Degradation Mechanism of AlGaAs/InGaAs Power Pseudomorphic High-Electron-Mobility Transistors under Large-Signal Operation

Abstract

We have comprehensively investigated the degradation mechanism of output power in AlGaAs/InGaAs pseudomorphic high-electron-mobility transistors (PHEMTs) under large-signal operation. The degradation of output power is caused by the decrease in maximum drain current (Imax) around the knee voltage (Vk) with an increase in drain resistance (Rd). The decrease in Imax originates from a degradation layer containing a significant amount of oxygen formed at the drain recess surface region. This layer causes a reduced carrier density in the drain region underneath, resulting in a decreased Imax and an increased Rd. The decrease in Imax is accelerated with increasing drain voltage, temperature, and humidity. These results suggest that the degradation of output power in the PHEMTs is mainly determined by the growth of a corrosion layer owing to an electrochemical reaction between O2 and/or H2O and the semiconductor surface. We successfully suppress the output power degradation due to this electrochemical corrosion reaction with the help of a special surface treatment prior to the deposition of a passivation film on the recess surface. We demonstrate a highly reliable RF operation of PHEMTs in air even without a hermetic package.