Polycrystalline/Amorphous HfO2 Bilayer Structure as a Gate Dielectric for β-Ga2O3 MOS Capacitors

We report the comparison of the atomic layer deposited polycrystalline (p-)/amorphous (a-) HfO
₂
bilayer gate dielectric with p-HfO
₂
/a-Al
₂
O
₃
for enhanced β-Ga
₂
O
₃
metal oxide semiconductor capacitors (MOSCAPs). A discrepancy in the temperature-dependent hysteretic behaviors is observed, and thus, pulse capacitance- voltage (C-V) measurements are employed to investigate interface properties at the border between the amorphous (Al
₂
O
₃
or HfO
₂
) and polycrystalline (HfO
₂
) oxide layers. The proposed p-HfO
₂
/a-HfO
₂
exhibits similar interface trap densities (Dit) at the interface between the bilayer dielectric and β-Ga
₂
O
₃
, and shows lower border trap density (Nbt). An effective barrier height of 1.62 eV for the p-HfO
₂
/a-HfO
₂
with a breakdown field of 9.1 MV/cm, which is higher than 1.01 eV of p-HfO
₂
/a-Al
₂
O
₃
, is obtained from the current density-voltage (J-V) characteristics using the Folwer-Nordheim model. Moreover, as compared with a p-HfO
₂
single layer, the additional a-HfO
₂
layer on top of p-HfO
₂
is beneficial to improve hysteretic and leakage characteristics, while maintaining its high-quality interface. The p-HfO
₂
/a-HfO
₂
bilayer with improved interface properties as well as a large positive flat-band voltage of 4.7 V is a promising candidate for the metal/high-k-stack of β-Ga
₂
O
₃
MOSCAPs.