Effects Of Polarization Orientation Research Articles

Charge transport in non-polar and semi-polar III-V nitride heterostructures

Compared to the intense research focus on the optical properties, the transport properties in non-polar and semi-polar III-nitride semiconductors remain relatively unexplored to date. The purpose of this paper is to discuss charge-transport properties in non-polar and semi-polar orientations of GaN in a comparative fashion to what is known for transport in polar orientations. A comprehensive approach is adopted, starting from an investigation of the differences in the electronic bandstructure along different polar orientations of GaN. The polarization fields along various orientations are then discussed, followed by the low-field electron and hole mobilities. A number of scattering mechanisms that are specific to non-polar and semi-polar GaN heterostructures are identified, and their effects are evaluated. Many of these scattering mechanisms originate due to the coupling of polarization with disorder and defects in various incarnations depending on the crystal orientation. The effect of polarization orientation on carrier injection into quantum-well light-emitting diodes is discussed. This paper ends with a discussion of orientation-dependent high-field charge-transport properties including velocity saturation, instabilities and tunneling transport. Possible open problems and opportunities are also discussed.

Piezoelectric Moduli of Piezoelectric Ceramics

The effective piezoelectric moduli of polycrystalline piezoelectric ceramics are calculated using a straightforward averaging method (a Voigt average) and a more rigorous effective‐medium theory recently developed for piezocomposites. The effects of polarization orientation within each crystallographic domain and the shape of the domain on the effective piezoelectric moduli are presented. The effective‐medium theory, which includes full coupling of the elastic and dielectric interactions, gives results in reasonable agreement with experimental ones.