Intentionally Carbon-Doped AlGaN/GaN HEMTs: Necessity for Vertical Leakage Paths

Dynamic on -resistance
$(R_{\rm ON})$
in heavily carbon-doped AlGaN/GaN high electron mobility transistors is shown to be associated with the semi-insulating carbon-doped buffer region. Using transient substrate bias, differences in
$R_{\rm ON}$
dispersion between transistors fabricated on nominally identical epilayer structures were found to be due to the band-to-band leakage resistance between the buffer and the 2-DEG. Contrary to normal expectations, suppression of dynamic
$R_{\rm ON}$
dispersion in these devices requires a high density of active defects to increase reverse leakage current through the depletion region allowing the floating weakly p-type buffer to remain in equilibrium with the 2-DEG.