Physical investigation of trap-related effects in power HFETs and their reliability implications

This work shows a detailed physical investigation of trapping effects in GaAs power HFETs. Two-dimensional numerical simulations, performed using a hydrodynamic model that includes impact ionization, are compared with experimental results of fresh as well as hot carrier-stressed HFETs in order to gain insight of intertwined phenomena like the kink in the DC output curves, the hot-carrier degradation of the drain current and the impact-ionizationdominated reverse gate current. Thoroughly consistent results show that: (i) the kink effect is dominated by the traps at the source-gate recess surface; (ii) as far as the hot-carrier degradation is concerned, only a simultaneous increase of the trap density at the drain-gate recess surface and at the channel-buffer interface (again at the drain side of the channel) is able to account for the simultaneous decrease of the drain current and the increase of the impact-ionization-dominated reverse gate current.