Observation of Hot Electron and Impact Ionization in N-Polar GaN MIS-HEMTs

This letter reports on the observation of hot-electron and impact-ionization mechanisms in N-polar GaN-based MIS-HEMTs designed for high frequency (RF) operation. Thanks to the extremely low gate leakage of such devices, we were able to demonstrate—for the first time—a correlation between electroluminescence (EL) and gate current in the semi-on state. In the semi-on state, the devices show a non-monotonic, bell-shaped behavior of the EL-versus-
${\text {V}}_{\text {GS}}$
and of the
${I}_{\text {G}}$
-versus-
${V}_{\text {GS}}$
characteristics, and the intensity of the EL signal is proportional to the
${I}_{G}\times {I}_{D}$
product. The results are experimental evidence for impact ionization: the related mechanisms are described in detail in the letter.