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.

A room-temperature photoelectrochemical etching process for n-type GaN films using a 0.04 M KOH solution and Hg arc lamp illumination is described. The process provides highly anisotropic etch profiles and high etch rates ͑Ͼ300 nm/min͒ at moderate light intensities ͑50 mW/cm 2 @365 nm͒. The etch rate and photocurrent are characterized as a function of light intensity for stirred and unstirred solutions, and the etch process is found to be diffusion limited for light intensities greater than 20 mW/cm 2 @365 nm. A reaction mechanism for the etch process is proposed.

Gallium nitride is used to fabricate high brightness blue and green light-emitting diodes in spite of high densities of extended structural defects. We describe a photoelectrochemical etching process that reveals the dislocation microstructure of n-type GaN films by selectively removing material between dislocations. The GaN whiskers formed by the etching have diameters between 10 and 50 nm and lengths of up to 1 μm. A correlation between the etched features and threading dislocations in the unetched film is confirmed through transmission electron microscopy studies. The whisker formation is believed to be indicative of electrical activity at dislocations in GaN.

A room-temperature photoelectrochemical wet etching process is described that produces smoothly etched GaN surfaces using KOH solution and Hg arc lamp illumination. Atomic force microscope measurements indicate a root-mean-square etched surface roughness of 1.5 nm, which compares favorably to the unetched surface roughness of approximately 0.3 nm. Etch rates of 50 nm/min were obtained using a KOH solution concentration of 0.02 M and an illumination intensity of 40 mW/cm2. It is shown that the smooth etching occurs under conditions of low KOH solution concentration and high light intensities, which result in a diffusion-limited etch process.

We describe a technique based on photoelectrochemical wet etching that enables efficient and accurate evaluation of dislocation densities in n-type GaN films. The etching process utilizes dilute aqueous KOH solutions and Hg arc lamp illumination to produce etched GaN “whiskers” by selectively etching away material around threading dislocations. The etched whiskers, each corresponding to a single threading dislocation, can be effectively imaged by plan-view scanning electron microscopy. The distribution and density of dislocations are then readily observed over very large sample areas. Transmission electron microscope and atomic force microscope studies of the GaN samples confirm the accuracy of the dislocation density obtained by the wet etching.