Phonons in epitaxially grown α-Sn1−xGex alloys

Abstract

We present a Raman scattering study of optical phonons in α-Sn1−xGex alloys (x≤0.08) grown by molecular beam epitaxy on CdTe (100) substrates. The Raman spectra provide strong evidence for the growth of high quality films in the diamond-structure phase. The composition dependence of the Raman modes shows some qualitative differences with results from the isomorphic Ge1−xSix system. We show that these differences can be understood in terms of a simple model that considers confinement and strain effects.

Features of polarized Raman spectra for homogeneous and non‐homogeneous compressively strained Ge1−ySny alloys

“…In GeSn alloys, most Raman investigations concentrate on the Ge–Ge peak, located slightly below 300 cm −1 . Only a small number of investigations discuss other Ge–Ge modes or the Ge–Sn and Sn–Sn‐like modes present in the spectra from GeSn alloys in the region 350–100 cm −1 . Furthermore, there are some discrepancies in the results reported in some of these papers.…”

Extended Compositional Range for the Synthesis of SWIR and LWIR Ge1–ySny Alloys and Device Structures via CVD of SnH4 and Ge3H8

“…This peak, when observed, is mounted on a broad continuum that extends to low Raman shifts, as seen in Figure a. Based on results from Si 0.5 Ge 0.5 alloys, the “Ge–Sn” mode frequency in Ge 0.5 Sn 0.5 has been estimated to be around 240 cm –1 . For y < 0.5, the frequency is expected to increase due to the compression of the Ge–Sn bond relative to the relaxed Ge 0.5 Sn 0.5 .…”

“…This is not the case in Ge 1– y Sn y alloys. Clear evidence of “Sn–Sn” and “Ge–Sn” modes is only seen in Sn-rich alloys . For Ge-rich samples, some authors have assigned a feature near 260 cm –1 to “Ge–Sn” modes .…”

“…Clear evidence of "Sn−Sn" and "Ge−Sn" modes is only seen in Sn-rich alloys. 36 For Ge-rich samples, some authors have assigned a feature near 260 cm −1 to "Ge−Sn" modes. 37 This peak, when observed, is mounted on a broad continuum that extends to low Raman shifts, as seen in Figure 6a.…”

“…Based on results from Si 0.5 Ge 0.5 alloys, the "Ge−Sn" mode frequency in Ge 0.5 Sn 0.5 has been estimated to be around 240 cm −1 . 36 For y < 0.5, the frequency is expected to increase due to the compression of the Ge−Sn bond relative to the relaxed Ge 0.5 Sn 0.5 . On the other hand, extrapolating the solid line in Figure 6c, one would predict the frequency of the "Ge−Ge" mode in Ge 0.5 Sn 0.5 to be around 260 cm −1 .…”