Lattice constant and substitutional composition of GeSn alloys grown by molecular beam epitaxy

Single crystal epitaxial Ge1−xSnx alloys with atomic fractions of tin up to x = 0.145 were grown by solid source molecular beam epitaxy on Ge (001) substrates. The Ge1−xSnx alloys formed high quality, coherent, strained layers at growth temperatures below 250 °C, as shown by high resolution X-ray diffraction. The amount of Sn that was on lattice sites, as determined by Rutherford backscattering spectrometry channeling, was found to be above 90% substitutional in all alloys. The degree of strain and the dependence of the effective unstrained bulk lattice constant of Ge1−xSnx alloys versus the composition of Sn have been determined.