Deep-level effects on slow current transients and current collapse in GaN MESFETs

Slow current transients in a GaN MESFET are analyzed by two-dimensional simulation in which deep levels in a semi-insulating buffer layer is considered. It is shown that when the drain voltage V_D is raised abruptly, the drain current overshoots the steady-state value, and when V_D is lowered, the drain current remains at a low value for some periods, showing drain lag behavior. This drain lag is shown to become a cause of so-called current collapse in the GaN MESFET.