Barrier height, interface charge & tunneling effective mass in ALD Al2O3/AlN/GaN HEMTs

Atomic layer deposited (ALD) high band gap (~6.5eV), high k (-9.1) Al₂O₃ has emerged as an attractive candidate to support vertical scaling of AIN/GaN HEMTs and its variants owing to its outstanding dielectric, thermal, and chemical properties. Integration of ALD oxides with GaN will enable lower gate leakage currents, high breakdown voltages, and surface passivation. In this work we present a comprehensive characterization of AIN/GaN MOS-HEMT gate stacks with ALD Al₂O₃ of various thicknesses. Through capacitance-voltage and Hall-effect measurements, we find the presence and propose an origin of benign donor-type interface charge (Q_int) at the AlN/Al₂O₃ junction, and relate its presence to the polarization charges in AlN. By studying tunneling transport in corresponding (Ni/Al₂O₃/Ni) M-I-M diodes, we extract the Ni/Al₂O₃ surface barrier height (Φb), the electron tunneling effective mass in Al₂O₃, and discuss the resulting HEMTs.