Gallium nitride and its alloys, AlGaN and InGaN, are essential but also challenging materials for the development of optoelectronic devices, such as visible or UV LEDs. The optical and electric properties of nano-objects such as 2D layers, quantum dots or nanowires are indeed directly affected by the concentration and the distribution of dopants. Mg is the most used p-type dopant for nitrides, however its impact on structural and optical properties is still not fully understood. In particular it is of the upmost importance to determine if it is homogeneously distributed or not. In metal organic chemical vapor deposition or hydride vapour phase epitaxy grown layers, for concentrations higher than 1018 cm-3, Mg has been observed to segregate into a variety of defects, inversion polarity, and pyramidal inversion domains . In molecular beam epitaxy (MBE) grown layers, the question is not solved for such low concentrations. However, higher concentration of Mg causes clustering or incorporation in interstitial sites . For this purpose, we have used atom probe tomography (APT), EDX both in SEM and TEM, and EELS with the aim to compare and determine which one is the most appropriate technique for providing qualitative and quantitative information on Mg low doping. The obtained results will be presented.
Mg-doped Al0.2Ga0.8N 2D layers grown by MBE have been studied with a concentration around 3×1019 at.cm-3 according to SIMS measurements. The sample has been prepared by FIB either as a thin layer for EELS and EDX investigations, or as a sharp needle for APT experiments.
For EDX as well as for EELS experiments, the main difficulty arises from the position of the emission line (Kα) or respectively absorption line of Mg (Mg K-edge), very close to that of Ga which is the main element of the sample. Adding to this, it has not been possible to observe Mg on TEM-EDX elemental maps.
Thanks to the use of a Bruker FlatQUAD detector in SEM-EDX mode with a very large solid angle data collection which ensures a very high counting rate, it has been possible to detect Mg and its concentration has been estimated around 3.8 ±1.4 x1019 at.cm-3 (Figure ). This is in very good agreement with SIMS experiments.
Finally, we have performed APT analyses on the same samples. The mass spectrum clearly shows the presence of Mg, its isotopes and also its alloys (Figure ). The concentration has been estimated around 3.2 ±2.5 x1019 at.cm-3 after data treatment. The 3D reconstruction of Mg (Figure ) shows a homogenous distribution of Mg. Statistical analyses are currently performed using first and k-nearest neighbor method in order to determine if the distribution is actually homogenous or not at small scale, and to try to have a more accurate measurement of the Mg content according to the method developed by Thomas Philippe et al.
 S.E.Bennet et al. Study of Mg-doped AlGaN/GaN superlattices using TEM coupled to APT – Ultramicroscopy 111 (2011) 207-211)
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 N.Grandjean et al. Control of the polarity of GaN films using an Mg adsorption layer – J.Cryst.Growth 251 (2003) 460
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 E. Robin et al., this conference proceedings
 T.Philippe et al. Clustering and nearest neighbour distances in atom probe tomography – Ultramicroscopy 109 (2009) 1304-1309
To cite this abstract:Lynda Amichi, Isabelle Mouton, Eric Robin, Vincent Delaye, Nicolas Mollard, Philippe Vennéguès, Samuel Matta, Julien Brault, Adeline Grenier, Pierre-Henri Jouneau, Catherine Bougerol; Quantifying Mg doping in AlGaN layers. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/quantifying-mg-doping-in-algan-layers/. Accessed: January 21, 2022
EMC Abstracts - https://emc-proceedings.com/abstract/quantifying-mg-doping-in-algan-layers/