Accurate measurements of the absorption coefficient around the direct band gap requires samples with thicknesses of a few microns, which must be grown on substrates or held on special holders. In the case of Ge, the thicknesses are between 4 μm and 15 μm. In the process of developing protocols for the growth of the needed Ge films on Si substrates, we discovered that chlorogermane H3GeCl is an excellent precursor for the low-temperature growth of Ge using Chemical Vapor Deposition (CVD). The molecule eliminates stable HCl, naturally yielding the GeH2 molecular fragments that are key to Ge growth by CVD.

To demonstrate the quality of the Ge layers grown via the chlorogermane route, we fabricated pin diodes and measured their I-V characteristics and optical responsivity and found them to be comparable or better to those obtained with alternative low-temperature precursors. This bodes well for the use of chlorogermane in industrial efforts to integrate Ge functionalities with silicon CMOS.