Analysis of hot carrier aging degradation in GaN MESFETs

In this paper the study of the effects of illumination on the drain current of GaN MESFETs are presented with the aim of discriminating effects due to traps on the device surface from those related with epitaxial material substrate and its interfaces. Illumination together with on-state stress are also used to investigate hot carrier degradation phenomena which consist in drain access resistance increase and consequently in drain current decrease: this can be attributed to the generation of deep levels and/or to increased trapped charge after hot-carrier test on the device surface access regions between the gate and the drain contacts. The degradation level is remarkably higher in unpassivated devices with respect to passivated ones. Hot carrier degradation can be recovered by thermal or R.T. storage without bias.