Effects of charge and dipole on flatband voltage in an MOS device with a Gd-doped HfO2 dielectric

Gd-doped HfO2 has drawn worldwide interest for its interesting features. It is considered to be a suitable material for N-type metal-oxide-semiconductor (MOS) devices due to a negative flatband voltage (V-fb) shift caused by the Gd doping. In this work, an anomalous positive shift was observed when Gd was doped into HfO2. The cause for such a phenomenon was systematically investigated by distinguishing the effects of different factors, such as Fermi level pinning (FLP), a dipole at the dielectric/SiO2 interface, fixed interfacial charge, and bulk charge, on V-fb. It was found that the FLP and interfacial dipole could make V-fb negatively shifted, which is in agreement with the conventional dipole theory. The increase in interfacial fixed charge resulting from Gd doping plays a major role in positive V-fb shift.