Polarization charge as a reconfigurable quasi-dopant in ferroelectric thin films

Abstract

Impurity elements used as dopants are essential to semiconductor technology for controlling the concentration of charge carriers. Their location in the semiconductor crystal is determined during the fabrication process and remains fixed. However, another possibility exists whereby the concentration of charge carriers is modified using polarization charge as a quasi-dopant, which implies the possibility to write, displace, erase and re-create channels having a metallic-type conductivity inside a wide-bandgap semiconductor matrix. Polarization-charge doping is achieved in ferroelectrics by the creation of charged domain walls. The intentional creation of stable charged domain walls has so far only been reported in BaTiO3 single crystals, with a process that involves cooling the material through its phase transition under a strong electric bias, but this is not a viable technology when real-time reconfigurability is sought in working devices. Here, we demonstrate a technique allowing the creation and nanoscale manipulation of charged domain walls and their action as a real-time doping activator in ferroelectric thin films. Stable individual and multiple conductive channels with various lengths from 3 μm to 100 nm were created, erased and recreated in another location, and their high metallic-type conductivity was verified. This takes the idea of hardware reconfigurable electronics one step forward.

Hall effect in charged conducting ferroelectric domain walls

“…McQuaid, private communication), (Bi 0.9 La 0.1 )FeO 3 (ref. 12)) and initial concerns that currents were not necessarily genuinely associated with enhanced conductivity (instead arising from undetected domain wall movement for example) have now been firmly allayed. Since the domains themselves are comparatively insulating, domain walls represent isolated conducting channels, which confine currents into narrow sheets.…”

“…There is an expectation that domain walls should have electronic band-structures that differ from domains1920, but there is also clear evidence that stress and/or electrostatic interactions with charged point defects can be important589101112212223. Key carrier information is still lacking, as basic transport characterization studies within the walls have been limited.…”

“…Several studies on domain wall conduction have noted the importance of polar discontinuities in determining or enhancing conduction589101112. The established model is that free charges in the ferroelectric matrix migrate to screen the near fields associated with polar discontinuities at ‘charged' domain walls2425.…”

Dielectric Permittivity Enhancement By Charged Domain Walls Formation In Stoichiometric Lithium Niobate

“…It is possible to create, displace, and erase the charged domain walls (CDW) by the application of the external electric field, which implies the possibility to build real-time reconfigurable devices. Currently, the influence of CDW on the conductivity [1], dielectric permittivity [2], and piezoelectric coefficient [3] of ferroelectrics has been revealed. It has been shown that the bulk properties can be effectively modified by formation of the high density of the domain walls [3].…”

Néel-like domain walls in ferroelectric Pb(Zr,Ti)O3 single crystals

“…While it is well known that properties of the ferroelectrics such as piezoelectric effect and permittivity are substantially enhanced by mobile and stationary domain walls2345, the ferroelectric domain walls themselves were found recently to possess unique properties that differ thoroughly from the bulk domains, for example, electronic conductivity678 and photovoltaic effect9. These results raise much interest101112 in further exploration of the properties of domain walls and their internal structures.…”