Mechanism for recoverable power drift in PHEMT's

A new degradation mechanism is proposed far output power drift under rf ove rdrive of pseudomorphic high electron mobility transistors (PHEMT's), Simil ar to the previously reported power-slump mechanism, the gradual reduction in output power is caused by a decrease in the peak drain current, However, unlike power slump that is usually associated with permanent damages, in t he present case the output power recovers readily once the rf input is inte rrupted. A possible mechanism for power drift involves charge trapping in t he surface passivation layer. The passivation charge relaxes the electrical field in the semiconductor, which in turn increases the occupation of the interface states between the passivation and semiconductor. Measurements of de and pulsed current-voltage (I-V) characteristics, rf large signal wavef orms, deep level transient spectroscopy, light and temperature effects, as well as metal-insulator-metal leakage support this supposition.