Fabrication of SrGe(2) thin films on Ge (100), (110), and (111) substrates

Semiconductor strontium digermanide (SrGe(2)) has a large absorption coefficient in the near-infrared light region and is expected to be useful for multijunction solar cells. This study firstly demonstrates the formation of SrGe(2) thin films via a reactive deposition epitaxy on Ge substrates. The growth morphology of SrGe(2) dramatically changed depending on the growth temperature (300−700 °C) and the crystal orientation of the Ge substrate. We succeeded in obtaining single-oriented SrGe(2) using a Ge (110) substrate at 500 °C. Development on Si or glass substrates will lead to the application of SrGe(2) to high-efficiency thin-film solar cells.