Gate-Lag in AlGaN/GaN High Electron Mobility Transistors: A Model of Charge Capture

Gate and drain current transients following the application of a step/pulse reverse bias to the gate of AlGaN/GaN HEMTs can be described by a superposition of 2- 3 extended exponents with characteristic times of the main process having activation energy of 0.7- 0.8 eV. The drain current relaxation is a consequence of charge trapping and movement in the AlGaN barrier. A qualitative model explains this process by movement of a step of charge trapped on deep states in the barrier and movement of the step toward the interface by multiple emission/capture hops. The process is assumed to be confined to channels in AlGaN (presumably dislocations) surrounded by potential barriers, preventing effective injection of the carriers into the channels with forward bias pulses. The model qualitatively explains the often reported appearance of hole- trap- like signals in deep level studies of AlGaN/GaN HEMT structures and the persistent changes in capacitance and current of these structures occurring upon pulsing and illumination. (c) The Author(s) 2017. Published by ECS. All rights reserved.