N-polar GaN: Epitaxy, properties, and device applications

In recent years, Gallium Nitride (GaN) has been established as a material of choice for high power switching, high power RF and lighting applications. In c-direction, depending on the surface termination III-nitrides have either a group III element (Al, In, Ga) polarity or a N-polarity. Currently, commercially available GaN-based electronic and optoelectronic devices are fabricated predominantly on Ga-polar GaN. However, N-polar nitride heterostructures due its intrinsic material properties, including opposite polarization field and more chemically reactive surface, can provide benefits for these applications. In this article, some of important electronic and optical properties of N-polar (In, Ga, Al)N thin films and heterostructures have been reviewed. Different techniques that have been used for the epitaxial growth of these materials including tri-halide vapor phase epitaxy (THVPE), metalorganic chemical vapor deposition (MOCVD), and plasma-assisted molecular beam epitaxy (PAMBE) have been discussed. Finally, some of important process technologies that have been developed for fabrication of N-polar GaN high electron mobility transistors are presented.