Investigation of the influence of the well and the barrierthicknesses in GaSb/AlSb/GaSb/AlSb/InAs double-barrier interbandtunneling structures

The tunneling currents of GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling (DBIT) structures were studied experimentally by varying the thickness of the well and the barrier layers systematically. The optimal thicknesses for the GaSb well and the AlSb barriers were found to be 6.5 and 1.0 nm, respectively, to obtain a high peak current density (19 kA/cm²), with a large peak-to-valley ratio of 4. The high peak current in the DBIT structure shows the strong effect of the resonant coherence of the wave function across the double barrier. For the case of a small GaSb well width (3 nm), a drastic reduction of the peak current was observed, an effect suggesting that the electron-wave function in the InAs couples primarily to the quantized light hole state in the GaSb well     

Lanthanum diffusion in the TiN/LaOx/HfSiO/SiO2/Si stack

Band edge Complementary Metal Oxide Semiconductor (CMOS) devices are obtained by insertion of a thin LaO_x layer between the high-k (HfSiO) and metal gate (TiN). High temperature post deposition anneal induces Lanthanum diffusion across the HfSiO towards the SiO₂ interfacial layer, as shown by Time of Flight Secondary Ions Mass Spectroscopy (ToF-SIMS) and Atom Probe Tomography (APT). Fourier Transform Infrared Spectroscopy in Attenuated Total Reflexion mode (ATR-FTIR) shows the formation of La-O-Si bonds at the high-k/SiO₂ interface. Soft X-ray Photoelectron Spectroscopy (S-XPS) is performed after partial removal of the TiN gate. Results confirm La diffusion and changes in the La chemical environment.     

M θ/G/1/m and M θ/G/1 systems with the service time dependent on the queue length

The M ^θ/G/1/m and M ^θ/G/1 queueing systems, in which the service time depends on the queue length and is determined at the beginning of service of a customer, are investigated. The average busy period and the stationary distribution of the number of customers in the system have been found via the approach based on the idea of V.S. Korolyuk’s potential method. As a special case, the M ^θ/G/1 queue with a single threshold of switching of service modes is examined. The results are checked using the simulation model constructed with the use of GPSS World software tools.     

Analysis of the /spl Sigma/-/spl Delta/ pulsed digital oscillator for MEMS

The aim of this paper is the analysis, simulation, and experimental verification of the /spl Sigma/-/spl Delta/ pulsed digital oscillator (PDO) topology. As it has been shown in previous works, the oscillation frequency and output spectrum in the PDO depend on the sampling frequency, the natural frequency of the microelectromechanical systems (MEMS) resonator and its damping factor. Here, extensive discrete-time simulations have been carried out which show that the normalized oscillation frequency as a function of the normalized natural frequency of the resonator is very similar to a distorted Devil's Staircase fractal. This nonlinear behavior is a direct consequence of the damping losses of the MEMS resonator. Analytical conditions for a perfect oscillation at the natural frequency of the resonator are also calculated. For this set of what we call "perfect" frequencies, it is also shown that the energy transfer from the electrical to the mechanical domain is maximum. Then a more generalized structure of the oscillator is considered and the drawn conclusions are tested against experimental results obtained from an oscillator prototype which uses a MEMS resonator with thermoelectric actuation and piezoresistive position sensing.     

Transient analysis of the MMPP/G/1/K queue

In this paper the transient behaviour of a finite-buffer queue fed by the Markov-modulated Poisson process is studied. The results include formulas for the transforms of transient queue size distribution, transient full buffer probability and transient delay (workload). Computational issues are discussed and numerical samples presented.This material is based upon work supported by the Polish Ministry of Scientific Research and Information Technology under Grant No. 3 T11C 014 26.     

Correction of the temperature effect on the solar cell Isc − Voc characteristic

In this paper we present a simple method to determine the thermal resistance of a solar cell from its experimental I_sc ? V_oc characteristic. The knowledge of this parameter permits one to obtain the cell junction temperature and, consequently, the real I_sc ? V_oc characteristic of the cell. The method, which does not require any additional measurement, has been applied to our devices: reasonable agreement between theory and experiment was obtained.     

Measuring the /spl omega/ - /spl beta/ Diagram of Periodic Structures (Correspondence)

One of the most important properties of a periodic structure is the shape of the /spl omega/ - /spl beta/ diagram. A common technique for measuring the /spl omega/ - /spl beta/ diagram is to form a resonant section by placing shorting planes at positions of symmetry within the periodic structure and to observe the resonant frequencies of the resulting resonator. Discussed in this correspondence is a technique wherein the far end of the periodic structure is shorted and the positions of nulls of voltage on an input line are observed as frequency is varied. From these nulls it is possible to determine the frequencies where the electrical length of the loaded structure is a multiple of /spl pi/ radians. Basically, it is a procedure for graphically determining points on the /spl omega/ - /spl beta/ diagram.     

Markovian analysis of the M/Ek/1 machine repair problem with spares

This paper considers the M^X/E_k/1 spare machine repair problem under steady state conditions. A Markovian approach is used as a solution technique to the machine repair problem with spares. The approach followed in this paper provides expressions for state probabilities and machine availability simultaneously. The results are of both practical and theoretical interest as an extension of the standard Poisson batch failure case.     

Scalability of the Si/sub 1-x/Ge/sub x/ source/drain technology for the 45-nm technology node and beyond

The authors present a study on the layout dependence of the silicon-germanium source/drain (Si/sub 1-x/Ge/sub x/ S/D) technology. Experimental results on Si/sub 1-x/Ge/sub x/ S/D transistors with various active-area sizes and polylengths are combined with stress simulations. Two technologically important configurations are investigated: the nested transistor, where a polygate is surrounded by other gates, and isolated transistors, where the active area is completely surrounded by isolation oxide. The channel stress, caused by epitaxial Si/sub 1-x/Ge/sub x/ is reduced substantially when the active area is decreased from a large size towards typical values for advanced CMOS technology nodes. Nested transistors with longer gate lengths are more sensitive towards layout scaling than shorter gates. Increasing recess depth and germanium concentration gives larger channel stress, but does not change layout sensitivity. Increased lateral etching leads to higher stress, as well as to reduced layout sensitivity. In small-size transistors, there exists an optimal recess depth, beyond which the stress in the channel will not increase further. For isolated transistor structures, the interaction between Si/sub 1-x/Ge/sub x/ and the isolating oxide can even lead to stress reduction when the recess depth is increased. When technology advances, active-area dimensions will be scaled together with gate lengths and widths. For typical sizes of advanced silicon CMOS Si/sub 1-x/Ge/sub x/ S/D transistors, simulations indicate that the channel stress can be maintained in future technology nodes.     

Analytical solution of the state-dependent Erlangian queue: M/Ej/1/N with balking

The objective of this paper is to derive the analytical solution of the truncated single-channel Erlangian queue M/E_j/1/N with balking and state-dependent service rate. The researcher deduces p_ns the probability of n units in the system (n = 1, 2, 3,…, N) and the customer in service being in phase backwards, i.e. j is the first phase of service and 1 is the last (a customer leaving phase 1 actually leaves the system). p₀ is the probability of an empty system by using the iterative method. At the end of this paper some special cases are obtained.     

On the stability of the pulsewidth-modulated C/spl acute/uk converter

It has been observed that a stabilizing controller for the state-space-average model of a pulsewidth-modulated (PWM) DC-DC converter does not automatically imply a stabilizing controller for the DC-DC converter itself, especially in the case of the C/spl acute/uk converter. By applying multifrequency averaging as a generalization of the state-space averaging technique, the stationary periodic signals of the C/spl acute/uk converter can be obtained by solving a set of linear equations. Using these equations, we are able to analyze stability aspects of the open-loop and closed-loop PWM C/spl acute/uk converter. Simulations are included in open- and closed-loop situations.     

An optical investigation of electronic excitations in the high temperature superconductors YBa/sub 2/Cu/sub 3/O/sub 7- delta / and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+ Delta /

The results of Raman scattering from superconducting gap excitations in the high T/sub c/ compounds YBa/sub 2/Cu/sub 3/O/sub 7- delta / and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+ Delta / are compared. In the normal state, both materials exhibit strong electronic interband scattering which manifests itself as a broad background continuum having both A/sub 1g/ and B/sub 1g/ symmetry components. At low temperatures a redistribution of this electronic scattering occurs, indicative of the formation of a superconducting gap in these compounds. The two symmetries exhibit distinct redistribution, however, denoting strong anisotropy. At temperatures well below T/sub c/, both compounds exhibit residual low-energy scattering, a feature suggestive of the coexistence of normal electrons and superconducting quasi-particles.<>     

On the /spl eta/-/spl kappa/ distribution

For original paper by Yacoub et al., see IEEE Trans. Broadcasting., vol.51, p.504-11 (2005 December).     

A Novel Approach to Analyzing the Occupancy of the Geo/Geo/∞ Queueing System

Discrete time queueing systems have been successfully used to model packet queues in computer and digital communications systems. In this article we introduce a novel approach to analyzing the Geo^X/Geo^Y/∞ queueing system, which is suitable for modelling high speed computer and communications systems. The approach is based on characterizing the system by a functional equation which is then solved recursively to give identical results to those obtained using other approaches.     

Nonlinear HEMT model formulated from the second-order derivative of the I-V and Q-V characteristics

In this paper, an empirical nonlinear model of high electron mobility transistors (HEMTs) suitable for a wide bias range is presented. Unlike the conventional large-signal models whose fitting parameters are coupled to the measured drain current and gate capacitance characteristics, the derived modeling equations are direct formulated from the second-order derivative of drain current (I-V) and gate charge (Q-V) with respect to gate voltage. As a consequence, the proposed nonlinear model is kept continuously differentiable and accurate enough to the higher-order I-V and Q-V derivatives. Besides, the thermal and trapping effects have been implemented in the large-signal model along with its dependence on temperature and quiescent-bias state. The composite nonlinear model is shown to accurately predict the S-parameters, large-signal power performances as well as the two-tone intermodulation distortion products for various types of GaAs and GaN HEMTs.     

Impact of the SiGe/Si interface structure upon the low temperature photoluminescence of a Si/Si1−xGex multiple quantum well

The effect of interfacial potential fluctuations of a Si/SiGe multiple quantum well structure upon the low-temperature exciton luminescence is reported. Exciton localisation at such potential fluctuations with a lateral period of 4–6 nm is observed as a strong blue-shift in the power dependence of the low-temperature photoluminescence (PL). To characterise the structure of the interfaces, X-ray diffraction and reflectivity, X-ray topography and transmission electron microscopy (TEM) were used. Moreover, annealing of the sample at temperatures well below the growth temperature leads to the formation of striations with a period of several micrometres along the [0 1 1] direction. These striations are due to Ge-concentration fluctuations and are accompanied by the observation of D-line emission due to misfit dislocations.     

On the impact of TiN film thickness variations on the effective work function of poly-Si/TiN/SiO/sub 2/ and poly-Si/TiN/HfSiON gate stacks

The impact of TiN film thickness variations on the effective work function (WF) of poly-Si/TiN/SiO/sub 2/ and poly-Si/TiN/HfSiON interfaces has been investigated. The electrical signatures of these gate stacks indicate that the concentration of Hf-Ti and Ti-Si bonds at the (poly-Si/TiN)/HfSiON and (poly-Si/TiN)/SiO/sub 2/ interface plays a significant role on the control of the gate stacks' WF. The density of these interfacial bonds and the related work function changes are correlated to the degree of nucleation of the TiN film on the dielectric.     

Application of MoSi/sub 2/ to the Double-Level Interconnections of I/sup 2/L Circuits

A new MoSi/sub 2/-CVD-Al double-level interconnection system is developed to obtain a high packing density in I/sup 2/L circuits. Taking advantage of MoSi/sub 2/, a fine pattern consisting of a Iinewidth of 2.5 /spl mu/m aid a spacing of 1 /spl mu/m is achieved for the first-level interconnections. This new system has a higher reliability than the normaf Al-CVD-Al structure because of the stability of the MoSi2 surface. The fundamental properties of 1/sup2/L gates with MoSi2 interconnections, namely, gain, propagation delay time, and toggle frequency of a T flip-flop, are measured. At practical injector currents, they show nearly the same values as with Al interconnectiorm The resistance effects of MoSi/sub 2/ interconnections are calculated with regard to the unbalance of the injector currents and increase of the propagation delay time. The calculations show that these effects can be ignored at an injector current of 1 /spl mu/A/gate. At higher injector currents, the MoSi/sub 2/ interconnection resistance must be taken into account in I/sup 2/L pattern layout.     

Impedances of an Elliptic Waveguide (For the /sub e/H/sub 1/ Mode)

The power-voltage, power-current and voltage-current impedances for the elliptical waveguide for the fundamental mode (/sub e/H/sub 1/ mode) are obtained by two different methods. The first method consists of using the exact fields inside a perfectly conducting elliptical pipe. Numerical results were obtained by numerical integration of the integrals involving Mathieu functions by the Gaussian Quadratures method by a digital computer. In the second method approximate fields which satisfy the boundary conditions were used. By this approximate method, actual expressions for the impedances are obtained as a function of minor to major diameter ratio with no need of numerical integration. The actual expressions for the impedance obtained by the approximate method give the impedance for elliptical waveguide within six per cent. On the basis of comparison with the exact numerical solution the expressions for the approximate impedance give the impedance of elliptical waveguide within three per cent if they are scaled by 1.03.