Type of presentation: Poster

MS-8-P-2808 FIB/TEM characterization of Si/Ge/Sn alloys

Benedetti A.1, Stefanov S.2, Chiussi S.2
1C.A.C.T.I, Vigo University, Campus Universitario, Vigo (Spain), 2Dpto. Fısica Aplicada, E.E. Industrial, Vigo University, Campus Universitario, Vigo (Spain)
abenedetti@uvigo.es

In recent years, GeSn has emerged as a valuable candidate for the convergence of Si based microelectronics and photonics.

However, the extreme low solubility of Sn and the large (14.7%) lattice mismatch between the elements rendered the use of conventional MBE and CVD growth methods problematic. On the other hand, a very promising alternative to the conventional MBE and CVD growth methods is given by pulsed laser induced epitaxy (PLIE), in which epitaxial GeSn is achieved through fast non-equilibrium solid-liquid-solid phase transitions1.

In order to assess the quality of the PLIE-grown GeSn films, a full characterisation in terms of cristallinity and morphology, as well as of Sn concentration and strain distribution, is required. 
In this work, several TEM as well as FIB based techniques are employed in this sense. HREM and BF/DF imaging are used to analyse crystallinity (Figs. 1,2) and defect distribution of the materials and STEM/EDS analysis to determine Sn distribution across the layers.
On the other hand, Geometrical Phase Analysis (GPA) provides, by analysing the phase variations between different regions, a detailed map of local distortion as well as revealing the presence of defects.

In particular, we focused on the relaxation mechanism of the initially pseudomorphic GeSn layers.
Finally, we present a preliminary analysis of the local distortion of Kikuchi lines, and hence the local strain fields, in PLIE-grown layers, obtained by Electron BackScattered Diffraction (EBSD) in a FIB. An example of EBSD pattern from the surface of a plain GeSn layer is shown in Fig.3.

References

1 - S. Stefanov, J. C. Conde, A. Benedetti, C. Serra, J. Werner, M. Oehme, J. Schulze, D. Buca, B. Hollander, S. Mantl, S. Chiussi

Laser synthesis of germanium tin alloys on virtual germanium

Appl. Phys. Letters 100, 104101 (2012)

Fig. 1: Fig. 1 - BF image of the whole structure

Fig. 2: Fig.2 – Cross sectional HREM image of the top surface of a GeSn layer, showing very good crystallinity.

Fig. 3: Fig. 3 – EBSD pattern from the surface of a GeSn layer