Self-screening induced abnormal stability of ferroelectric phase in GeTe ultrathin films

Abstract

A stable ferroelectric phase or Curie temperature (Tc) above room temperature is essential for ferroelectric devices. However, the fast Tc drop of ferroelectric thin films has become a vital factor inhibiting the scaling down of ferroelectric devices. Many efforts have been made to slow down the Tc drop in conventional insulating ferroelectric thin films, but they are costly and complex. A semiconducting ferroelectric, GeTe, is proposed in this letter, which shows an abnormal stability of the ferroelectric phase as the film thickness decreases to as thin as 3 nm. The ferroelectric Curie temperatures of GeTe thin films with different thicknesses have been studied using variable-temperature Raman measurements. The self-screening process of free carriers provided by intrinsic Ge vacancies in GeTe films plays an important role in cancelling the depolarization field according to first principles calculations and results in an abnormal stability of ferroelectricity in ultrathin GeTe films. Self-screening by free carriers in GeTe unravels that the ferroelectric phase could remain stable in low dimension semiconducting ferroelectrics. These results provide a straightforward solution for high density ferroelectric devices and show promising application of semiconducting ferroelectrics in large current ferroelectric diodes.