Theoretical Assessment of the Influence of Mesa Size and Shape on the Two-dimensional Electron Gas Properties of AlGaN/GaN Heterojunctions PDF Download
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Author: Jean-Lou Gosselin
Publisher:
ISBN:
Category :
Languages : en
Pages : 137
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Book Description
AlGaN/GaN heterostructure field-effect transistors (HFETs) are strong candidates for high-power and high-frequency applications. Even in the absence of doping, thanks to high polarization fields, often a two-dimensional electron gas (2DEG) of unprecedented concentrations forms at these heterojunctions. Control over this carrier induction process is crucial in achieving normally-off field-effect transistors (i.e., transistors of zero standby power consumption). One way to achieve this is through polarization engineering. Mesa-isolation geometry seemingly offers interesting avenues to reduce the piezoelectric polarization at the heterointerface, and as a result means for polarization engineering. Using a Poisson-Schrödinger self-consistent solver, the effect of strain on the sheet charge density is investigated in the context of one-, two- and three-dimensional simulations of AlGaN/GaN heterostructures. Properties of the two-dimensional electron gas are detailed and the influences of Aluminum mole fraction, AlGaN barrier thickness, GaN cap layer inclusion are investigated. The carrier confinement in the 2DEG is explored in the case of two-dimensional version of the simulations. Through these studies, the effect of shrinking the size of the mesa on lowering the 2DEG concentration is confirmed. Through performing three-dimensional simulations, the effects of cross-sectional geometry on the average sheet charge density and the threshold voltage are presented. It is shown that as the perimeter-to-area ratio is increased, the carrier concentration decreases, and the threshold voltage becomes less negative. Via these studies, the degree of effectiveness of geometry as means for polarization engineering is, for the first time, theoretically quantified.
Author: Jean-Lou Gosselin
Publisher:
ISBN:
Category :
Languages : en
Pages : 137
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Book Description
AlGaN/GaN heterostructure field-effect transistors (HFETs) are strong candidates for high-power and high-frequency applications. Even in the absence of doping, thanks to high polarization fields, often a two-dimensional electron gas (2DEG) of unprecedented concentrations forms at these heterojunctions. Control over this carrier induction process is crucial in achieving normally-off field-effect transistors (i.e., transistors of zero standby power consumption). One way to achieve this is through polarization engineering. Mesa-isolation geometry seemingly offers interesting avenues to reduce the piezoelectric polarization at the heterointerface, and as a result means for polarization engineering. Using a Poisson-Schrödinger self-consistent solver, the effect of strain on the sheet charge density is investigated in the context of one-, two- and three-dimensional simulations of AlGaN/GaN heterostructures. Properties of the two-dimensional electron gas are detailed and the influences of Aluminum mole fraction, AlGaN barrier thickness, GaN cap layer inclusion are investigated. The carrier confinement in the 2DEG is explored in the case of two-dimensional version of the simulations. Through these studies, the effect of shrinking the size of the mesa on lowering the 2DEG concentration is confirmed. Through performing three-dimensional simulations, the effects of cross-sectional geometry on the average sheet charge density and the threshold voltage are presented. It is shown that as the perimeter-to-area ratio is increased, the carrier concentration decreases, and the threshold voltage becomes less negative. Via these studies, the degree of effectiveness of geometry as means for polarization engineering is, for the first time, theoretically quantified.
Author: Hassan Rahbardar Mojaver
Publisher:
ISBN:
Category :
Languages : en
Pages : 129
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Book Description
Since their advent, polar AlGaN/GaN hetero-junction field effect transistors (HFETs) have drawn a great deal of attention especially in high frequency/high power applications. However, the superb prospects of these transistors are affected by a few drawbacks such as aging/crack formation under strain, presence of high gate-leakage, and challenging realization of enhancement-mode (normally-off) devices. Quite recently, study of quaternary AlInGaN barriers has been presented as a promising avenue for fulfilling various design demands including: lattice matching, polarization matching, and positive shifting the inherently negative threshold voltage of AlGaN/GaN HFETs. However, thus far only a limited scope of theoretical studies on AlInGaN/GaN hetero-structure characteristics has been reported. As part of this thesis, the two dimensional electron gas (2DEG) characteristics of gated metal-face wurtzite AlInGaN/GaN hetero-junctions as function of physical and compositional properties of the hetero-junction are theoretically evaluated using the variational method. According to this study, a considerable shift in the positive direction for the threshold voltage of AlInGaN/GaN HFETs can be achieved by engineering both the spontaneous and the piezoelectric polarization (using a quaternary AlInGaN barrier-layer of appropriate mole-fractions). Succeeding this study, a novel quaternary lattice-match layer structure based on employing a bilayer barrier for improving the carrier confinement in the channel of enhancement-mode AlInGaN/GaN HFETs is for the first time proposed. It is shown that while the proposed layer structure substantially improves the carrier confinement in the GaN channel layer, it also upholds the merits of employing a lattice-match barrier towards achieving an enhancement-mode operation. One of the most important device characteristics of AlGaN/GaN HFETs which is often poorly understood is the gate-leakage current. As part of this thesis, reverse gate-leakage of AlGaN/GaN HFETs is studied over a wide range of lattice-temperatures. While unveiling an obscure path for gate leakage through the mesa sidewall, a model considering different leakage paths, including the identified sidewall leakage, is presented. It is illustrated that the sidewall path to the 2DEG is associated with the Poole-Frenkel electron emission. The novel contribution of the present analysis is that it postulates that in absence of absolute uniformity, Fowler-Nordheim (FN) tunneling takes place through only a small portion of the surface of the barrier, which boasts the highest electric field or the smallest Schottky barrier height. This consideration, allows the model to avoid unrealistic values for quantities such as effective electron mass (that has plagued many of the existing models). Also as part of this thesis work, process recipe for microfabrication of submicron gate AlGaN/GaN HFETs using electron beam lithography was developed at McGill's nano-tools micro-fabrication facilities. The results of DC characterization of the fabricated transistors along with the results of the DC stress test are presented.
Author: Aniruddha Dey
Publisher:
ISBN:
Category :
Languages : en
Pages : 54
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Book Description
A Matlab simulation modelling was performed in this project to observe the effects of twodimensional electron gases in Aluminum Gallium Nitride (AlxGa1 -xN) /Gallium Nitride (GaN) based heterojunction. These heterostructures are suitable for high electron mobility transistors and are induced by strong polarization effect. Polarization effect depends on spontaneous charge and piezoelectric charge. An analytical model has been developed to find the piezoelectric charge. In order to determine the sheet carrier charges induced by piezoelectric charge varying the aluminum composition has been computed by Newton iterative method. If Al composition increases in AlGaN, the relaxation factor r(x) of AlGaN layer thickness increases for AlGaN/GaN junction interface. Again, the piezoelectric polarization increases with increase of Al composition, but decreases with the relaxation factor r(x). The evidence of the heterojunction physics has been shown in results and discussions.
Author: Yuxing Ren
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
AlGaN/GaN high-mobility transistor (HEMT) has been attracting people's attention and is proved to have satisfactory performance due to its related properties such as high break-down voltage, high saturation velocity, high frequency, etc. Molecular Beam Epitaxy (MBE) is one of the methods used for growth of high-quality AlGaN/GaN heterostructure with a two-dimensional electron gas (2DEG) in between. The high mobility of the 2DEGs, which is essential for ideal device performance, is determined by the charge density of the 2DEG. It is influenced by not only Al composition and AlGaN thickness, but also by dislocation density and the MBE background impurity. In order to achieve a high mobility, the relationship of mobility and 2DEG charge density is studied systematically on samples with various Al composition and AlGaN thickness grown by plasma-assisted MBE. Hall measurement is adopted for the measurement of 2DEG mobility and corresponding charge density. GaN bulk substrate and GaN template substrate with different dislocation densities are used for MBE growth as a comparison study on the influence of dislocation density. A gate control method is also explored on one specific sample with fixed dislocation density and background impurity to experimentally study the relationship of mobility and 2DEG density. Temperature-dependent Hall measurement is conducted to study transport property at low-temperature where the mobility is mainly limited by dislocation and background impurity rather than phonons. By analyzing the experimental data and comparing with theoretical calculations, the influence of dislocation density and background impurity is explained.
Author: Swaroop Jallipeta
Publisher:
ISBN:
Category :
Languages : en
Pages : 42
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Book Description
The main objective of this graduate project is to develop an analytical model of AlGaN/GaN high electron mobility transistor (HEMT) device for studying the sheet carrier density in the quantum well and cut-off frequency. This analytical model has been developed by using Matlab. The sheet carrier density in the triangular quantum well has been evaluated by the influence of layer thickness of the doped AlGaN and AlN spacer layer as well as the gate-source biasing to understand the quality of heterojunction and carrier transport. The cut-off frequency has been computed to study the effect of channel length on RF performance of the device. The graduate project constitutes the introduction of the project in Chapter 1, Gallium Nitride material in Chapter 2, HEMT material in Chapter 3, Theory and model in Chapter 4 and results and discussions in Chapter 5.
Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2616
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Book Description
Author: Matteo Meneghini
Publisher: Springer
ISBN: 3319431994
Category : Technology & Engineering
Languages : en
Pages : 383
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Book Description
This book presents the first comprehensive overview of the properties and fabrication methods of GaN-based power transistors, with contributions from the most active research groups in the field. It describes how gallium nitride has emerged as an excellent material for the fabrication of power transistors; thanks to the high energy gap, high breakdown field, and saturation velocity of GaN, these devices can reach breakdown voltages beyond the kV range, and very high switching frequencies, thus being suitable for application in power conversion systems. Based on GaN, switching-mode power converters with efficiency in excess of 99 % have been already demonstrated, thus clearing the way for massive adoption of GaN transistors in the power conversion market. This is expected to have important advantages at both the environmental and economic level, since power conversion losses account for 10 % of global electricity consumption. The first part of the book describes the properties and advantages of gallium nitride compared to conventional semiconductor materials. The second part of the book describes the techniques used for device fabrication, and the methods for GaN-on-Silicon mass production. Specific attention is paid to the three most advanced device structures: lateral transistors, vertical power devices, and nanowire-based HEMTs. Other relevant topics covered by the book are the strategies for normally-off operation, and the problems related to device reliability. The last chapter reviews the switching characteristics of GaN HEMTs based on a systems level approach. This book is a unique reference for people working in the materials, device and power electronics fields; it provides interdisciplinary information on material growth, device fabrication, reliability issues and circuit-level switching investigation.
Author: Debdeep Jena
Publisher: Springer Science & Business Media
ISBN: 0387368310
Category : Science
Languages : en
Pages : 523
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Book Description
Polarization Effects in Semiconductors: From Ab Initio Theory to Device Applications presents the latest understanding of the solid state physics, electronic implications and practical applications of the unique spontaneous or pyro-electric polarization charge of wurtzite compound semiconductors, and associated piezo-electric effects in strained thin film heterostructures. These heterostructures are used in wide band gap semiconductor based sensors, in addition to various electronic and opto-electronic semiconductor devices. The book covers the ab initio theory of polarization in cubic and hexagonal semiconductors, growth of thin film GaN, GaN/AlGaN GaAlN/ AlGaInN, and other nitrides, and SiC heterostructures. It discusses the effects of spontaneous and piezoelectric polarization on band diagrams and electronic properties of abrupt and compositionally graded heterostructures, electronic characterization of polarization-induced charge distributions by scanning-probe spectroscopies, and gauge factors and strain effects. In addition, polarization in extended defects, piezo-electric strain/charge engineering, and application to device design and processing are covered. The effects of polarization on the fundamental electron transport properties, and on the basic optical transitions are described. The crucial role of polarization in devices such as high electron mobility transistors (HEMTs) and light-emitting diodes (LEDs) is covered. The chapters are authored by professors and researchers in the fields of physics, applied physics and electrical engineering, who worked for 5 years under the "Polarization Effects in Semiconductors" DOD funded Multi Disciplinary University Research Initiative. This book will be of interest to graduate students and researchers working in the field of wide-bandgap semiconductor physics and their device applications. It will also be useful for practicing engineers in the field of wide-bandgap semiconductor device research and development.
Author: R. K. Sharma
Publisher: Springer
ISBN: 3319976044
Category : Technology & Engineering
Languages : en
Pages : 1260
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Book Description
This book disseminates the current knowledge of semiconductor physics and its applications across the scientific community. It is based on a biennial workshop that provides the participating research groups with a stimulating platform for interaction and collaboration with colleagues from the same scientific community. The book discusses the latest developments in the field of III-nitrides; materials & devices, compound semiconductors, VLSI technology, optoelectronics, sensors, photovoltaics, crystal growth, epitaxy and characterization, graphene and other 2D materials and organic semiconductors.
Author: Farid Medjdoub
Publisher: MDPI
ISBN: 3036505660
Category : Technology & Engineering
Languages : en
Pages : 242
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Book Description
Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits. In particular, the following topics are addressed: – GaN- and SiC-based devices for power and optoelectronic applications – Ga2O3 substrate development, and Ga2O3 thin film growth, doping, and devices – AlN-based emerging material and devices – BN epitaxial growth, characterization, and devices
