Spontaneous and Piezoelectric Polarization in Nitride Heterostructures

Abstract

This chapter presents an overview of spontaneous and piezoelectric polarization effects in nitride semiconductors, and of their consequences for III-V nitride material properties and device behavior. Polarization effects are of particular importance in III-V nitrides because the wurtzite crystal structure leads to the existence of a nonzero spontaneous polarization that theoretical studies suggest differs considerably in magnitude between AIN and GaN. Recent theoretical results have indicated that nitride semiconductors also possess a large spontaneous polarization, associated with which will be electrostatic charge densities analogous to those produced by piezoelectric polarization fields. The elucidation of polarization and its influence on nitride heterostructure materials and device physics necessarily entails a clear understanding as well of the issue of crystal polarity. Recent work has demonstrated that polarization effects can exert a pronounced influence on heterostructure material properties and device physics and, furthermore, that these effects can be used to achieve substantial improvements in various aspects of device performance.