Abstract
This thesis focuses on the improvement of the performances of LEDs emitting in the UV-C range. They are attracting more and more attention, especially since 2 years with the appearance of COVID-19, thanks to the germicidal power of ultraviolet radiation. However, the performances of UV LEDs strongly drops as their emissionwavelength decreases to reach the UV-C range. For this reason, a detailed study is proposed on the first part of this thesis, aiming at improving the surface morphology and the crystalline quality of the AlGaN buffer layers withhigh Al content (70%) through a parametric study. Then, multiple quantum wells (MQWs) are grown on top of this AlGaN buffer layer and first optimizations of the MQW growth conditions lead to an IQE of 20% at 268 nm.Nevertheless, the radiative efficiency of AlGaN quantum wells can be improved by reducing the dislocations density coming from the AlN/sapphire template used. One way to overcome some of these problems is to perform the growth of the whole UV LED structure on AlGaN nanopyramids. This approach is discussed in the second part of this manuscript.Thanks to the selective area growth of AlGaN nanopyramids, the dislocations coming from the substrate can be filtered through the dielectic mask, and the internal electric field in the quantum wells grown on the semi polar facets can be reduced. A detailed study is presented in the last two chapters on the selective area growth of AlGaNnanopyramids, highlighting the influence of the mask design on the pyramid morphology as well as the deposition on the mask surface, due to the short diffusion length of Al atoms. Using a conventional growth method, the AlGaN truncated pyramids have a very low Al composition in their core, the Al atoms being concentrated on the pyramid edges. In contrast, using a pulsed growth mode, the Al incorporation can start as soon as the growth begins : these results can be explained by the hydrogen etching of GaN taking place when the growth is stopped. 100% AlGaN nanopyramids have been thus obtained. First trials on AlGaN/AlGaN MQWs grown on these nanopyramids present an emission at 285 nm.