The binary alloy germanium tin has already been presented as a direct group IV semiconductor at high tin concentrations and specific strain. Therefore, it offers a promising approach for the monolithic integrated light source towards the optical on-chip communication on silicon. However, the main challenge faced by many researchers is the achievement of high tin concentrations and good crystal quality. The key issues are the lattice mismatch to silicon and germanium, as well as the limited solid solubility of tin in germanium of less than 1%. Therefore, this paper presents a systematic investigation of the epitaxial growth conditions of germanium tin with tin concentrations up to 17%. For this, we performed two growth experiments utilizing molecular beam epitaxy. In one experiment, we varied the growth temperature for the epitaxy of germanium tin with 8% tin to investigate the inter-growth temperature stability. In the second experiment, we focused on the strain-relaxation of germanium tin, depending on different tin concentrations and doping types. The results of subsequent material analysis with x-ray diffraction and scanning electron microscopy allow us to narrow the epitaxial window of germanium tin. Furthermore, we present a possible explanation for the unique relaxation mechanism of germanium tin, which is significantly different from the well-known relaxation mechanism of silicon germanium.

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Mn 5 Ge 3 can be used as a ferromagnetic contact material to fabricate spintronic devices. Here, we show that Mn 5 Ge 3 can be fabricated with a simple germanidation process by evaporating Mn on undoped and doped Ge on Si followed by a thermal annealing step to form the ferromagnetic Mn 5 Ge 3 phase. This solid phase preparation of Mn 5 Ge 3 is a robust process with a minor dependence on the annealing parameters. The formation of Mn 5 Ge 3 can be realized using undoped as well as highly doped p-Ge and n-Ge with different doping levels. The interface of Mn 5 Ge 3 is atomically sharp which leads to very low contact resistivities<1 × 10 −7 Ω cm 2 .

Low-temperature magnetoresistance measurements of n- and p-doped germanium–tin (Ge1-y Sn y ) layers with Sn concentrations up to 8% show contributions arising from effects of weak localization for n-type and weak antilocalization for p-type doped samples independent of the Sn concentration. Calculations of the magnetoresistance using the Hikami–Larkin–Nagaoka model for two-dimensional transport allow us to extract the phase-coherence length for all samples as well as the spin–orbit length for the p-type doped samples. For pure Ge, we find phase-coherence lengths as long as (349.0 ± 1.4) nm and (614.0 ± 0.9) nm for n-type and p-type doped samples, respectively. The phase-coherence length decreases with increasing Sn concentration. From the spin–orbit scattering length, we determine the spin-diffusion scattering length in the range of 20–30 nm for all highly degenerate p-type doped samples irrespective of Sn concentration. These results show that Ge1-y Sn y is a promising material for future spintronic applications.