Study of Sn migration during relaxation of Ge1-xSnx layers using atom probe tomography



Ge1-xSnx is receiving a growing interest in the semiconductor community as it is predicted that at ∼10% Sn concentration, unstrained Ge1-xSnx will exhibit a direct band gap leading to potentially important Opto-electronic applications. In strained Ge1-xSnx the expected concentration of Sn for this crossover from an indirect towards a direct bandgap is even lower. Moreover Sn has a ∼13% lattice mismatch with Ge opening up possibilities for strain engineering in high mobility CMOS devices based on Ge. Although Ge1-xSnxlayers have been grown using various methods like molecular beam epitaxy, CVD growth etc. with Sn concentrations as high as 10%, one is faced with the problem of limited Sn-solubility in Ge and hence the corresponding limits beyond which the layer starts to relax. Understanding relaxation mechanisms and kinetics of these layers requires insight at the atomic scale of Sn-migration processes for which Atom Probe Tomography (APT) is a powerful tool. In this paper we use APT for characterizing Ge1-xSnxlayers and compare the Sn location and redistributions for fully strained and partially relaxed films. Comparing the Sn-distributions and their local surroundings we see a tendency for the Sn to locally cluster forming enriched regions, in the relaxed sample, while the majority of the enriched regions still remains embedded in the lattice planes. A small fraction of the Sn atoms is delocalized out of the lattice planes (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)