Effects of reverse gate-drain breakdown on gradual degradation of power PHEMTs

The gradual degradation effects of reverse gate-drain breakdown which often occurs in high-efficiency operation of power PHEMTs were studied. Similar to MESFETs, PHEMTs were founded to be susceptible to breakdown-induced trap formation in the silicon-nitride surface passivation, the figure of merit against such degradation being approximately two orders of magnitude lower for PHEMTs than for MESFETs. Thus, even if a PHEMT has the same breakdown voltage as a MESFET, the former cannot be driven with as high a drain voltage as the latter. In addition, unlike MESFETs, PHEMTs can undergo an initial power expansion before power slump, due to breakdown-induced donor activation. Therefore, care must be taken to stress PHEMTs sufficiently in order to ascertain their stability against degradation.