The role of interface defect states in n- and p-type Ge metal-ferroelectric-semiconductor structures with Hf${}_{0.5}$Zr${}_{0.5}$O${}_2$ ferroelectric

The discovery of ferroelectricity in doped HfO${}_2$ represents an excellent opportunity to overcome the obstacles in manufacturing reliable ferroelectric field effect transistors (FeFET) for nonvolatile memory applications, considering that HfO${}_2$ is compatible with Si and Ge and it is already used in semiconductor industry. The presence of interface defects may have detrimental effects on the operation of FeFETs, so their role is systematically investigated in this study in correlation with the substrate doping. Metal-ferroelectric-semiconductor (MFS) structures are fabricated by depositing Hf${}_{0.5}$Zr${}_{0.5}$O${}_2$ (HZO) layers on n-type Ge substrate. Their electric properties are compared with those of MFS structures obtained by depositing HZO on p-type Ge, to study the influence of the doping. It is found that, although the ferroelectric properties of HZO are similar, the capacitance and impedance of the MFS structures behave differently. For n-Ge, the occupation probability of a large number of low-lying interface defect acceptor states, charges the interface negatively which adversely affects the C-V response of the MFS, albeit without harming the ferroelectric (P-V) hysteresis. Although the interface defects do not harm ferroelectricity, they could inhibit inversion in p-type Ge or accumulation in n-type Ge so they should be taken into account when designing Ge FeFET devices. (© 2021 Wiley‐VCH GmbH)