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To accelerate the development of GaN power devices, reproducible fabrication of p-type GaN (p-GaN) segments by ion-implantation (I/I) that enables selective-area doping is preferred. In this Letter, the results of time-resolved photoluminescence (PL) and spatially resolved cathodoluminescence (CL) measurements on p-GaN fabricated by I/I are presented. The p-GaN samples of a 220-nm-deep box-shaped Mg concentration profile ([Mg] = 3×1018 cm−3) were fabricated by sequential I/I of Mg and N followed by atmospheric-pressure post-implantation annealing (PIA). During PIA, Mg redistribution was guided by N-I/I-induced vacancies. The intensities of PL peaks originating from Mg acceptors were increased by increasing the PIA temperature (Ta), indicating progressive activation of Mg and simultaneous decrease in the concentration of nonradiative recombination centers (NRCs). As a result, a record-long room-temperature PL lifetime for the near-band edge emission of Ga-polar Mg-implanted p-GaN (1.4 ps) was obtained when Ta = 1300 °C. Because the species of major vacancy-type defects in the present sample was determined as vacancy clusters comprised of few Ga-vacancies (VGa) and N-vacancies (VN) such as (VGaVN)2–3, the NRC concentration is roughly estimated at around 1017 cm−3 provided that (VGaVN)2–3 are major NRCs with the electron-capture-coefficient of 7×10−6 cm3 s−1. Cross-sectional CL linescan images revealed certain activation of Mg from the surface to the leading edge of the box-shaped [Mg] profile, while NRCs remained at the depths right below the box-shaped profile. The results support advantages of using the vacancy-guided Mg redistribution technique for controlling the activated [Mg] profile and realizing p-type Ga-polar GaN:Mg segments by I/I.

Spatially resolved photoluminescence (PL) of methylammonium lead iodide (MAPbI3) films in planar heterojunction solar cells is probed by time-resolved confocal microscopy to study the interface effect on PL intensity-voltage (PL-V) hysteresis. Negligible PL-V hysteresis is observed at the interfacial area, while significant hysteresis is observed in the bulk film. PL lifetime imaging of the perovskite device reveals inhomogeneous charge extraction due to variation of the interfacial contact quality. Poor interfacial contact leads to more severe PL-V hysteresis in the bulk perovskite film. The PL-V characteristics also suggest that voltage-driven ion migration may lead to redistribution of charge traps, and consequently affect the nonradiative charge recombination and the PL intensity in MAPbI3 films.

In carbon-doped GaN (GaN:C) buffers used in a GaN-on-Si technology, the buffer is embedded in between transition and channel layers. This makes the analysis of buffer properties difficult due to e.g., carrier injection from or potential drop at these adjacent layers. Here, we analyze capacitance- and current-voltage characteristics of 200–300 nm thick GaN:C ([C] = 1019 cm−3) layers which are embedded between a top metal electrode and bottom n-doped GaN (n-GaN). Such structures allow a better potential control in GaN:C and thus determination of the band diagram quantitatively. The accumulation of negative charge (concentration up to 6 × 1017 cm−3) with bias is observed in GaN:C at both polarities. For biases Vappl +1.7 V, accumulated negative charges in GaN:C raise an energy barrier of ∼1.1 eV for electron injection from n-GaN ...

The initial mode of damage in multidirectional composites is the accumulation of matrix cracks in the off-axis plies. Remote laser Raman spectroscopy, using aramid (Kevlar 49®) fibers as Raman strain sensors, has been employed to monitor the local strains in cracked crossply composites. The strain magnification in the 0° ply caused by 90° matrix cracking are measured at different levels of loading. A relationship between the values of strain magnification and the distance between the position of the fibers sensors vis-a-vis the crack front has been established. The effect of damage progression within the 0° plies on the remaining∕surviving glass fibers is modeled satisfactorily and verified against predictions on the basis of a generalized plane strain model by assuming that the 90° ply “expands” in relative size against the 0° ply thickness.

A sensing probe has been introduced to profile the magnetic fields in a 2.45GHz, high-power single-mode microwave cavity. The treatment of a ferrite sample inside the cavity has established that, during the heating process, there is an unusual concentration of a magnetic field around the sample. During field heating, intense magnetic fields have been monitored, and are analogous to the redistribution of an electric field reported by Riedel and Svoboda [Proceedings of the Eighth Ampere Conference and Microwave Heating (2001)] in their simulation studies on microwave sintering.

We modelize the photoinduced formation of switchable diffraction gratings in polymer-based liquid-crystalline composite materials. The model assumes that redistribution of molecules is due to mass diffusion and incorporates a realistic kinetic description of polymerization processes. Numerical simulations predict two different kinds of structure that have already been experimentally observed. Two parameters governing the phenomenon are pointed out, which determine the structure that will be formed after the curing process has been completed.

Carrier redistribution in organic/inorganic (poly(3,4-ethylenedioxy thiophene/poly(styrenesulfonate)polymer)-Si) heterojunction determined from infrared ellipsometry

The microscopic photoinduced charge redistribution on the surface of an organic dye composite layer was directly observed using Kelvin probe force microscopy (KFM) coupled with a laser source. The organic layer composed of chloroaluminum phthalocyanine and N,N′-dioctadecyl-3,4,9,10-perylene tetracarboxylic-diimide was cast onto the surface of nano-TiO2 film. Under illumination, the surface potential morphologies of the organic layer changed from large fluctuation to relatively uniform features. Such a phenomenon was associated with the photoinduced charge transfer between the dye composite and nano-TiO2, which was rationalized in terms of energy level alignment. Considering that the KFM have been proved to be a visual technique in the characterization of nanomaterials, we have presented a method to visualize the photoinduced charge transfer in microscopic scale.

Laser diodes with nonidentical multiple quantum wells could have the lasing wavelength very insensitive to temperature variation. For temperature varying from 33 to 260 K, the lasing energy changes less than 5 meV, while the band gap energy changes more than 50 meV. The origin is due to the strongly temperature-dependent Fermi–Dirac distribution, which favors carriers in high-energy states at large temperature. The temperature-induced carrier redistribution could even cause negative characteristic temperature for a certain temperature range because the low-energy quantum wells behave like reservoirs to overcome the detrimental influence of temperature.

Long-range oxygen motion has been observed in Pt/Pb(Zr,Ti)O3/Ir thin-film structures after electrical fatigue cycling at room temperature. Through an exchange anneal, isotopic 18O was incorporated as a tracer into bare Pb(Zr,Ti)O3 (PZT) films, allowing secondary ion mass spectrometry measurements of the tracer profile evolution as a function of the number of polarization reversals. Observation of 18O tracer redistribution during voltage cycling, which is presumably mediated by oxygen vacancy motion, was found to be strongly dependent upon the thermal history of the film. However, there was no strong correlation between the extent of 18O tracer redistribution and the extent of polarization suppression induced by voltage cycling. Our results suggest that oxygen vacancy motion plays, at most, a secondary role in ferroelectric fatigue of PZT thin films.

Poly-Si/SiO2/Si diodes in which oxides were grown thermally under wet oxidation conditions and subsequently treated by a post-oxidation anneal (POA) have been characterized electrically and chemically before and after applying negative-bias-temperature stress (NBTS). It was confirmed that NBTS produces interface states and that POA suppresses the interface state production. Nuclear reaction analysis indicated that NBTS results in hydrogen redistribution within the oxide layer. POA was shown to partly suppress such hydrogen accumulation. Hydrogen is thus clearly shown to influence the stability against NBTS.

In this letter, we demonstrate rapid decomposition in Ge-doped SiO2 glass under high-energy electron irradiation, and comment on possible mechanisms for the interaction of the electron-beam with the glass. Nanometer-scale modifications in Ge-doped SiO2 glasses can be obtained by the redistribution of Ge in the glasses as a result of patterned electron-beam writing.

Salt weathering is a major cause of deterioration of buildings and monuments of cultural heritage. We have determined the underlaying moisture and ion transport within a representative building material by measuring the time evolution of NaCl-saturated samples during one-sided drying using nuclear magnetic resonance. The measured NaCl concentration profiles reflect the competition between advection to the surface and redistribution by diffusion. By representing the measured moisture and NaCl profiles in an efflorescence pathway diagram (EPD) the crystallization is also taken into account. The pathways followed in the EPD indicate that for historical objects in general, crystallization at the surface cannot be avoided. ©2002 American Institute of Physics.

Annealing atmosphere effects on domain structures and electrical properties of Pb[(Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5]O3 (PZN–PZT) ferroelectric materials were investigated. The PZN–PZT specimens were annealed in argon, air, oxygen, and PbZrO3 atmospheres after being sintered at 1100 °C in air. The as-sintered specimens were composed of large plate-like domains. When the specimen was annealed in flowing oxygen atmosphere for 8 h at 960 °C, the domains were refined into fine twin-like domains; whereas when the specimen was annealed in argon atmosphere, the domains were modified into needle-like structures. These modifications to the domain structures have a strong effect on the electromechanical properties of this material. The formation and redistribution of lead and oxygen vacancies during thermal annealing were responsible for those variations in domain structures and electrical properties.

The effects of hydrogen dilution, subtle boron compensation, and light-soaking on the gap states of hydrogenated amorphous silicon films (a-Si:H) near and above the threshold of microcrystallinity have been investigated in detail by the constant photocurrent method and the improved phase-shift analysis of modulated photocurrent technique. It is shown that high hydrogen dilution near the threshold of microcrystallinity leads to a more ordered network structure and to the redistribution of gap states; it gives rise to a small peak at about 0.55 eV and a shoulder at about 1.2 eV below the conduction band edge, which are associated with the formation of microcrystallites embedded in the amorphous silicon host matrix. A concurrent subtle boron compensation is demonstrated to prevent excessive formation of microcrystallinity, and to help promote the growth of the ordered regions and reduce the density of gap defect states, particularly those associated with microcrystallites. Hydrogen-diluted and appropriately boron-compensated a-Si:H films deposited near the threshold of microcrystallinity show the lowest density of the defects in both the annealed and light-soaked states, and hence, the highest performance and stability. (C) 2001 American Institute of Physics.

Carbon was implanted into GaAs at the energy of 1 MeV with doses between 1×1013 and 2×1015 cm−2 at temperatures of 80 K, nominal room temperature (RT), and 300 °C. A markedly higher electrical activation was obtained in the samples implanted at 80 K compared to those implanted at RT or 300 °C, attaining a maximum hole concentration of 2×1019 cm−3. The redistribution of the C profile during rapid thermal annealing at temperatures from 700 to 950 °C for 10 s was found negligible, independently of the implantation temperature. Similar improvements in the electrical properties were also verified in samples implanted at 80 K with a lower energy of 60 keV. We consider that despite the light mass of C ions, the reduced dynamic annealing at 80 K allows the accumulation of an abundance of As vacancies, which assist the C activation as a p-type dopant.

We show that β-phase boron–carbon–nitrogen (C2BN) structures energetically favor segregation into superlattices of alternating diamond and cubic boron nitride (cBN) layers. Local-density functional calculations of total energies using pseudopotential approximations and a plane-wave basis set of the β-C2BN systems with different thicknesses of alternating diamond and cBN layers grown along the (001) direction found a decrease in the formation energy with an increase in the layer thickness. We consider this phenomenon to be a result of the charge redistribution in each layer due to interface formation. Our study indicates that the deviation of charge distributions from those in pure diamond and cBN structures due to the existence of BN–C junctions in β-C2BN may result in difficulties in its synthesis.

We report atom probe results on impurity oxygen dissolution in a Zr65Cu15Al10Pd10 metallic glass and its redistribution during nanocrystallization. Approximately 0.1 at. % impurity oxygen is detected from the as-melt-spun Zr65Cu15Al10Pd10 metallic glass. Oxygen redistribution occurs during annealing. In some crystallites, oxygen up to 4 at. % is detected, and virtually no oxygen is dissolved in the remaining amorphous phase. This result directly demonstrates that impurity oxygen promotes the crystallization by forming metastable phases containing high content oxygen and thereby influences the kinetics of crystallization.

The temperature dependences of the fundamental excitonic resonance in PbS and PbSe quantum dots fabricated by various technologies are experimentally determined. Above ∼150 K, sub-linearities of the temperature shifts and halfwidths are observed. This behavior is analyzed within the existing standard models. Concordant modeling, however, becomes possible only within the frame of a three-level system that takes into account both bright and dark excitonic states as well as phonon-assisted carrier redistribution between these states. Our results show that luminescence characterization of lead-salt quantum dots necessarily requires both low temperatures and excitation densities in order to provide reliable ensemble parameters.

The influence of ion mass on transient enhanced diffusion (TED) and defect evolution after ion implantation in Si has been studied by atomistic simulation and compared with experiments. We have analyzed the TED induced by B, P, and As implants with equal range and energy: TED increases with ion mass for equal range implants, and species of different mass but equal energy cause approximately the same amount of TED. Heavier ions produce a larger redistribution of the Si atoms in the crystal, leading to a larger excess of interstitials deeper in the bulk and an excess of vacancies closer to the surface. For high-mass ions more interstitials escape recombination with vacancies, are stored in clusters, and then contribute to TED. TED can be described in terms of an effective “+n” or “plus factor” that increases with the implanted ion mass.

A combination of nuclear reaction analysis, high‐resolution sectioning methods, and time‐resolved reflectivity have been used to study the boron redistribution from a shallow δ‐doped layer in silicon, following deep amorphization and subsequent solid phase epitaxial growth (SPEG). A significant fraction of the boron was found to move into the top 20 nm undoped Si cap layer after SPEG. Over the temperature range of 550–600 °C, the fraction of boron accumulating in the cap layer is increased with the SPEG temperatures. Boron redistribution was enhanced in the sample which was etched in HF prior to SPEG. Possible contributing factors are discussed.

We report on the laser‐induced permanent changes of the critical current (Ic) and normal resistance (Rn) of YBa2Cu3O7−x (YBCO) step‐edge Josephson junctions. The 2‐ to 20‐μm‐wide junctions were prepared from a 200‐nm‐thick YBCO film deposited by a pulsed KrF excimer laser onto 300‐nm‐high steps etched in the LaAlO3 substrate. The laser modification experiments were performed by illuminating the junctions at 50 K with a focused Ar‐ion laser beam of various intensities. Depending on the illumination power density, either increase or decrease of the junction Ic has been observed. In particular, after illumination at the 0.6×105 W/cm2 power level, a 75% enhancement of Ic and increase of the IcRn product up to 25% were obtained without a measurable change in the junction critical temperature. The laser‐induced modifications were very reproducible and remained unchanged even after a subsequent room‐temperature/helium thermal cycling of the sample. Photoassisted, thermally activated oxygen redistribution in the ...

Electron paramagnetic resonance (EPR) studies of low hydroxyl synthetic silica optical fibers have revealed the presence of a 13 G hyperfine splitting of the Si E’ center which is associated with weakly bonded hydrogen molecules in the silica structure. The fibers were previously exposed to hydrogen at room temperature. During an annealing of the silica fibers at 100 °C in air, the 13 G doublet was observed to decline and disappear while the 74 G doublet and the Si E’ signal were growing. The result correlates with the redistribution of hydrogen molecules and is relevant to the environmental aging that is encountered in fiber optical waveguides under certain conditions.

Carbon implantation into Si at a temperature of 950 °C and at doses in the range of 0.2×1018 to 1×1018 cm−2 at 200 keV results in the formation of β‐SiC buried layers having the same orientation as the Si matrix. Under these conditions redistribution of the implanted species occurs enabling the formation of a buried layer of β‐SiC with an overlayer of high quality single crystal Si which is free of structural defects. The quality of the Si overlayer and the β‐SiC buried layer was investigated by Rutherford backscattering and transmission electron microscopy. A mechanism for the formation of the β‐SiC without the generation of defects in the Si matrix is proposed.

Results are reported of measurements of depth profiles and stability against redistribution with annealing up to 800 or 900 °C, for implanted Be, C, Mg, Si, S, Zn, Ge, and Se as dopants in GaN. The results confirm the high‐temperature stability of dopants in this material up to temperatures that vary from 600 to 900 °C. S redistributes for temperatures above 600 °C, and Zn and Se, for temperatures above 800 °C. All of the other elements are stable to 900 °C. These results indicate that direct implantation of dopants rather than masked diffusion will probably be necessary to define selective area doping of III–V nitride device structures based on these results for GaN.

Diffusion of ion implanted Be in AlxGa1−xAs was studied as a function of Al concentration and annealing temperature and was compared to diffusion in GaAs. The behavior of Be in AlxGa1−xAs is similar to that in GaAs, even showing the anomalous behavior of increasing redistribution with decreasing temperature. The diffusivity of Be appears to increase with Al content which may be due to increasing bonding strength of matrix atoms with the addition of Al, preventing the easy transferral of Be from interstitial to substitutional sites. The oversaturation of Be interstitials may also explain the persistence of anomalous diffusion behavior in AlxGa1−xAs with respect to anneal temperature. This is discussed in terms of the substitutional‐interstitial diffusion mechanism, the relative amount of interstitial and substitutional Be, and the relative difficulty of moving from an interstitial to a substitutional site.

Implantation damage is believed to play a significant role in dopant diffusion. Described here is an attempt to modify the point defect damage profile of a 40 keV, 29Si implant in GaAs by chemically etching away the top 100 A of the sample after implantation. In these samples, no Si diffusion was observed after annealing, while significant Si redistribution did occur in a similar sample which received no post‐implant etch. trim simulations predict an excess Ga vacancy surface layer and excess Ga interstitials deeper in the sample. It is thought that by removing the vacancy‐rich surface layer, the etch alters the implant damage profile and thus the diffusion behavior of the Si. Surface effects from etching as related to the Si diffusion are shown to be consistent with a vacancy‐assisted diffusion mechanism. Evidence that this model may be applicable to B implants in Si is also shown.

Hydrogen incorporation depths of ≥1 μm are measured for 2H plasma exposure of GaN and AlN at 250–400 °C for 30 min. The concentration of 2H incorporated is in the range 5–10×1017 cm−3 for GaN and 5–30×1018 cm−3 for AlN under these conditions. No redistribution of the hydrogen is observed for annealing temperatures up to 800 °C, but at 900 °C there is substantial loss of hydrogen from the samples. Similar results are obtained for 2H implantation into GaN, AlN, and InN, with no significant redistribution observed up to 500–600 °C in either AlN or InN, and motion only at 900 °C in GaN. The thermal stability of hydrogen in III‐V nitrides explains previous results for Mg‐doped GaN grown using NH3, where post‐growth annealing at high temperatures was required to achieve appreciable doping efficiencies.

A method for improving the luminous efficiency of a ZnS:Mn ac thin film electroluminescent device by modifying the structure to include thin, 100 A, barrier layers of a Y2O3 is presented, with experimental comparisons of devices showing a fourfold increase in efficiency. The results are discussed in terms of electron tunneling and field redistribution as the mechanisms responsible for the enhancement of efficiency.

The spatial distribution of point defects near semiconductor surfaces affects the efficiency of devices. Near-surface band bending generates electric fields that influence the spatial redistribution of charged mobile defects that exchange infrequently with the lattice, as recently demonstrated for pile-up of isotopic oxygen near rutile TiO2 (110). The present work derives a mathematical model to describe such redistribution and establishes its temporal dependence on defect injection rate and band bending. The model shows that band bending of only a few meV induces significant redistribution, and that the direction of the electric field governs formation of either a valley or a pile-up.

A large magnetic modulation, accompanied by stable bipolar resistive switching (RS) behavior, was observed in a Mn:ZnO film by applying a reversible electric field. A significant enhancement of the ferromagnetism of the film, to about five times larger than that in the initial (as-grown) state (IS), was obtained by switching the film into the low resistance state. X-ray photoelectron spectroscopy demonstrated the existence of abundant oxygen vacancies in the IS of the film. We suggest that this electric field-induced magnetic switching effect originates with the migration and redistribution of oxygen vacancies during RS. Our work indicates that electric switching is an effective and simple method to increase the ferromagnetism of diluted magnetic oxide films. This provides a promising direction for research in spintronic devices.

The electronic properties of vanadium in silicon have been studied using deep level transient spectroscopy (DLTS), high resolution Laplace DLTS, capacitance voltage measurements and secondary ion mass spectroscopy (SIMS). Vanadium was implanted into float zone (FZ) grown n-type and FZ and Czochralski (Cz) grown p-type Si and implantation damage was removed through annealing between 700 and 900 °C. DLTS measurements were carried out to determine the electronic characteristics of vanadium-related defects in silicon. It is argued that the dominant electrically active defect is related to interstitial vanadium (Vi) atoms. The distribution of implanted vanadium is seen to differ between Czochralski and FZ silicon, with redistribution of vanadium atoms occurring significantly faster in Cz-Si. We suggest that in FZ-Si the Vi atoms interact with implantation induced vacancies and move to the substitutional site where they are much less mobile. At the peak concentration of vanadium, determined by SIMS to be ∼1015 ...

The redistribution of carbon during molecular beam epitaxy (MBE) growth of GaAs n‐i‐p+‐i‐n structures using silicon and carbon as n‐type and p‐type dopants, respectively, is shown by secondary ion mass spectrometry (SIMS) analysis and electrochemical capacitance‐voltage measurements. Diffusion of carbon into the surface layer is clearly observed when the carbon concentration in the p+ region exceeds ∼6×1019 cm−3. The data also shows that a significant fraction of the diffused carbon is electrically active.

The multiple DX levels are studied by using the rate‐window scan method of deep level transient spectroscopy. It is found that the electron concentrations in the individual DX levels do not always increase monotonically with filling time, showing a charge redistribution effect. This charge redistribution in the DX levels indicates that the DX center is negatively charged and that each defect site is able to generate multiple states in different levels. The charge redistribution effect unambiguously rules out all existing small lattice relaxation models, while it is understood within the broken‐bond negative U model.

It has been found that the electron capture transients of the individual DX levels in Si‐doped AlGaAs include two regimes: net capture and redistribution. In this letter, by analyzing both of these regimes, the electron capture kinetics of DX centers are determined for the first time. It is found that the capture rate for an empty state is proportional to the square of the free carrier concentration. These kinetics are predicted only by the negative U model in which two electrons are captured sequentially via an intermediate one‐electron state.

The redistribution of Zn in the base region of GaAs‐AlGaAs heterojunction bipolar transistor structures during growth by organometallic vapor phase epitaxy has been examined with respect to the presence of Si doping in the emitter‐contact, emitter, and collector/subcollector layers, and as a function of Zn doping concentration and Si counterdoping level in the p+ base. For a growth temperature of 675 °C the Zn shows no significant redistribution up to concentrations of 3×1019 cm−3 without Si doping. The addition of Si to the adjacent AlGaAs emitter and collector/subcollector layers causes substantial diffusion of Zn from the base, while Si doping of the GaAs emitter contact results in even greater Zn redistribution. Under these conditions, the Zn concentration in the base attains a maximum value of ∼7×1018 cm−3. Silicon counterdoping in the base region retards the Zn diffusion, while strain introduced by an InGaAs cap layer has no effect on the Zn redistribution.

The redistribution of Be and Mg implants upon post‐implant annealing is studied in order to evaluate the influence of implant damage on the diffusion process. Rapid uphill diffusion is observed in the peak of Mg implants in GaAs, whereas Be implants show only uniform, concentration‐dependent diffusion. This behavior is explained by the substitutional‐interstitial‐diffusion mechanism and computer simulations of damage‐produced point defects. In the region of uphill diffusion, the dopants diffuse from areas of excess interstitials toward areas of excess vacancies. A critical concentration of point defects is necessary to initiate uphill diffusion. Uphill diffusion can be induced in Be implants by co‐implanting with a heavier element such as Ar.

cited By 10; International audience; The 2D optical field intensity distribution in sub-micron, ultrathin, and crystalline gold platelets is investigated by two-photon luminescence (TPL) microscopy. In particular, the evolution of the TPL maps as the particle morphology undergoes a transition from triangular to hexagonal reveals that the signatures of the high-order surface plasmon states sustained by the platelets follows the same C3v to C6v symmetry redistribution. Experimental observations are precisely accounted for by theoretical simulations based on the Green dyadic method.

We report on the visualization of n-p junctions formed by oxygen vacancy movement under the application of an electric field in a Ca-doped BiFeO3 thin film through spatially resolved scanning photocurrent mapping. The photocurrent mapping, in conjunction with the spectroscopic approach, provides clues to local electronic structures and defect levels associated with oxygen vacancies. These observations provide insights into the spatial redistribution of oxygen vacancies in an electric field.

A gate stack structure with an organic-polymer tunneling gate insulator on a C60-containing organic-polymer layer was developed for use as nonvolatile flash memory. Examination of the memory characteristics revealed substantial flatband voltage shifts for both electron and hole injections into C60 molecules. A long retention time was obtained for electron injection. Charge redistribution phenomena were observed in the electron retention characteristics immediately after the bias application was terminated. This proposed stack structure of organic polymers opens the door to the development of inexpensive electronic memories.

The resistive switching characteristics of SrTiO3 metal-insulator-metal capacitors are investigated. The current-density versus voltage (J-V) characteristics show asymmetry at all temperatures examined, with resistive switching behavior observed at elevated temperatures. The asymmetry is explained by the relative lack of electron traps at one electrode, which is determined from the symmetric J-V curve obtained at room temperature due to the redistribution of the dominant electrical defects in the film. We present evidence for the model of resistive switching originating from defect diffusion (possibly oxygen vacancies) at high temperatures.

The capacitance dispersion in La and Mg co-substituted BiFeO3 thin film has been studied at different stages of polarization switching. A negative capacitance (NC) behavior is observed in the sample that is fatigued above 109 switching cycles. The origin of the NC is investigated through analyzing relaxation processes and charge transport kinetics by admittance spectroscopy. An activation energy of ∼0.6 eV and a zero field mobility μ0=5.33±0.02×10−13m2/Vs are thus obtained. A physical mechanism is proposed to explain this behavior. It involves a redistribution of oxygen vacancies, which are trapped at the film/electrode interface during the fatigue process.

It is shown that current-activated pressure-assisted densification (CAPAD) is sensitive to the Peltier effect. Under CAPAD, the Peltier effect leads to a significant redistribution of heat within the sample during the densification. The densification of highly p-doped silicon nanoparticles during CAPAD and the properties of the obtained samples are investigated experimentally and by computer simulation. Both, simulation and experiments, indicate clearly a higher temperature on the cathode side and a decreasing temperature from the center to the outer shell. Furthermore, computer simulations provide additional insights into the temperature profile which explain the anisotropic properties of the measured sample.

Atom probe tomography was used to study the redistribution of platinum and arsenic atoms after Ni(Pt) silicidation of As-doped polycrystalline Si. These measurements were performed on a field-effect transistor and compared with those obtained in unpatterned region submitted to the same process. These results suggest that Pt and As redistribution during silicide formation is only marginally influenced by the confinement in microelectronic devices. On the contrary, there is a clear difference with the redistribution reported in the literature for the blanket wafers. Selective etching used to remove the non-reacted Ni(Pt) film after the first rapid heat treatment may induce this difference.

Both n-type and p-type doping of silicon is at odds with the charge transfer predicted by Pauling electronegativities and can only be reconciled if we no longer regarding dopant species as isolated atoms but rather consider them as clusters consisting of the dopant and its four nearest neighbor silicon atoms. The process that gives rise to n-type and p-type effects is the charge redistribution that occurs between the dopant and its neighbors, as we illustrate here using electronic structure calculations. This view point is able to explain why conventional substitutional n-type doping of carbon has been so difficult.

A multiscale method is proposed to analyze the internal redistribution of tensile strain applied to silicon ⟨100⟩ nanowires and its effect on electron effective masses m∗. Nonperiodic, realistic models of unprecedented size containing up to 2.2×107 atoms (652×26×26 nm3) allow the identification of nonuniform redistribution patterns specific to the constraints applied to impose external strain. Depending on how the external strain is imposed, silicon nanowires can show m∗ behavior similar to strained bulk silicon, or, as a function of nanowire size, can display intrinsic strain large enough that external strain hardly reduces m∗ further. For nanowire cross section sizes smaller than 8×8 nm2 quantum confinement leads to an increase in m∗ which cannot be compensated for by tensile strain.

Shallow n+ layers in Ge are formed by phosphorus implantation and subsequent millisecond flash lamp annealing. Present investigations are focused on the dependence of P redistribution, diffusion and electrical activation on heat input into the sample and flash duration. Furthermore, the influence of pre-amorphization implantation and pre-annealing is studied. In contrast to conventional annealing procedures an activation up to 6.5×1019 cm-3 is achieved without any dopant redistribution and noticeable diffusion. Present results suggest that independently of pre-treatment the maximum activation should be obtained at a flash energy that corresponds to the onset of P diffusion. The deactivation of P is explained qualitatively by mass action analysis which takes into account the formation of phosphorus-vacancy clusters.

The authors used x-ray diffraction to investigate strain and composition in SiGe nanorings formed during partial Si capping of self-assembled SiGe/Si(001) islands. The obtained results are corroborated with selective wet chemical etching experiments. Clear evidence is provided that rings are composed of a Ge rich core surrounded by Si richer ridges indicating that a substantial material redistribution occurs during the shape transformation from SiGe islands to rings. The results suggest that SiGe ring formation is driven by strain relief.

We report on a real-time Rutherford backscattering spectrometry study of the erratic redistribution of Pt during Ni silicide formation in a solid phase reaction. The inhomogeneous Pt redistribution in Ni(Pt)Si films is a consequence of the low solubility of Pt in Ni2Si compared to NiSi and the limited mobility of Pt in NiSi. Pt further acts as a diffusion barrier and resides in the Ni2Si grain boundaries, significantly slowing down the Ni2Si and NiSi growth kinetics. Moreover, the observed incorporation of a large amount of Pt in the NiSi seeds indicates that Pt plays a major role in selecting the crystallographic orientation of these seeds and thus in the texture of the resulting Ni1−xPtxSi film.

Overgrowth of self-assembled quantum dots usually changes their shape and composition due to surface exchange reactions and redistribution of adatoms. As shown for PbSe dots, this can be completely suppressed by covering the dots with ultrathin EuTe or SrTe barrier layers, based on the large EuTe and SrTe binding energies. The model is supported by annealing experiments that show that these barrier layers also suppress the usual coarsening and Ostwald ripening process.