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High temperature thermal annealing

Feng Wu

October 25, 2016 - Posted in Discussion
​​High-temperature thermal annealing: a new technique to improve the crystal quality of AlN layer
For the group-III nitrides grown by MOCVD, it was well established that a buffer layer, either GaN or AlN, grown at low temperature, played a key role in the crystal quality of the epitaxial layer grown on this buffer layer. However, the dislocation density of III-nitride layers grown on sapphire is still very high, usually above 1e10cm-2, especially for AlN layer, due to the low surface mobility of Al adatoms. Recently, a group from Mie University and Tohoku University in Japan published a paper showing that the crystal quality of AlN buffer layer can be significantly improved by just annealing at high temperature in a carbon-saturated N2–CO mixture gas ambient. 

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By annealing the AlN buffer layer at high temperature, they found that not only the crystal quality of AlN buffer layer was improved a lot, but also the surface morphology, as shown in Fig. 2, 3 and 4. Based on this high-quality buffer layer, they grew a 2 µm AlN layer, which had a very low dislocation density of 4.7 × 108 cm−2. More recently, they demonstrated that by thermal annealing in a nitrogen ambient, the surface morphology of sputtered AlN film grown on sapphire substrates markedly changed from columnar-structure morphology to a step and terrace morphology, and simultaneously the dislocation density decreased significantly.

This new finding may have a significant influence on the growth of high-quality group-III nitrides. Such as, if the AlN layer is grown at very high temperature, what will happen to it? Can the crystal quality of it be improved a lot? I think this is a very interesting area which needs more investigation and study.

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