Influence of impact ionization stresses on AlGaAs-InGaAs HEMT performances

Pseudomorphic HEMTs are widely used in medium power applications. Users are concerned by the reliability of PHEMT-based technologies submitted to RF overdrive. In particular, III-V FETs may suffer from impact ionization effect and surface related mechanisms. The small-signal response of interface states at passivated III-V semiconductor surfaces has been measured over a wide frequency range from 1 Hz to microwave frequencies (Iizuka et al, 1997). During RF operation, impact ionization mechanisms often occur in the channel and their influence on the reliability of devices is not well known. In this work, the effect of life-tests performed on PHEMTs biased in the impact ionization regime with or without thermal stress has been analyzed by monitoring the evolution of DC electrical characteristics and their temperature dependence. The reverse gate current is measured as a function of temperature to observe the behavior of surface traps located at the drain edge of the gate in access regions. Correlation between drain current transients, temperature dependence of the reverse gate current and the on-state breakdown loci is discussed to evaluate both the influence of surface traps on electrical parameters and their evolution after aging.