Hydrogen transport in doped and undoped polycrystalline silicon

Hydrogen diffusion in B, P, and undoped poly-Si is investigated. The diffusion activation energy, E_A, depends significantly on the Fermi energy, E_F, and the H concentration. E_A varies between 0.1 eV and 1.69 eV, accompanied by a variation of the diffusion prefactor D₀ by 12 orders of magnitude. Using the theoretical value of D₀, the energy required to yield the measured diffusion coefficients was calculated. depends strongly on E_F and agrees well with the theoretical E_F dependence of the formation energies of H⁺ or H⁻. To account for this behavior a modified H transport model based on trap-limited diffusion is proposed.     

Extraction of interface states at emitter–base heterojunctions in AlGaAs/GaAs heterostructure bipolar transistors using sub-bandgap photonic excitation

Distribution of interface states at the emitter–base heterojunctions in heterostructure bipolar transistors (HBTs) is characterized by using current–voltage characteristics using sub-bandgap photonic excitation. Sub-bandgap photonic source with a photon energy E_ph which is less than the energy bandgap E_g (E_g,GaAs = 1.42, E_g,AlGaAs = 1.76 eV) of emitter, base, and collector of HBTs, is employed for exclusive excitation of carriers only from the interface states in the photo-responsive energy range at emitter–base heterointerface. The proposed method is applied to an Al_0.3Ga_0.7As/GaAs HBT (A_E = W_E × L_E = 250 × 100 μm²) with E_ph = 0.943 eV and P_opt = 3 mW. Extracted interface trap density D_it was observed to be D_it,max  4.2 × 10¹² eV⁻¹ cm⁻² at emitter–base heterointerface.     

On the geometrical dependence of low-frequency noise in SiGe HBTs

We present an investigation of the dependence of low-frequency noise on device geometry in advanced npn silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs). The devices examined in this work have fixed emitter width (W_E = 0.4 μm), but varying emitter length (0.5 μm  L_E  20.0 μm), and thus the ratio of the emitter perimeter (P_E) to the emitter area (A_E) varies widely, making it ideal for examining geometrical effects. The SPICE noise parameter A_F extracted from these devices decreases with increasing L_E. Furthermore, the low-frequency noise measured on SiGe HBTs with significantly different P_E/A_E ratios suggests a possibility that the fundamental noise source for the diffusion base current may be located at the emitter periphery. Transistors with different distances between the emitter edge and the shallow trench edge (XEC), and shallow trench edge to deep trench edge (XTC), are also investigated. The SiGe HBTs with a smaller value of XEC have higher low-frequency noise, but no significant difference is found in devices with varying XTC. Explanations of the observed noise behavior are suggested.     

The effects of monovacancies on the terrace width during sublimation from the (111) surface of a diamond-like crystal

Using the three-dimensional Monte Carlo model, the effect of monovacancies on the diffusion exchange between the steps on the (111) surface of a diamond-like crystal during sublimation was investigated. The critical terrace width L_cr (the distance from the step edge to the nearest stable vacancy islands) was determined as a function of the relationship between the energy of adatom formation at the smooth terrace E_n and the energy of adatom desorption from the terrace E_d with retention of the sum of these energies E_sub=E_n+E_d, which characterizes the sublimation of a substance. A well-pronounced maximum exists in the dependences L_cr(E_n) obtained. The formula is suggested which well describes the dependences L_cr(E_n) for various values of E_sub. The extrapolation of the dependence L_cr(E_n) to the value E_sub=4.2 eV, which is characteristic of Si, permits us to compare the model results with the experimental data of other authors. The explanation of a threefold increase in the terrace width, which is observed experimentally at about 1500 K, is suggested.     

Using a WLFSR to Embed Test Pattern Pairs in Minimum Time

We propose a methodology for reducing the number of test cycles needed by a Weighted LFSR (WLFSR) to reproduce a 2P × W test matrix T of P pattern pairs. The methodology introduces a very small number of extra cells into the WLFSR and uses appropriate combinational mapping logic in order to make the time be equal to that required by a (W + )-bit WLFSR to generate vectors containing the W bits of the first pattern for each pair plus the extra bits. We present an algorithm that makes the value of be less than or equal to log₂, where is the size of the maximum subset of pairs in T with identical first patterns. This is a significant improvement over the time E _P,W · P required by a trivial approach that uses a WLFSR with W cells to generate the first patterns of the pairs and a P × W ROM to store the second patterns of the pairs. Experimental results on the application of the methodology to the embedding of test matrices for path delay faults are particularly encouraging, even for very large numbers of test pattern pairs that are necessary for provably high fault coverage.     

Interaction of α radiation with iron-doped n-type silicon

Deep-level transient spectroscopy (DLTS) measurements were carried out on low-doped n-silicon before and after irradiation with 5.48 MeV α particles at room temperature with a fluence of 10¹⁰ α particles/cm². The DLTS measurements on the samples identified three electron levels E₁, E₂ and E₃ before irradiation. The deep-levels characteristic studies include emission rate signatures, activation energies, defect concentrations and capture cross sections. It was found that all pre-existing defects decreased their amplitudes during irradiation. The decrease in activation energy of level E₃ and noticeable suppression of level E₁ was also observed after irradiation. It was clearly seen that the composite peak E₃ (combination of E₂ and E₃) was successfully resolved after irradiating with α particles. α-irradiation is seen to lead a significant suppression of the iron interstitial defect, and without causing any change in its room temperature annealing characteristics.     

Photoreflection studies of band offsets at the heterojunction in strained short-period GaAs/GaAsP superlattices

Energies of band-to-band transitions with the involvement of the quantum-confinement subbands are determined from the photoreflection spectra of the strained short-period GaAs/GaAs_0.6P_0.4 superlattice. Strains caused by the mismatch of the crystal lattice in the GaAs and GaAs_0.6P_0.4 layers are calculated on the basis of the observed shift of the fundamental-transition energy in GaAs_0.6P_0.4. Positions of minibands in the superlattice are simulated in relation to the potential jump at the heteroboundary; the Kronig-Penney model is used in the calculations. Comparison of the results of simulation with experimental data shows that the studied superlattice is of type I with weakly localized electrons and light holes. The potential jump at the heteroboundary in the conduction band amounts to ΔE _c /ΔE _g =0.15.     

A 167-Processor Computational Platform in 65 nm CMOS

A 167-processor computational platform consists of an array of simple programmable processors capable of per-processor dynamic supply voltage and clock frequency scaling, three algorithm-specific processors, and three 16 KB shared memories; and is implemented in 65 nm CMOS. All processors and shared memories are clocked by local fully independent, dynamically haltable, digitally-programmable oscillators and are interconnected by a configurable circuit-switched network which supports long-distance communication. Programmable processors occupy 0.17$ hbox{mm}^{2}$ and operate at a maximum clock frequency of 1.2 GHz at 1.3 V. At 1.2 V, they operate at 1.07 GHz and consume 47.5$~$mW when 100% active, resulting in an energy dissipation of 44 pJ per operation. At 0.675 V, they operate at 66 MHz and consume 608$ muhbox{W}$ when 100% active, resulting in a total energy dissipation of 9.2 pJ per ALU or MAC operation.      

First Passage Time Analysis in Wireless Sensor Networks for SPR and MPR Systems

In this paper, we study the performance of Slotted ALOHA in an elementary process in wireless sensor networks, in which sensors are activated by rare events and transmit packets to a single sink node within single hop. The time cost of the process can be viewed as a first passage time and we give the expectation of time and energy cost which is dependent on both the size of active nodes and their transmission rate by a first passage time analysis. Meanwhile, given the size of active nodes n, we demonstrated that the optimal transmission rate λ_min(n) by which the first passage time attains its minimum, is nearly . Our result indicates that time cost of the process in which each node transmits packet with transmission rate λ_min(n) increases nearly linearly with n increasing. We present the maximum likelihood estimate (MLE) of the size of active nodes from the viewpoint of sink nodes so that activated nodes can adjust its transmission rate to improve the performance of the process. Energy dissipation and time cost of the procedure in the channel model of Multi Packet Reception (MPR) are considered also. Numerical results indicate that both time cost and energy consumption of the procedure in MPR channel is superior to that in Single Packet Reception (SPR) channel while the transmission rate near or less than the optimal values with which time costs attain their minimum. Otherwise the energy dissipation in MPR channel is more than that in SPR channel although comparison of time cost in the above two channels reveals the superiority of MPR channel.

The model of self-compensation and pinning of the Fermi level in irradiated semiconductors

A model is developed to analyze numerically the electrical properties and the steady-state (limiting) position of the Fermi level (F _lim) in tetrahedral semiconductors irradiated with high-energy particles. It is shown that an irradiated semiconductor represents a highly compensated material, in which F _lim is identical to 〈E _G〉/2, where 〈E _G〉 is the average energy gap between the conduction band and valence band within the entire Brillouin zone of the crystal. The experimental values of F _lim, the calculated values of 〈E _G〉/2, and the data on the electrical properties of irradiated semiconductors are presented. The chemical trends controlling the variation in the quantity F _lim in groups of semiconductors with the similar types of chemical bonding are analyzed.     

A Distributed Algorithm for Dynamic Channel Allocation

Recent demand for mobile telephone service has been growing rapidly while the electro-magnetic spectrum of frequencies allocated for this purpose remains limited. Any solution to the channel assignment problem is subject to this limitation, as well as the interference constraint between adjacent channels in the spectrum. Channel allocation schemes provide a flexible and efficient access to bandwidth in wireless and mobile communication systems. In this paper, we present an efficient distributed algorithm for dynamic channel allocation based upon mutual exclusion model, where the channels are grouped by the number of cells in a cluster and each group of channels cannot be shared concurrently within the cluster. We discuss the algorithm and prove its correctness. We also show that the algorithm requires at most (worst case) O(N _gN _n logN _n) messages, where N _g is the number of groups and N _n is the number of neighbors. This is compared to Choy's algorithm which requires O(N _g ²N _n), where N _g is the number of groups and N _n is the number of neighboring cells in the system. We report our algorithm's performance with several channel systems using different types of call arrival patterns. Our results indicate that significant low denial rate, low message complexity and low acquisition time can be obtained using our algorithm.     

Charge storage and data retention characteristics of forming gas-annealed Gd2O3-nanocrystal nonvolatile memory cell

Trapping characteristics of forming gas-annealed Gd₂O₃ nanocrystal (Gd₂O₃-NC) memories were studied in detail. The trapping energy can be obtained from the data retention characteristic for different absolute temperature (T). The discharging time (τ) was extracted from a linear fitting curve of the data retention characteristic. From the relationship between ln(1/τT²) and 1/kT, the trapping energy was evaluated. Based on the retention properties, the discharge mechanisms of electrons in shallow and deep traps are correlated to the charge loss time. The observed values of the trapping energy demonstrated that deep traps are passivated by hydrogen species after FGA treatment; the difference of programming and erasing (P/E) speed of the memories between the samples with- and without-FGA treatment can be explained by this passivation process. A band diagram is proposed to explain the behavior of the charge loss mechanism. The fact that the endurance of Gd₂O₃-NC memories are not significantly degraded by the FGA treatment indicates that, though the deep traps are passivated by hydrogen, the reliability of the Gd₂O₃-NC memories is not affected. The method of FGA treatment enables the determination of the discharge process in nanocrystal memories.     

Anomalous Photoconduction of Low-Temperature Charge-Density Wave in NbS<Subscript>3</Subscript>-II as a Physical Basis of a Method for Detection of Weak Signals

The effect of IR radiation on photoconduction of two charge-density waves (CDWs) in the monoclinic phase of quasi-1D conductor NbS₃ (NbS₃-II) is studied. For the CDW-1 that emerges at a temperature of Т_Р1 = 360 К, threshold field E_t increases with irradiation power W. For CDW-2 that emerges at a temperature of T_P2 = 150 K, field E_t decreases due to IR irradiation, which proves anomalous character of CDW-2 and indicates direct photoactivation of its sliding. Extremely high sensitivity of the measured signal to IR radiation is obtained using stimulation of the CDW coherence by the microwave field.     

Energy efficient collaborative communications in AWGN and Rayleigh fading channel in wireless sensor networks

Collaborative communication produces high power gain and significantly reduces bit error rate (BER) if both frequency and phase synchronization are achieved. In this paper, a novel collaborative communication system with imperfect phase and frequency synchronization that includes the influence of noise and fading is proposed, modeled, theoretically analyzed, and simulated. Mathematical expressions are derived for the received power as a function of number of collaborative nodes and BER as a function of signal to noise ratio (E_b ∕ N₀). To analyze the energy efficiency of our proposed collaborative communication system, energy consumption of the system is modeled, simulated, and analyzed by considering the parameters of the off‐the‐shelf products. Analytical and simulation results showed that the proposed system produces significant power gain and reduction in BER in the presence of phase errors, frequency errors, additive white Gaussian noise, and Rayleigh fading. A detailed theoretical analysis and Monte Carlo simulation revealed that the proposed collaborative communication system is an energy efficient communication system that can be implemented in sensor networks, as approximately N (number of collaborative nodes) times less total transmitted power is required than for the single input single output communication for a specifies transmission range. Copyright © 2012 John Wiley & Sons, Ltd.     

Participation of the electron subsystem of a crystal in the reactions of defect-complex decomposition in semiconductors

The reactions of defect-complex decomposition in semiconductors are considered. The contribution from the electron subsystem to the reaction rate is taken into account by adding a change in the electron-subsystem energy of a crystal (as a result the reaction) to the energy barrier of the reaction. The theoretical and experimental data are compared by the example of the reactions of E-center decomposition in the n-type phosphorus-doped silicon. The dependence of temperature of isochronous annealing of E centers on a donor-impurity concentration is explained. The first stage of annealing (T _ann≈400 K) in a low-resistivity silicon is caused by the decomposition of the E center and can be explained using the model of a vacancy as the double acceptor center with a negative correlation energy and values of vacancy charge-exchange levels E _V (0/-)=E _c -0.99 eV, E _V (-/—)=E _c =?0.39 eV. From the comparison between calculated and experimental data, the dissociation energy of E center and the degeneracy factor are obtained to be U _a0≈0.96 eV and $g_E^ - /g_E^0 = 1/16$ , respectively.     

Dissociation energies of a C<Subscript>i</Subscript>C<Subscript>s</Subscript> complex and the <Emphasis Type="Italic">A</Emphasis> center in silicon

Reactions of annealing of A centers (VO) and complex centers consisting of interstitial carbon atoms and substitutional carbon atoms (C_iC_s) in n-Si irradiated with fast electrons or ⁶⁰Co gamma quanta were analyzed. The kinetics of isochronous annealing of the above centers was evaluated. By comparing the results of calculations with published experimental data, which were obtained by measuring the concentration of centers with the level E_c?0.17 eV in the course of isochronous heat treatment of irradiated n-Si, the dissociation energy E for the C_iC_s complex was estimated at 1.10±0.05 eV. The activation energy for annealing of this center was found to be equal to \(E_{aC_i C_s } \approx 2.0eV\). The dissociation energy for the A center was estimated at E_A=1.94 eV.     

Structurally complex two-hole and two-electron slow traps with bikinetic properties in <Emphasis Type="Italic">p</Emphasis>-ZnTe and <Emphasis Type="Italic">n</Emphasis>-ZnS crystals

Thermal-activation and photoactivation methods were used to ascertain the existence of two-hole traps in p-ZnTe crystals and two-electron traps in n-ZnS. It was found that these traps have a large number of energy states that are grouped in two series of levels: E_V+(0.46–0.66) eV and E_V+(0.06–0.26) eV in p-ZnTe and E_C?(0.6–0.65) eV and E_C?(0.14–0.18) eV in n-ZnS. Both the hole and the electron traps belong to the class of slow traps with bikinetic properties. These traps feature normal kinetic properties in the state with a single trapped charge carrier and feature anomalous kinetic properties in the state with two charge carriers. Multiple-parameter models allowing for a relation of traps in p-ZnTe and n-ZnS to the vacancy-impurity pairs distributed according to their interatomic distances and localized in the region of microinhomogeneities with collective electric fields that repel the majority charge carriers are suggested. The main special features of behavior of electron and hole traps are explained consistently using the above models.     

A new recursive algorithm for the reliability evaluation of a distributed program

The reliability of a distributed program is very sensitive to the ways of file distribution, and communication system topology. It is usually much more complex to analyze the reliability of distributed program than that of the network reliability. This paper presents a distributed program reliability analysis algorithm that is developed based on the concept of sharp operation. The algorithm provides a (E−n+2) * E memory space requirement and O(n+E+E*N_t) computation time, where E is the number of edges, n is the number of nodes, and N_t is the number of file spanning trees in the corresponding graph of distributed system, respectively. Compared with existing algorithms, the proposed algorithm is considered more economic both in time and space.     

Optical properties of PbS thin films

The complex dielectric function of PbS thin films is studied by spectroscopic ellipsometry in the spectral range from 0.74 to 6.45 eV at a temperature of 293 K. The critical energies are determined to be E ₁ = 3.53 eV and E ₂ = 4.57 eV. For both energy regions, the best fit is attained at the critical point 2D (m = 0). In addition, the Raman spectra and the optical-absorption spectra of PbS thin films are studied. From the dependence of the quantity (αhν)² on the photon energy hν, the band gap is established at E _g = 0.37 eV.