Mechanisms of RF Current Collapse in AlGaN–GaN High Electron Mobility Transistors

The physical mechanisms underlying RF current collapse effects in AlGaN-GaN HEMTs are investigated by means of measurements and numerical device simulations. Our study suggests that 1) both surface and buffer traps can contribute to RF current collapse through a similar physical mechanism involving capture and emission of electrons tunneling from the gate; 2) surface passivation strongly mitigates RF current collapse by reducing the surface electric field and inhibiting electron injection into traps; 3) for surface-trap densities lower than 9e12 cm-2, surface potential barriers in the 1-2 eV range can coexist with surface traps having much a shallower energy and therefore inducing RF current collapse effects characterized by relatively-short time constants.