Abstract: An optical semiconductor device includes: a mesa that is provided on a surface in a <011> direction of a semiconductor substrate having a (100) plane orientation and being of a first conductivity type, and includes a first cladding layer of the first conductivity type, an active layer, and a second cladding layer of a second conductivity type; a semi-insulating buried layer that buries both sides of the mesa, is provided on the semiconductor substrate, and includes a first region and a second region farther from the mesa than the first region; an insulation film provided on the first and second regions of the buried layer; and an electrode provided on the mesa and the insulation film on the first region; wherein a surface of the first region is at a height equal to or lower than a surface of the mesa, and lowers at farther distances from the mesa.

Abstract: An optical semiconductor device includes: a mesa that is provided on a surface in a <011> direction of a semiconductor substrate having a (100) plane orientation and being of a first conductivity type, and includes a first cladding layer of the first conductivity type, an active layer, and a second cladding layer of a second conductivity type; a semi-insulating buried layer that buries both sides of the mesa, is provided on the semiconductor substrate, and includes a first region and a second region farther from the mesa than the first region; an insulation film provided on the first and second regions of the buried layer; and an electrode provided on the mesa and the insulation film on the first region; wherein a surface of the first region is at a height equal to or lower than a surface of the mesa, and lowers at farther distances from the mesa.

Abstract: There is provided an optical semiconductor device having a first optical semiconductor element including an InP substrate, a lower cladding layer formed on the InP substrate, a lower optical guide layer which is formed on the lower cladding layer and is composed of AlGaInAs, an active layer which is formed on the lower optical guide layer and has a multiple quantum well structure where a well layer and a barrier layer that is formed of AlGaInAs are alternately stacked, an upper optical guide layer which is formed on the active layer and is composed of InGaAsP, and an upper cladding layer formed on the upper optical guide layer.

Abstract: There is provided an optical semiconductor device having a first optical semiconductor element including an InP substrate, a lower cladding layer formed on the InP substrate, a lower optical guide layer which is formed on the lower cladding layer and is composed of AlGaInAs, an active layer which is formed on the lower optical guide layer and has a multiple quantum well structure where a well layer and a barrier layer that is formed of AlGaInAs are alternately stacked, an upper optical guide layer which is formed on the active layer and is composed of InGaAsP, and an upper cladding layer formed on the upper optical guide layer.

Abstract: There is provided an optical semiconductor device having a first optical semiconductor element including an InP substrate, a lower cladding layer formed on the InP substrate, a lower optical guide layer which is formed on the lower cladding layer and is composed of AlGaInAs, an active layer which is formed on the lower optical guide layer and has a multiple quantum well structure where a well layer and a barrier layer that is formed of AlGaInAs are alternately stacked, an upper optical guide layer which is formed on the active layer and is composed of InGaAsP, and an upper cladding layer formed on the upper optical guide layer.

Abstract: A semiconductor laser includes an active layer, a first GaAs layer formed on the active layer, the first GaAs layer including a plurality of recessed portions periodically arranged, each of the recessed portions including a bottom surface of a (100) crystal surface and a slope including a (111) A crystal surface at least in parts, the recessed portion being disposed in contact with each other or with a minimal gap between each of adjacent ones of the recessed portions, the width of the bottom surface being greater than the minimal gaps, an InGaP layer formed on the recessed portion, and a second GaAs layer formed on the InGaAs layer over the recessed portion.

Abstract: An optical semiconductor device includes an active layer, a first semiconductor layer formed above the active layer and made from a semiconductor material containing Al, a second semiconductor layer formed above the first semiconductor layer and made from a semiconductor material which does not contain any one of Al and P and whose band gap is greater than that of the active layer, and a third semiconductor layer formed above the second semiconductor layer and made from a semiconductor material which does not contain Al but contains P. The second semiconductor layer is formed such that the first semiconductor layer and the third semiconductor layer do not contact with each other.

Abstract: In a p-type clad layer, not only a p-type dopant Zn but also Fe is doped. Its Zn concentration is 1.5×1018 cm?3 and the Fe concentration is 1.8×1017 cm?3. In a semi-insulating burying layer, Fe is doped as an impurity generating a deep acceptor level and the concentration thereof is 6.0×1016 cm?3. The Fe concentration in the p-type clad layer is thus three times higher than the Fe concentration in the burying layer.

Abstract: A semiconductor laser includes an active layer, a first GaAs layer formed on the active layer, the first GaAs layer including a plurality of recessed portions periodically arranged, each of the recessed portions including a bottom surface of a (100) crystal surface and a slope including a (111) A crystal surface at least in parts, the recessed portion being disposed in contact with each other or with a minimal gap between each of adjacent ones of the recessed portions, the width of the bottom surface being greater than the minimal gaps, an InGaP layer formed on the recessed portion, and a second GaAs layer formed on the InGaAs layer over the recessed portion.

Abstract: An optical semiconductor device includes an active layer, a first semiconductor layer formed above the active layer and made from a semiconductor material containing Al, a second semiconductor layer formed above the first semiconductor layer and made from a semiconductor material which does not contain any one of Al and P and whose band gap is greater than that of the active layer, and a third semiconductor layer formed above the second semiconductor layer and made from a semiconductor material which does not contain Al but contains P. The second semiconductor layer is formed such that the first semiconductor layer and the third semiconductor layer do not contact with each other.

Abstract: There is provided an optical semiconductor device having a first optical semiconductor element including an InP substrate, a lower cladding layer formed on the InP substrate, a lower optical guide layer which is formed on the lower cladding layer and is composed of AlGaInAs, an active layer which is formed on the lower optical guide layer and has a multiple quantum well structure where a well layer and a barrier layer that is formed of AlGaInAs are alternately stacked, an upper optical guide layer which is formed on the active layer and is composed of InGaAsP, and an upper cladding layer formed on the upper optical guide layer.

Abstract: An optical semiconductor device with a semiconductor laser formed over a semiconductor substrate, and a modulator formed over the semiconductor substrate and continuously arranged with the semiconductor laser, wherein the semiconductor laser includes a first region having a diffraction grating with a phase shift, a second region arranged between the first region and the modulator, and in which the diffraction grating is not formed, and a common active layer formed over the first region and the second region, a first electrode injecting a current into the common active layer.

Abstract: In a p-type clad layer, not only a p-type dopant Zn but also Fe is doped. Its Zn concentration is 1.5×1018 cm?3 and the Fe concentration is 1.8×1017 cm?3. In a semi-insulating burying layer, Fe is doped as an impurity generating a deep acceptor level and the concentration thereof is 6.0×1016 cm?3. The Fe concentration in the p-type clad layer is thus three times higher than the Fe concentration in the burying layer.

Abstract: A 1.3-?m wavelength band buried-heterostructure semiconductor laser includes a semiconductor substrate, a multiple quantum well active layer including quantum well layers and barrier layers, a buried layer in contact with side faces of the multiple quantum well active layer, wherein the barrier layers are made from AlGaInAsP or AlGaInAs, and an Al composition of the barrier layers is 0.275 or less.

Abstract: In order to reduce the parasitic capacitance of the device and obtain an enhanced high-speed response characteristic while assuring the reliability of the device, a semiconductor device is provided such that it comprises: a mesa structure formed on a semiconductor substrate and including a first cladding layer, an active layer, a second cladding layer, a first protective layer and a second protective layer each covering respective side of the active layer, and a cap layer formed between the first protective layer and the second protective layer and covering the top surface of the active layer, wherein aluminum is included only in the active layer; and a buried layer for burying the mesa structure, wherein the first cladding layer, the first protective layer, the second protective layer, and the second cladding layer constitute the side of the mesa structure.