Optical critical points of Si_xGe_1−x−ySn_yalloys with high Si content

Abstract

We extend the analysis of optical transition energies above 1.5 eV in ternary Si x Ge 1−x−y Sn y alloys grown by molecular beam epitaxy to a composition range in which 1−x−y is as low as 0.405. Simple models for transition energies assume a quadratic dependence on material content. Comparing our results to existing predictions of the transition energies based on results obtained from samples with much lower Si and Sn content, however, we find a significant disagreement between experiment and theory, indicating that the assumption of a quadratic dependence might not be valid for the entire composition range of the ternary alloy.

Electrical characterization of n-doped SiGeSn diodes with high Sn content

“…Three different alloy compositions were selected and chosen to approximately match the lattice constant of the underlying Ge. Material composition and strain were investigated using x-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS) [13]. RBS measurement results are reported in table 1.…”

Raman shifts in MBE‐grown SixGe1 − x − ySny alloys with large Si content

“…For each sample, one RSM and three rocking curves for three positions of interest on the sample were measured. [9,13] To investigate the crystal quality, samples were characterized by scanning TEM (STEM) in high-angle annular dark-field (HAADF) mode, which can provide compositional information (the image contrast is proportional to Z 1.7 , where Z is the atomic number). Furthermore, an EDXS analysis was conducted in STEM mode to examine the compositional distribution as well as the homogeneity of the grown Si x Ge 1 − x − y Sn y thin films.…”

“…Quantitative information on composition for all samples was obtained from RBS measurements, as published elsewhere. [9,13] We note that the RUMP simulation software was used for fitting of the random RBS spectra with normalization with respect to the Ge buffer, as recommended by Xu et al [16] An example fit and detailed discussion is provided by Wendav et al [9] Table 1 shows the compositional information for the three different positions on the wafer, that is, at the center (I), at half the radius (II), and at the edge (III) of each wafer. For all samples, the Sn content as obtained from RBS measurements was found to increase from the center towards the edge of the wafer (Table 1).…”

“…[6,7,[10][11][12] For further development of Si x Ge 1 − x − y Sn y growth techniques and devices, it is crucial to correctly characterize their composition and lattice properties because those parameters decisively influence both electronic and optoelectronic characteristics. [13] Although material composition and strain can be measured with a high degree of accuracy using Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD), these techniques are time-consuming and give information averaged over a relatively large area of the sample, much larger than the typical device size. This makes them unsuitable for the characterization of submicrometer-scale variations of composition and strain, which occur, for example, in selective semiconductor growth processes or after structuring.…”

“…[14,15] An extension to Si x Ge 1 − x − y Sn y alloys with higher Si content, as they can be obtained by molecular beam epitaxy (MBE), is not necessarily straightforward. It was previously found for material properties such as critical points in the optical density of states [13] that a compositional dependence established for alloys with low Si and Sn content can fail to provide an accurate description of the behavior for Si x Ge 1 − x − y Sn y alloys with high Si content. As a result, the relationship between composition and strain parameters and Raman spectra for Si x Ge 1 − x − y Sn y alloys with high Si content does not necessarily have to follow the trends observed for lower Si and Sn fractions.…”