Domain engineering in LiNbO3 crystals by e-beam and features of spatial distribution of electric field: Experiment and computer simulation

Abstract

Domain gratings with different periods were formed on −Z surfaces of lithium niobate using direct electron beam writing (DEBW) at an accelerating voltage of 15 kV. Features of the gratings obtained were compared to computer simulation results of spatial distribution of an electric field for various schemes of e-beam charges disposed near the sample surface. The Monte Carlo method was used to calculate the injection charge distribution. The electrical potential distribution in irradiated samples was determined by the numerical solution of the Poisson equation. The electric field created by the injected charges was calculated both near the surface and by the depth of the irradiated samples. Peculiarities of the field distribution have been found, in which the formation of regular domain gratings is broken due to the proximity of the injected charges. Based on computer simulations and the experimental results of DEBW (at 15 kV), the search for irradiation schemes was carried out to reduce the limitations in grating periods by decreasing the accelerating voltage of electrons up to 10 kV.

Deepening of domains at e-beam writing on the −Z surface of lithium niobate

“…The opposite +Z surface of the thick samples (∼500 µm) was grounded by a deposited layer of aluminum. In DEBW, irradiated square arrays like those in [29] were used. The squares were placed on the nodes of the grid whose lines were parallel to the chosen orthogonal crystallographic axes X and Y on the cut −Z of LN.…”

“…The selection of H x parameter values for S1 and S2 is based on the results of [29], where it was shown that in the selected DEBW scheme at 15 kV the value of this parameter equal to 3 µm is the threshold proximity of injected charges, at which point regular periodically poled LN structures are still formed.…”

“…The spatial distribution of electric field for various irradiation schemes was analyzed by computer simulation, the methodology of which is described in detail in [29]. The Monte Carlo method was used to find the injected charge distribution (Q s ).…”

“…Similarly to [29], a function of the following form was used to approximate the distribution of the charge injected by irradiation of a square with side h:…”

“…Some publications have reported on the special properties and influence of the LN surface on processes related to nucleation and to domain growth kinetics [25,26]. Moreover, the charging of dielectric materials with an e-beam is known to form a complicated distribution of charges in the surface layer, which can affect the distribution of the electric field and conditions of nucleation of domains under different irradiation schemes [27][28][29]. Further development of the DEBW technique and its implementation in micro-and nanoelectronics (for example, in optical integrated devices) requires a more detailed study of the regularities of domain formation in the near-surface zone of irradiated LN samples.…”