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Fabrication and Characterization of Self-assembled Ferroelectric Linear and Nonlinear Photonic Crystals: GaN and LiNbO3 L.-H. Peng, H.-M. Wu, and C.-M. Lai

2.1 Introduction Ferroelectrics distinguish themselves from the commonly-known dielectrics or semiconductors by having a homogeneous spontaneous polarization (Ps ) due to the crystal’s symmetry. The direction of Ps of a ferroelectric crystal can be changed at a temperature higher than the material’s Curie point Tc or by applying an external field above a threshold value related to the crystal’s coercive field Ec [1]. Single domain bulk ferroelectric crystals can be conveniently produced by using the technique of external electric field poling during the crystal growth [2]. Periodically inverted ferroelectric domains can be obtained by applying a series of short electrical pulses with a suitable waveform across a pair of electrodes on a proper ferroelectric substrate [3]. For the latter approach, caution should be exercised to avoid the back-switching of Ps due to an internal field that arises from the crystal’s non-stoichiometric defects. The capability for a ferroelectric crystal/thin film to locally switch its polarization direction and to retain a structure with an alternating sign of polarization states can substantially modify the material’s tensor properties and result in novel device applications. According to tensor analysis, all the odd higher-rank tensors such as the nonlinear susceptibility χ (2) , the piezoelectric modulus dij k , and the electro-optic coefficient rij k , which are of the third rank, will have their sign changed with the flipping of Ps , whereas the sign of the even-ranked tensors such as the linear susceptibility χ (1)

L.-H. Peng (B) · H.-M. Wu Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan, R.O.C. e-mail: [email protected] C.-M. Lai Department of Electronic Engineering, Ming Chuan University, Taoyuan, Taiwan, R.O.C. P. Ferraro et al. (eds.), Ferroelectric Crystals for Photonic Applications, Springer Series in Materials Science 91, DOI 10.1007/978-3-642-41086-4_2, © Springer-Verlag Berlin Heidelberg 2014

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will remain unchanged. This unique property makes ferroelectrics a promising material for applications in the field of quantum electronics and optoelectronics [4]. For example, high-density data storage can utilize the reversibility of Ps by fast switching the ferroelectric domain between opposite polarization states [5]. Applications related to energy storage and charge amplification can benefit from ferroelectric devices characterized with spatially graded polarizations [6]. When a periodic sign reversal of Ps appears in a “head-to-head” configuration, the discontinuity of Ps can generate a periodic distribution of localized charge density whose sign also will change periodically at the domain boundaries. The coupling of lattice vibrations with the electromagnetic waves can render various long-wavelength optical properties such as microwave resonance, diele