Hot carrier aging degradation phenomena in GaN based MESFETs

In this paper hot carrier degradation study in unpassivated and passivated GaN MESFETs will be presented: the observed drain current decrease will be proven to be consequent of a drain access resistance increase. In order to discriminate the effects due to traps on the device surface from those related with epitaxial material substrate and its interfaces, the influence of illumination on the drain current has been investigated by means of DC and gate-lag pulsed characterization. The measurements under light and under dark conditions lead us to suppose that the drain access resistance increase can be attributed to the generation of deep levels and/or to increased trapped charge after hot-carrier test on the device surface in the access regions between the gate and the drain contacts. The amount of degradation has been found to be remarkably higher in unpassivated devices with respect to passivated ones. Hot carrier degradation has been observed to be recovered by thermal or room temperature storage without applied bias.