Al 0.85 Ga 0.15 N/Al 0.6 Ga 0.4 N High Electron Mobility Transistors on Native AlN Substrates with >9 MV/cm Mesa Breakdown Fields

Introduction: 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.