Process for producing Iron carbide wherein, in a first stage, Iron ore is reduced to sponge iron using a reducing gas containing at least 90% hydrogen, on a nitrogen-free basis, to produce a sponge iron having a carbon content of less than 1% wt. Diaphragms and optical receiving devices suitable to implement the method are described. The disordered quantum well active region is formed by rapid thermal annealing in which defects from one or two InP defect layers diffuse into the parts of the quantum well active region to be disordered. A flange member is provided on an outer wall of the vacuum chamber to cover an opening in the wall.