Epitaxial Ge1-xSnx alloys are grown separately on a Ge-buffer/Si(100) substrate and directly on a Si(100) substrate by molecular beam epitaxy (MBE) at low temperature. In the case of the Ge buffer/Si(100) substrate, a high crystalline quality strained Ge0.97Sn0.03 alloy is grown, with a χmin value of 6.7% measured by channeling and random Rutherford backscattering spectrometry (RBS), and a surface root-mean-square (RMS) roughness of 1.568 nm obtained by atomic force microscopy (AFM). In the case of the Si(100) substrate, strain-relaxed Ge0.97Sn0.03 alloys are epitaxially grown at 150°C-300°C, with the degree of strain relaxation being more than 96%. The X-ray diffraction (XRD) and AFM measurements demonstrate that the alloys each have a good crystalline quality and a relatively flat surface. The predominant defects accommodating the large misfit are Lomer edge dislocations at the interface, which are parallel to the interface plane and should not degrade electrical properties and device performance. Epitaxial Ge1-xSnx alloys are grown separately on a Ge-buffer / Si (100) substrate and directly on a Si (100) substrate by molecular beam epitaxy (MBE) at low temperature. In the case of the Ge buffer / Si ) substrate, a high crystalline quality strained Ge0.97Sn0.03 alloy is grown with a χmin value of 6.7% measured by channeling and random Rutherford backscattering spectrometry (RBS), and a surface root mean-square (RMS) roughness of 1.568 nm obtained by atomic force microscopy (AFM). In the case of the Si (100) substrate, strain-relaxed Ge0.97Sn0.03 alloys are epitaxially grown at 150 ° C-300 ° C, with the degree of strain relaxation being more than 96%. The X-ray diffraction (XRD) and AFM measurements demonstrate that the alloys each have a good crystalline quality and a relatively flat surface. The predominant defects accommodating the large misfit are Lomer edge dislocations at the interface, which are parallel to the interface plane and should not degrade electrical properties and de vice performance.