Abstract
GaN has been widely used to develop devices for high-power and high-frequency applications owing to its higher breakdown voltage and high electron saturation velocity. The GaN HEMT radio frequency (RF) power amplifier is the first commercialized product which is fabricated using the conventional Au-based III–V device manufacturing process. In recent years, owing to the increased applications in power electronics, and expanded applications in RF and millimeter-wave (mmW) power amplifiers for 5G mobile communications, the development of high-volume production techniques derived from CMOS technology for GaN electronic devices has become highly demanded. In this article, we will review the history and principles of each unit process for conventional HEMT technology with Au-based metallization schemes, including epitaxy, ohmic contact, and Schottky metal gate technology. The evolution and status of CMOS-compatible Au-less process technology will then be described and discussed. In particular, novel process techniques such as regrown ohmic layers and metal–insulator–semiconductor (MIS) gates are illustrated. New enhancement-mode device technology based on the p-GaN gate is also reviewed. The vertical GaN device is a new direction of development for devices used in high-power applications, and we will also highlight the key features of such kind of device technology.
Highlights
Gallium nitride (GaN) is a high-potential semiconductor material
It has been used to fabricate high-electron mobility transistors (HEMTs) for applications in power devices and radio frequency (RF) power amplifiers because of its superior material characteristics compared with silicon (Si)-based materials, including a wide bandgap, high breakdown electric field, and high electron saturation velocity, as shown in Figure 1 [1,2]
According to the energy band structure of the GaN HEMT, there is a potential energy well at the junction of aluminum gallium nitride (AlGaN) and GaN, and there will be a transportable energy state formed by the accumulation of electrons in this energy well, as shown in Figure 3 [17,19]
Summary
Gallium nitride (GaN) is a high-potential semiconductor material. It has been used to fabricate high-electron mobility transistors (HEMTs) for applications in power devices and radio frequency (RF) power amplifiers because of its superior material characteristics compared with silicon (Si)-based materials, including a wide bandgap, high breakdown electric field, and high electron saturation velocity, as shown in Figure 1 [1,2]. A transistor with a high-electron mobility channel can be created (i.e., HEMT). The aluminum gallium nitride (AlGaN)/gallium nitride (GaN) heterojunction was first reported in 1991 [7], and the first AlGaN/GaN HEMT was subsequently developed in 1993 [8,9], where superior channel electron mobility was demonstrated. The GaN HEMT can be operated at 50 V with an output power over 200 W for mobile communication applications using silicon carbide (SiC) as the substrate [11,12,13]. In 2001, a research team from the University of California at Santa Barbara reported a GaN HEMT for power switch application fabricated on SiC, which possessed a breakdown voltage higher than 1000 V [14].
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