Sharif Digital Repository

We compare noise characteristics of Al0.3Ga0.7N /GaN/ Al0.06Ga0.94N/GaN DC-HEMT and Al0.3Ga 0.7N /GaN HEMT. The DC-HEMT exhibits high gain and high current and low noise. The noise characteristics are calculated as a function of gate voltage as well as drain voltage. The noise curve versus gate voltage also shows three regions. And also the noise curve versus drain voltage shows two regions. The first region is related to the triode region of the transistor where the noise decreases with increase of the drain voltage. The second region is related to the saturation region of the transistor where the noise is almost constant  

In this article, we have used quantum and semiclassical models to analyse the electrical characteristics of gate all around silicon nanowire transistor (GAA SNWT). A quantum mechanical transport approach based on non-equilibrium Green's function (NEGF) method with the use of mode space approach in the frame work of effective mass theory has been employed for this analysis. Semiclassical drift diffusion mode space (DDMS) approach has also been used for the simulation of GAA SNWT. We have studied the short-channel effects on the performance of GAA SNWT and evaluated the variation of the threshold voltage, the subthreshold slope (SS), the leakage current and the drain-induced barrier lowering... 

In this paper we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analysis is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporates the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

In this paper, a method of determining physical dimension of Double Barrier Quantum Well (DBQW) of Resonance Tunneling Diodes (RTDs) is presented by using I-V characteristic governing on them. In this procedure, first we have used performance metrics related to RTDs I-V characteristic such as Peak to Valley Current Ratio (PVCR), peak current density (JP), valley current density (JV) and Voltage Swing (VS), and by some other arbitrary points, we have fitted a curve to the RTD current-voltage equation by MATLAB software. Then we have obtained the physical parameter of I-V equation and adjusted some of them with modification coefficients. Next, by choosing the material of barriers and the well... 

A Gate All Around Nanowire Transistor (GAA NWT) which employs source heterojunction and strained channel is proposed which improves device characteristics. A quantum mechanical transport approach based on nonequilibrium Green's function (NEGF) method in the frame work of effective mass theory is employed in this analysis. We evaluate the variation of the threshold voltage, the subthreshold slope, ON and OFF state currents when channel length decreases. It is shown that the source heterojunction strained channel GAA NWT gives high performance transistors values of the scaled transconductance and ON current that are greater than conventional silicon GAA NWT. Furthermore, comparison of... 

In this paper by solving Dirac equation, we present an analytical solution to calculate energy levels and wave functions of mono- and bilayer graphene quantum dots. By supposing circular quantum dots, we solve Dirac equation and obtain energy levels and band gap with relations in a new closed and practical form. The energy levels are correlated with a radial quantum number and radius of quantum dots. In addition to monolayer quantum dots, AA- and AB-stacked bilayer quantum dots are investigated and their energy levels and band gap are calculated as well. Also, we analyze the influence of the quantum dots size on their energy spectrum. It can be observed that the band gap decreases as quantum... 

In this paper, we perform self-consistent field relaxation and electronic structure calculations of tetragonal B3N3 based on density functional theory, using LDA pseudopotential in the pressure range between − 30 and + 160 GPa. Although metallic B3N3 has a honeycomb structure, according to the electronic band structure, it has bulk properties (not layered) with effective mass non-interacting electron gas behavior near Fermi level (not Dirac massless) and a small anisotropy, about 0.56 in effective mass in the direction of MA relative to XM. Electronic calculations of the B3N3 under pressure show that increasing positive pressure causes the decrease of Fermi energy and total electronic... 

We investigate hot spot effects on increasing THz emission of the frequency modes in a square mesa structure with constant hot spot size in different positions, without applying magnetic field. We show that in the presence of hot spot at any position, the average of emitted power intensity level is increased. The frequency modes that the position of their field concentration is more matched with hot spot position are more excited. Accordingly, in the case with hot spot located at center of a-axis or b-axis, frequency modes TM(m,n) with even indices m or n is more excited and in the case in which hot spot is located at the corner of a-axis or b-axis, frequency modes TM(m,n) with odd indices m... 

This article presents a novel armchair graphene nanoribbon (AGNR) field-effect transistor with engineered nanopores for resonant tunneling. Two rectangular nanopores are punched to create two potential barriers and one quantum well. Channel and source and drain contacts are AGNR, indicating structure homogeneity. Nonequilibrium Green's function and Poisson's equations are used for structural analysis. The input variables are well width (WW), drain voltage (VD), and barrier width (BW). The effects of repositioning nanopores and AGNR type (i.e., semiconductor and semimetal) are also studied. The impact of the parameters on the density of states, transmission probabilities, peak current (IP)... 

For the first time, we present self-consistent solution of ultrathin body device structures to investigate the device parameters variation on the characteristics of nanoscale MOSFET. Our two dimensional (2-D) device simulator Is based on Nonequlibrium Green's Function (NEGF) forma lism. Starting from a basic structure (DG-MOSFET) with a gate length of 10 nm, variation of gate length, channel thickness, gate oxide parameters was carried out in connection with the numerical calculation of device characteristics. In this work Quantum transport equations are solved in 2-D by NEGF method in active area of the device to obtain the charge density and Poisson's equation is solved in entire domain of... 

The comprehensive optical-electrical-gain-thermal self-consistent model of the 1.55 μm AlGaInAs Photonic Crystal vertical cavity surface emitting diode lasers (PhC VCSELs) with buried tunnel junction (BTJ) has been applied to optimize its threshold characteristics. It shows that, for 5 μm devices, the room temperature (RT) threshold current equal to only 0.59 mA and maximum operating temperature equal to as much as 380 K. Results suggest that, the 5 μm AlGaInAs PhC VCSELs seem to be the most optimal ones for light sources in high performance optical communication systems  

We present an analytical model to analyze the influence of carrier dynamics on the static and dynamic responses of transistor laser (TL). Our analysis is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. We show that the details of the dc and small signal behavior of transistor lasers are strongly affected by the escape and capture times of carriers in quantum well (QW). Also, the effects of carrier recombination lifetime in the quantum well and base regions on the TL static and dynamic performances are investigated  

An equivalent circuit model for the design and analysis of two-section gain lever quantum dot (QD) laser is presented. This model is based on the three level rate equations with two independent carrier populations and a single longitudinal optical mode. By using the presented model, the effect of gain lever on QD laser performances is investigated. The results of simulation show that the main characteristics of laser such as threshold current, transient response, output power and modulation response are affected by differential gain ratios between the two-sections  

We derive the noise equivalent circuit model of semiconductor self-assembled quantum-dot (QD) lasers (SAQDL) from the rate equations including Langevin noise sources. This equivalent circuit allows a straightforward calculation of the noise of an SAQDL combined with electronic components. Using the presented model, we study how the carrier dynamics influences relative intensity noise (RIN) of QD lasers. We demonstrate that RIN is degraded with larger inhomogeneous broadening. Furthermore, we show that RIN is enhanced for lower quantum-dot coverage level  

In this paper, for the first time, we present a semiclassical noise model for InAs/GaAs quantum dot (QD) laser considering two photon modes, i.e., ground and first excited states lasing. This model is based on the five level rate equations. By using this model, the effect of temperature variations on relative intensity noise (RIN) of QD laser is investigated. We find that the RIN significantly degrades when excited state (ES) lasing emerges at high temperature. Furthermore, we investigate the influence of the quantum dot numbers on the RIN properties  

In this paper, a silicon-on-insulator (SOI) p-n-p-n tunneling field-effect transistor (TFET) with a silicon doped hafnium oxide (Si:HfO2) ferroelectric gate stack is proposed and investigated via 2D device simulation with a calibrated nonlocal band-to-band tunneling model. Utilization of Si:HfO2 instead of conventional perovskite ferroelectrics such as lead zirconium titanate (PbZrTiO3) and strontium bismuth tantalate (SrBi2Ta2O9) provides compatibility to the CMOS process as well as improved device scalability. By using Si:HfO2 ferroelectric gate stack, the applied gate voltage is effectively amplified that causes increased electric field at the tunneling junction and reduced tunneling... 

In this paper, a three-dimensional (3D) analytical solution of the electrostatic potential is derived for the tri-gate tunneling field-effect transistors (TG TFETs) based on the perimeter-weighted-sum approach. The model is derived by separating the device into a symmetric and an asymmetric double-gate (DG) TFETs and then solving the 2D Poisson’s equation for these structures. The subthreshold tunneling current expression is extracted by numerical integrating the band-to-band tunneling generation rate over the volume of the device. It is shown that the potential distributions, the electric field profile, and the tunneling current predicted by the analytical model are in close agreement with... 

Nanoscale Shielded channel transistors are investigated by solving the two-dimensional Poisson equation self-consistently with ballistic quantum transport equations for first time. We present self-consistent solutions of ultrathin body device structures to investigate the effect of electrically shielded channel region which impose charge controlling in the channel region on the characteristics of nanoscale DG-MOSFET. The simulation method is based on Nonequlibrium Green's Function (NEGF). Starting from a basic structure with a gate length of 10 nm, the effect of gate length variation on the performance of the device has been investigated. © 2007 IEEE  

In this paper the electrical characteristics of a novel nanoscale double-gate MOSFET (DG-MOSFET) have been investigate by a full Quantum Mechanical simulation framework. This framework consists of Non-Equilibrium Green's Function (NEGF) solved self-consistently with Poisson's Equation. Quantum transport equations are solved in two-dimension (2-D) by recursive NEGF method in active area of the device to obtain the charge density and Poisson's equation is solved in entire domain of simulation to get potential profile. Once self-consistently achieved all parameters of interest (e.g. potential profile, charge density, DIBL, etc) can be measured. In this novel DG-MOSFET structure, a front gate... 

APS (3-Aminopropyl) trimethoxysilane) and APhS (p-Aminophenyl) trimethoxysilane) are the most commonly used linkers on a silicon surface. We investigate the surface properties of the structures, including APS or APhS on a silicon substrate. The studied structures consist of APS or APhS linkers with one, two, or three bonds with a substrate, which is a thin layer of Si with crystal orientation 〈1 0 0〉 or 〈1 1 1〉. Using a first-principles study based on density functional theory (DFT), we investigated the electronic and optical properties of the silicon-linker interface, such as interface states, orbital location, dielectric function, and photon absorption. The effects of linker type, number...