A method of generating a germanium structure includes performing an epitaxial depositing process on an assembly of a silicon substrate and an oxide layer, wherein one or more trenches in the oxide layer expose surface portions of the silicon substrate. The epitaxial depositing process includes depositing germanium onto the assembly during a first phase, performing an etch process during a second phase following the first phase in order to remove germanium from the oxide layer, and repeating the first and second phases. A germanium crystal is grown in the trench or trenches. An optical device includes a light-incidence surface formed by a raw textured surface of a germanium structure obtained by an epitaxial depositing process without processing the surface of the germanium structure after the epitaxial process.