A method of generating an optical device comprising a germanium structure, the method comprising: providing an assembly comprising a silicon substrate having an oxide layer on a surface thereof, wherein the oxide layer comprises a number of trenches (16, 16a, 16b), each trench (16, 16a, 16b) extending to and exposing a portion of the surface of the silicon substrate, wherein a trench depth is larger than a trench width, the number of trenches (16, 16a, 16b) being at least one; performing an epitaxial depositing process on the assembly to grow up a germanium crystal of the germanium structure on each exposed portion of the silicon substrate, each germanium crystal being formed in the associated trench (16, 16a, 16b) and on regions of the oxide layer adjoining the associated trench (16, 16a, 16b), wherein the epitaxial depositing process comprises: 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; forming electrical connections to parts of the germanium structure and/or the silicon substrate so as to generate a sensor element capable of converting incident light into an electrical signal, wherein at least parts of the silicon substrate and/or the germanium structure are doped so that a pn junction or a pin junction is formed by the silicon substrate and the germanium structure, wherein the germanium structure has a raw textured surface forming a light incidence surface of the optical device without further processing the germanium structure, wherein the orientation of the surface of the silicon substrate on which the germanium structure is formed is <100>, wherein the raw textured surface comprises a pyramid shape associated with the or each germanium crystal. providing an assembly comprising a silicon substrate having an oxide layer on a surface thereof, wherein the oxide layer comprises a number of trenches (16, 16a, 16b), each trench (16, 16a, 16b) extending to and exposing a portion of the surface of the silicon substrate, wherein a trench depth is larger than a trench width, the number of trenches (16, 16a, 16b) being at least one; performing an epitaxial depositing process on the assembly to grow up a germanium crystal of the germanium structure on each exposed portion of the silicon substrate, each germanium crystal being formed in the associated trench (16, 16a, 16b) and on regions of the oxide layer adjoining the associated trench (16, 16a, 16b), wherein the epitaxial depositing process comprises: 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; 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; forming electrical connections to parts of the germanium structure and/or the silicon substrate so as to generate a sensor element capable of converting incident light into an electrical signal, wherein at least parts of the silicon substrate and/or the germanium structure are doped so that a pn junction or a pin junction is formed by the silicon substrate and the germanium structure, wherein the germanium structure has a raw textured surface forming a light incidence surface of the optical device without further processing the germanium structure, wherein the orientation of the surface of the silicon substrate on which the germanium structure is formed is <100>, wherein the raw textured surface comprises a pyramid shape associated with the or each germanium crystal.