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) Al
2
O
3
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 Al
2
O
3
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/Al
2
O
3
junction, and relate its presence to the polarization charges in AlN. By studying tunneling transport in corresponding (Ni/Al
2
O
3
/Ni) M-I-M diodes, we extract the Ni/Al
2
O
3
surface barrier height (Ф
B
), the electron tunneling effective mass in Al
2
O
3
, and discuss the resulting HEMTs.