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

The physical mechanisms underlying RF current- collapse effects in AlGaN-GaN high-electron-mobility transistors are investigated by means of measurements and numerical device simulations. This paper suggests the following conditions: 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 9 x 1012 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.