A germanium waveguide is formed from a P-type silicon substrate that is coated with a heavily-doped N-type germanium layer and a first N-type doped silicon layer. Trenches are etched into the silicon substrate to form a stack of a substrate strip, a germanium strip, and a first silicon strip. This structure is then coated with a silicon nitride layer.

A electro-absorption optical modulator includes a multiple quantum well composed of a plurality of layers including a plurality of quantum well layers and a plurality of barrier layers that are alternately stacked, the plurality of quantum well layers and the plurality of barrier layers including an acceptor and a donor; a p-type semiconductor layer in contact with an uppermost layer of the plurality of layers; and an n-type semiconductor layer in contact with a lowermost layer of the plurality of layers, the multiple quantum well being 10% or more and 150% or less of the p-type semiconductor layer in a p-type carrier concentration, and in the multiple quantum well, an effective carrier concentration which corresponds to a difference between the p-type carrier concentration and an n-type carrier concentration is ±10% or less of the p-type carrier concentration of the multiple quantum well.

A semiconductor laser array includes: a plurality of semiconductor lasers configured to oscillate in a single mode at oscillation wavelengths different from one another, each semiconductor laser including an active layer including a multi-quantum well structure including a plurality of will layers and a plurality of barrier layers laminated alternately, and an n-side separate confinement heterostructure layer and p-side separate confinement heterostructure layer configured to sandwich the active layer therebetween in a thickness direction, band gap energies of the n-side separate confinement heterostructure layer and the p-side separate confinement heterostructure layer being greater than band gap energies of the barrier layers of the active layer. The active layer is doped with an n-type impurity.

The semiconductor laser device includes: an activation layer having at least one first quantum dot layer and at least one second quantum dot layer having a longer emission wavelength than the first quantum dot layer. The gain spectrum of the active layer has the maximum values at the first wavelength and the second wavelength longer than the first wavelength corresponding to the emission wavelength of the first quantum dot layer and the emission wavelength of the second quantum dot layer, respectively. The maximum value of the gain spectrum at the first wavelength is defined as the first maximum value, and the maximum value of the gain spectrum at the second wavelength is defined as the second maximum value. The first maximum value is larger than the second maximum value.

A semiconductor laser according to an embodiment of the present disclosure includes a semiconductor stack section. The semiconductor stack section includes a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, in which the second semiconductor layer is stacked on the first semiconductor layer and includes a ridge having a band shape, and an active layer. The semiconductor stack section further has an impurity region that is at least a portion of a region not facing the ridge and that is located at a position deeper than at least the active layer, in which the impurity region has an impurity concentration of the second conductivity type higher than an impurity concentration of the second conductivity type in a region, of the second semiconductor layer, facing the ridge.

A quantum cascade laser device includes a semiconductor substrate, an active layer provided on the semiconductor substrate, and an upper clad layer provided on a side of the active layer opposite to the semiconductor substrate side and having a doping concentration of impurities of less than 1×10.sup.17 cm.sup.−3. Unit laminates included in the active layer each include a first emission upper level, a second emission upper level, and at least one emission lower level in their subband level structure. The active layer is configured to generate light having a center wavelength of 10 μm or more due to electron transition between at least two levels of the first emission upper level, the second emission upper level, and the at least one emission lower level in the light emission layer in each of the unit laminates.

A germanium waveguide is formed from a P-type silicon substrate that is coated with a heavily-doped N-type germanium layer and a first N-type doped silicon layer. Trenches are etched into the silicon substrate to form a stack of a substrate strip, a germanium strip, and a first silicon strip. This structure is then coated with a silicon nitride layer.

Embodiments of the invention include a III-nitride light emitting layer disposed between an n-type region and a p-type region, a III-nitride layer including a nanopipe defect, and a nanopipe terminating layer disposed between the III-nitride light emitting layer and the III-nitride layer comprising a nanopipe defect. The nanopipe terminates in the nanopipe terminating layer.

An embodiment relates to a surface-emitting laser element, a light-emitting device comprising same, and a method for manufacturing same. A surface-emitting laser element according to an embodiment may comprise: a substrate; a first reflective layer disposed on the substrate; an active layer disposed on the first reflective layer; an aperture region disposed on the active layer and including an aperture and an insulation region; and a second reflective layer disposed on the aperture region. The doping level of the aperture region may be (X+3)XXE18(atoms/cm.sup.3) A ratio (b/a) of a second minimum diameter (b) to a first maximum diameter (a) of the aperture may be [95.0−(2X/3)]% to [99.9−(X/3)]%, wherein X may be 0 to 3.

A monolithic integrated semiconductor random laser comprising substrate, lower confinement layer on the substrate, active layer on the lower confinement layer, upper confinement layer on the active layer, strip-shaped waveguide layer longitudinally made in middle of the upper confinement layer, P.sup.+ electrode layer divided into two segments and made on the waveguide layer and N.sup.+ electrode layer on a back face of the lower confinement layer, wherein the two segments correspond respectively to gain region and random feedback region. The random feedback region uses a doped waveguide to randomly feedback light emitted by the gain region and then generates random laser which is random in frequency and intensity. Further, the semiconductor laser is light, small, stable in performance and strong in integration.