A semiconductor device comprises a plurality of quantum structures comprising predominantly germanium. The plurality of quantum structures are formed on a first semiconductor layer structure. The quantum structures of the plurality of quantum structures have a lateral dimension of less than 15 nm and an area density of at least 8×1011 quantum structures per cm2. The plurality of quantum structures are configured to emit light with a light emission maximum at a wavelength of between 2 μm and 10 μm or to absorb light with a light absorption maximum at a wavelength of between 2 μm and 10 μm.