Threshold Voltage Control in AlGaN/GaN/AlGaN Double-Heterostructure MISHFET Utilizing 2-D Electron and Hole Gases

Conventional AlGaN/GaN metal-insulator–semiconductor heterostructure field-effect transistors (MISHFETs) are affected by trapped charges at the dielectric/AlGaN interface causing instabilities and quasi-permanent shifts of the threshold voltage. In this work, we investigate the charging and especially discharging processes of these interface states in AlGaN/GaN/AlGaN double-heterostructure (DH) MISHFET with an Al2O3 gate dielectric. Appropriately designed, these dopant-free devices contain a polarization-induced 2-D electron gas (2DEG) as well as a 2-D hole gas (2DHG). After applying large gate biases, the Al2O3/AlGaN interface is known to persistently capture electrons from the 2DEG in deep states resulting in a positive threshold voltage shift. Here, we demonstrate that the interface can be actively discharged by carriers from the 2DHG when a sufficiently large negative gate bias is applied, resulting in a negative threshold voltage shift. These mechanisms of charge trapping and detrapping are correlated to the design parameters and biasing conditions of the device. In addition, we investigate low- and high-temperature characteristics and show that these devices can be operated like a memory-type component.