Over the last decade, gallium nitride has emerged as an excellent material for the fabrication of power devices. Among the semiconductors for which power devices are already available on the market, GaN has the widest energy gap, the largest critical field, the highest saturation velocity, thus representing an excellent material for the fabrication of high speed/high voltage components.The presence of spontaneous and piezoelectric polarization allows to create a 2-dimensional electron gas, with high mobility and large channel density, in absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable high frequency operation, with consequent advantages in terms of miniaturization.For high power/high voltage operation, vertical device architectures are being proposed and investigated, and 3-dimensional structuresfin-shaped, trench-structured, nanowire-basedare demonstrating a great potential. Contrary to silicon, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This tutorial paper describes the physics, technology and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main properties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail, to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN, and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight on the most relevant aspects gives the reader a comprehensive overview on present and next-generation GaN electronics. IntroductionOver the past decade, gallium nitride has emerged as an excellent material for the fabrication of power semiconductor devices. Thanks to the unique properties of GaN, diodes and transistors based on this material have excellent performance, compared to their silicon counterparts, and are expected to find wide application in the next-generation power converters. Owing to the flexibility and the energy efficiency of GaN-based power converters, the interest towards this technology is rapidly growing: the aim of this tutorial is to review the most relevant physical properties, the operating principles, the fabrication parameters, and the stability/reliability issues of GaN-based power transistors. For introductory purposes, we start summarizing the physical reasons why GaN transistors achieve a much better performance than the corresponding silicon devices, to help the reader understanding the unique advantages of this technology.The properties of GaN devices allow the fabrication of high-efficiency (near or above 99 %)...

In this paper, we present the fabrication and Direct Current/high voltage characterizations of AlN-based thin and thick channel AlGaN/GaN heterostructures that are regrown by molecular beam epitaxy on AlN/sapphire. A very high lateral breakdown voltage above 10 kV was observed on the thin channel structure for large contact distances. Also, the buffer assessment revealed a remarkable breakdown field of 5 MV/cm for short contact distances, which is far beyond the theoretical limit of the GaN-based material system. The potential interest of the thin channel configuration in AlN-based high electron mobility transistors is confirmed by the much lower breakdown field that is obtained on the thick channel structure. Furthermore, fabricated transistors are fully functional on both structures with low leakage current, low on-resistance, and reduced temperature dependence as measured up to 300 °C. This is attributed to the ultra-wide bandgap AlN buffer, which is extremely promising for high power, high temperature future applications.

High power electronics using wide bandgap materials are maturing rapidly, and significant market growth is expected in a near future. Ultra wide bandgap materials, which have an even larger bandgap than GaN (3.4 eV), represent an attractive choice of materials to further push the performance limits of power devices. In this work, we report on the fabrication of AlN/AlGaN/AlN high-electron mobility transistors (HEMTs) using 50% Al-content on the AlGaN channel, which has a much wider bandgap than the commonly used GaN channel. The structure was grown by metalorganic chemical vapor deposition (MOCVD) on AlN/sapphire templates. A buffer breakdown field as high as 5.5 MV/cm was reported for short contact distances. Furthermore, transistors have been successfully fabricated on this heterostructure, with low leakage current and low on-resistance. A remarkable three-terminal breakdown voltage above 4 kV with an off-state leakage current below 1 μA/mm was achieved. A regrown ohmic contact was used to reduce the source/drain ohmic contact resistance, yielding a drain current density of about 0.1 A/mm.