Lateral Charge Distribution and Recovery of Dynamic R_ON in AlGaN/GaN HEMTs

Lateral distribution of buffer charge trapping is investigated in AlGaN/GaN high-electron-mobility transistors (HEMTs) using a capacitance-based sense-node technique. Devices which are a Schottky-gate HEMT with an additional Schottky sense contact positioned between gate and drain can be used to monitor a lateral variation in 2-D electron gas (2-DEG) depletion as the device recovers from trapping. This paper reveals three distinct trapping types and subsequent recovery behavior in devices with varying passivation nitride stoichiometry. The results demonstrate that the two time-constant recoveries often seen in GaN HEMTs is in part due to a laterally localized charge and in part a distributed charge in the buffer. In addition, the observation of a shoulder in the capacitance-voltage curves during device recovery indicates a pinchoff shift for only a fraction of the area under the sense contact. This effect suggests a submicrometer lateral variation of trapping in the device.