22p23s, 2s22p23p, and 2s22p23d configurations of the N i isoelectronic sequence have been calculated for the ions Ar xii, Ti xvi, Fe xx, Zn xxiv, and Kr xxx and for electron densities up to 1024 cm-3. Electron collisional monopole excitation from the 2s22p3 ground configuration to the 2s22p23p configuration contributes significantly to the populations of the excited levels and results in relatively large 2s22p23p populations. The population inversions and laser gain for transitions between the 2s22p23s and 2s22p23p configurations are calculated. It is also found that large population inversions and gain occur between levels in the 2s22p23p configuration and levels in the 2s22p23d configuration that cannot decay to the ground configuration by an electric dipole transition. For these potential laser transitions of the type 2s22p23p‐2s22p23d, the reabsorption of the radiation from the lower laser level is less of a problem than for the 2s22p23s‐2s22p23p laser transitions. The 2s22p23p 4P5/2‐2s22p23d 4D7/2 and 2s22p23p 2F7/2‐2s22p23d 2G9/2 transitions represent promising transitions for overcoming some of the problems of opacity in dense plasmas. At high electron densities where the excited levels become collisionally mi- xed, the intensities of the x‐ray transitions from the 2s22p23p levels to the 2s2p4 levels decrease relative to the x‐ray transitions from the 2s22p23s and 2s22p23d levels. The density dependence of these x‐ray line ratios is presented. View full abstract»

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  • Transport of ions at atmospheric pressure using an electrostatic surface wave

    Page(s): 2253 - 2259
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    Ion motion is considered in a gas above a dielectric surface, upon which an electrostatic surface wave propagates. A field‐independent mobility is assumed to adequately characterize the local ion motion in the field of the surface wave. For proper values of amplitude, wavelength, and phase velocity of the surface wave, stable transport of ions above the dielectric surface is found. Ion drift velocities of the order of 100 m/s or more may be obtained. The nature of the ion motion is discussed. Finally, an experiment is described which demonstrates the transport properties of the electrostatic surface wave. Excellent agreement is found between the experimental results and theoretical predictions. View full abstract»

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  • Gradual bulk degradation in (AlGa)As laser diodes during - 20 °C tests due to arsenic out‐diffusion

    Page(s): 2260 - 2264
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    AlxGa1-xAs laser diodes tested in vacuum (10-6 Torr) at a -20 °C heat sink temperature (Tj ∼0 °C) and with an average drive current of 160 mA for one set of diodes (test 1), and 190 mA for another set (test 2), were found to have small decreases in output power due to facet degradation, heat sink degradation, and bulk degradation. Analyses described in this paper show that the degradation mechanism causing the largest decrease in output power was gradual bulk degradation due to arsenic (As) out‐diffusion from the active region. The arsenic out‐diffusion was most likely caused by a processing anomaly. The data further indicate that the As out‐diffusion increases with current. The results from this research can be used to identify a possible cause and accelerating stress of long‐term gradual degradation. It was also observed that defects created by this degradation mechanism (suspected to be As vacancies) caused little change in the forward voltage at 1 mA. View full abstract»

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  • Research on the characteristics of H2 Raman conversion pumping by a 1‐J XeCl excimer laser

    Page(s): 2265 - 2273
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    Detailed results are presented of a high‐efficiency Raman conversion of a 1‐J XeCl excimer laser with an unstable resonator. We had 90% photon conversion of 18‐MW‐power XeCl laser radiation with 39% photon efficiency to the third Stokes order at 499 nm. The effects of rare‐gas concentration in a H2–rare‐gas mixture on the Raman conversion characteristics were investigated. Finally, stimulated Raman scattering between the excited states of H2 at high gas pressure was observed, and conditions for generating these lines are discussed. View full abstract»

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  • Effect of chirality on the Doppler shift and aberration of light waves

    Page(s): 2274 - 2277
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    The Doppler shift and aberration effects are examined for the case of plane electromagnetic wave propagation in optically active or chiral media. These phenomena are found to separate a single monochromatic plane wave into two waves, as observed in a coordinate system in motion with respect to the source. It is shown that the Doppler effect is manifested as two shifted frequencies, one for each of the chiral eigenmodes, while the aberration results in two apparent directions of propagation, one for each eigenmode. Therefore, when motion is involved (either a moving source or a moving observer), a monochromatic single plane wave in one frame may be observed as two plane waves with unequal frequencies and differing directions of propagation in the other. The resulting double frequency shift is plotted as a function of relative velocity. View full abstract»

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  • Inhomogeneous Biot waves in layered media

    Page(s): 2278 - 2284
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    A description, using transfer matrices, is given of the propagation of the three inhomogeneous Biot waves in layered porous media. This is applied to predict the surface impedance of porous layered materials at oblique incidence, and an example is presented. View full abstract»

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  • Temperature distributions and molten zones induced by heating with line‐shaped electron beams

    Page(s): 2285 - 2296
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    A recently developed time‐resolved reflectivity technique has been used to characterize the temperature distributions and molten zones induced in silicon‐on‐insulator structures by heating with scanned line‐shaped electron beams. Measured temperature distributions were compared to theoretical predictions from a one‐dimensional heat‐flow model, which assumes that the heat flow parallel to the surface can be ignored. The results from the experiments and the predictions from the numerical model were also compared to predictions from an analytical model for heating of a homogeneous material. The range of heating conditions for which the one‐dimensional approximation was suitable was determined, and it was found to be satisfactory for heating with line beams of more than 200‐μm width at sweep speeds greater than 5 cm/s. Conditions which produced melting of the silicon film were explored, and it was found that the numerical model did not adequately describe this phase transition. The discrepancy between the theoretical predictions and the observed results can be explained by the need to supercool the liquid silicon by approximately 155 °C before it freezes. View full abstract»

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  • Response times and energy partitioning in electron‐beam‐excited plasmas

    Page(s): 2297 - 2306
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    Excimer lasers are typically excited by electron beams (e beams) with initial energies of 100’s of keV to a few MeV. The e‐beam response time is the interval required for beam electrons and their energetic secondary electrons to slow below the first inelastic thresholds of the buffer gas, below which the electrons thermalize by elastic momentum transfer collisions. In this paper, e‐beam response times for rare gases and for gas mixtures typically used for excimer lasers are discussed using results from a Monte Carlo simulation. Issues pertaining to energy partitioning (W values in mixtures and effective electron temperatures) are also discussed. We find that e‐beam response times may be ≫10’s of ns in gas mixtures of a few atm. As these times are commensurate with the rise time of e‐beam pulses or the width of shorter pulses, beam slowing effects must be considered when modeling these phases of e‐beam pumping. View full abstract»

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  • Current channel migration and magnetic field penetration in a perfectly conducting plasma with emitting, conducting boundaries

    Page(s): 2307 - 2314
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    In collisionless simulations of the plasma erosion opening switch, a highly conductive plasma allows magnetic field penetration through the entire length of the plasma, to depths almost two orders of magnitude greater than the collisionless skin depth, c/ωpe. Field penetration is accomplished by a narrow (skin‐depth‐like) current channel that migrates through the plasma. The plasma behind the current channel is unable to shield the rising magnetic field from the body of the plasma and allows it to penetrate almost instantly and completely through the plasma up to the current channel. The migration of the channel and the penetration of the field appear to occur in the absence of both Coulomb collisions and instabilities. These unusual features are permitted by the electric field structure in the plasma behind the current channel and the presence of conducting boundaries that can emit electrons. View full abstract»

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  • Ratio of Balmer line intensities resulting from dissociative excitation of molecular hydrogen in an ionizing plasma

    Page(s): 2315 - 2319
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    We have estimated the cross section for the production of excited hydrogen atoms from the emission cross sections for Lyman and Balmer lines when molecular hydrogen is dissociated into excited atoms. We have constructed a collisional‐radiative model for the system of ground‐state hydrogen molecules, excited hydrogen atoms, and protons, in a plasma and have calculated the population density distribution of the excited states. The resulting emission‐line intensity ratios for the Balmer series lines are plotted against electron density. We expect these results to be useful for studies of plasmas containing molecular hydrogen, such as occur in the outer region of tokamak plasmas. View full abstract»

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  • The plasma oxidation of titanium thin films to form dielectric layers

    Page(s): 2320 - 2324
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    A remote indicatively coupled radio frequency plasma has been used to oxidize titanium thin films evaporated onto silicon substartes. The substrate was heated during oxidation to temperatures between 200 and 500 °C using a resistively heated furance. Titanium dioxide layers were formed of thicknesses from 53 to 150 nm. The crystal structure was shown to be rutile by x‐ray diffraction for oxidation temperatures of 500 °C. These samples were also seen to have a thin interfacial silicon dioxide layer. Measurements on 1‐mm Al dot capacitors showed the leakage current of a 53‐nm film oxidized at 500 °C to be below 10-8 A at a 2‐V bias. Good capacitance‐voltage characteristics were observed for high oxidation temperatures, with a dielectric constant of between 15 and 22 for the TiO2/SiO2 layers. The refractive index of the layers was measured by ellipsometry to be 2.5–2.6. Plasma oxidation thus provides a low‐temperature method of forming titanium dixoide thin films. View full abstract»

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  • Simulation of the switching performance of an optically triggered pseudo‐spark thyratron

    Page(s): 2325 - 2331
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    The optically triggered pseudo‐spark, also known as the back‐lit thyratron, is a low‐pressure plasma switch having an unheated metallic cathode, which has performance specifications competitive with conventional hot cathode thyratrons. In this paper a computer simulation of the BLT is presented. The simulation consists of a 2 1/2 ‐dimensional time‐dependent continuum model for electron and ion transport using the local field approximation. The model includes an external circuit, and the user may specify the type of gas, pressure, geometry, and electrode materials. Predictions for the anode delay time are compared to experiment as a function of pressure (p), cathode‐anode spacing (d), and trigger fluence. We find that switch closure depends critically on the formation of a virtual anode in front of the cathode hole by generation of positive space charge, and that the anode delay time decreases with increasing p, trigger fluence d, and cathode hole diameter. We also find switch performance is not well characterized by the pd product as in other plasma switches. Rather, we find these quantities depend separately on p and d in a manner which is a function of the geometry of the cathode. View full abstract»

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  • Physical properties of alkoxy‐cyanotolane liquid crystals

    Page(s): 2332 - 2337
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    A simple method for synthesizing alkoxy‐cyanotolanes (nOCDP) is presented. Optical and electro‐optical properties of three nOCDP liquid crystals and an eutectic mixture were evaluated in their nematic range. Birefringence and viscoelastic coefficient results of nOCDP are compared with alkyl‐cyanotolanes at reduced temperatures. Molecular conformation is found to make an important contribution to the observed birefringence, and so does clearing temperature to the measured viscoelastic coefficient. View full abstract»

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  • Averaging fourth‐rank elastic tensors for textured polycrystalline aggregates without physical symmetry

    Page(s): 2338 - 2341
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    The fourth‐rank tensor averaging method due to Morris [J. Appl. Phys. 40, 447 (1969)] is further extended to textured cubic materials with no physical symmetry. The coefficients of the nine linearly independent elements of the transformation matrix [Tijkl], as well as the relevant fifty‐four relations for the calculation of the remaining Tijkl, are derived and presented in tabular form. It is also noted that for orthotropic physical symmetry and cubic crystal symmetry, the number of the linearly independent elements Tijkl is three instead of 15. The applicability of the present analysis is demonstrated by a comparative study. View full abstract»

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  • State equation for shape‐memory alloys: Application to Cu‐Zn‐Al

    Page(s): 2342 - 2348
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    We deal with the hysteretic behavior of partial cycles in the two‐phase region associated with the martensitic transformation of shape‐memory alloys. We consider the problem from a thermodynamic point of view and adopt a local equilibrium formalism, based on the idea of thermoelastic balance, from which a formal writing follows a state equation for the material in terms of its temperature T, external applied stress σ, and transformed volume fraction x. To describe the striking memory properties exhibited by partial transformation cycles, state variables (x,σ,T) corresponding to the current state of the system have to be supplemented with variables (x,σ,T) corresponding to points where the transformation control parameter (-σ and/or T) had reached a maximum or a minimum in the previous thermodynamic history of the system. We restrict our study to simple partial cycles resulting from a single maximum or minimum of the control parameter. Several common features displayed by such partial cycles and repeatedly observed in experiments lead to a set of analytic restrictions, listed explicitly in the paper, to be verified by the dissipative term of the state equation, responsible for hysteresis. Finally, using calorimetric data of thermally induced partial cycles through the martensitic transformation in a Cu‐Zn‐Al alloy, we have fitted a given functional form of the dissipative term consistent with the analytic restrictions mentioned above. View full abstract»

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  • The effect of anodization on the electromigration drift velocity in aluminum films

    Page(s): 2349 - 2355
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    The electromigration drift velocity has been measured, using the Blech–Kinsbron [Thin Solid Films 25, 327 (1975)] edge displacement method, for aluminum thin films under different thicknesses of anodization. The drift velocity is found to decrease with increasing anodization thickness. The results are interpreted in terms of a change in the self‐diffusivity of aluminum as a result of the compressive stresses imposed by the anodized layer. The effect of the variation of diffusivity with stress on the stress distribution within a drifting thin‐film sample is discussed. View full abstract»

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  • Thermal conductivity of La3-xRxS4 where R=Sm, Eu, and Yb

    Page(s): 2356 - 2362
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    The thermal diffusivity values of La2.7Sm0.3S4 , La2.3Sm0.7S4 , La2.7Eu0.3S4 , La2.2Eu0.8S4 , La2.8Yb0.2S4 , and La2.3Yb0.7S4 were measured by the flash diffusivity method from 400 to 1000 °C. The values ranged from 0.007 to 0.018 cm2 /s. The thermal conductivities of the six ternary rare‐earth sulfides were calculated from the thermal diffusivity data and ranged from 10.7 to 31.6 mW/cm °C. Of the alloys measured, La2.2Eu0.8S4 had the highest thermoelectric figure of merit at 1000 °C (0.52×10-3 °C-1). All of the samples had an oxysulfide present at the grain boundaries which degraded their high‐temperature performance. View full abstract»

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  • Formation of PtSi in the presence of Al and a Cr barrier layer

    Page(s): 2363 - 2366
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    The effect of Cr as a barrier between PtSi and Al is studied by analyzing the reactions of the Al/Cr/Pt/Si (2000 Å/1000 Å/1000 Å/Si substrate) structures. Electrical measurement shows a rapid rise in sheet resistance after annealing at 400 °C. Structural analysis shows extensive reactions between Al and Cr at such temperatures. The PtSi formed remains little changed until 550 °C, and is converted to PtAl2 at higher temperatures. The results are compared with those using W, Ti‐W, and carbon barriers, and the roles of barrier materials on the stability of the Al/PtSi metallurgy are discussed. View full abstract»

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  • Diffusant‐immobilization and medium‐degradation effects in the diffusion of chemically reactive gas through layered polymers

    Page(s): 2367 - 2375
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    Thin polymeric barrier layers are often interposed between sensitive surfaces and other polymeric layers in which corrosive species slowly evolve as by‐products of curing or decomposition. The corrosive species considered here are chemically reactive gases. Reducing the number of reactive species that can diffuse to sensitive surfaces ameliorates problems with corrosion, debonding, and the loss of mechanical strength or dielectric breakdown resistance. As some of the diffusing, reactive species are chemically immobilized in the barrier, the polymer’s diffusion coefficient is reduced. We write the resulting nonlinear diffusion equation in a form having special cases which are linear, facilitating the required analysis of multilayered systems. In the case of high doses of reactive gas impinging on one face of a thick slab of polymer, we calculate concentration profiles that agree well with the available experimental data, supporting the validity of the linearization procedure. In the case of low doses of corrosive species evolving over long periods of time in one layer of a two‐layer system, we calculate typical concentration profiles and compute the barrier effectiveness of the second layer in protecting an adjacent surface. The barrier effectiveness is seen to increase faster with a decreasing barrier diffusion coefficient than with an increasing diffusant‐immobilization rate in the barrier. Graphical results for the barrier effectiveness are given as a function of the barrier thickness and diffusion coefficient. View full abstract»

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  • Strain relief mechanisms and the nature of dislocations in GaAs/Si heterostructures

    Page(s): 2376 - 2380
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    The nucleation and glide of misfit dislocations in the GaAs/Si system has been investigated using transmission electron microscopy. GaAs epilayers of different thicknesses were examined by electron microscopy (plan and cross section) and the elastic strain remaining in the film has been related to the average spacing of the misfit dislocations at the interface. The 1000‐Å‐thick GaAs epilayer contains mostly 60° misfit dislocations with an average spacing larger than the equilibrium dislocation spacing, which implies that the misfit strain is not fully relieved. The 2000‐Å and thicker GaAs epilayers contain predominantly 90° misfit dislocations with an average spacing between the dislocations less than the equilibrium dislocation spacing. The formation of sessile 90° dislocations at the interface is explained on the basis of a reaction of two 60° dislocations. A model is developed based on minimum energy considerations to determine the strain‐versus‐thickness relationship. The theoretical predictions of strain relaxation are compared with experimental observations using high‐resolution electron microscopy. View full abstract»

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  • Oxidation of tin on silicon substrate by rapid isothermal processing

    Page(s): 2381 - 2387
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    We report an oxidation study of an Sn overlayer on Si(100) carried out at 400 °C by rapid isothermal processing (RIP) and furnace processing. Single oxide phase SnO2 could be obtained only by rapid isothermal processing. Based on x‐ray diffraction, x‐ray photoelectron spectroscopy, high‐frequency capacitance‐voltage characteristics, and breakdown measurements, improved quality of dielectric films was obtained by RIP. A possible explanation based on the difference in the radiation spectrum of the two sources of energy is also given. View full abstract»

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  • Substrate‐driven ordering microstructure in GaxIn1-xP alloys

    Page(s): 2388 - 2394
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    The effect of substrate misorientation on {111} ordering in GaxIn1-xP epilayers grown on (001) GaAs substrates by metalorganic vapor‐phase epitaxy has been studied by transmission electron microscopy. Among the four possible variants, only the { 1/2   1/2   1/2 }B are observed, and the substrate misorientation toward (11¯0) can disymmetrize the two B variants to a point such that only one remains. We show that the diffuse intensity observed along (001) originates from a modulation of the degree of order. When the domain size is comparable to the characteristic length of the modulation, domain boundaries and antiphase boundaries contribute to the diffuse scattering, giving rise to the reported wavy diffuse intensity. We propose a few simple rules controlling the growth process at the atomistic level, from which the absence of the { 1/2   1/2   1/2 }A variants, as well as the selection effect of the [11¯0] steps on the two remaining variants may be explained. From existing literature, the validity of these rules seems to be rather general. Finally, considering reports that the ordered structure observed here is not at equilibrium, we suggest that the latter is growth induced. The necessary conditions for such an ordering mechanism to operate are identified. View full abstract»

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  • Self‐aligned TiN barrier formation by rapid thermal nitridation of TiSi2 in ammonia

    Page(s): 2395 - 2401
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    Partial or full nitridation of TiSi2 layers has been achieved by rapid thermal nitridation in pure ammonia. Several analytical techniques such as transmission electron microscopy, x‐ray photoemission spectroscopy, and Rutherford backscattering, have been used to study the nitridation process. It was found that a 60‐s anneal at 900 °C was sufficient to yield a 20–30 nm TiN layer on top of the TiSi2 layer, provided that the starting TiSi2 surface was free of Si or Ti oxides. Annealing at 1000 °C for 60 s, on the other hand, nitrided the entire 95‐nm TiSi2 layer. Detailed structural and chemical analysis of the samples before and after nitridation showed that the nitridation process takes place by nitrogen atoms bonding to Ti atoms and displacing the Si atoms. The dissociated Si atoms diffuse towards the TiSi2/Si interface forming an epitaxial layer of nonuniform thickness on the Si substrate. The resulting TiN layer is substantially thinner than the starting TiSi2 layer. It has a somewhat rough top surface and a very nonuniform interface with the underlying TiSi2 or Si. A small amount of Si remains on the top surface mostly in the form of Si3N4. View full abstract»

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  • Magnetic effects on optical energy gap values of (CuIn)1-z Mn2z Te2 alloys

    Page(s): 2402 - 2406
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    Measurements of optical absorption were made as a function of temperature in the range 15–300 K to give optical energy gap E0 values for polycrystalline samples of (CuIn)1-z Mn2z Te2 alloys with z=0.4 and 0.5. Absorption edges were observed for both the ordered and disordered zinc‐blende phases and also for a lower energy transition assumed to be an internal Mn2+ transition. As confirmed by magnetic susceptibility data, the dominant phase in these alloys was the ordered zinc blende. For this phase, the variation of E0 with temperature in the vicinity of the magnetic transition temperature Tg was analyzed to give the magnetic contribution ΔE, which increases the value of E0. ΔE was determined as the difference between the experimental values of E0 and an extrapolation from higher temperatures where the magnetic contribution is negligible. These values of ΔE were fitted to the relation d/dt(ΔE)=-Pt, where t=∥T-Tg ∥/Tg , and good agreement was found with previous theoretical predictions for the effect on the band gap of a critical point such as Tg . As predicted, different behavior was observed close to Tg and at temperatures outside the critical range, μ having a value close to zero in the first range and close to 0.5 in the second. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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P. James Viccaro
Argonne National Laboratory