Direct, prediction- and smoothing-based Kalman and particle filter algorithms

We address the recursive computation of the filtering probability density function (pdf) p_n|n in a hidden Markov chain (HMC) model. We first observe that the classical path p_n−1|n−1→p_n|n−1→p_n|n is not the only possible one that enables to compute p_n|n recursively, and we explore the direct, prediction-based (P-based) and smoothing-based (S-based) recursive loops for computing p_n|n. We next propose a common methodology for computing these equations in practice. Since each path can be decomposed into an updating step and a propagation step, in the linear Gaussian case these two steps are implemented by Gaussian transforms, and in the general case by elementary simulation techniques. By proceeding this way we routinely obtain in parallel, for each filtering path, one set of Kalman filter (KF) equations and one generic sequential Monte Carlo (SMC) algorithm. Finally we classify in a common framework four KF (two of which are original), which themselves can be associated to four generic SMC algorithms (two of which are original). We finally compare our algorithms via simulations. S-based filters behave better than P-based ones, and within each class of filters better results are obtained when updating precedes propagation.     

Electrical and thermoelectric properties of ZnO under atmospheric and hydrostatic pressure

Temperature (for T = 77–400 K) and pressure (for P ≤ 8 GPa) dependences of conductivity σ(T,P). Hall coefficient R _H(T, P), and Seebeck coefficient Q(T) were studied in single-crystal n-ZnO samples with the impurity concentration N _i = 10¹⁷ ? 10¹⁸ cm^?3 and free-electron concentration n = 10¹³?10¹⁷ cm^?3. Single crystals were grown by the hydrothermal method. Dependence of the ionization energy of a shallow donor level on the impurity concentration E _d1(N _d) is determined, along with the pressure coefficients for the ionization energy ?E _d1/?P and static dielectric constant ?x/?P. A deep defect level with the energy E _d2 = 0.3 eV below the bottom of the conduction band is found. The electron effective mass is calculated from the obtained data on the kinetic coefficients R _H(T) and Q(T).     

Versatile analog squarer and multiplier free from body effect

This paper proposes the analog CMOS squarer and the four-quadrant analog CMOS multiplier. The major advantages of the proposed circuits are low voltage supply, multifunction of output, and insensitive to the threshold voltage variation caused by body effect. The versatile squarer has two inputs (V _in and I _in ). Its output can be the square of V _in or the square of I _in . The versatile four-quadrant multiplier has four inputs (V _X , I _X , V _Y , and I _Y ). Its output can be the product of V _X and V _Y , the product of I _X and I _Y , the product of V _X and I _Y , or the product of V _Y and I _X . Therefore, the proposed circuits can be applied more than conventional circuits and have good performance. Second-order effects and frequency response are analyzed. Simulation results have verified the workability of the circuits. Experimental results are done to confirm the operation of the circuits.     

Origin of forward bias capacitance peak and intersection behavior of C and G/w of Ag/p-InP Schottky barrier diodes

Frequency-dependent electrical characteristics of Ag/p-InP diodes have been determined using impedance spectroscopy at room temperature. Series resistance (R_s) and interface state(s) (N_ss) values were extracted from capacitance (C) and conductance (G/w) data using the Nicollian and Goetzberger and Hill–Coleman methods, respectively. C and G/w data were also corrected in the whole measured bias voltage range to obtain real diode capacitance C_c and conductance G_c values in order to see the effects of R_s. Both the C–V and R_s–V plots showed anomalous peak in depletion region especially at low frequencies due to the existence of N_ss. C–V and G/w–V plots crossed at a certain bias voltage and this point shifted toward negative bias voltages with increasing frequency and then disappeared at 3 MHz. Also, decrease in C values corresponds to an increase in G/w values in the same bias voltages.     

On completeness and multi-channel sampling

A bandlimited input x is applied as a common input to m linear time-invariant filters (channels) which are ‘independent’ in a certain sense. We investigate, from a unified point of view using the concept of completeness, the problem of uniquely reconstructing the input x for all time values from samples of the m outputs, each output being sampled at the uniform rate of σ/gqm samples/second, where σ is the positive frequency bandwidth of the input signal.For the lowpass input case and independent channels, perfect reconstruction is always possible; similarly for the case of a bandpass input and an even number of channels, recovery of the input can also be accomplished at a rate of σ/mπ samples/second. However, for an odd number m of channels and a bandpass input, it is shown that the rate σ/mπ samples/second at the outputs no longer suffices to determine the input uniquely unless 2ω₀m/σ is an odd integer, a constraint on the relation between the center frequency of the band, ω₀, and the bandwidth σ. To obtain a sampling theorem when the number of channels is odd and in the absence of such a positioning constraint, a higher sampling rate per channel must be employed.In those cases which permit a unique determination of the input from samples of the output channels, it is shown that a linear scheme involving m linear time-invariant post-filters can be used to effect the input reconstruction.     

Input Locality and Hardness Amplification

We establish new hardness amplification results for one-way functions in which each input bit influences only a small number of output bits (a.k.a. input-local functions). Our transformations differ from previous ones in that they approximately preserve input locality and at the same time retain the input size of the original function. Let f:{0,1} ⁿ →{0,1} ^m be a one-way function with input locality d, and suppose that f cannot be inverted in time $\exp(\tilde{O}(\sqrt{n}\cdot d))$ on an ε-fraction of inputs. Our main results can be summarized as follows:

• If f is injective then it is equally hard to invert f on a (1?ε)-fraction of inputs.
• If f is regular then there is a function g:{0,1} ⁿ →{0,1} ^m+O(n) that is d+O(log³ n) input local and is equally hard to invert on a (1?ε)-fraction of inputs.

A natural candidate for a function with small input locality and for which no sub-exponential time attacks are known is Goldreich’s one-way function. To make our results applicable to this function, we prove that when its input locality is set to be d=O(logn) certain variants of the function are (almost) regular with high probability. In some cases, our techniques are applicable even when the input locality is not small. We demonstrate this by extending our first main result to one-way functions of the “parity with noise” type.     

Analytical modeling and parameter extraction of top and bottom contact structures of organic thin film transistors

This paper proposes a structure based model of an organic thin film transistor (OTFT) and analyzes its device physics. The analytical model is developed for the top contact structure by mapping the overlap region to the resistance (in the vertical direction) that includes the contact and the bulk sheet resistances. Total device resistance includes the vertical resistance per unit area of the contact region and the sheet resistance of the channel. In addition, the drain and the gate voltages take into account the potential drop across the respective contacts. The gate bias dependent mobility is considered in place of constant mobility, since; it is more realistic and relevant to the organic TFTs. The proposed analytical model is also applied to the bottom contact structure and the current–voltage (I–V) characteristics are obtained. Furthermore, a differential method is employed to extract the parameters, such as, mobility enhancement factor γ, threshold voltage V_T, mobility µ_B, characteristic length L_C, vertical resistance R_V and contact resistance R_C. Finally, the model is validated in terms of electrical characteristics and performance parameters for both top and bottom contact structures. The analytical model results are in close agreement with the experimental results.     

Hot electron noise and g-r noise in short-channel JFETs

Hot electron noise in short-channel JFETs is measured above 150°K and generation-recombination noise due to donors is measured below 120°K, where it predominates over the first. The hot electron noise increases with increasing V_GS - V_P for a given temperature T and increasing with decreasing T at a given V_GS - V_P. The g-r noise in donors increases very rapidly with decreasing temperature and is found to be governed by an activation energy between E₀ and 2E₀, where E₀ is the activation energy of the donors. The theories of these effects can qualitatively explain the data; for the g-r noise it must be taken into account that the activation energy of the donors decreases with increasing electric field (Poole-Frenkel effect).     

Polymers from phenyl-substituted benzodithiophene and tetrafluoridequinoxaline with high open circuit voltage and high fill factor

A series of new copolymers from tetrafluoridequinoxaline (ffQx) and three distinctive phenyl (alkoxy-1-meta-fluorophenyl, alkoxyphenyl and alkylthiophenyl) substituted benzodithiophene (BDT), namely, PffQx-m-fPO, PffQx-PO and PffQx-PS, were designed and synthesized. Photophysical properties, charge mobilities and morphologies of the three polymers have been intensively investigated. Benefitted from the effects of phenyl and fluorine substituents on the backbone, all the polymers possess deep the highest occupied molecular orbital (HOMO) levels. In particular, PffQx-PS has a lower bimolecular recombination and deeper HOMO energy level, which contributes to the higher fill factor (FF, ca. 70%) and higher open-circuit voltage (V_oc, ca. 0.93 V) of the polymer solar cells (PSCs) with the polymer as donor and PC₇₁BM as acceptor. All the PSCs with the ffQx-based polymers as donor exhibited V_ocS higher than 0.9 V and power conversion efficiencies over 7% (7.0% for PffQx-m-fPO, 7.4% for PffQx-PO and 8.0% for PffQx-PS).     

A direct-construction approach to multidimensional realization and LFR uncertainty modeling

This article proposes a direct-construction realization procedure that simultaneously treats all the involved variables and/or uncertain parameters and directly generates an overall multidimensional (n-D) Roesser model realization or linear fractional representation (LFR) model for a given n-D polynomial or causal rational transfer matrix. It is shown for the first time that the realization problem for an n-D transfer matrix G(z ₁, . . . , z _n ), which is assumed without loss of generality to be strictly causal and given in the form of G(z ₁, . . . , z _n )=N _r (z ₁, . . . , z _n )D _r ^?1 (z ₁,..., z _n ) with D _r (0, . . . , 0)=I and N _r (0, . . . , 0)  = 0, can be essentially reduced to the construction of an admissible n-D polynomial matrix Ψ for which there exist real matrices A, B, C such that N _r (z ₁, . . . , z _n ) = CZΨ and Ψ D _r ^?1 (z ₁, . . . , z _n ) = (I ? AZ)^?1 B with Z being the corresponding variable and/or uncertainty block structure, i.e., ${Z={\rm diag} \{z_1I_{r_1},\ldots,z_nI_{r_n} \}}$ . This important fact reveals a substantial difference between the 1-D and n-D (n ≥  2) realization problems as in the 1-D case Ψ can only be a monomial matrix and never a polynomial one. Necessary and sufficient conditions for Ψ to satisfy the above restrictions are given and algorithms are proposed for the construction of such an admissible n-D polynomial matrix Ψ with low order (for an arbitrary but fixed field of coefficients) and the corresponding realization. Symbolic and numerical examples are presented to illustrate the basic ideas as well as the effectiveness of the proposed procedure.     

Fabrication and characterization of p-n junctions based on ZnO and CuPc

p-n Junctions based on zinc oxide (ZnO) and copper-phthalocyanine (CuPc) were fabricated using pulsed laser deposition and thermal evaporator techniques, respectively. Current-voltage (I-V) characteristics of the ZnO-CuPc junction showed rectifying behavior. Various junction parameters such as barrier height and ideality factor were calculated using I-V data and observed to be 0.63 ± 0.02 eV and 4.0 ± 0.3, respectively. Cheung and Norde’s method were used to compare the junction parameters obtained by I-V characteristics.     

Growth of Ge1 − x Sn x solid solution films and study of their structural properties and some of their photoelectric properties

From the charge state and closeness of the covalent radii of molecules of the solution-forming components, the possibility of the formation of the solutions Si_{1 ? x} Ge _x , Si_{1 ? x} Sn _x , (Si₂)_{1 ? x} (SnC) _x , Ge_{1 ? x} Sn _x , (Ge₂)_{1 ? x} (SiSn) _x , (SiC)_{1 ? x} (GeC) _x , (GeC)_{1 ? x} (SnC) _x , and (SiGe)_{1 ? x} (SnC) _x based on chemical elements of Group IV has been predicted. Single-crystal films of the substitutional solid solution Ge_{1 ? x} Sn _x (0 ≤ x ≤ 0.03) have been grown on Ge substrates by liquid-phase epitaxy. X-ray diffraction patterns, spectral photosensitivity, and the I–V characteristics of the obtained n-Ge-p-Ge_{1 ? x} Sn _x heterostructures have been investigated. The lattice parameters of the epitaxial film and the substrate a _f = 5.6812 Å and a _s = 5.6561 Å have been determined. The spectral photosensitivity of the n-Ge-p-Ge_{1 ? x} Sn _x heterostructures encompasses the photon energy range from 0.4 to 1.4 eV. It is shown that the forward portion of the I–V characteristics of the investigated structures at low voltages (up to 0.5 V) is described by the exponential dependence I = I ₀exp(qV/ckT) and at high voltages (V > 0.5 V), by the power dependence I ∝ V ^α with the values α = 2 at V = (0.5–0.9) V, α = 1.3 at V = (0.9–1.4) V, and α = 2 at V > 1.4 V. The experimental data are explained within the double injection model for the n-p-p structure using the drift mechanism of current transport in the ohmic relaxation mode taking into account the inertia of the electron exchange inside a recombination complex.     

Potential and limitations of Schottky-barrier barritt devices

Computer simulation of various Schottky-barrier structures is carried out to investigate the large-signal properties of these devices. Comparison between Schottky-barrier devices and their p-n junction counterparts are also made to evaluate the potential and limitations of these devices and to explain the difference in performance between them. It is shown that among various Schottky-barrier structures, the M-n-i-p⁺ structure is the most powerful one and the M-n-p-p⁺ device is the most efficient one. Furthermore, Schottky-barrier devices with low barrier heights for minority carriers (less than 0.2 eV) are capable of producing power levels close to the generated power of p-n junction devices. Investigation of the temperature dependence of the large-signal performance of these devices shows that Schottky barriers are more sensitive and exhibit their optimum performance close to room temperature value. At low temperature, the output power is limited by the low minority carrier injection, whereas at high temperature the limitation is due to the velocity-modulation losses in the injection and low-field regions of the device.     

Formation and annealing of metastable (interstitial oxygen)-(interstitial carbon) complexes in n- and p-type silicon

It is shown experimentally that, in contrast to the stable configuration of (interstitial carbon)-(interstitial oxygen) complexes (C _i O _i ), the corresponding metastable configuration (C _i O _i *) cannot be found in n-Si based structures by the method of capacitance spectroscopy. The rates of transformation C _i O _i * →C _i O _i are practically the same for both n- and p-Si with a concentration of charge carriers of no higher than 10¹³ cm^?3. It is established that the probabilities of the simultaneous formation of stable and metastable configurations of the complex under study in the case of the addition of an atom of interstitial carbon to an atom of interstitial oxygen is close to 50%. This is caused by the orientation dependence of the interaction potential of an atom of interstitial oxygen with an interstitial carbon atom, which diffuses to this oxygen atom.     

Temperature and frequency dependent electrical and dielectric properties of Al/SiO2/p-Si (MOS) structure

The electrical and dielectric properties of Al/SiO₂/p-Si (MOS) structures were studied in the frequency range 10 kHz-10 MHz and in the temperature range 295-400 K. The interfacial oxide layer thickness of 320 Å between metal and semiconductor was calculated from the measurement of the oxide capacitance in the strong accumulation region. The frequency and temperature dependence of dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tan δ) and the ac electrical conductivity (σ_ac) are studied for Al/SiO₂/p-Si (MOS) structure. The electrical and dielectric properties of MOS structure were calculated from C-V and G-V measurements. Experimental results show that the ε′ and ε″ are found to decrease with increasing frequency while σ_ac is increased, and ε′, ε″, tan δ and σ_ac increase with increasing temperature. The values of ε′, ε″ and tan δ at 100 kHz were found to be 2.76, 0.17 and 0.06, respectively. The interfacial polarization can be more easily occurred at low frequencies, and the number of interface state density between Si/SiO₂ interface, consequently, contributes to the improvement of dielectric properties of Al/SiO₂/p-Si (MOS) structure. Also, the effects of interface state density (N_ss) and series resistance (R_s) of the sample on C-V characteristics are investigated. It was found that both capacitance C and conductance G were quite sensitive to temperature and frequency at relatively high temperatures and low frequencies, and the N_ss and R_s decreased with increasing temperature. This is behavior attributed to the thermal restructuring and reordering of the interface. The C-V and G/ω-V characteristics confirmed that the N_ss, R_s and thickness of insulator layer (δ) are important parameters that strongly influence both the electrical and dielectric parameters and conductivity in MOS structures.     

Study of the long-wavelength optic phonons in AlGaInP and AlGaInAs

The investigation of the lattice dynamics of (Al_xGa_1−x)_yIn_1−yP quaternary semiconductor alloys lattice matched to GaAs has been made by Raman scattering. The Raman spectra exhibit three-mode behavior depending on the composition. A modified random element isodisplacement (MREI) model is generalized to the III-V (A_xB_1−x)_1−yC_yD-type quaternary alloys, describing the behavior of the optical phonons. The calculated result of two quaternary mixed crystals, (Al_xGa_1−x)_yIn_1−yP and (Al_xGa_1−x)_yIn_1−yAs, is in good agreement to the experimental data.     

High frequency excess noise and flicker noise in GaFs FETs

The noise parameter α = R_ng_m, where R_n is the noise resistance and g_m the transconductance, was measured for n-channel GaAs FETs. At lower frequencies α varies as 1/f, as expected for flicker noise, whereas at higher frequencies α attains a limiting value α_∞ that is larger than expected for thermal noise. Arguments are presented to show that the high-temperature value of α_∞ is due to a geometry effect, possibly aided by a temperature-independent hot electron effect, whereas the low-temperature data reflect a temperature-dependent hot electron effect. The flicker noise is practically temperature independent, and is attributed to the large interface between semiconductor and oxide.     

Analysis of recursive convolutional codes and turbo codes as sources with memory

The paper proposes a general method to analyze discrete sources with memory. Besides the classical entropy, we define new information measures for discrete sources with memory, similar to the information quantities specific to discrete channels. On the base of this method, we show for the first time that, as result of convolutional and turbo encoding, sources with memory are obtained. We apply this information analysis method for the general case of a recursive convolutional encoder of rate R_CC = 1/n₀ and memory of order m, and for a turbo encoder of rate R_TC = 1/3, with two systematic recursive convolutional component encoders. Each component encoder has memory of order m, and is built based on the same primitive feedback polynomial. For the convolutional and turbo codes, the information quantities H(Y/S), H(S,Y), H(S/Y), H(Y), H(S) and I(S,Y) have been computed, where S and Y denote the set of states and the set of messages of the encoder, respectively. The analysis considered two cases: n₀ ≤ m + 1 and n₀ > m + 1. When n₀ = m + 1, the mutual information I(S,Y) is maximum and equal to m, as is the entropy of the set of states. For turbo codes, the quantity I(S,Y) also depends on the input bit and on its probability.     

Frequency and voltage dependency of interface states and series resistance in Al/SiO2/p-Si MOS structure

The capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics of Al/SiO₂/p-Si metal-oxide-semiconductor (MOS) Schottky diodes have been measured in the voltage range from ?3 to +3 V and frequency range from 5 KHz to 1 MHz at room temperature. It is found that both C and G/ω of the MOS capacitor are very sensitive to frequency. The fairly large frequency dispersion of C–V and G/ω–V characteristics can be interpreted in terms of the particular distribution of interface states at SiO₂/Si interface and the effect of series resistance. At relatively low frequencies, the interface states can follow an alternating current (AC) signal that contributes to excess capacitance and conductance. This leads to an anomalous peak of C–V curve in the depletion and accumulation regions. In addition, a peak at approximately ?0.2 V appears in the R_s–V profiles at low frequency. The peak values of the capacitance and conductance decrease with increasing frequency. The density distribution profile of interface state density (N_ss) obtained from C_HF–C_LF capacitance measurement also shows a peak in the depletion region.     

Thermal Conductivity and ZT in Disordered Organic Thermoelectrics

For decades, continuous attempts have been made to improve the figure of merit (ZT) of thermoelectrics. The theory behind the Seebeck effect itself is well researched, but the problem with ZT is related to materials properties that offset one another. This work analyzed the link between the site energy distributions and thermal conductivity of oxidized poly(3,4-ethylenedioxythiophene-tosylate) (PEDOT:Tos), which was reported to be a good organic thermoelectric. To understand how heat flow was affected by “disorder” in PEDOT:Tos and the associated electron–phonon interactions, we computed the values of the thermal conductivity κ and ZT using materials parameters extracted from the open literature. By varying the values of the parameters separately, we were able to identify their individual influence on κ and ZT. Our results suggest that ZT is most sensitive to changes in σ, the bandwidth of the density of states (DOS) of the transport sites, and less so to changes in n _eff, the effective carrier density. Our simulations also suggested that ZT could become exceptionally large (approaching a value of ~20) if σ were lowered to 1 meV to 2 meV. This would be a tremendous approach to increase ZT in oxidized PEDOT:Tos.