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

Atomic layer deposited (ALD) high band gap (∼6.5eV) [1], high k (∼9.1) Al2O3 has emerged as an attractive candidate to support vertical scaling of AlN/GaN HEMTs [2] 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 AlN/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 (Qint) 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 (ФB), the electron tunneling effective mass in Al2O3, and discuss the resulting HEMTs.