Semiconductor rib waveguide optical modulator with heterojunction control electrode cladding

An optical modulator which comprises:

• (a) a first semiconductive epitaxial layer essentially of Al.sub.x Ga.sub.1-x R on a semiconductor substrate;
• (b) a second semiconductive epitaxial waveguide layer for propagating optical radiation, said waveguide layer being essentially of Al.sub.y Ga.sub.1-y R which has been grown on an exposed surface of the first epitaxial layer, where R is selected from the group consisting of arsenic and phosphorus, O<y<x, and said second epitaxial layer having a relatively thick optical rib waveguide portion and a relatively thin slab portion, said rib waveguide portion having a plateau surface;
• (c) a third layer on a first surface portion of the plateau surface of the second epitaxial layer, said third layer consisting essentially of a chemical compound material having a bulk electrical resistivity which is at least an order of magnitude lower than those of both the first and second epitaxial layers and having at least one chemical constituent element which is different from every chemical element of the semiconductor constituent materials of the first and second epitaxial layers.

Semiconductor apparatus for modulating optical radiation, which comprises

• (a) a semiconductor waveguide layer for propagating optical radiation parallel to a surface of said waveguide layer, said semiconductor waveguide layer having a relatively thick rib waveguide portion and a relatively thin slab portion contiguous with said rib waveguide portion, said rib waveguide portion having a plateau surface;
• (b) optical modulation means including a cladding layer in heterojunction contact with at least a portion of said plateau surface, said cladding layer being of an optically transparent material whose free carrier concentration is at least one order of magnitude more than that of the said waveguide layer and whose bulk refractive index is lower than that of the waveguide layer, said transparent material being a compound composed essentially of chemical constituent elements at least one of which is not a constituent element of the said waveguide layer.