Time Domain and Nyquist Analysis of InGaAs-GaAs Semiconductor Self-Assembled Quantum Dot Lasers Based on Transfer Matrix Method

AAbstract: Transfer function of the InGaAs/GaAs SAQD laser is calculated using its rate equations. Using the calculated transfer function, time and frequency analysis can be implemented completely. In the time domain, the calculated transfer function can show the transient and steady state response of the laser. Also this transfer function can be used in circuit simulator such as SPICE in order for analyzing the electro-optical VLSI circuits. After the calculation of the transfer function, time domain together with Nyquist responses has been calculated. The effect of carrier dynamics on the output response of the laser is analyzed in this case. Nyquist diagram is selected in this analysis because one can predict the closed loop system using the open loop system. Unlike the systems such as interconnects and transistors that are analyzed before, the results reveal that in SAQDLs, the ratio of the transient peak overshoot in the output power to stable output power is very large. Accordingly in integrated circuits that use SAQDLs, amplification of each overshoots in output power of the laser can deteriorate the input of the next circuit module on the chip or shock to it. This increases the importance of the stability analysis in SAQDLs for more reliability

Vacancy Defects Induced Magnetism in Armchair Graphdiyne Nanoribbon

Spin-polarized electronic and transport properties of Armchair GraphdiyneNanoribbons (A-GDYNR) with single vacancy (SV), two types of configurations fordouble vacancy (DV1, DV2) and multi vacancy (MV) defects are studied by nonequilibriumGreen’s function (NEGF) combined with density functional theory (DFT).The results demonstrate that the A-GDYNR with the SV has the lowest formationenergy and the most energetically favorable. The SV induces a 2.08 μB magneticmoment while the DV2 possess no magnetism into A-GDYNR. Analyzing the bandstructures shows that the perturbation in A-GDYNR caused by the SV, DV1 and MVbreaks the degeneracy and appears new bands around the Fermi level which indicate astrong spin splitting. Moreover, using density of states (DOS) analysis, it is illustratedthat the appeared flat bands correspond to the localized states which mainly contributeby the carbon atoms near the vacancies. The calculated current-voltage characteristicsfor A-GDYNR with the SV, DV1, and MV reveal that the spin degeneracy is obviouslybroken. As well, a high spin-filtering efficiency around 90% is found at the bias voltageof 0.3V for A-GDYNR with the SV. Our findings illustrate that we can obtain AGDYNRswith especial magnetic properties by removing carbon atoms from AGDYNR

Design of seamless graphene inverter together with its transfer matrix modeling

Abstract: A seamless graphene inverter including graphene nanoribbon field effect transistor (GNRFET) and graphene interconnect is proposed. The seamless structure is suggested to eliminate the ohmic, schottky, and parasitic resistances in the junction of the traditional interconnects with the Gate, Source and Drain of GNRFET. After that, using the circuit models of the graphene devices that are used in the proposed structure, transfer matrix model of the proposed seamless graphene inverter is calculated and extracted. All of the capacitive, inductive and scattering effects are included in the assumed circuit models of the GNRFET - graphene interconnect and consequently in the overall matrix model of the seamless graphene inverter. Elimination of the ohmic, schottky and parasitic resistances causes to improve in the working speed of the proposed inverter. Extraction of the transfer matrix model of the seamless graphene inverter and calculation of its step time response, relative stability and frequency bandwidth confirms this improvement. The advantage of the transfer matrix model of the proposed inverter is that any change in the physical parameters of the graphene nanoribbons that are used in the structure can be included in the model and one can analyze the effect of it in all of the technology nodes. Using the circuit model and the extracted transfer matrix, anyone can evaluates various stability analyses such as Nyquist, Bode and Nichols together with the time-frequency responses of the graphene seamless inverter used in very large scale integrated (VLSI) circuits

Electronic Conductance Modulation of Armchair Graphyne Nanoribbon by Twisting Deformation

Abstract  The electronic and transport properties of armchair α-graphyne nanoribbons (α-AGyNRs) are studied using density functional theory with non-equilibrium Green function formalism. The α-AGyNRs are considered with widths N = 6, 7 and 8 to represent three distinct families behavior  in presence of twisting. The band structure, current-voltage characteristic, transmission spectra, molecular energy spectrum, molecular projected self-consistent Hamiltonian (MPSH), and transmission pathways are studied for α-AGyNRs with θ= 0º, 30º, 60º and 90º. The results indicate that 6 and 7 α-AGyNRs devices are semiconductor, while 8 α-AGyNR device has metallic character. Moreover, these behaviors are preserved by applying the twist. Our theoretical study shows that the electronic  conduction of α-AGyNRs can be tuned by twisted deformation. The maximum modulation of conductance at 1.2 V is obtained 69.94% for 7 α-AGyNR device from θ=0º to θ=90º. The investigation of MPSH demonstrates that distribution of charge density get localized  on twisting sites which impact on the electron tunneling across the scattering region

Circuit model and transfer matrix model of mixed multiwall carbon nanotube interconnects-

Using multi transmission line (MTL) model, a compact circuit model for mixed multiwall carbon nanotube (MMWCNT) interconnects is proposed. Using the proposed circuit model, an algorithmic model is proposed for calculating the transfer matrix of these interconnects. In the proposed circuit model and also algorithmic model, capacitive, inductive and tunneling effects between the carbon layers is considered. Moreover the concept of distributed circuit block parameters is proposed for this type of interconnects. This model is compact because it can be used in wide range and technology of interconnects. Also using this model, any change in the physical parameters of the nanotubes can be considered in the circuit model and algorithmic model. Using the circuit model and algorithmic model one can calculate various stability and time domain responses for MMWCNT interconnects in VLSI circuits. In this paper after proposing the circuit model and algorithmic model, we have calculated step time response and Nyquist response of MMWCNT interconnects. The results show that by increasing the length and diameter of the tubes, the delay of the interconnects is increased and its stability is increased too

Introduction of the structure, modeling and analysis of junctionless heterostructure Si/Si1-xGex transistor

In Junctionless transistors, the source-channel-drain doping is of the same type and level, hence, the process of making Junctionless transistors is easier than inverting mode transistor. Despite this benefit, reducing the transconductance of Junctionless transistors due to reduced carrier velocity makes the operation of this type of transistor difficult for analog, radio frequency and high frequency noise usages. An effective method that increases the trans-conductance of Junctionless transistors without reducing efficiency is using a heterogeneous structure in the channel. In the present article, using Si and Si1-xGex materials in the channel is proposed and modeled so as to enhance the transconductance of Junctionless transistor. The special structure of the proposed transistor, called JL-Si / Si1-xGex, eliminates the intervalley scattering between valleys of ∆2 and ∆4. This increases the velocity of the electron and consequently enhances the transconductance. The outcomes of the modelling of the proposed JL-Si / Si1-xGex heterostructure transistor indicate the maximum transconductance of 2.5 mS / um, which increases 50% compared to similar silicon transistor. Moreover, calculations which are extracted from modelling demonstrate that the proposed JL-Si / Si1-xGex transistor has a unity gain cutoff frequency of 750 GHz, minimum noise figure of 65.0 dB, and an available gain of 28.5 dB. The parameters of cut-off frequency, minimum noise figure and available gain of the proposed JL-Si / Si1-xGex transistor have been improved by 34%, 62.5% and 53%, respectively, compared to the JL-Si transistor with similar dimensions. The proposed device can be suitable candidate for RFIC applications