Dual field effects in spinel ferrite field effect devices: electrostatic carrier doping and redox reactions

Spinel ferrite is a good candidate as a tunable magnetic semiconductor with high T$_{\mathrm{C}}$. Here, we report the gate-induced conductance modulation of (Fe$_{\mathrm{3-x}}$Zn$_{\mathrm{x}})$O$_{\mathrm{4}}$ solid solution to demonstrate the dual contributions of volatile and non-volatile field effects arising from electronic carrier doping and redox reactions using field effect device structure with a ferroelectric Pb(Zr,Ti)O$_{\mathrm{3}}$ and an ionic liquid DEME-TFSI. In the Pb(Zr,Ti)O$_{\mathrm{3}}$/(Fe$_{\mathrm{2.5}}$Zn$_{\mathrm{0.5}})$O$_{\mathrm{4}}$ FET, the gate voltage dependence of channel conductance on the (Fe,Zn)$_{\mathrm{3}}$O$_{\mathrm{4}}$ layer shows the typical hysteresis behavior reflecting the ferroelectric polarization, indicating the static carrier modulation [1] . In contrast, in the DEME-TFSI/(Fe$_{\mathrm{2.5}}$Zn$_{\mathrm{0.5}})$O$_{\mathrm{4}}$ FET, a large hysteresis observed in the drain current vs gate voltage characteristics is not accounted for solely by electrostatic doping, strongly suggesting the presence of chemical reactions[2]. In more details, the characteristic hysteresis virtually disappears for the heavily Zn substituted system,(Fe$_{\mathrm{2.2}}$Zn$_{\mathrm{0.8}})$O$_{\mathrm{4}}$ with less carrier concentration [3]. These observations revealed the coexistence of two types of field effects in the Fe$_{\mathrm{3-x}}$Zn$_{\mathrm{x}}$O$_{\mathrm{4}}$ devices, and the tuning of field-effect characteristics via composition engineering should be extremely useful for fabricating high-performance oxide field-effect devices. References; [1] Appl. Phys. Lett. 98 (2011) 102506, [2] Adv. Mater. Interfaces 1 (2014) 1300108, [3] Sci. Rep. 4 (2014) 5818.