Nonpolar and semipolar Group III nitride-based materials

GaN and its alloys with InN and AIN are materials systems that have enabled the revolution in solid-state lighting and high-power/high-frequency electronics. GaN-based materials naturally form in a hexagonal wurtzite structure and are naturally grown in a (0001) c-axis orientation. Because the wurtzite structure is polar, GaN-based heterostructures have large internal electric fields due to discontinuities in spontaneous and piezoelectric polarization. For optoelectronic devices, such as light-emitting diodes and laser diodes, the internal electric field is generally deleterious as it causes a spatial separation of electron and hole wave functions in the quantum wells, which, in turn, likely decreases efficiency. Growth of GaN-based heterostructures in alternative orientations, which have reduced (semipolar orientations) or no polarization (nonpolar) in the growth direction, has been a major area of research in recent years. This issue highlights many of the key developments in nonpolar and semipolar nitride materials and devices.