ABSTRACT
III-nitride (III-N) heterojunction bipolar transistors (HBTs) have been a highly anticipated transistor technology since the inception of III-N semiconductors for microelectronics in the 1990s. HBTs offer highly compact solutions to high-power radio frequency (RF) amplifiers when compared to field-effect transistor (FET)–based monolithic microwave integrated circuits (MMICs). The uniform turn-on characteristics enable inherent processing robustness. The wide dynamic range and better impedance matching characteristics also make HBTs a favorable choice of device technology for linear amplifiers. In addition, GaN-based HBTs provide unparalleled added values to ultrahigh power density operations under extreme conditions (i.e., highly corrosive, high radiation-doses, and high-temperature environments). Despite numerous advantages of III-N-based HBTs, the technology development has lagged far behind the III-N-based heterostructure FET (HFET) developments. Today, III-N high-electron mobility transistors (HEMTs) have demonstrated their feasibility for high power density (>30 W/mm) and compact RF electronics. III-N HBTs, on the other hand, are still in a very early stage of technology development.
