Abstract: A first doped region (20) is grown on a semiconductor substrate (1) as a superlattice region having alternate layers (21, 22) of a first and second semiconductor material followed by a waveguide region (30) having at least a superlattice region with alternate layers (31, 32) of the first and second semiconductor materials. A second doped region (40) is then grown as a superlattice including alternate layers (41, 42) of the first and second semiconductor materials on the waveguide region (30). The first and second doped regions (20 and 40) are grown so that the layers (21, 22, 41, 42) of the first and second semiconductor materials are sufficiently thin and are sufficiently highly doped as to become disordered during growth so that the first and second doped regions (20 and 40) are formed by an alloy of the first and second semiconductor materials having a lower refractive index and larger bandgap than the waveguide superlattice region (30).

Abstract: Optical absorption data for a semiconductor sample is derived by providing a p-type layer (4) of the semiconductor sample between two larger band gap p-type cladding layers (3,5) on an n-type substrate (1). A p-type buffer layer (2) may be present on the substrate (1). Optical radiation is directed towards the p-n junction (6) between the substrate (1) and the buffer layer (2) through a transparent electrode (8) on the outer cladding layer (5). A further electrode (7) contacts the substrate (1) whereby an electric signal can be derived which is related to the voltage generated by the photovoltaic effect at the p-n junction. This signal is indicative of the absorption in the semiconductor sample (4) of the incident radiation in the wavelength range above the absorption edges of both cladding layers and below the wavelength limit at which the p-n junction is sensitive.