(Magic Dopant) Amphoteric Behavior of a Redox‐Active Transition Metal Ion in a Perovskite Lattice: New Insights on the Lattice Site Occupation of Manganese in SrTiO3

It is demonstrated that a transition metal redox‐active ion can exhibit amphoteric dopant substitution in the SrTiO₃ perovskite lattice. In stoichiometric SrTiO₃, the manganese dopant is preferably accommodated through isovalent substitution as Mn²⁺ on the strontium site and as Mn⁴⁺ on the titanium site. Previous studies have suggested that either type of substitution is possible for compositions with tailored Sr/Ti stoichiometry. Using electron paramagnetic resonance (EPR) spectroscopy, the site occupancy of dilute concentrations of manganese is investigated in SrTiO₃ as a function of the Sr/Ti ratio. The tuned Sr/Ti ratio can be used to manipulate the nature of the manganese substitution, and it is shown that Sr‐rich compositions (Sr/Ti > 1.001) processed in air result in B‐site isovalent doping. For B‐site substituted manganese ions, a new EPR signal for aliovalent Mn²⁺ is observed in compositions annealed under reducing atmosphere. The concentration of oxygen vacancies observed with EPR is also shown to depend on the Sr/Ti stoichiometry. With improved control over the site of substitution and valence state, doping with a transition metal redox‐active ion may facilitate the ability to engineer new electronic functionality into the perovskite lattice.     

Lightpath Versus Semi-Lightpath: Some Studies on Optimal Routing in WDM Optical Networks

This paper deals with the problem of optimal dynamic routing in WDM optical networks with wavelength-changing facilities available at some of the nodes. The route may be either a lightpath (i.e., wavelength continuous channel) or a semi-lightpath (i.e., wavelength-converted channel). We attempt to estimate in this work the gain in blocking probability, when we move from lightpath routing to semi-lightpath routing, keeping the number of wavelengths fixed, in a given circuit switched network. We ensure optimal (minimum cost) routing in both the cases by using the algorithm of Banerjee et al. [7,8] (called Algorithm-I in this paper) for lightpaths and that of Chlamtac et al. [6] (called Algorithm-II) for semi-lightpaths. Our results indicate that, for both the algorithms, the blocking probability (P _B), as expected, increases with network load. At light load, P _B for Algorithm-I is always larger than that for Algorithm-II. But the rate of increase in P _B is slightly higher in case of Algorithm-II, so that there is a crossover point where P _B for Algorithm-II exceeds P _B for Algorithm-I. This probably happens due to the irregularities in the semi-lightpaths at heavy loads when almost all routes are exhausted in the network. However, since this crossover phenomenon occurs at a very congested status of the network, it has little significance over the real life operation of a network. It only suffices to indicate that, under heavy load, both the algorithms are equally insufficient, and conversion does not improve the situation as might have been expected intuitively.     

Decreased low frequency noise by hydrogen passivation of polysilicon emitter bipolar transistors

The effect of hydrogen passivation by forming gas annealing (FGA) on the bipolar junction transistor low frequency noise was investigated. The results demonstrated a reduced 1/f noise component by a factor of five after FGA, which resulted in a reduced corner frequency. An equivalent input noise spectral density (S_IB) dependence on base current (I_B) of S_IBI²_B and on emitter area (A_E) of S_IBA_E⁻¹ was observed, both before and after FGA. The interpretations of the results were (a) the 1/f noise was due to carrier number fluctuation, (b) the noise sources were homogeneously distributed over the polysilicon/monosilicon emitter interfacial oxide, and (c) the noise sources were passivated by hydrogen.     

Modeling of the body current in a Bi-MOS hybrid-mode environment

The body current I_B of deep submicron lightly doped drain pMOSFETs has been investigated. Based on the experimental results, an analytical I_B model, applicable for devices operating in a Bi-MOS hybrid-mode environment, has been developed for the first time. The proposed model is able to effectively characterize the measured I_B results over a wide range of independently applied biases (gate, drain and body) and gate lengths (from 1 μm down to 0.25 μm). The possibility of minimizing or even eliminating the undesired I_B is also explored and discussed for the first time.     

[[2n,n]] Additive quantum error correcting codes

The self-orthogonal condition is analyzed with respect to symplectic inner product for the binary code that generated by [B1 I B2 B3],where Bi are the binary n ×n matrices,I is an identity matrix.By the use of the binary codes that generated by [B1 I B2 B2B1^T],asymptotic good[[2n ,n ]]additive quantum codes are obtained.     

Superfluid-insulator transition in “Dirty” ultracold Fermi gas

Superfluid-insulator transition in an ultracold Fermi gas in the external disorder potential of the amplitude V ₀ is studied as a function of its concentration n and the magnetic field B in the presence of the Feshbach resonance. We find the zero temperature phase diagrams in the plane (B, n) at a given V ₀ and in the plane (V ₀, n) at a given B. We study the transition between cases of classical and quantum random potentials which can be implemented by tuning intensity of speckles. Our results for the Bose-Einstein condensation side of the diagram are also valid for a Bose gas. The text was submitted by the authors in English.     

Controlling Phase Assemblage in a Complex Multi‐Cation System: Phase‐Pure Room Temperature Multiferroic (1−x)BiTi(1−y)/2FeyMg(1−y)/2O3–xCaTiO3

A room temperature magnetoelectric multiferroic is of interest as, e.g., magnetoelectric random access memory. Bulk samples of the perovskite (1?x)BiTi_(1?y)/2Fe_yMg_(1?y)/2O₃–xCaTiO₃ (BTFM–CTO) are simultaneously ferroelectric, weakly ferromagnetic, and magnetoelectric at room temperature. In BTFM–CTO, the volatility of bismuth oxide, and the complex subsolidus reaction kinetics, cause the formation of a microscopic amount of ferrimagnetic spinel impurity, which complicates the quantitative characterization of their intrinsic magnetic and magnetoelectric properties. Here, a controlled synthesis route to single‐phase bulk samples of BTFM–CTO is devised and their intrinsic properties are determined. For example, the composition x = 0.15, y = 0.75 shows a saturated magnetization of 0.0097μ_B per Fe, a linear magnetoelectric susceptibility of 0.19(1) ps m^?1, and a polarization of 66 μC cm^?2 at room temperature. The onset of weak ferromagnetism and linear magnetoelectric coupling are shown to coincide with the onset of bulk long‐range magnetic order by neutron diffraction. The synthesis strategy developed here will be invaluable as the phase diagram of BTFM–CTO is explored further, and as an example for the synthesis of other compositionally complex BiFeO₃‐related materials.     

Electroluminescence of the unconfined heterostructure p-GaInAsSb/p-InAs at liquid-helium temperatures

The electroluminescence of the single unconfined type-II heterojunction p-GaInAsSb/p-InAs was investigated in the temperature range T=4.2–77 K. As the temperature was reduced below T=77 K, the luminescence bands with maxima at 311 meV (band A) and 384 meV (band B) were found to shift toward higher energies. At 4.2 K, the short-wave band split into two bands, B ₁ and B ₂. These results are explained in terms of a model involving recombinations of electrons from the conduction band to an acceptor level of InAs, and also recombinations of electrons and holes localized in self-consistent quantum wells on either side of the heterojunction. Fiz. Tekh. Poluprovodn. 31, 1216–1219 (October 1997)     

Strong Damping‐Like Spin‐Orbit Torque and Tunable Dzyaloshinskii–Moriya Interaction Generated by Low‐Resistivity Pd1−xPtx Alloys

Despite their great promise for providing a pathway for very efficient and fast manipulation of magnetization, spin‐orbit torque (SOT) operations are currently energy inefficient due to a low damping‐like SOT efficiency per unit current bias, and/or the very high resistivity of the spin Hall materials. This work reports an advantageous spin Hall material, Pd_1?xPt_x, which combines a low resistivity with a giant spin Hall effect as evidenced with three independent SOT ferromagnetic detectors. The optimal Pd_0.25Pt_0.75 alloy has a giant internal spin Hall ratio of >0.60 (damping‐like SOT efficiency of ≈0.26 for all three ferromagnets) and a low resistivity of ≈57.5 µΩ cm at a 4 nm thickness. Moreover, it is found that the Dzyaloshinskii–Moriya interaction (DMI), the key ingredient for the manipulation of chiral spin arrangements (e.g., magnetic skyrmions and chiral domain walls), is considerably strong at the Pd_1?xPt_x/Fe_0.6Co_0.2B_0.2 interface when compared to that at Ta/Fe_0.6Co_0.2B_0.2 or W/Fe_0.6Co_0.2B_0.2 interfaces and can be tuned by a factor of 5 through control of the interfacial spin‐orbital coupling via the heavy metal composition. This work establishes a very effective spin current generator that combines a notably high energy efficiency with a very strong and tunable DMI for advanced chiral spintronics and spin torque applications.     

An Effective Approach for the Development of Reliable YBCO Bulk Cryomagnets with High Trapped Field Performances

Widespread use of YBa₂Cu₃O_7‐δ (Y123) bulk superconductors as source of strong magnetic fields requires development of high‐performance materials sufficiently reliable with improved thermal transfer ability. An effective approach based primarily on the growth of bulk Y123 single domains comprising a holes‐network to diminish the oxygen diffusion paths is reported here, as well as their progressive annealing at high temperature under oxygen pressure to reduce undue stresses and processing time. Finely, it aims to stimulate the thermal exchange inside the superconductor and compensate for induced magnetic stresses during the field‐trapping process. The approach brings considerable time and energy savings, and turns out to knock down barriers having stymied hitherto the use of Y123 bulk superconductors for engineering applications. Indeed, it enables the achievement of a pore‐free and crack‐free microstructure yielding marked fracture toughness and promoting large size persistent current loops, thereby boosting the trapped field performances. The fostering of the internal thermal exchange leads the maximum trapped field B_max to shift to higher temperatures by up to 14 K. A value B_max of 6.34 T is attained at 17 K on ≈16 mm‐diameter reinforced pellet (disk area s = 1.99 cm²), resulting in an outstanding field density B_max/s=3.19 Tcm^?2.     

Parabolic negative magnetoresistance in p-Ge/Ge1−x Six heterostructures

Quantum corrections for the conductivity due to the weak localization (WL) and the disorder-modified electron-electron interaction (EEI) are investigated for the high-mobility multilayer p-Ge/Ge_1−x Se_x heterostructures at T=(0.1–20) K in magnetic field B up to 1.5 T. Negative magnetoresistance with logarithmic dependence on T and linear in B ² is observed for B⩾0.1 T. Such a behavior is attributed to the connection between the classical cyclotron motion and the EEI effect. The Hartree part of the interaction constant is estimated (F _σ =0.44) and the WL and EEI contributions to the total quantum correction Δσ at B=0 are separated (Δσ _WL≈0.3Δσ; Δσ ^ee ≈0.7Δ σ). Fiz. Tekh. Poluprovodn. 33, 1073–1075 (September 1999) This article was published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Some useful properties of cross--energy operator

In this paper, some useful properties of cross-Ψ_B-energy operator, which measures the interaction between two signals, are provided. We show that Ψ_B is a generalization of some extensions of Teager–Kaiser operator to complex signals. Due to its bilinearity, Ψ_B satisfies the quadratic superposition principle. We point out the link between the Ψ_B and the Lie bracket, which measures the instantaneous differences in the relative change between two signals. We show how the Ψ_B operator can handle wideband signals using bandpass filtering. We also show how the quadratic superposition law can be used for detection purpose.     

Low-temperature relaxation of a solid solution of iron in gallium phosphide

Electron spin resonance (ESR) and the Hall effect are used to investigate low-temperature relaxation of solid solutions of iron in gallium phosphide, as well as the distribution profiles for paramagnetic iron centers in GaP located at A-site (g=2.02) and B-site (g=2.133). The data obtained are consistent with the idea that the A-site corresponds to an iron atom in a substitutional position, i.e., Fe _S ³⁺ (Ga) (3d ⁵), whereas the B-site corresponds to an interstitial neutral iron atom, i.e., Fe _i ⁰ (3d ⁸). As a solid solution of GaP: Fe undergoes low-temperature relaxation, the A-centers are observed to be stable against annealing in the temperature range 293–800 K. In contrast, the intensity of the ESR spectrum from the B-center has complicated kinetics that qualitatively resembles the annealing kinetics of paramagnetic Fe _i ⁰ -centers in silicon. Fiz. Tekh. Poluprovodn. 33, 385–388 (April 1999)     

Polyhedral Oligomeric Silsesquioxanes Based Ultralow-k Materials: The Effect of Cage Size

Polyhedral oligomeric silsesquioxanes (POSS) are of considerable interest as building blocks for preparing low-k materials. To date T₈ POSS has been extensively investigated while the potential of larger POSS cages remain an unexplored area. Herein, the first known contribution to map the role of POSS cage size on the dielectric and other comprehensive properties of hybrid materials with identical chemical compositions is described. First, three vinyl POSS (T₈, T₁₀, and T₁₂) species are isolated from a commercial POSS mixture. Then, they are converted to benzocyclobutene functionalized and thermo-crosslinked hybrid materials. It is found that the cage size can strongly affect their k values, more importantly, showing a linear decrease while increasing the cage volumes (k  = 2.24, 2.02, and 1.83 for c-T₈B₈, c-T₁₀B₁₀, and c-T₁₂B₁₂, respectively). This finding highlights a profound influence of POSS cage changes on dielectric properties and could be used to predict ultralow-k (1.5–1.1) materials by extrapolating to larger T₁₄, T₁₆, and T₁₈ POSS cages. Meanwhile, varying the cage size has no obvious effect on the materials’ other properties, and all of them exhibit good comprehensive properties. Moreover, such low-k values can persist at high temperature and high humidity conditions, which affords some promising (ultra)low-k dielectrics for modern integrated circuit development.     

An Outage Analysis of Multibranch Diversity Receivers with Cochannel Interference in α-μ, κ-μ, and η-μ Fading Scenarios

Wireless communications systems in a frequency reuse environment are subject to cochannel interference. In order to improve the system performance, diversity techniques are deployed. Among the practical diversity schemes used, Equal-Gain Combining (EGC) appears as a reasonably simple and effective one. Unfortunately, the exact analysis of the outage probability of EGC receivers is rather intricate for it involves the evaluation of multifold nested integrals. It becomes mathematically intractable with the increase of the number of diversity branches and/or interferers. For example, for N _B diversity branches and N _I arbitrary independent cochannel interferers, the exact formulation using the convolutional approach requires 2 + N _B  + (N _B × N _I ) nested integrals, which, very quickly, and for any practical system, turns out to be mathematically intractable. In this paper, we propose accurate approximate formulations for this problem, whose results are practically indistinguishable from the exact solution. In our model, the system is composed by N _B branches and N _I interferers so that the desired signals are coherently summed, whereas the interfering signals are incoherently summed at the EGC receiver. Three sets of fading scenarios, namely α-μ , κ-μ, and η-μ, are investigated. The proposed approach is indeed flexible and accommodates a variety of mixed fading scenarios for desired and interfering signals.     

Variation resilient subthreshold SRAM cell design technique

This article presents a circuit technique for designing a variability resilient subthreshold static random access memory (SRAM) cell. The architecture of the proposed cell is similar to the conventional 10T SRAM cell with the exception that dynamic threshold MOS is used for the read/write access FETs and cell content body bias scheme is used for bitline droppers (FETs used to drop bitlines). Moreover, the proposed bitcell utilises single differential port unlike conventional 10T bitcell which utilises dual differential ports. The proposed design offers 2.1× improvement in T _RA (read access time) and 3.2× improvement in T _WA (write access time) compared to CON10T at iso-device-area and 200?mV. It exhibits three roots in its read voltage transfer characteristic (VTC) even at 150?mV showing its ability to function as a bistable circuit. The combination of write and read VTCs for write static noise margin of the proposed design also shows single root signifying its write-ability even at 150?mV. It proves its robustness against process variations by featuring narrower spread in T _RA distribution (by 1.3×) and in T _WA distribution (by 1.2×) at 200?mV.     

Call queueing in circuit-switched networks

Consider a circuit-switched network whereC source switches are connected to a destination switch via a tandem switch. Circuit-switched networks traditionally employ a Blocked Calls Lost (BCL) call admission control: a call is rejected if all access circuits from the originating switch to the tandem switch are busy, or if allB outgoing circuits from the tandem switch to the destination switch are busy. This paper investigates a simple extension to the BCL control. Rather than reject all blocked calls, the Blocked Calls Queued (BCQ) control holds some blocked calls by storing their call signalling information in a buffer at the tandem switch. These calls will later be connected when circuits become available. The BCQ model is solved using standard methods requiring O(BC) storage locations and O(B ² C) arithmetic operations. We show that the BCQ control becomes effective if calls are rejected (source rejection) when all access circuits are busy. We demonstrate that the BCQ control with source rejection achieves a substantial reduction in the loss probability at the expense of a small connection delay.This work was supported by a grant from the Foundation for Research Development Communications Systems Programme.     

Rapid thermal chemical vapor deposition of in-situ boron doped polycrystalline SIxGe1-x

In-situ doped polycrystalline Si_xGe_1-x (x = 0.7) alloys were deposited by rapid thermal chemical vapor deposition (RTCVD) using the reactive gases SiH₂Cl₂, GeH₄ and B₂H₆ in a H₂ carrier gas. The depositions were performed at a total pressure of 4.0 Torr and at temperatures 600° C, 650° C and 700° C and different B₂H₆ flow rates. The conditions were chosen to achieve high doping levels in the deposited films. Our results indicate negligible effect of B₂H₆ flow on the deposition rate. The depositions follow an Arrhenius type behavior with an activation energy of 25 kcal/mole. Boron incorporation in the films was found to follow a simple kinetic model with higher boron levels at lower deposition rates and higher B₂H₆ flow rates. As-deposited resistivities as low as 2 mΩ-cm were obtained. Rapid thermal annealing (RTA) in the temperature range 800-1000° C was found to reduce the resistivity only marginally due to the high levels of boron activation achieved during the deposition process. The results indicate that polycrystalline Si_xGe_1-x films can be deposited by RTCVD with resistivities comparable to those reported for in-situ doped polysilicon.     

Low-field current transport mechanisms in rf magnetron sputter deposited boron carbide (B5C)/p-type crystalline silicon junctions in the dark

Measurements of the forward and reverse currents in an undoped rf magnetron sputter deposited boron carbide (B₅C)/p-type Si(111) junction have been made in the dark in the temperature range 120–300K at low-bias voltages (0–0.3V). A diode-like behaviour of the junction current has been observed in this low-bias region at all temperatures but with a rather large reverse (leakage) current I _R, particularly at high temperatures (I _R≈2 μA at V = ?0:3V and T = 290 K). The forward ‘voltage factor’ A (T) was found to decrease with increasing temperature as A (T)≈q/ηk _B T, with relatively high values of the ‘ideality factor’ η(about 3.5–4), probably due to the existence of an interfacial layer. The temperature dependence of the measured junction current (forward and reverse) flowing at low bias voltages and of the forward ‘current factor’ I _0F can be described satisfactorily by a model of the tunnelling of thermally excited carriers, including tunnelling via impurity localized levels, of the form I (T) ∝ exp [?C/T ^1/3] over the entire temperature range studied (120–300K). A high density of ‘localized’ energy states as large as 10¹⁸ cm^?3 eV^?1 was estimated, which can be attributed in part to ‘extrinsic’ interface states that could have been formed throughout the fabrication procedures of the rf sputter deposited B₅C/p-crystalline silicon junction studied. Another possible cause of such large concentration of ‘localized’ states is the ‘intrinsic’ interface states produced by the lattice mismatch between the polycrystalline boron carbide and crystalline silicon semiconductors as well as of the high intrinsic defect concentration caused by structural imperfections that often exist in boron carbide compounds.     

High injection effects on noise characteristics of Si BJTs and SiGe HBTs

We present a physically based comparison of the current spectral densities in a SiGe heterojunction bipolar transistors (HBT) and a Si bipolar junction transistor (BJT) of identical geometry and doping levels, based on the direct evaluation of emitter, base and collector current fluctuations. An ensemble Monte Carlo (EMC) simulator self-consistently coupled with a 2D Poisson solver has been employed for the calculations. In the studied bias range, the largest reduction of the RF current noise values in the HBT as compared with the BJT derives from the spectral density of base current fluctuations, S_JB, and from the spectra of the cross-correlation between emitter and base current fluctuations, S_JBJE. This is due to the fact that the base current in the HBT is strongly reduced as a consequence of the lower gap of the SiGe base. At low injection, the collector spectral density S_JC exhibits a typical shot noise response while S_JB is governed by thermal noise. At high injection, the presence of hot carriers in the base–collector junction (which are less important in the HBT than in the BJT due to the SiGe/Si hetero-interface), the high carrier concentration in the base and the base push-out provokes the deviation of S_JC from the pure shot behavior. Under these conditions, the S_JB term can be neglected in the total noise analysis of the HBT for lower values of J_C, than in the BJT due to the Ge content benefits.