Fabrication, Performance and Degradation Mechanism of Aluminum Gallium Nitride/gallium Nitride Heterostructure Field-effect Transistors


Book Description

Tremendous efforts to realize the potential of Al-GaN/GaN HFETs have been made over the last decade focusing on improving microwave power performance via optimizing material growth and semiconductor processing technologies. As the device performance is getting mature, the device's reliability becomes a major concern for manufacturability of commercially available AlGaN/GaN HFETs. However, comprehensive study on the reliability of these devices is still lacking.










Gallium Nitride (GaN)


Book Description

Addresses a Growing Need for High-Power and High-Frequency Transistors Gallium Nitride (GaN): Physics, Devices, and Technology offers a balanced perspective on the state of the art in gallium nitride technology. A semiconductor commonly used in bright light-emitting diodes, GaN can serve as a great alternative to existing devices used in microelectronics. It has a wide band gap and high electron mobility that gives it special properties for applications in optoelectronic, high-power, and high-frequency devices, and because of its high off-state breakdown strength combined with excellent on-state channel conductivity, GaN is an ideal candidate for switching power transistors. Explores Recent Progress in High-Frequency GaN Technology Written by a panel of academic and industry experts from around the globe, this book reviews the advantages of GaN-based material systems suitable for high-frequency, high-power applications. It provides an overview of the semiconductor environment, outlines the fundamental device physics of GaN, and describes GaN materials and device structures that are needed for the next stage of microelectronics and optoelectronics. The book details the development of radio frequency (RF) semiconductor devices and circuits, considers the current challenges that the industry now faces, and examines future trends. In addition, the authors: Propose a design in which multiple LED stacks can be connected in a series using interband tunnel junction (TJ) interconnects Examine GaN technology while in its early stages of high-volume deployment in commercial and military products Consider the potential use of both sunlight and hydrogen as promising and prominent energy sources for this technology Introduce two unique methods, PEC oxidation and vapor cooling condensation methods, for the deposition of high-quality oxide layers A single-source reference for students and professionals, Gallium Nitride (GaN): Physics, Devices, and Technology provides an overall assessment of the semiconductor environment, discusses the potential use of GaN-based technology for RF semiconductor devices, and highlights the current and emerging applications of GaN.







Vertical Gallium Nitride PowerDevices: Fabrication and Characterisation


Book Description

Efficient power conversion is essential to face the continuously increasing energy consumption of our society. GaN based vertical power field effect transistors provide excellent performance figures for power-conversion switches, due to their capability of handling high voltages and current densities with very low area consumption. This work focuses on a vertical trench gate metal oxide semiconductor field effect transistor (MOSFET) with conceptional advantages in a device fabrication preceded GaN epitaxy and enhancement mode characteristics. The functional layer stack comprises from the bottom an n+/n--drift/p-body/n+-source GaN layer sequence. Special attention is paid to the Mg doping of the p-GaN body layer, which is a complex topic by itself. Hydrogen passivation of magnesium plays an essential role, since only the active (hydrogen-free) Mg concentration determines the threshold voltage of the MOSFET and the blocking capability of the body diode. Fabrication specific challenges of the concept are related to the complex integration, formation of ohmic contacts to the functional layers, the specific implementation and processing scheme of the gate trench module and the lateral edge termination. The maximum electric field, which was achieved in the pn- junction of the body diode of the MOSFET is estimated to be around 2.1 MV/cm. From double-sweep transfer measurements with relatively small hysteresis, steep subthreshold slope and a threshold voltage of 3 - 4 V a reasonably good Al2O3/GaN interface quality is indicated. In the conductive state a channel mobility of around 80 - 100 cm2/Vs is estimated. This value is comparable to device with additional overgrowth of the channel. Further enhancement of the OFF-state and ON-state characteristics is expected for optimization of the device termination and the high-k/GaN interface of the vertical trench gate, respectively. From the obtained results and dependencies key figures of an area efficient and competitive device design with thick drift layer is extrapolated. Finally, an outlook is given and advancement possibilities as well as technological limits are discussed.







Fabrication, Characterization, and Simulation of Gallium-Nitride Heterojunction Field-Effect Transistors


Book Description

This thesis presents the fabrication, characterization, and off-state gate leakage simulation of Al x Ga 1−x N/GaN Heterojunction Field-Effect Transistors (HFETs). GaN HFETs are promising devices for high power, high frequency applications such as microwave amplifiers. This is due to the numerous benefits of the GaN material system including high electron mobility, breakdown field, saturation velocity, and thermal conductivity. This thesis is broken down into two major components. The first and most significant covers the fabrication and characterization of Al x Ga 1−x N/GaN HFETs. Devices were fabricated at McGill University’s Nanotools Microfabrication laboratory using a custom designed process flow. This process flow builds on previous work and presents Ohmic contact results of Ti/Al/Ti/Au and Ti/Al/Ti/Al/Ti/Au metalizations. A complete description of the process flow is provided including technology characterization results, such as mesa height profiling, where applicable. Electrical characterization of fabricated devices is performed. Results show an average contact resistance across temperature of 3.39Ωmm for the Ti/Al/Ti/Au metalization and 3.22Ωmm for the Ti/Al/Ti/Al/Ti/Au metalization. Full contact resistance results are provided over a wide range of temperature. The Ti-Al multi-layer metalization also outperforms the Ti/Al/Ti/Au metalization in terms of drain current density ( 0.12A/mm vs. 0.09A/mm ) and transconductance ( 60mS/mm vs. 40mS/mm ). Off-state gate leakage and current-voltage profiling are also carried out. The second part of this thesis concerns gate leakage current in Al x Ga 1−x N/GaN HFETs. A new off-state gate leakage model is presented to determine the variation in leakage mechanisms with the change in barrier layer aluminum mole fraction. A new metric of turning point is introduced to show where Fowler-Nordheim tunneling becomes the dominant leakage mechanism. Results show that as Al mole fraction is increased, the turning point becomes more negative and total gate leakage increases. Finally, improvements to the fabrication process and simulations are presented.