AlGaN channel field effect transistors with graded heterostructure ohmic contacts

摘要

We report on ultra-wide bandgap (UWBG) Al_(0.75)Ga_(0.25)N channel metal-insulator-semiconductor field-effect transistors (MISFETs) with heterostructure engineered low-resistance ohmic contacts. The low intrinsic electron affinity of AlN (0.6 eV) leads to large Schottky barriers at the metal-AlGaN interface, resulting in highly resistive ohmic contacts. In this work, we use a reverse compositional graded n~(++) AlGaN contact layer to achieve upward electron affinity grading, leading to a low specific contact resistance (ρ_(sp)) of 1.9 × 10~(-6) Ω cm~2 to n-Al_(0.75)Ga_(0.25)N channels (bandgap ～5.3eV) with non-alloyed contacts. We also demonstrate UWBG Al_(0.75)Ga_(0.25)N channel MISFET device operation employing the compositional graded n~(++) ohmic contact layer and 20 nm atomic layer deposited Al_2O_3 as the gate-dielectric.