Abstract
Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semiconductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and 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 us to create a two-dimensional electron gas, with high mobility and large channel density, in the 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 a 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 three-dimensional structures—fin-shaped, trench-structured, nanowire-based—are demonstrating great potential. Contrary to Si, 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 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 into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics.
Highlights
29 sistors based on this material have excellent performance, compared to their Si counterparts,[1] and are expected to find wide applications in the next-generation power converters
The EC − 1.12 eV, the EC − 0.64 eV, and the EC − 0.6 eV levels found in Ref. 390 have been referred to as VGa–O-related defects, whereas other deep levels detected outside the band of reference for this particular type of native defect have been associated to VN–VGa complexes or to simple gallium vacancies
To suppress the gate current, which is a requirement for power transistors, isolated-gate AlGaN/gallium nitride (GaN) MIS-high-electron mobility transistors (HEMTs) have been proposed and developed.[1,507]. These include both unrecessed or partially recessed MIS-HEMTs, in which the gate dielectric is deposited onto the AlGaN barrier, and fully recessed MIS-HEMTs, where the AlGaN barrier is completely removed under the gate region so that the gate dielectric is formed onto the GaN buffer region
Summary
Gallium nitride (GaN) has emerged as 26 an excellent material for the fabrication of power semiconductor. D audio amplifiers, robotics, and synchronous rectification Such devices can have ON-resistances below 2 mΩ (for drain currents up to 90 A),[17] or up to 100–200 mΩ (for operating currents in the range 0.5–5 A), depending on the final application.[18,19] (b) High voltage (VDS,max up to 650 V) finds applications in telecommunication servers, industrial converters, photovoltaic inverters, servo motor control,[20] lighting applications, power adapters, converters for consumer electronics,[21] class D amplifiers,[22] and datacenter SMPS.[23,24] (c) Devices with ultrahigh voltage (VDS,max above 1 kV). Operation at high frequencies may exacerbate the degradation processes related to hard-switching events For this reason, it is of utmost importance to understand the degradation processes of GaN power devices and to identify ways and strategies for improving the robustness of the components. This paper helps the reader to understand the advantages of GaN technology and get familiar with the main performance, design, and reliability aspects
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