Abstract: A semiconductor waveguide layer is provided in an optical semiconductor integrated circuit device comprising a passive region having at least a branch and an active region having at least a laser diode connected to the branch and at least a photo-diode connected to the branch. The active region is in contact with the passive region. The waveguide layer selectively extends over the passive region and the active region. The semiconductor waveguide layer in the active region has a wavelength composition larger than that in the passive region. The waveguide layer has a semiconductor crystal structure which is continuous not only over the active and passive regions but also at a boundary between the active and passive regions.

Abstract: Disclosed herein is a semiconductor optical waveguide-integrated light-receiving device comprising a waveguide-type photodetector and a passive optical waveguide which are selectively formed on the same substrate, wherein the width of mask for a selective growth is varied along the waveguiding direction so as to simultaneously form core layers which differ from each other in absorption edge wavelength. The core layer may be formed with an MQW layer. It is also featured that waveguide width of the photodetector is made larger than the waveguide width of the optical waveguide. The photodetector and the optical waveguide may be buried by an n--InP layer.

Abstract: The invention provides an avalanche photodiode multilayer structure comprising an absorption layer for absorbing photons and subsequent generation of electron hole pairs, a field relaxation layer in contact with the absorption layer and a multiplication layer in contact with the field relaxation layer. The multiplication layer comprises a plurality of periods of first and second layers. The first layer has a first graded energy band gap being gradually increased in a direction toward which traveling electrons are being accelerated by a predetermined electric field. The second layer has a second graded energy band gap being gradually decreased in the same direction. Both a conduction band edge and a valance band edge are free from any discontinuities and are sloped down toward the same direction through the first and second layers when the first and second layers are being applied with the electric field.

Abstract: An avalanche photodiode includes an avalanche multiplication layer including a superlattice structure consisting of a plurality of barrier and well layers both lattice matched to InP such that the plurality of barrier and well layers are alternately provided one layer on the other layer. The barrier layers consist of InAlAs and the well layers consist of InCaAlAs quarternary system mixed crystal having a forbidden width smaller than 1 eV.

Abstract: An avalanche photodiode comprising an uppermost layer of one conductivity type, a second layer of the other conductivity type wherein the electrons or hole having the greater ionization rate are the minority carriers, a third layer of the second type, having a smaller bandgap than the second layer and wherein the electrons or holes having the greater ionization rate are the majority carriers, and a multi-layer heterojunction structure between the second and third layers comprising alternate layers of the second conductivity type having a bandgap as large as the second layer and layers having a bandgap between those of the second and third layers.