The authors have used HfO2 and SiO2 separately in order to compare their mobilities with equivalent oxide thickness (EOT).
However, I could not understand why the authors set the thickness of HfO2 = 4.888 nm to have its EOT of 2 nm while relative permittivity of HfO2=22 and SiO2=3.9 respectively.
I thought for the HfO2 to have EOT of 2nm, it should have 2 nmX4.888 / 3.9= 2.5nm.