Sn distribution in Ge/GeSn heterostructures formed by sputter epitaxy method

Abstract

Ge/GeSn heterostructure was formed on Ge and Ge virtual substrates using the sputter epitaxy method, and the Sn profiles at the Ge/GeSn heterostructure were investigated using secondary ion mass spectrometry (SIMS). The growth temperature of the Ge/GeSn heterostructure was about 215 and 250 °C, and the thicknesses of the Ge and GeSn layers were about 90 and 70 nm, respectively. The growth rates of Ge and GeSn were relatively high and were about 0.36 and 0.4 nm/sec, respectively. The Sn content of the formed GeSn layers was estimated using an X-ray diffraction (XRD) two-dimensional reciprocal space map and was about 9 %. From the results of the atomic force microscopy and the transmission electron microscopy, the interface of the Ge/GeSn heterostructure was sharp and the surface was flat. At the Ge/GeSn interface in the sample formed at 215 °C, the Sn concentration was decreased at 3.4 nm/dec, and the 1/e decay length was about 15Å, which were smaller than 8 nm/dec and 35 Å in the previous report. The Sn diffusion depended on the growth temperature and the underlayer. The gradient of the Sn content at the 390-nm-thick GeSn layer was estimated using SIMS and was about 0.55 %/μm in the sputter epitaxy method, which was smaller than 6.2 %/μm in the previous reports. From the XRD measurements, the 390-nm-thick GeSn layer had no strain relaxation. It is considered that a high-growth rate and no strain relaxation contribute to limiting the Sn diffusion, and uniform Sn content GeSn layers were obtained.