Silicidation-induced band gap shrinkage in Ge epitaxial films on Si

Abstract

Ge epitaxial films on Si grown at high temperatures show a shrinkage in the direct band gap $E_g^{\Gamma }$ as a result of the tensile strain accumulated during the cooling process after growth, making it a promising candidate for effective photon detection in L-band telecommunications. However, because of strain relaxation at temperatures >750 °C, only about 0.20% tensile strain can be accumulated at most. This leads to a direct band gap of 0.773 eV, corresponding to 1605 nm and is not enough to cover the whole L band (1561–1620 nm). In this letter, we report the strain enhancement in epitaxial Ge films induced by the formation of ${\mathrm{C54TiSi}}_2$ on the backside of the Si wafers. The backside ${\mathrm{C54-TiSi}}_2$ layer not only forms a good electric contact, but also increases the tensile strain of the Ge film on the front side from 0.20% to 0.24% and a further direct band gap shrinkage from 0.773 to 0.765 eV, corresponding to 1620 nm, which covers the whole L band. Since the silicidation process is compatible with Si complementary metal-oxide-semiconductor technology, this technique is promising to achieve low cost L-band photon detection completely with tensile strained Ge on Si.