The role of fluorine ions in GaN heterojunction transistors: applications and stability

Abstract

GaN based heterojunction devices, especially in the form of AlGaN/GaN high electron mobility transistors (HEMTs), are capable of delivering high-frequency power amplifiers and power switches with performances far superior than those offered by the mainstream silicon technology and other advanced semiconductor technologies. Rapid progress has been made in material growth and device processing technologies during the last decade. Meanwhile, there remain technical challenges to overcome. For example, unlike the silicon MOSFET technology, in which the devices' threshold voltage can be locally adjusted in the processing stage by ion implantation, the threshold voltage of conventional Cplane Ga-face AlGaN/GaN high electron mobility transistors (HEMTs) is mainly determined in the material growth stage, and exhibit large negative values due to the strong spontaneous and piezoelectric polarization effect, even without any intentional doping. A robust approach to modulating the local potential and local carrier concentration in AlGaN/GaN HEMTs was developed based on the fluorine plasma ion implantation technology. The most significant development based on this technology is the demonstration of self-aligned enhancement-mode (or normally-off) AlGaN/GaN HEMTs with low on-resistance. The stability of fluorine ions in III-nitride is of great importance to applications since it will ultimately determine the E-mode HEMTs' reliability. This paper attempts to address the stability of fluorine ions in III-nitride materials and devices based on a series of experimental and theoretical studies.