Ferroelectric Phase Transitions in Films with Depletion Charge

TL;DR

This paper investigates how depletion charge affects ferroelectric phase transitions in thin films, revealing that it causes polarization separation, reduces transition temperature, and influences domain formation, with implications for device performance.

Contribution

It provides a detailed analysis of the effects of depletion charge on ferroelectric phase transitions, including polarization behavior and domain structure formation, which was previously overlooked.

Findings

Phase transition remains second order despite depletion charge.

Depletion charge suppresses ferroelectricity near electrodes.

Depletion charge facilitates domain formation, impacting device performance.

Abstract

We consider ferroelectric phase transitions in both short-circuited and biased ferroelectric-semiconductor films with a space (depletion) charge which leads to some unusual behavior. It is shown that in the presence of the charge the polarization separates into `switchable' and `non-switchable' parts. The electric field, appearing due to the space charge, does not wash out the phase transition, which remains second order but takes place at somewhat reduced temperature. At the same time, it leads to a suppression of the ferroelectricity in a near-electrode layer. This conclusion is valid for materials with both second and first order phase transitions in pure bulk samples. Influence of the depletion charge on thermodynamic coercive field reduces mainly to the lowering of the phase transition temperature, and its effect is negligible. The depletion charge can, however, facilitate an appearance of the domain structure which would be detrimental for device performance (fatigue). We discuss some issues of conceptual character, which are generally known but were overlooked in previous works. The present results have general implications for small systems with depletion charge.