Atomic insight into Ge1−xSnx using atom probe tomography

Ge(1−x)Sn(x) is receiving a growing interest in the scientific community, as it has important applications in opto-electronic devices, ( as stressor) Source/Drain materials for Ge and SiGe MOSFETS. It is predicted that at 10% Sn concentration or even lower, unstrained Ge(1−x)Sn(x) will exhibit a direct band gap. Moreover, in strained Ge(1−x)Sn(x) the expected concentration of Sn for this cross-over is even lower.As the theoretical Sn incorporation in Ge(1−x)Sn(x) is less than 1%, and Ge(1−x)Sn(x) is prone to relaxation, routes towards the growth of metastable strained films has been extensively explored. Although Ge(1−x)Sn(x) films (with x up to 10%) have been grown using various methods like molecular beam epitaxy, CVD growth etc. there remain issues with tendency of these layers to relax. Detailed studies on the relaxation mechanisms and effects on the Sn-atoms require suitable characterization techniques. Various techniques have been used to study the surface of the film, crystallography or concentration of Sn in the film but none of them provides information at the atomic scale as they average over many layers and atoms. Atom probe tomography (APT) analysis, on the other hand, is one such method that can provide atomic scale resolutions (∼0.3 nm) due to its ability to perform atom by atom analysis.In this paper we explore the use of APT for characterizing Ge(1−x)Sn(x) layers. We comment on the difference of field evaporation values of Ge and Sn in Ge(1−x)Sn(x) layer by taking a closer look at the co-evaporation of the two elements and comment on the accuracy of depth reconstruction of APT for Ge(1−x)Sn(x) layer. Comparing the Sn-distributions and their local surroundings we saw a tendency for the Sn to locally enrich forming Sn clusters. Higher order clusters were observed for the relaxed sample.

► We studied Ge(1−x)Sn(x) layers using atom probe tomography. ► Optimum operating conditions to characterize Ge1−xSnx layer are described. ► Distribution of Sn w.r.t lattice position in the crystal matrix is studied. ► Co-relation between the formation of Sn–Vacancy complexes and relaxation of the layer is also proposed.