Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

The growth of large-area, patterned and oriented ZnO nanowires on silicon using a low temperature silicon-CMOS compatible process is demonstrated. Nanowire synthesis takes place using a thin nucleation layer of ZnO deposited by radiofrequency magnetron sputtering, followed by a hydrothermal growth step. No metal catalysts are used in the growth process. The ZnO nanowires have a wurtzite structure, grow along the c-axis direction and are distributed on the silicon substrate according to the pre-patterned nucleation layer. Room temperature PL measurements of the as-grown nanowires exhibit strong yellow-red emission under 325 nm excitation that is replaced by ultraviolet emission after annealing. This method can be used to integrate patterned 1D nanostructures in optoelectronic and sensing applications on standard silicon CMOS wafers.

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High density two dimensional hole gas (2DHG) with a charge density of 1.1×1013 cm-2 has been demonstrated for the first time in GaN/AlGaN heterostructures. The 2DHG is induced by negative polarization charges at the GaN/AlGaN interface. The layer structures have been designed based on theoretical simulation results to maximize the 2DHG charge density. The heterostructures have been grown on sapphire substrate by metal organic chemical vapor deposition. Hall mobility of the 2DHG of 16 cm2 V-1 s-1 has been measured at room temperature with sheet resistance of 35 kΩ/sq.

A comprehensive overview of novel high voltage GaN field effect transistors (FETs) based on the Polarization Superjunction (PSJ) concept and a cost-effective approach towards manufacturing these high performance devices are presented. Current challenges impeding wider adoption of GaN power switching transistors in applications, and latest results of scaled-up PSJ-FETs from POWDEC KK, have also been discussed. The article also presents hard-switching characteristics of 400V-to-800V boost converter constructed using a PSJ-FET grown on sapphire substrate and the future direction of GaN power semiconductor technology based on monolithic integration for advanced power electronics.