Carrier transport across heterojunction interfaces

A general theory is presented to describe the carrier transport across heterojunction interfaces. In matching the boundary conditions at the interface, the conservation of total energy and perpendicular momentum is assumed and the difference of effective masses on two sides of the junction is taken into account. The quantum mechanical transmission coefficient is calculated by a combined numerical and WKB method. Application of the present model to an Al_xGa_1?xAsGaAs N-n heterojunction is performed and it gives rise to rectifying characteristics together with non-saturated reverse current. Comparison with the classical thermionic emission model is made to show the significance of tunneling and effect of quantum mechanical reflection.     

Simulation of quantum transport in monolithic ICs based on In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As RTDs and HEMTs with a quantum hydrodynamic transport model

A new quantum hydrodynamic transport model based on a quantum fluid model is used for numerical calculations of different quantum sized devices. The simulation of monolithic integrated circuits of resonant tunneling structures and high electron mobility transistors (HEMT) based on In/sub 053/Ga/sub 0.47/As-In/sub 052/Al/sub 0.48/As-InP is demonstrated. With the new model, it is possible to describe quantum mechanical transport phenomena like resonant tunneling of carriers through potential barriers and particle accumulation in quantum wells. Different structure variations, especially the resonant tunneling diode area and the gate width of the HEMT structure, show variable modulations in the output characteristics of the monolithic integrated device.     

Double Gate MOSFET Modeling Based on Adaptive Neuro‐Fuzzy Inference System for Nanoscale Circuit Simulation

As the conventional silicon metal‐oxide‐semiconductor field‐effect transistor (MOSFET) approaches its scaling limits, quantum mechanical effects are expected to become more and more important. Accurate quantum transport simulators are required to explore the essential device physics as a design aid. However, because of the complexity of the analysis, it has been necessary to simulate the quantum mechanical model with high speed and accuracy. In this paper, the modeling of double gate MOSFET based on an adaptive neuro‐fuzzy inference system (ANFIS) is presented. The ANFIS model reduces the computational time while keeping the accuracy of physics‐based models, like non‐equilibrium Green's function formalism. Finally, we import the ANFIS model into the circuit simulator software as a subcircuit. The results show that the compact model based on ANFIS is an efficient tool for the simulation of nanoscale circuits.     

Modeling the electrical characteristics of Schottky contacts in low-dimensional heterostructure devices

This paper deals with the modeling of the electronic characteristics of semiconductor devices based on Schottky contacts in low-dimensional systems. For the capacitance-voltage characteristics, a quasi-two-dimensional quantum mechanical model is developed and validated. For the current-voltage characteristics, a unified model is presented, considering both the tunneling as well as the thermionic emission mechanisms. Our theoretical predictions suggest that for photodetection applications the use of these contacts, replacing conventional metal-semiconductor junctions, can reduce the dark current by at least one order of magnitude.     

Characterization and modelling of carrier distribution and gate capacitance in MOS structure inversion layer

Based on the carrier distribution in three-dimensional semi-classical and twodimensional quantum mechanical cases, the concept of surface layer effective density-of-states (SLEDOS) is proposed. Then a simplified method of calculating the band bending and subband energies is employed to investigate quantum mechanical effects (QMEs) in MOS structure inversion layer. The method is unique compared with published methods in its reversed nature of the iteration procedure. It has high efficiency and good convergence characteristics and gives satisfactorily coincident results with rigorous but more complicated selfconsistent calculations. The method is applicable in both quantum mechanical and semi-classical cases. The subband occupation of inversion layer carrier and the two-dimensional density-of-states in semi-classical and quantum mechanical cases are then calculated. QMEs on inversion layer carrier density and surface potential are analysed on the basis of the method. Gate capacitance in the MOS structure inversion region is formulated for both quantum mechanical and semiclassical cases, and QMEs on gate capacitance are analysed.     

A self-consistent two-dimensional model of quantum-wellsemiconductor lasers: optimization of a GRIN-SCH SQW laserstructure

A two-dimensional model for quantum-well lasers that solves, self-consistently, the semiconductor equations together with the complex scalar wave equation is described. It incorporates a position- and wavelength-dependent gain function which is derived from a quantum mechanical calculation. Such a model enables one to predict the characteristics of a quantum-well laser with a minimal number of empirical parameters. The output of the model includes light-current characteristics, the current distribution, and the optical field intensity distribution, obtained simultaneously in the calculation. Examples for modeling GRIN-SCH SQW (graded-index separate confinement heterostructure single quantum well) ridge wave guide lasers are given, and good agreement with experimental results is obtained. The model is used to optimize the geometry of a GRIN-SCH SQW laser for minimum threshold current and maximum efficiency     

A comparative study for quantum transport calculations of nanosized field-effect transistors

This article presents a comparative study on quantum mechanical frameworks between the widely used local Quasi-Fermi Level (QFL) model and a recently developed top of the barrier splitting (TBS) model. Both models are based on an atomistic quantum mechanical solver using the linear combination of bulk band method (LCBB). The QFL model uses the local Quasi-Fermi Level to represent the local equilibrium and calculate the occupied charge density as well as the current flow along the channel. The TBS model extracts scattering state information from the stationary solution of the system, then calculates the charge density as well as the ballistic and tunneling current. Using these two models, the 10 nm and 22 nm double-gate ultra-thin-body structures are simulated. Comparisons in occupied charge densities, self-consistent potentials as well as the I–V characteristics between these two models are presented. It is found that the QFL model significantly overestimate the subthreshold charge density inside the channel, as well as the current, while it works fine in the ON state of the device. It is also found that the results from both QFL and TBS models tend to coincide with each other as the drain bias approaching zero.     

Analytical computation of electrical parameters in GAAQWT and CNTFET with identical configuration using NEGF method

A two-dimensional quantum mechanical model is presented for calculating carrier transport in ultra-thin gate-all-around quantum wire transistor (GAAQWT) and carbon nanotube field effect transistor (CNTFET) using coupled mode space approach. Schrödinger and Poisson’s equations are self-consistently solved involving Non-Equilibrium Green’s Function (NEGF) formalism under the ballistic limit along with dissipative effects in terms of self-energy at both the source and drain ends. Effect of structural parameters on drain current, channel length modulation parameter, quantum capacitance, transconductance, subthreshold swing (SS) and drain induced barrier lowering (DIBL) are studied assuming occupancy of only a few lower sub-bands, where comparison is performed taking all other factors, biases and dimensions identical. High-k dielectric (HfO₂) independently surrounding the quantum wire (GaAs) and carbon nanotube shows higher drain current and transconductance for GAAQWT but lower quantum capacitance than that obtained for CNTFET. A smaller variation of CLM for CNFET speaks in favour of it for digital quantum circuit applications, whereas GAAQWT is suitable candidate for low-power applications. Effect of structural parameters is investigated within fabrication limit to analyse the effect on electrical characteristics under lower biasing ranges.     

Influence of internal mechanical stresses on the characteristics of GaAs light-emitting diodes

A systematic investigation of the influence of internal mechanical stresses on the characteristics of gallium arsenide light-emitting diodes (LED’s) is performed. The LED structures are grown by liquid-phase epitaxy from a confined volume of a melt based on a solution of GaAs in Ga. The melt is doped with silicon or with silicon and tin. It is shown that the magnitude and sign of the internal mechanical stresses in the epitaxial layer are determined by the impurity concentration in the melt. The LED’s fabricated from epitaxial structures with the smallest internal mechanical stresses have the greatest quantum efficiency and the slowest rate of degradation of their parameters. A model of the reorganization of the defect structure of gallium arsenide, which describes the observed phenomena, is proposed. Fiz. Tekh. Poluprovodn. 32, 1393–1398 (November 1998)     

A comparative study of NEGF and DDMS models in the GAA silicon nanowire transistor

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 (DIBL) when channel length gets shorter. The results showed that quantum mechanical effects increase the threshold voltage and decrease the leakage current, whereas it has also an impact on the SS and DIBL. We have also investigated the effects of high-κ materials as gate dielectric on the device performance.     

Modeling of GaAs/AlGaAs MODFET inverters and ring oscillators

Detailed understanding of the MODFET inverter chains is lacking and present designs are based on ground rules developed by trial and error. We developed a simple and straightforward model for the current-voltage characteristics using results from numerical solutions of the quantum mechanical problem; this model agrees very well with experimental results obtained in our laboratory. High-frequency gate capacitance voltage characteristics for a wide gate voltage range was modeled for the first time in a similar fashion. These models were used to simulate a chain of inverters at 77 and 300 K for a wide range of supply voltage and load current. The maximum device speed is obtained for small supply voltages, ≤ 1 V both at 300 and 77 K, where the effects of transconductance degradation and large gate capacitance are minimized. The devices exhibit under 10-ps switching times both at 300 and 77 K, with 77 K logic swing being much larger. The results are in qualitative agreement with the reported experimental results.     

一种新的MOS结构量子化效应修正模型

从载流子在 MOS结构反型层内的经典分布和量子化后的子带结构出发 ,提出了经典的和量子化的表面有效态密度 (SL EDOS:Surface layer effective density- of- states)的概念。利用表面有效态密度的概念建立了经典理论框架和量子力学框架内的电荷分布模型。该模型包含了强反型区表面电势的变化对载流子浓度的影响 ,具有很高的计算效率和稳定性。在模型基础上 ,研究了量子化效应对反型层载流子浓度和表面电势的影响。     

Quantum mechanical effects on noise properties of nanoelectronic devices: application to Monte Carlo simulation

A discussion about the quantum mechanical effects on noise properties of ballistic (phase-coherent) nanoscale devices is presented. It is shown that quantum noise can be understood in terms of quantum trajectories. This interpretation provides a simple and intuitive explanation of the origin of quantum noise that can be very salutary for nanoelectronic engineers. In particular, an injection model is presented that, coupled with a standard Monte Carlo algorithm, provides an accurate modeling of quantum noise. As a test, the standard results of noise in tunneling junction devices are reproduced within this approach.     

Gain in injection lasers based on self-organized quantum dots

The analytical form of the dependence of the gain on pump current density for lasers with an active region based on self-organized quantum dots is derived in a simple theoretical model. The proposed model is shown to faithfully describe experimental data obtained for laser diodes based on InGaAs quantum dots in an AlGaAs/GaAs matrix, as well as InAs quantum dots in an InGaAs/InP matrix. The previously observed gain saturation and switching of the lasing from the ground state to an excited state of the quantum dots are studied. The influence of the density of quantum-dot arrays on the threshold characteristics of lasers based on them is examined on the basis of this model. Fiz. Tekh. Poluprovodn. 33, 215–223 (February 1999)     

超导电路与体声波谐振器组成的量子iSWAP门方案

高保真度量子门的物理实现是量子计算和量子通信的关键技术之一。根据电路量子声动力学和量子电动力学,提出了由两个具有较长相干时间的超导transmon qubit和一个具有高机械品质因数的薄膜体声波谐振器组成的量子门方案,体声波谐振器起到类似微波光子通道的作用,使两个transmon qubit之间实现量子态交互。该文先用Butterworth van Dyke模型分析体声波谐振器在方案中的等效电路,构建系统的量子化哈密顿量,再用二能级原子 声子混合量子态形式编码系统的量子态,通过调节外磁场来调控系统的输入态,系统的输出态可通过测量模块得到。在Jaynes Cummings模型下,该系统能完成具有高保真度的量子相位交换（iSWAP）门操作。     

Experimental realization of a new transistor

The authors report on the fabrication and characteristics of a unipolar, three-terminal, resonant-tunneling transistor. The operating principle of this new transistor is based on the fact that the quantum mechanical resonant-tunneling probability of hot electrons between the emitter and the collector is switched almost completely on and off, when either the base or the collector bias is swept. The emitter injects hot electrons to the second lowest subband of a thin (100 Å in this work) GaAs quantum well. Subsequently, the hot electrons will either resonantly tunnel to the collector, or relax to the lowest subband and contribute to the base current. As a result of resonant transmission, at 77 K the current-voltage characteristics of the transistor display negative differential resistance with extremely large (4691) peak-to-valley ratio. Furthermore, when biased near resonance, a maximum DC current gain of ~1.2 and a maximum AC current gain of ~11.9 were observed. The first use of a new `tunneling-in and tunneling-out' scheme in contacting a thin quantum well is also demonstrated     

Multidimensional Modeling of Nanotransistors

In this paper, we review our recent work using the nonequilibrium Green's function method to model nanotransistors. After presenting a motivation for the need of quantum mechanical modeling, an account of the equations and implementation is given for both 1-D and 2-D modeling. Examples are given to highlight the use of the developed models. Finally, possible future directions in quantum mechanical modeling of transport in nanotransistors are highlighted along with computational challenges.     

GCS法及多晶区量子效应的集约建模

提出了一种新的建立集约模型的方法,即栅电容修正法.此方法考虑了新型效应对栅电压的依赖关系,且可以对各种效应相对独立地建模并分别嵌入模型中.另外,利用该方法和密度梯度模型建立了一个多晶区内量子效应的集约模型.该模型与数值模拟结果吻合.模型结果和模拟结果均表明,多晶区内的量子效应不可忽略,且它对器件特性的影响与多晶耗尽效应相反.     

GCS法及多晶区量子效应的集约建模

提出了一种新的建立集约模型的方法,即栅电容修正法.此方法考虑了新型效应对栅电压的依赖关系,且可以对各种效应相对独立地建模并分别嵌入模型中.另外,利用该方法和密度梯度模型建立了一个多晶区内量子效应的集约模型.该模型与数值模拟结果吻合.模型结果和模拟结果均表明,多晶区内的量子效应不可忽略,且它对器件特性的影响与多晶耗尽效应相反.     

Capacitance-voltage study of heterostructures with InGaAs/GaAs quantum wells in the temperature range from 10 to 320 K

Heterostructures with single strained InGaAs/GaAs quantum wells have been studied by measuring the capacitance-voltage characteristics in a wide range of temperatures and test signal frequencies. Based on the analysis of experimental capacitance-voltage characteristics, a temperature shift of the peak in the apparent profile of a majority carrier’s concentration is revealed and a quantitative model of this phenomenon is proposed. The effect of incomplete impurity ionization on the experimentally found quantum well’s charge is determined. It is established by numerical simulation and fitting of capacitance-voltage characteristics that the conduction band’s discontinuity for heterostructures with strained In _x Ga_{1 − x} As/GaAs quantum wells (x = 0.225) remains constant and equal to 172 ± 10 meV at temperatures from 320 to 100 K.