Threshold voltage modulation mechanism of high-performance normally-off AlGaN/GaN gates-separating groove HFET

In this paper, we report on a novel enhancement-mode AlGaN/GaN gates-separating groove heterostructure field-effect transistor (GSG HFET), in which a block barrier exists between the double gates as realized by dry etching. The current transport dominated by thermionic emission or thermionic field emission results in a high drain current density. The threshold voltage modulation mechanism of AlGaN/GaN GSG HFET is investigated. Due to the increasing of block barrier height and width, the threshold voltage shifts obviously towards to the positive direction with increasing the gate length or gate-to-gate distance (Lgg). By optimizing the device structure, a threshold voltage of 1.8 V and a comparable drain current density of 550 mA/mm are obtained at Lgg = 180 nm, while the values of 2.5 V and 370 mA/mm are obtained at Lgg = 280 nm. Moreover, it's noteworthy that the threshold voltage is less sensitive to recess depth and etching time. The devices show high-uniformity threshold voltage within etching time range from 8 to 9 min.