Simulation of surface state effects in the transient response of AlGaN/GaN HEMT and GaN MESFET devices

Numerical 2D transient simulations of surface trap effects in AlGaN/GaN HEMT and GaN MESFET devices have been performed. The influence of donor- and acceptor-type traps on drain current characteristics has been studied, when the gate voltage is pulsed. Opposite behaviour in the response mechanism of both devices has been found. The current collapse and related dispersion effects are due to acceptor-type traps, acting as electron traps, in MESFET devices, whereas for HEMT devices, donor-type traps, acting as hole traps, are the origin of these effects. Free hole accumulation on the top surface plays a decisive role in the behaviour of the HEMT. A detailed study about density, ionization, energy level and spatial distribution of traps reveals conclusive results in the two devices analysed.