Mechanisms of gate lag in GaN/AlGaN/GaN high electron mobility transistors

Abstract

The presence of electronic traps in GaN-based transistors limits device performance and reliability. It is believed that material defects and electronic states on GaN surface act as the trapping centers. In spite of extensive investigation of trapping phenomena, the physics of the active defects is not completely understood. Charge trapping in the device structure is reflected in gate lag, a delayed response of the channel current to modulation of the gate potential. Gate lag studies provide essential information about the traps allowing identification of the active defects. In this paper we review gate lag in GaN-based high electron mobility transistors (HEMTs). Current transient spectroscopy, a characterization method based on gate lag measurements, is applied for trap identification in AlGaN/GaN HEMTs grown by plasma-assisted molecular beam epitaxy. In particular we focus on the processes of electron capture and emission from the traps. Probing the charge transfer mechanisms leading to gate lag allows us to extract the trap characteristics including the trapping potential, the binding energy of an electron on the trap, and the physical location of the active centers in the device.