Isolation degradation of InAlAs/InGaAs/InP HEMTs due to bias stress depending on passivation films formed by PCVD

We have observed the degradation of pinch-off characteristics of InAlAs/InGaAs high electron mobility transistors (HEMTs) with SiN passivation film after the bias stress test, which has been resulted from an increase of leakage current on InP surface. On the other hand, the device passivated by SiO/sub 2/ film does not show any degradation. The stability of the isolation characteristic for InP is strongly affected by the surface passivation film formed by plasma-enhanced chemical vapor deposition (PCVD). In order to improve the device reliability, SiO/sub 2/ is more suitable than SiN for a stable passivation to InP surface.