RELIABILITY OF ALINAS INGAAS/INP HEMT WITH WSI OHMIC CONTACTS/

We have investigated the degradation mechanism of Al0.48In0.52As/In0.5 3Ga0.47As/InP high electron mobility transistors (HEMTs) using WSi ohm ic electrodes. Cross-sectional transmission electron microscopy (TEM) observation and energy dispersive x-ray (EDX) analysis reveal impuriti es diffusion of gate electrode (titanium: Ti) and fluorine (F) in the AlInAs layer after a high temperature (T-a = 170 degrees C operating l ife test for 500 h. The decrease of drain current (I-ds) during life t est shows linear dependence on square root of aging time. It suggests that the degradation is controlled by a diffusion mechanism. Hence, th e estimated degradation mechanism of this device is related with decre ase of carrier concentration in the epitaxial layer by these diffused impurities. On the other hand, TEM and EDX show no degradation of WSi/ InGaAs interface after aging. Therefore, the WSi electrode for this ty pe of HEMT demonstrates excellent high stability under the accelerated operating life test.