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Numerical Methods For Partial Differential Equations

The Physics of Low-dimensional Semiconductors: An Introduction; J.H. Davies, Cambridge University Press, UK, ISBN 0-521-48491-X, $44.95

In this Letter we present the electrical and electro-optical characterization of single crystalline germanium nanowires (NWs) under tensile strain conditions. The measurements were performed on vapor–liquid–solid (VLS) grown germanium (Ge) NWs, monolithically integrated into a micromechanical 3-point strain module. Uniaxial stress is applied along the ⟨111⟩ growth direction of individual, 100 nm thick Ge NWs while at the same time performing electrical and optical characterization at room temperature. Compared to bulk germanium, an anomalously high and negative-signed piezoresistive coefficient has been found. Spectrally resolved photocurrent characterization on strained NWs gives experimental evidence on the strain-induced modifications of the band structure. Particularly we are revealing a rapid decrease in resistivity and a red-shift in photocurrent spectra under high strain conditions. For a tensile strain of 1.8%, resistivity decreased by a factor of 30, and the photocurrent spectra shifted by 88 meV...

Tuning the Electro-optical Properties of Germanium Nanowires by Tensile Strain

Due to resource constraints in wireless sensor networks and the presence of unwanted conditions in communication systems and transmission channels, the suggestion of a robust method which provides battery lifetime increment and relative security is of vital importance. This paper considers the secure communication in wireless sensor networks based on new robust adaptive finite time chaos synchronization approach in the presence of noise and uncertainty. For this purpose, the modified Chua oscillators are added to the base station and sensor nodes to generate the chaotic signals. Chaotic signals are impregnated with the noise and uncertainty. At first, we apply the modified independent component analysis to separate the noise from the chaotic signals. Then, using the adaptive finite-time sliding mode controller, a control law and an adaptive parameter-tuning method is proposed to achieve the finite-time chaos synchronization under the noisy conditions and parametric uncertainties. Synchronization between the base station and each of the sensor nodes is realized by multiplying a selection matrix by the specified chaotic signal which is broadcasted by the base station to the sensor nodes. Simulation results are presented to show the effectiveness and applicability of the proposed technique.

Secure communication in wireless sensor networks based on chaos synchronization using adaptive sliding mode control

The international technology roadmap of semiconductors (ITRS) is approaching the historical end point and we observe that the semiconductor industry is driving complementary metal oxide semiconductor (CMOS) further towards unknown zones. Today's transistors with 3D structure and integrated advanced strain engineering differ radically from the original planar 2D ones due to the scaling down of the gate and source/drain regions according to Moore's law. This article presents a review of new architectures, simulation methods, and process technology for nano-scale transistors on the approach to the end of ITRS technology. The discussions cover innovative methods, challenges and difficulties in device processing, as well as new metrology techniques that may appear in the near future.

State of the Art and Future Perspectives in Advanced CMOS Technology.

In this work we present an analysis of frequency response of Si-Si0.12Ge0.73Sn0.15/Si0.11Ge0.73Sn0.16 n-p-n mid-infrared transistor laser (TL) with strain balanced Ge0.85Sn0.15 quantum well (QW) in the base. The frequency response of TL for common base (CB) configuration is calculated from small signal relationship between the photon density (s(jω)) and emitter current density ( je(jΩ)) by solving laser rate equation and continuity equation considering the virtual states as a conversion mechanism. The intrinsic response of TL with and without quantum capture and escape effect of carriers on modulation bandwidth are also shown. Further, bandwidth of TL in CB configuration is obtained as ~4.5 GHz at 2 mA bias current with zero resonance and it increases with larger escape time and reduced capture time of carrier in QW.

Analysis of carrier dynamic effects on frequency response of tin incorporated group-IV alloy-based transistor laser

In this work, a mathematical model has been developed to analyze the effect of the number of quantum dot layers on the performance of solar cells. We have developed an analytical expression to obtain the spectral response and conversion efficiency of p-i-n solar cells with multi-layer interdiffused InGaAs quantum dots embedded in the GaAs matrix. Each layer consists of lens-shaped quantum dots having a non-homogenous composition due to interdiffusion. The comparative analysis of as-grown and interdiffused dots shows that neglecting the effect of interdiffusion leads to an overestimation of the photocurrent density of a solar cell. According to this study, including QDs layers increases the EQE toward longer wavelengths, increasing the short circuit density. However, a trade-off is observed between the photocurrent and open circuit voltage on increasing the number of quantum dot layers. In the proposed model, we have incorporated the impact of interdiffusion to predict the photocurrent density and open-circuit voltage of realistic-shaped quantum dot-based solar cells. In addition, the effect of spacer layer thickness on photocurrent density has also been discussed. The computed values were reasonably consistent with the reported experimental data. 

Efficiency enhancement of solar cells using multi-layer interdiffused InGaAs/ GaAs quantum dots: A numerical approach

A challenging task in wireless sensor network (WSN) is to deliver authentic data between source nodes and sink nodes. The collision or dead lock occurs when two or more close nodes are attempted to send data at the same time to the others node. To avoid such dead lock situation in the network we propose a nonlinear mathematical model. The effect of nonlinearity often renders a periodic solution unstable for certain parametric choices even a very small change in initial conditions can lead to different result in chaotic systems which appears to exhibit chaos for a range of parametric values when long time behavior studied. The local stability conditions for the system have been discussed and analyzed. Numerically simulations have been carried out to study the complex behavior of the system for reasonable ranges of parameters in WSN.

Energy-Aware Chaotic Communication in Wireless Sensor Network

The dependency of effective free carrier lifetime on the lateral dimensions of the Silicon on Insulator (SOI) p-i-n optical rib waveguide has been demonstrated Effect of reverse bias on the same is also studied Since carrier generation through two photon absorption is omnipresent in Si, the lifetime of the free carriers plays an important role in determining the net achievable Raman gain in SOI waveguides as it affects nonlinear absorption loss due to free carriers A detailed analytical model has been derived for the assessment of effective lifetime of free carriers in reverse bias condition in various geometrical features of the waveguide

http://ieeexplore.ieee.org/iel7/6723859/6733445/06733555.pdf

Effect of geometry and reverse bias on free carrier lifetime in p-i-n structured optical rib waveguide

This work investigates performance of strain balanced SiGeSn/GeSn multi quantum well infrared photodetector by numerical analysis. Expression of responsivity is obtained by solving rate equation and continuity equation at steady state considering carrier transport mechanism across multiple well-barrier interfaces. The result shows a significant responsivity is achieved in mid-IR wavelength region which further increase on with no. of wells. Responsivity is also studied under variation of Sn content in quantum well.

Mukul K. Das

Papers

Analysis of carrier dynamic effects on frequency response of tin incorporated group-IV alloy-based transistor laser

Efficiency enhancement of solar cells using multi-layer interdiffused InGaAs/ GaAs quantum dots: A numerical approach

Energy-Aware Chaotic Communication in Wireless Sensor Network

Effect of geometry and reverse bias on free carrier lifetime in p-i-n structured optical rib waveguide

Numerical analysis of tin incorporated group IV alloy based MQWIP