High Power Pulse Reliability of GaAs Power FETs

A study was made of degradation and burnout of GaAs power FETs resulting from high power RF pulses on the gate while operating at X-band. Burnout power per unit gate width (W/mm) was found to be an important parameter. The failure mechanisms were found to be subsurface burnout and high-field induced metal bridging from the gate to the source or drain. Numerical simulations show high current density transients at the gate and hot electron thermal transients at the source and drain. Hot electrons are created near the edges of the gate and at the source and drain regions by a high power pulse. It is suggested that these lead to degradation by recoil-enhanced interdiffusion at the gate and thermally-induced metal-GaAs interdiffusion, mainly at the source and drain. If such degradation progresses to the point where filamentary metal-GaAs interdiffusions reach the substrate/active channel interface, subsurface burnout is initiated by thermal runaway.