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Journal of Applied Physics

Issue 9 • Date May 1995

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Displaying Results 1 - 25 of 98
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Oxygen precipitation in silicon

    Page(s): 4169 - 4244
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    A review is presented of the recent advances in the study of oxygen precipitation and of the main properties of oxide precipitates in silicon. After a general overview of the system ‘‘oxygen in silicon,’’ the thermodynamics and the kinetics of the precipitate formation are treated in detail, with major emphasis on the phenomenology; subsequently, the most important techniques for the characterization of the precipitates are illustrated together with the most interesting and recent results. Finally, the possible influence of oxygen precipitation on technological applications is stressed, with particular attention to recent results regarding device yield. Actually, the essential novelty of this review rests on the attempt to give an extended picture of what has been recently clarified by means of highly sophisticated diagnostic methods and of the influence of precipitation on the properties of semiconductor devices. © 1995 American Institute of Physics. View full abstract»

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  • Application of quadrupole ion trap for the accurate mass determination of submicron size charged particles

    Page(s): 4245 - 4250
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    An optical method is developed for the precise mass determination of submicron size charged particles. The measurement is carried out in a hyperbolic quadrupole ion trap electrode system in vacuum by adjusting particle trajectory star shape patterns. This method does not involve gravity so this may be suitable to use in space applications in weightlessness. Due to the imperfect electrode alignment of the ion trap the mass/charge ratio can now be calculated by means of the corresponding electrical parameters with a relative accuracy of 103. Since the measured parameter is frequency the relative accuracy of the mass measurement could later be increased to 106. Combined with stepwise electron loss events induced by UV radiation it is possible to determine the mass of a single particle in the 109–1012 amu range with similar precision. These findings would seem to indicate the feasibility of a novel optical method for high precision mass determination of a single particle in the submicron diameter range. © 1995 American Institute of Physics. View full abstract»

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  • A comparative study on the thermal characteristics of vertical‐cavity surface‐emitting lasers

    Page(s): 4251 - 4258
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    This paper presents a comparative study of the thermal characteristics of four types of vertical‐cavity surface‐emitting lasers (VCSELs). They include the dielectric‐isolated top‐emitting p‐type substrate VCSEL, the ion‐implantation isolated top‐emitting n‐type substrate VCSEL, the dielectric‐isolated bottom‐emitting n‐type substrate VCSEL, and the junction‐isolated etched‐well n‐type substrate VCSEL. Microscale electrical and heat conduction effects are taken into account by employing reduced and anisotropic electrical and thermal conductivities for the Bragg reflectors. Solutions for both the electrical potential and temperature fields are obtained numerically. The calculated device temperature rise compares well with available experimental data. The simulation results show that among the studied lasers the p‐type substrate laser has the best intrinsic thermal performance. Local temperature distributions in these lasers reveal that a large temperature drop occurs across the Bragg reflectors. This study demonstrates that the AlAs concentration and the structure of the Bragg reflectors strongly affect the device temperature rise due to the difference in thermal conductivity. The study also suggests that a thicker top contact should be used to reduce the thermal resistance of these devices. © 1995 American Institute of Physics. View full abstract»

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  • Influence of cavity length and emission wavelength on the characteristic temperature in AlGaAs lasers

    Page(s): 4259 - 4262
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    The dependence of the characteristic temperature T0 on the cavity length and lasing wavelength is theoretical and experimentally analyzed. The devices are straight separate confinement heterostructure lasers with active layer thickness of 30 and 12 nm grown by low temperature liquid phase epitaxy. The recent observation that for very short lasers T0 is an increasing function of the cavity length is confirmed, and explained in terms of the threshold current cavity length dependence. The temperature dependence of the threshold current Ith gives T0 as high as 307 K for a quantum well laser with cavity length L=168 μm. © 1995 American Institute of Physics. View full abstract»

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  • Quasi‐static electrical resonances and optical bistability in periodic composite materials

    Page(s): 4263 - 4273
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    A variational approach is used to examine the possibility of bistable behavior in a two‐component metal‐dielectric composite medium with a periodic microstructure where one component has a Kerr‐ type field dependent part in the dielectric constant ϵ while the field independent part of ϵ in both materials is in general complex. It is shown that under certain conditions bistable behavior can occur even though the field dependent nonlinearity is weak everywhere. This is achieved by operating the material sufficiently close to one of its sharp quasi‐static, microgeometric electrical resonances. The physical characteristics of the threshold intensity are worked out and considerations made on how to optimize the chances for observing optical bistability in such a material. © 1995 American Institute of Physics. View full abstract»

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  • Cross sections and quantum yields of the 3 μm emission for Er3+ and Ho3+ dopants in crystals

    Page(s): 4274 - 4279
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    We have measured the lifetimes of the 2.8 μm emission band for Er3+‐ and Ho3+‐doped fluorides including LiYF4, BaY2F8, LaF3, and KY3F10, and for numerous oxides such as Y3Al5O12, YAlO3, La2Be2O5, and other crystals. Several quantum yields and branching ratios were experimentally evaluated as well, in order to determine the radiative lifetime of the upper laser level for the 2.8 μm transition. This information was employed to assess the cross sections of the 2.8 μm infrared emission band for several of these crystals, which involves the 4I11/24I13/2 transition for Er, and the 5I65I7 for Ho. © 1995 American Institute of Physics. View full abstract»

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  • Finite‐time optimum refrigeration cycles

    Page(s): 4280 - 4284
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    A class of conceptual optimum refrigeration cycles is considered with a fixed overall heat conductance and a specified refrigerant operating temperature range to bound the optimization problems. These cycles deal with maximum refrigeration power, maximum refrigeration load, and maximum heat rejection load for the case of a heat pump. The resulting one degree of freedom problems are solved with a variable arithmetic mean temperature difference in the heat exchangers. The maximum refrigeration power solution yields an analytical closed form optimality rule which constitutes a close lower bound solution to the maximum refrigeration load and maximum heat rejection load problems. © 1995 American Institute of Physics. View full abstract»

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  • Particle charging in low‐pressure plasmas

    Page(s): 4285 - 4292
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    Particles embedded in a plasma acquire a net charge as a result of collisions with electrons and ions. Due to the stochastic nature of encounters between particle and charged species, the instantaneous charge fluctuates. The static properties of the charge fluctuations are quantified for particles surrounded by an undisturbed plasma in orbital motion limit. For particles that satisfy the condition e2/4πϵ0RkTe≪1 the charge distribution is a Gaussian function whose average and variance is related to the ion and electron currents toward the particle. For a Maxwellian plasma, in particular, analytical solutions are developed for the average charge and the variance as a function of the parameters of the plasma ne/ni, Te/Ti, and Me/Mi. Finally, the methodology is extended to non‐Maxwellian plasmas using the Druyvesteyn as an example. © 1995 American Institute of Physics. View full abstract»

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  • Spatial variations of radio frequency plasma density caused by a step‐change of secondary electron emission coefficient

    Page(s): 4293 - 4301
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    A two‐dimensional analytical model for the effect of a nonuniform secondary electron emission coefficient (γ) on the powered electrode of a radio frequency plasma was developed. The nonuniformity was a step change in the value of γ. The ambipolar diffusion equation, including ionization by thermal and secondary electrons, took the form of a Helmholtz equation for which the solution by separation of variables was a series of cosine functions. The discontinuity of γ on the electrode engendered substantial nonuniformity of plasma density. For example, the nonuniformity at the sheath edge of an Ar plasma (50 mTorr, 200 V) was 40% for a substrate having a γ of 0.027 and resting on a platen having a γ of 1.00. © 1995 American Institute of Physics. View full abstract»

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  • Kinetics of compositional disordering of AlGaAs/GaAs quantum wells induced by low‐temperature grown GaAs

    Page(s): 4302 - 4306
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    Compositional disordering of GaAs/AlGaAs quantum wells due to the presence of low‐temperature grown GaAs (by molecular beam epitaxy) was studied. Ga vacancy enhanced interdiffusion was found to be the mechanism underlying the observed intermixing. Diffusion equations were solved numerically to obtain the band profile after intermixing. The transition energies in the quantum wells under various annealing conditions were solved and agree very well with the observed photoluminescence emission peaks. The diffusivity of Ga vacancies and that of induced Al‐Ga interdiffusion were obtained. The vacancy induced interdiffusion diffusivity was found to have an activation energy of 4.08 eV, which is smaller than the activation energy of interdiffusion diffusivity of normal temperature grown GaAs/AlGaAs heterostructures. This is a clear indication of enhanced interdiffusion due to the presence of low‐temperature grown GaAs. © 1995 American Institute of Physics. View full abstract»

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  • Laser‐induced structural modifications of glassy carbon surfaces

    Page(s): 4307 - 4311
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    Structural modifications induced by pulsed laser irradiations in the surface layers of glassy carbon have been monitored by reflection high energy electron diffraction, Raman spectroscopy, and electron energy loss spectroscopy. The glassy carbon samples were irradiated by 30 superimposed laser pulses (λ´=6.943 nm). The energy density (100–500 mJ/cm2 per pulse) delivered to the material and the repetition rate of the laser (0.05 Hz) have been chosen so that the temperature increase of the irradiated surface layers was below the melting point of the glassy carbon. The combined use of the analysis techniques indicated that the beginning of the solid state processes, leading to microstructural modifications of the surface layers, occurs at energy density of 300 mJ/cm2. An increase of the average crystalline size of graphitic clusters occurs upon radiation performed at fluences of 300 and 400 mJ/cm2, whereas at higher energy density the material undergoes complete amorphization. The analysis of chemical state and microstructure of the irradiated samples clearly demonstrates that graphitization or, conversely amorphization of glassy carbon surface layers can be achieved by a proper choice of the laser irradiation conditions. © 1995 American Institute of Physics. View full abstract»

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  • Study of molecular‐beam epitactic growth of GaAs on (100) ScxE1-xAs/GaAs

    Page(s): 4312 - 4320
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    The growth of GaAs on (100)ScxEr1-xAs/GaAs (x=0 and 0.3) by molecular‐beam epitaxy has been studied using transmission electron microscopy. The initial stages of the three‐dimensional growth of GaAs on lattice‐matched Sc0.3Er0.7As have been investigated at different growth temperatures. Besides (100) epitactic GaAs, there are also areas of {111}‐ and {122}‐oriented GaAs observed on ScxEr1-xAs. The latter has a simple twin relationship with the neighboring (100) GaAs. Areas of {111}‐oriented GaAs have been observed only at growth temperatures above 400 °C and with moderate growth rates. The GaAs islands grown at 480 °C are faceted on {110} and {111} low‐index planes. These GaAs islands are elongated along 〈011〉 directions. The anisotropy of the island shape is greater at higher growth temperatures. The growth of GaAs on ScxEr1-xAs as islands is considered to be due to chemical rather than strain effects. The morphology of GaAs layers grown on ScxEr1-xAs is shown to have a strong dependence on the growth conditions. © 1995 American Institute of Physics. View full abstract»

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  • Lattice matched GaAs/Sc0.3Er0.7As/GaAs heterostructures grown on various substrate orientations

    Page(s): 4321 - 4328
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    Lattice‐matched heterostructures of GaAs/Sc0.3Er0.7As/GaAs have been grown on GaAs substrates with various orientations by molecular beam epitaxy and characterized by transmission electron microscopy. The Sc0.3Er0.7As layer usually has good epitaxy on GaAs; the purpose of this study is to investigate the overgrowth of GaAs on Sc0.3Er0.7As. In comparison with the samples grown on nominal (100) substrates, the epitactic growth of GaAs on Sc0.3Er0.7As is slightly improved on a vicinal substrate oriented (100) 6° off towards (111)A. {311} and {211} are shown to be preferred orientations for the epitactic growth of GaAs/Sc0.3Er0.7As/GaAs heterostructures. The epilayers grown on {311} and {211} substrates are epitactically well aligned, and the density of planar defects (stacking faults and microtwins) in the overgrown GaAs layer is significantly reduced. It is suggested that the mixed {111} and {100} character surfaces assist the nucleation of GaAs on Sc0.3Er0.7As. Stacking faults and microtwins are the major defects for the epilayers grown on (110) substrates. For samples grown on (111)B‐oriented substrates, twinning at the interfaces occurs frequently even when selftwinning inside each material is eliminated. © 1995 American Institute of Physics. View full abstract»

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  • Generation of thermally induced defects in buried SiO2 films

    Page(s): 4329 - 4333
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    We show that annealing of the buried oxide layer used for device isolation generates point defects in the SiO2 film and that this defect generation is independent of temperature above 1000 °C. Electron paramagnetic resonance data obtained on thermally grown buried oxides and those fabricated by ion implantation indicate that the defect is intrinsic to the structure of SiO2 and is associated with an oxygen deficient environment. The similarity in the generation of the defects studied here and the formation of SiO observed in earlier studies of low pressure high temperature oxidation suggests that the formation of the buried oxide defect is related to the reduction of SiO2 and the release of SiO. © 1995 American Institute of Physics. View full abstract»

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  • Nucleation of the Al4Mn alloy during containerless solidification in a drop tube

    Page(s): 4334 - 4338
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    The undercooling and nucleation of Al4Mn alloy have been investigated by containerless solidification in a 1.2 m long drop tube, where molten droplets of the alloy solidified in the vacuum. Droplets in various sizes were collected at the bottom of the tube. It is found by x‐ray and electron diffractions that besides the orthorhombic Al6Mn and β‐Mn phases, two approximants of the decagonal quasicrystal, one approximant of the icosahedral quasicrystal and decagonal domains can be observed in the as‐solidified droplets. However, due to the different cooling rate or undercooling in the samples of different sizes, the phases mentioned above will appear in different amounts. The relationship between the phase composition and the sample size is discussed on the basis of the classical nucleation and growth theories. © 1995 American Institute of Physics. View full abstract»

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  • SnTe‐doping of GaAs grown by atomic layer molecular beam epitaxy

    Page(s): 4339 - 4342
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    Using x‐ray diffraction and ellipsometry we have studied the incorporation process of SnTe in GaAs for n‐type doping. Combining these two techniques allows us to decide whether SnTe is incorporated pairwise, as has been proposed in the literature. We found SnTe doping to change the E1 and E11 critical point parameters in a way similar to that previously reported for n‐type Si‐doped GaAs. X‐ray diffraction and Hall measurements show that the free carrier concentration is more than 1/2 of the [Sn]+[Te] concentration. We thus conclude that a large proportion of SnTe is incorporated as independent Sn and Te dopant atoms. © 1995 American Institute of Physics.   View full abstract»

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  • Analysis of the vibrational mode spectra of amorphous SiO2 films

    Page(s): 4343 - 4348
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    The spectral line shapes and the absorption frequencies of the oxygen related infrared active vibrational modes in amorphous SiO2 are studied both experimentally and by simulation. Experimental data were obtained on oxides grown thermally in the temperature range from 800 to 1050 °C and on oxides deposited at 300 °C by plasma enhanced chemical deposition. The transverse optic (TO) mode centered around 1090 cm-1 is found to have a line shape and peak frequency which varies significantly with film thickness while the longitudinal optic (LO) mode at 1256 cm-1 is invariant. Data on both modes and on refractive index is used to demonstrate consistently that the 800 °C grown oxide is 1.6%–2.0% denser than that grown at 1050 °C. For thin oxides (≪10 nm) there is evidence from both TO and LO modes that interfacial oxide is denser than the ‘‘bulk.’’ The data on deposited oxides suggest that caution must be exercised in extending the analysis to their case. © 1995 American Institute of Physics.   View full abstract»

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  • Elastic properties of rigid fiber‐reinforced composites

    Page(s): 4349 - 4360
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    We study the elastic properties of rigid fiber‐reinforced composites with perfect bonding between fibers and matrix, and also with sliding boundary conditions. In the dilute region, there exists an exact analytical solution. Around the rigidity threshold we find the elastic moduli and Poisson’s ratio by decomposing the deformation into a compression mode and a rotation mode. For perfect bonding, both modes are important, whereas only the compression mode is operative for sliding boundary conditions. We employ the digital‐image‐based method and a finite element analysis to perform computer simulations which confirm our analytical predictions. © 1995 American Institute of Physics. View full abstract»

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  • New bounds on the elastic moduli of suspensions of spheres

    Page(s): 4361 - 4372
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    We derive rigorous three‐point upper and lower bounds on the effective bulk and shear moduli of a two‐phase material composed of equisized spheres randomly distributed throughout a matrix. Our approach is analogous to previously derived three‐point cluster bounds on the effective conductivity of suspensions of spheres. Our bounds on the effective elastic moduli are then compared to other known three‐point bounds for statistically homogeneous and isotropic random materials. For the case of totally impenetrable spheres, the bulk modulus bounds are shown to be equivalent to the Beran–Molyneux bounds, and the shear modulus bounds are compared to the McCoy and Milton–Phan‐Thien bounds. For the case of fully penetrable spheres, our bounds are shown to be simple analytical expressions, in contrast to the numerical quadratures required to evaluate the other three‐point bounds. © 1995 American Institute of Physics. View full abstract»

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  • Fourth order elastic moduli of diamond structure materials

    Page(s): 4373 - 4379
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    The values of the fourth order elastic moduli (FOEM) for the diamond structure elements, silicon and germanium, have been calculated. The derivation utilizes the Keating model, assuming that both the third and fourth order terms in the interaction potential are composed of a bond‐stretch, an angle‐bend, and a mixed bond‐stretch angle‐bend term. The three force constants in the fourth order interaction potential are evaluated from the measurements of the sound velocity under pressure, hence, numerical values for all 11 FOEM may be obtained. The set of FOEM thus calculated shows markedly different characteristics than the analogous quantities for other materials, e.g., the alkali halides. © 1995 American Institute of Physics.   View full abstract»

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  • Short‐range ordering in face‐centered‐cubic Ni3Al

    Page(s): 4380 - 4383
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    Films of fcc Ni3Al with suppressed short‐range order (SRO) were prepared by physical vapor deposition of Ni3Al onto room‐temperature substrates. Extended electron energy‐loss fine‐structure spectra were obtained from both Al K and Ni L23 edges. After the samples were annealed for various times at 150 °C, a moderate growth of SRO was observed in the first‐nearest‐neighbor environments of both the Al and Ni atoms. As prepared, these fcc Ni3Al materials, and presumably others having similar heat evolutions as measured by differential scanning calorimetry, have a high degree of chemical disorder. © 1995 American Institute of Physics. View full abstract»

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  • Microstructural aspects and mechanism of the C49‐to‐C54 polymorphic transformation in titanium disilicide

    Page(s): 4384 - 4388
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    Microstructural study of the C49–TiSi2 to C54–TiSi2 polymorphic transformation has been performed to elucidate microstructural evolution and possible mechanism of the phase transformation. It has been shown that the nucleation of the C54–TiSi2 is heterogeneous, and preferentially takes place at triple grain junctions or grain boundaries. The interphase interfaces between C49 and C54 disilicides are often ragged with incoherent characteristics. The growth of the C54 phase is found to proceed by advancing the highly mobile incoherent interfaces in all directions toward the heavily faulted C49 phase. No rigorous orientation relationships are found between the two phases. The microstructural features of the transformation bear some massive characteristics. © 1995 American Institute of Physics. View full abstract»

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  • Thermal stress in GaN epitaxial layers grown on sapphire substrates

    Page(s): 4389 - 4392
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    Thermal stress in GaN epitaxial layers with different thicknesses grown on sapphire substrates by metalorganic vapor phase epitaxy using an AlN buffer layer was investigated. Biaxial compressive stress in the GaN layer, due to the difference in the thermal expansion coefficients between GaN and sapphire, was obtained by measuring the curvature of wafer bending, and the observed stress agreed with the calculated stress. In Raman measurements, the E2 phonon peak of GaN was found to shift and broaden with the stress as a consequence of the change of the elastic constants with strain. The frequency shift Δω (in cm-1) was obtained for the first time, given by the relation: Δω=6.2 σ, where the biaxial stress σ is expressed in GPa. © 1995 American Institute of Physics. View full abstract»

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  • The influence of annealing on the interface properties of low‐dose Si implanted n‐layers in semi‐insulating InP

    Page(s): 4393 - 4398
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    Differential Hall measurement and secondary ion mass spectrometry have been used to characterize the influences of room temperature Si implantation and annealing on the electrical properties of n‐layers formed by direct implantation into liquid‐encapsulated‐Czochralski grown, Fe‐doped InP substrates. The Si activation is affected by the background Fe level. The anneal‐time influenced the electron mobility near the channel‐substrate interface. Mobility degradation at the interface, present with customary anneal, could be avoided using long time anneal. The mobility changes have been correlated with the changes in the Fe distribution near the interface. The customary anneal‐time introduced an Fe accumulation behind Rm, the maximum of the Si profile, followed by an Fe depletion. However, after long time anneals an Fe depletion was created between the Rm and Rm+2dRp of the Si profile and the Fe accumulation shifted behind Rm+2dRp. 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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Editor
P. James Viccaro
Argonne National Laboratory