Abstract: An indium phosphate semiconductor substrate is prepared for subsequent growth of epitaxial layers to form a semiconductor device. In the preparation, the substrate is first annealed to promote any tendency for surface accumulation of impurity atoms by diffusion from the substrate and to promote impurity atom removal from the surface of the substrate. The substrate is then surface etched to remove further impurities and to provide a clean, flat surface for subsequent epitaxial layer growth. The final stage of preparation involves growing a semi-insulating buffer layer on the substrate to isolate the device epitaxial layers from the substrate.

Abstract: A semiconductor laser amplifier includes both a waveguide layer and an active layer. In use, an optical wave in the active layer interacts with the waveguiding layer to reduce the polarisation sensitivity of the amplifier. A short, thick active layer is not required, typical dimensions being 250 or 500 .mu.m long, by 0.2 .mu.m high. The mesa is typically about 2 .mu.m wide, but may be wider.

Abstract: An optical detector such as a pin photodiode or avalanche photodiode is provided with an integral dielectric filter (8). The optical filter (8) preferably comprises a plurality of layers of silicon and silicon monoxide. If the detector is a PIN diode, the filter (8) may be provided on the underside of a substrate (1) before growth of the diode is commenced on the other side.

Abstract: A method for the growth of a semi-conductor material on a substrate by vapour phase epitaxy, comprises establishing a gas flow in each of a plurality of ducts, and moving the substrate, in a single plane of movement, from one duct to another. Suitable apparatus for use in the method comprises a plurality of ducts; apparatus for establishing a gas flow along each duct; a substrate support member, on which there may be a groove for the location of a substrate; and apparatus for moving, e.g. rotating, the support member. In use, the substrate is exposed sequentially to at least two of the gas flows, e.g. to grow GaInAs on InP.