Thermodynamic stability of the spontaneous polarization and the space charge layer in ferroelectric/semiconductor heterostructures

The feasibility of memory retention of ferroelectric field-effect devices, their miniaturization limit and its dependence on their heterostructures are studied using the Ginzburg-Landau theory. For a ferroelectric directly formed on a semiconductor, the depolarization instability is shown to be negligible. To confirm the results, the depolarization instability is experimentally reexamined. For an insulating ferroelectric formed on a semiconductor via a thin insulator, the single-domain is destabilized, if there are no defects or traps. An appropriate number density of the interfacial traps stabilizes the spontaneous polarization only at one polarity. Alternatively, spontaneous polarization is stabilized by the semiconductivity of the ferroelectric. This changes the depolarization instability from destabilization of the ferroelectricity to reduction of the electric flux. Ferroelectric field-effect transistors (FETs) have the potential for miniaturization and long memory retention, although the switching speed may be intrinsically limited in conventional ferroelectric/insulator/semiconductor structures.