Molecular beam epitaxy growth and optical properties of GaN quantum disks in AlN nanowires were investigated, with the purpose of controlling the emission wavelength of AlN nanowire-based light emitting diodes. Besides GaN quantum disks with a thickness ranging from 1 to 4 monolayers, a special attention was paid to incomplete GaN disks exhibiting lateral confinement. Their emission consists of sharp lines which extend down to 215 nm, in the vicinity of AlN band edge. The room temperature cathodoluminescence intensity of an ensemble of GaN quantum disks embedded in AlN nanowires is about 20 % of the low temperature value, emphasizing the potential of ultrathin/incomplete GaN quantum disks for deep UV emission.

We report a two-step process to obtain smooth and vertical {10-10} m-plane facets in AlGaN/GaN separate confinement heterostructures designed to fabricate ultraviolet lasers emitting at 355 nm. The process combines inductively coupled plasma reactive ion etching with crystallographic-selective wet etching using a KOH-based solution. The anisotropy in the wet etching allows the fabrication of flat, parallel facets without degradation of the multilayer ensemble. The optical performance of the lasers is strongly improved (reduction of the lasing threshold by a factor of two) when using the two-step process for the definition of the cavity, in comparison to cavities fabricated by mechanical cleaving.

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The engineering of the internal electric field inside III-nitride devices opens up interesting perspectives in terms of device design to boost the radiative efficiency, which is a pressing need in the ultraviolet and green-to-red spectral windows. In this context, it is of paramount importance to have access to a tool like off-axis electron holography which can accurately characterize the electrostatic potentials in semiconductor heterostructures with nanometer-scale resolution. Here, we investigate the distribution of the electrostatic potential and chemical composition in two 10-period AlN/GaN (20 nm/20 nm) multilayer samples, one of these being non-intentionally doped and the other with its GaN layers heavily doped with Ge at a nominal concentration ([Ge] = 2.0 ± 0.2 × 1021 cm–3) which is close to the solubility limit. The electron holography experiments demonstrate the effects of free carrier screening in the case of Ge doping. Furthermore, in the doped sample, an inversion of the internal electric field is observed in some of the AlN layers. A correlated study involving holography, electron dispersive X-ray spectroscopy, and theoretical calculations of the band diagram demonstrates that the perturbation of the potential can be attributed to Ge accumulation at the heterointerfaces, which paves the way to the use of Ge delta doping as a design tool to tune the electric fields in polar heterostructures.