By using Landau-Ginzburg-Devonshire theory, we numerically calculated the static conductivity of charged domain walls with different incline angles with respect to the spontaneous polarization vector in the uniaxial ferroelectric semiconductors of $n$ type. We used the effective mass approximation for the electron and hole density of states, which is valid at an arbitrary distance from the domain wall. Due to the electron accumulation, the static conductivity drastically increases at the inclined head-to-head wall by 1 order of magnitude for small incline angles θ ∼ π/40 and by 3 orders of magnitude for the perpendicular domain wall (θ $=$ π/2). There are space-charge regions around the charged domain walls, but the quantitative characteristics of the regions (width and distribution of the carriers) appear very differently for the tail-to-tail and head-to-head walls in the considered donor-doped ferroelectric semiconductor. The head-to-head wall is surrounded by the space-charge layer with accumulated electrons and depleted donors with the same thickness (∼40−100 correlation lengths). The tail-to-tail wall is surrounded by the thin space-charge layer with accumulated holes with thicknesses of ∼5–10 correlation lengths, a thick layer with accumulated donors with thicknesses of ∼100−200 correlation lengths, as well as the layer depleted by electrons with thicknesses of ∼100−200 correlation lengths. The conductivity across the tail-to-tail wall is at least an order of magnitude smaller than the one for the head-to-head wall due to the low mobility of the holes, which are improper carriers. The results are in qualitative agreement with recent experimental data for LiNbO${}_3$ doped with MgO.

The physical basis of the domain engineering in ferroelectrics and its application to lithium niobate crystals were reviewed. The unified kinetic approach to the domain structure evolution in electric field was formulated and its validity for understanding the variety of observed domain evolution scenarios was demonstrated. The kinetics and statics of the domain structure in the crystals of lithium niobate family including congruent, stoichiometric, and MgO doped ones have been discussed. The main stages of the periodical poling process and related problems have been pointed out. The basic poling techniques applied for creation of the periodical domain structures in bulk crystals and waveguides were compared. The recent applications of the periodically poled lithium niobate for light frequency conversion using second harmonic generation and optical parametric oscillation, excitation of the surface acoustic waves, and generation of terahertz radiation have been discussed. The special attention has been paid for achievements in fabrication of high-power optical parametric oscillation and integrated optical devices with periodically poled lithium niobate. The future trends in periodical poling and development of the nanodomain engineering which will allow to create the nanoscale domain patterns necessary for utilization of the new nonlinear interactions were reviewed.

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In nonlinear optics applications employing quasiphase matching, short-pitch domain gratings are generally required for the efficient generation of visible and ultraviolet light. Here we introduce an improved electric-field poling technique, which incorporates spontaneous backswitching and leads to uniform short-pitch domain structures. The total volume of backswitched material, and hence the duty cycle of the backswitched domain grating, can be accurately controlled. First-order single-pass continuous-wave second harmonic generation of 60 mW at 460 nm is achieved at 6.1%/W efficiency in 0.5-mm-thick 4-μm-period backswitch-poled lithium niobate.

The modification of Kolmogorov–Avrami theory for real objects accounting for the finiteness of the transformed object/media is proposed. It takes into account the changing of the domain growth dimensionality (“geometrical catastrophe”) during the switching process. The validity of the proposed approach has been confirmed by model experiments and computer simulation. By this approach we have obtained the essential information about phase kinetics concealed in integrated experimental data. The method has been successfully used for the description of domain kinetics during the fast switching in ferroelectric single crystals and thin films. The scenario of domain evolution and voltage dependence of the main kinetic parameters have been discussed.