Al0.85Ga0.15N/Al0.6Ga0.4N High Electron Mobility Transistors on Native AlN Substrates with >9 MV/cm Mesa Breakdown Fields

The large critical electric field (E
_C
) of ultra-wide band bandgap (UWBG) semiconductors makes them attractive candidates for next-generation high power and high frequency electronics. High Al-content AlGaN high electron mobility transistors (HEMTs) are among the most widely reported UWBG devices, but most are epitaxially grown on foreign substrates with significant dislocation densities (>10
⁹
cm
^-2
) that may compromise material quality and reduce E
_C
. For example, the breakdown limits of buffer mesas for AlN MESFETs [1] and AlN/Al
_0.5
Ga
_0.5
N HEMTs [2] on sapphire were 3.1 MV/cm and 6 MV/cm, respectively. Here, we demonstrate Al
_0.85
Ga
_0.15
N/Al
_0.6
Ga
_0.4
N HEMTs grown on native AlN substrates, and report that the AlGaN layers can withstand fields >9 MV/cm.