R. Ragi

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.

An Explicit Quantum-Mechanical Compact Model for the I-V Characteristics of Cylindrical Nanowire MOSFETs

In this paper, we developed an analytical quantum-mechanical model for the I-V characteristics of cylindrical nanowire junctionless MOSFETs. Our compact model is based on the Landauer formalism to describe the ballistic current transport, as well as in a novel approach to solve the coupled Schrödinger and Poisson equations, in which the radial potential distribution is described as a perturbed harmonic oscillator potential. This approach reduces the complexity of the model derivation and provides an analytical expression for the eigenenergies within the quantum wire. As a consequence, our simplified model takes into account the relevant quantum effects arising from the cylindrical carried confinement but provides explicit and easy to handle expressions for the device characteristics. The proposed model is validated in comparison to available experimental results, with agreement equivalent to much more complex approaches.

I-V characteristics of Schottky contacts based on quantum wires

In this paper we derive the I-V characteristics of Schottky contacts based on bulk metal to semiconductor quantum wires interfaces. The obtained results show that quantum confinement is a strong reduction of the reverse saturation current when compared to conventional Schottky contacts. Numerical simulations are carried out to highlight the advantages of using these proposed heterodimensional interfaces in applications involving low-noise photodetectors and low-leakage gate electrodes.

Modeling the C-V Characteristics of Heterodimensional Schottky Contacts

Abstract This paper addresses the capacitance-voltage (C-V)characteristics of heterodimensional Schottky diodes, inwhich the Schottky metal is placed in direct contact toa two-dimensional electron gas and the confinedelectron behavior directly dictates the deviceperformance. We develop a novel quasi-2D model forthe C-V characteristics of the device, by starting from aself-consistent solution of the Schrodinger and Poissonequations in the growth direction. The model isvalidated by contrasting the theoretical results withexperimental data from an AlGaAs/GaAs devicefabricated in our laboratory. 1. Introduction The properties of electrons in an inversion layerhave attracted interest since the 1930’s, when Lilienfeldconceived the field-effect transistor. Further attentionhas been motivated by the enhanced transport propertiesof the two-dimensional electron gas (2-DEG) formed atmodulation doped heterointerfaces, where the inversionlayer isquantized in the growth direction. Already inthe early 90’s High Electron-Mobility Transistors(HEMTs) based on this principle displayed poweramplification well above 100 GHz with outstandingnoise performance.This paper is concerned with devices based on afurther extension of the modulation doping concept byusing heterodimensional interfaces, i.e., interfacesbetween materials of dissimilar dimensions. In ourspecific case, this interface is a Schottky barrier laterallyconnecting a three-dimensional (3D) metal and a two-dimensional (2D) electron gas.In fact, heterodimensional diodes, transistors andphotodetectors present several attractive features such aslow capacitance due to the small effective cross-section,excellent noise and transport characteristics due to the2D electron gas and a high breakdown voltage, makingthem very promising for high-frequency applications [1-2].In order to illustrate the motivation for studyingheterodimensional devices we briefly revisit the questionof computing the thermionic emission current in suchdevices. In fact,straighforward extension of Bethe’stheory, considering both the proper two-dimensionaldensity of states as well as energyquantization in thegrowth direction for a 2-DEG with only onesignificantly populated subband, yields [3]:1 (1)kTqVexpkTEexpkTqJ A* T3 2 exp B

Transistores de alta mobilidade eletrônica (HEMTs): Princípios de operação e características eletrônicas

The teaching of semiconductor devices physics is absolutely fundamental to the development of microelectronics. However, introductory courses in this area are frequently limited to report over-simplified analytical models which allow intuitive understanding, but are unable to capture the full complexity of today’s devices. On the other hand, in more advanced courses, accurate numerical models are developed, but the most intuitive view is sometimes lost. In this work, we seek to contribute in order to allow the beginner to make the connection between the two approaches (numerical vs. analytical modeling). To this end, we have developed a study on the electronic characteristics of High Electron Mobility Transistors (HEMTs), comparing results obtained with a simplified analytical models with those provided by an accurate numerical modeling, based on the finite difference method. The results are compared with available experimental results and the validity conditions for the analytical model are established.

A novel self consistent calculation approach for the capacitance‐voltage characteristics of semiconductor quantum wire transistors based on a split‐gate configuration

Purpose – The purpose of this paper is to develop an efficient numerical algorithm for the self‐consistent solution of Schrodinger and Poisson equations in one‐dimensional systems. The goal is to compute the charge‐control and capacitance‐voltage characteristics of quantum wire transistors.Design/methodology/approach – The paper presents a numerical formulation employing a non‐uniform finite difference discretization scheme, in which the wavefunctions and electronic energy levels are obtained by solving the Schrodinger equation through the split‐operator method while a relaxation method in the FTCS scheme (“Forward Time Centered Space”) is used to solve the two‐dimensional Poisson equation.Findings – The numerical model is validated by taking previously published results as a benchmark and then applying them to yield the charge‐control characteristics and the capacitance‐voltage relationship for a split‐gate quantum wire device.Originality/value – The paper helps to fulfill the need for C‐V models of quan...