Abstract: For aligning holes in substrates with the light emitting regions of light emitting diodes, particularly Burrus type diodes, an etchant based on an alkaline peroxide solution is ejected or sprayed onto the masked surface of the substrate. The etchant is selective and also avoids production of insoluble oxides in partially etched holes, as often happens in conventional processes. The invention is particularly applicable to producing holes through substrates to align optical fibres with the light emitting regions.

Abstract: A light emitting diode structure has one or more convex lens formations formed on the surface through which the light issues to provide larger incident angles and reduce internal reflection. Conveniently the structure comprises a multi-layer epitaxially grown structure, and the lens or lenses may be formed integral with the outer surface.

Abstract: For a reversed bias double heterostructure diodes, particularly GaAs diodes, electroabsorption can be obtained with reverse bias and light emission can be obtained with forward bias. However bulk absorption is large at wavelengths close to the band edge, where light emission occurs. Thus light emission through a modulator at zero bias is low. By providing for the light emulsion to be at a larger wavelength than that corresponding to the band edge high modulation efficiencies can be obtained. This is achieved by suitably doping the emitter differently as compared with the modulator so that light emission occurs at wavelengths greater than that at the fundamental energy gap.

Abstract: Accurate alignment between an optical fiber and a light emitting diode -- having a double heterostructure -- is obtained by building the multilayer heterostructure on a substrate surface on which has previously been formed a mesa. After formation of the structure, and forming of a contact on the outermost layer of the structure, in alignment with the mesa, the substrate is etched to form a clearance hole centered on the mesa, which is also removed. The mesa is of the same diameter as the optical fiber and removal of the mesa provides a recess which accurately locates the fiber relative to the light emitting area.