Theoretical stability of the polarization in a thin semiconducting ferroelectric

Abstract

The size effect in ferroelectrics is examined by considering the semiconductivity of the ferroelectric. This approach is applied to a theoretical investigation of the stability of the spontaneous polarization in a ferroelectric film on a semiconductor using a homogeneous Ginzburg-Landau theory. The band structure in the ferroelectric/insulator/semiconductor is rigorously incorporated in the theory, as if for a conventional semiconductor heterostructure such as GaAs/͑Ga,Al͒As. The carriers generated in the ferroelectric are found to change drastically the stability of the spontaneous polarization and its size effect. Numerical and simple analytical results are presented for BaTiO 3 and, mostly, for PbTiO 3. The spontaneous polarization in a single-domain ferroelectric on a semiconductor is shown to be bistable and induce a semiconductor space charge D. The value of D is a tiny fraction of the spontaneous polarization and agrees with experimentally estimated values. Namely, the experimental quasiequilibrium D values are mostly intrinsically limited by the heteroband structure, not by the technological difficulties. Moreover, the D value for a finite insulator thickness was found to be mainly determined by the insulator thickness and the semiconductor properties of the ferroelectric, and was relatively insensitive to the ordinary ferroelectric properties and the trap densities at the interface. The theory forecasts possible limitations of the transistors using this structure. Nonetheless, a long retention of the semiconductor space-charge D by a very thin ferroelectric can be realized by the advancement of the technology. Additionally, the stability of very thin ferroelectrics on semi-insulating substrates and the switching of ferroelectrics on parent materials of the high-T c superconductors are successfully explained.

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

“…234,[385][386][387] In parallel, the properties of spatially separated ferroelectric-semiconductor systems were explored as driven by FeFET and FeRAM applications. [388][389][390][391][392][393] Much of these results are summarized in an excellent recent review by Hong et al 393 However, recent studies have demonstrated that in ambient conditions the screening is ionic in nature, and hence polarization dynamics at open surfaces should be considered as coupled surface electrochemical-bulk polarization switching process, as discussed in Section IV. Surprisingly the theory for such coupling was developed by Stephenson and Highland only recently, 229 and remained largely unused.…”

Pyroelectric properties of polydomain epitaxial Pb(Zr1−x,Tix)Karthik1, Martin2 2011Phys. Rev. B

“…30 For the thick films considered here, we can also neglect the depolarization field due the finite conductivity of the PZT thin films. 31 The free energy is supplemented by the relevant mechanical boundary conditions for the mono/polydomain structures. 23,30 For the monodomain ferroelectric states, the mechanical boundary conditions give the in-plane strain components as The absence of forces acting on the free surfaces implies .…”

Ferroelectric phase transitions in films with depletion charge

“…It is expected, therefore, that at the metal-ferroelectric contact a depletion zone and the corresponding (depletion) charge distribution is formed, similar to situation with usual semiconductor-metal contacts. The corresponding electronic structure and related effects were extensively discussed for layered metal-semiconducting ferroelectric systems [2][3][4][5][6][7][8]. The depletion effects are especially important in switching devices [6].…”