Impact of Surface Treatments and Post-Deposition Annealing Upon Interfacial Property of ALD-Al₂O₃ on a-Plane GaN

Optimization of interface characteristics between dielectric and non-polar GaN surface is very important and urgent for vertical GaN MOS device whose channel is perpendicular to the conventional cplane. In this work, the effects of piranha cleaning and N2 post deposition annealing (PDA) to the interface between atomic-layer-deposited (ALD)-Al
₂
O
₃
and a-plane GaN samples were comprehensively investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and photo-assisted capacitance-voltage (C-V) measurements. The piranha cleaning and N2 annealing can improve interface characteristics through the reduction in surface roughness and Ga-O bonds, respectively. Therefore, the frequency dispersion and hysteresis are nearly suppressed with a low interface trap quantity (Qit) of 4.1 x 10
¹¹
cm
^-2
and a low average interface state density (Dit) of 2.04 x 10
¹¹
cm
^-2
·eV
^-1
from photoassisted C-V measurements, showing the great promise of utilizing piranha pretreatment, buffered oxide etch (BOE) dip, and N
₂
annealing as an effective route to improve the vertical GaN MOS interface properties.