We demonstrated the heteroepitaxial growth of single-crystal faceted Ge nanowires (NWs) by electron-beam evaporation on top of Si (111) substrates. Despite the non-ultrahigh vacuum growth conditions, scanning electron microscope and transmission electron microscope images show that NWs have specific crystallographic growth directions ([111],[110], and [112]) and that specific surface crystallographic planes ({111} or {110}) correspond to the [110] and [112] growth directions. Moreover, we studied in detail the Ge NWs structural properties. The temperature dependence of the NW length and of the frequency of each crystallographic orientation has been elucidated. Finally, the microscopic growth mechanisms have been investigated.