Time-dependent conduction current in lithium niobate crystals with charged domain walls

Abstract

We present the experimental study of the increase and decrease of the abnormal conduction current appeared during polarization reversal at elevated temperatures (120-250 C) in stoichiometric and MgO doped lithium niobate single crystals. It is shown that the conduction current is caused by existence of the through charged domain walls. The time dependence of the conduction current has been measured in low electric field immediately after partial switching. The maximal value of the conduction current in crystal with through charged domain walls is of 4-5 orders of magnitude higher than in initial single domain state. The activation energy is 1.1 eV.

Thickness, humidity, and polarization dependent ferroelectric switching and conductivity in Mg doped lithium niobate

“…High conductivity states in Mg:LN have been reported for polarization switching from up to down states 15,19 and have been ascribed to highly charged inclined head-to-head domain walls that accumulate electrons. 19,20 In the FORC experiments, high currents up to 6100 nA were measured on the þz sample at Mg:LN stripes for all atmospheric conditions (see Figures 7(b)-7(d) acquired at 695 V). Information on the local conductivity was extracted by omitting transient currents due to polarization switching and capacitive contributions related to the square voltage pulses during FORC spectroscopy.…”

“…[5][6][7][8][9][10] Due to its good nonlinear optical properties and high resistance to photorefraction, 11,12 highly Mg doped LN (Mg:LN) has gained significant interest for applications in optics as quasi phase matched devices. [13][14][15] Ferroelectric properties of LN change upon Mg doping and in numerous poling experiments 13,[15][16][17] lower coercive fields and longer stabilization times for freshly poled domains 15,18,19 have been observed, as well as unidirectional high conductivity states 15,19 that were ascribed to charged domain walls. 20 However, the ferroelectric behavior that a material shows is, apart from its intrinsic properties, also strongly dependent on the presence of screening charge at polar interfaces.…”

Interface modulated currents in periodically proton exchanged Mg doped lithium niobate

“…The higher conductivity at domain walls likely stem from the local vertical and lateral electric fields arising from the polarization discontinuity in the vicinity of and across domain walls, which are expected to be inclined, thus charged, in Mg:LN. 10,16,40 The preferential surface migration of photogenerated electrons in LN at domain walls can also be observed in silver photodeposition experiments by the formation of metallic nanostructures due to the reduction of Ag þ ions along those boundaries. 12,14,15 Applying external electric fields allows for measureable current flow through electrode interfaces determined by the quantitative distribution of photogenerated charge carriers in the sample.…”

“…[7][8][9] Nevertheless, little is known about charge transport through Mg:LN and its technologically relevant structurally modified proton exchanged (PE) phase under the influence of such interfaces. Reports of high conductivity states in macroscopic poling experiments 3,10 that involve sample-electrode interfaces and externally applied electric fields have attracted attention, since these findings demonstrate potential application of Mg:LN as ferroelectric semiconductor devices. Further microscopic studies of the multifunctional interplay between switched polarization and conductivity that allow for bistable resistance states upon external application of strong electric field pulses were presented in a previous work and related to sample and voltage polarity.…”

“…16 Other studies showed high conductance of charged walls adjacent to through-domains after polarization reversal with a high applied voltage. 10 Here, photocurrents across a hexagonal domain switched at an area that consists of a thin (%800 nm) Mg:LN layer that is vertically confined by a buried PE layer are investigated. Since the domain wall has no direct contact with the bottom electrode, the observed currents cannot stem from electrons injected locally by the bottom electrode.…”