Fixed charge in high- k /GaN metal-oxide-semiconductor capacitor structures

The location and nature of fixed charge states in high-k/GaN metal-oxide-semiconductor capacitor structures are characterized by analyzing flatband voltage shifts in high-frequency capacitance-voltage measurements. It is shown that a significant fixed, positive sheet charge forms at Al2O3/GaN interfaces, but not at HfO2/GaN interfaces. Furthermore, an interface dipole is created at HfO2/Al2O3 interfaces, which causes an abrupt shift in the flat band voltage as HfO2 is introduced to form HfO2/Al2O3 bilayer dielectrics. The observed dependence of the flatband voltage shift on the relative thicknesses of the dielectrics comprising the bilayer dielectrics is discussed.