Abnormal widening of the domain touching the electrode during in-plane local switching in lithium niobate

Abstract

The qualitatively different domain evolution scenarios for different polarities of applied voltage pulses have been studied. For positive pulse, the domain demonstrates only slight width increase during further switching and high stability during subsequent domain imaging. For negative pulse, faster domain widening at the electrode as compared to the domain base leads to change in the type of charged domain wall (CDW) from tail-to-tail (t2t) to head-to-head (h2h) as well as formation of the domain teeth at CDW and an array of wedge-like domains. Additional domain imaging leads to reconstruction of the wedge-like domain with t2t CDW. It was demonstrated by numerical simulation that the switching field is above the threshold for step generation in wide region along the electrode. This field stimulates the formation of above-mentioned domain structure. The absence of this effect for positive pulse has been attributed to the huge difference in conductivity of t2t and h2h CDWs. The current along conductive h2h CDW after domain touching results in decrease in the tip bias due to voltage drop on the series resistance. The stability of the domains growing from the tip was attributed to effective screening of depolarization field by the injected charge. The ineffective screening at the electrode due to absence of charge injection stimulates domain backswitching. The obtained knowledge is useful for further development of domain engineering methods in thin films for the fabrication of periodically poled waveguides.