We report on the performance of AlGaN/GaN/AlN heterostructure field-effect transistors (HFETs) grown over slightly-off c-axis, single-crystal, bulk AlN substrates. Dc and rf characteristics of these devices were comparable to HFETs grown on semi-insulating SiC. The obtained results demonstrate that bulk AlN substrates are suitable for fabricating high-power microwave AlGaN/GaN transistors.

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An approach for growing high-quality AlGaN/AlN multiple quantum wells (MQW) emitting in deep UV region is proposed. The structures are deposited on bulk AlN substrates. Structural analysis by using x-ray diffraction confirms high crystalline quality of these structures. Photoluminescence dependences on excitation intensity and temperature under band-to-band excitation of AlN barrier layers and under selective excitation of the quantum wells are presented. Al0.5Ga0.5N/AlN MQW grown on bulk AlN demonstrate emission at 260 nm with high emission intensity. Stimulated emission of these structures at 258 nm was observed. The results prove great potential of growing structures with high-aluminum-content layers on bulk AlN substrates.

The influence of different parameters, such as temperature, flow rate of NH3, and pressure, in the crystal growth process of GaN micron-size nanoporous particles through the direct reaction of Ga and NH3 has been studied. Temperature influences porosity and the coalescence of the individual pores. Flow rate of NH3 influences the degree of nanoporosity of the particles. Pressure is the main parameter controlling the external shape of the particles by modulation of the crystal growth rate along or perpendicular to the c crystallographic direction. It also seems to play a role in controlling the size of the pores that can be obtained. Programmed and controlled changes in pressure during the growth experiment resulted in interesting nanoporous structures with benefits for extraction of light and fabrication of electrical contacts on these particles.

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We present a technique for the direct deposition of nanoporous GaN particles on Si substrates without requiring any post-growth treatment. The internal morphology of the nanoporous GaN particles deposited on Si substrates by using a simple chemical vapor deposition approach was investigated, and straight nanopores with diameters ranging between 50 and 100 nm were observed. Cathodoluminescence characterization revealed a sharp and well-defined near band-edge emission at ∼365 nm. This approach simplifies other methods used for this purpose, such as etching and corrosion techniques that can damage the semiconductor structure and modify its properties.

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