Abstract
A set of AlGaN/GaN high electron mobility transistor devices has been investigated using step-stress
testing, and representative samples of undegraded, source-side-degraded, and drain-side-degraded
devices were examined using electron microscopy and microanalysis. An unstressed reference
sample was also examined. All tested devices and their corresponding transmission electron
microscopy samples originated from the same wafer and thus received nominally identical
processing. Step-stressing was performed on each device and the corresponding current–voltage
characteristics were generated. Degradation in electrical performance, specifically greatly increased
gate leakage current, was shown to be correlated with the presence of crystal defects near the gate
edges. However, the drain-side-degraded device showed a surface pit on the source side, and another
region of the same device showed no evidence of damage. Moreover, significant metal diffusion into
the barrier layer from the gate contacts was also observed, as well as thin amorphous oxide layers
below the gate metal contacts, even in the unstressed sample. Overall, these observations emphasize
that gate-edge defects provide only a partial explanation for device failure.
