Progress in efficient doping of high aluminum-containing group III-nitrides

The group III-nitride (InN, GaN, and AlN) class of semiconductors has become one of two that are critical to a number of technologies in modern life-the other being silicon. Light-emitting diodes made from (In, Ga) N, for example, dominate recent innovations in general illumination and signaling. Even though the (In, Ga) N materials system is fairly well established and widely used in advanced devices, challenges continue to impede development of devices that include aluminum-containing nitride films such as (Al, Ga) N. The main difficulty is efficient doping of films with aluminum-rich compositions; the problem is particularly severe for p-type doping, which is essential for Ohmic contacts to bipolar device structures. This review briefly summarizes the fundamental issues related to p-type doping, and then discusses a number of approaches that are being pursued to resolve the doping problem or for circumventing the need for p-type doping. Finally, we discuss an approach to doping under liquid-metal-enabled growth by molecular beam epitaxy. Recent results from a number of groups appear to indicate that p-type doping of nitride films under liquid-metal-enabled growth conditions might offer a solution to the doping problem-at least for materials grown by molecular beam epitaxy. (C) 2018 Author(s).