Fabrication and Characterization of Self-assembled Ferroelectric Linear and Nonlinear Photonic Crystals: GaN and LiNbO3

Ferroelectrics distinguish themselves from the commonly-known dielectrics or semiconductors by having a homogeneous spontaneous polarization (P s) due to the crystal’s symmetry. The direction of P s of a ferroelectric crystal can be changed at a temperature higher than the material’s Curie point T c or by applying an external field above a threshold value related to the crystal’s coercive field E c. Single domain bulk ferroelectric crystals can be conveniently produced by using the technique of external electric field poling during the crystal growth. 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. For the latter approach, caution should be exercised to avoid the back-switching of P s 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.