The metastable Ge_1-xSn_x alloy system is an interesting group IV semiconductor material with potential applications in the fabrication of midinfrared optoelectronic devices. Considerable attention has been given to Ge_1-xSn_x alloys because they offer the opportunity to realize the fascinating idea of having a direct energy gap material based fully on group IV elements. Band structure calculations show that Ge_1-xSn_x has a direct band gap continuously tunable from ~0.5 to 0 eV at Sn concentrations from 0.09 to 0.25 approximately, besides because of the absence of polar optical scattering, intrinsic to IV-IV alloys and lower effective mass of Ge, it is expected that Ge_1-xSn_x exhibits high carrier mobility. However, the growth of single phase crystals presents several problems associated with the limited bulk solubility exhibited by Sn in Ge, the large lattice mismatch between Sn and Ge and lower surface free energy of Sn versus Ge leading to the surface segregation of Sn. Additionally, the mutual maximum solubility of Ge and Sn is less than 1%. Therefore, Ge_1-xSn_x alloys are metastable and grown under non-equilibrium conditions. The recent synthesis of good crystalline quality Ge_1-x Sn_x thin films and the experimental observation of an indirect to direct band gap transition make feasible the eventual fabrication.