Patent ID: 8330140

Claim:
A semiconductor light emitting device comprising: a semiconductor substrate; and an active layer provided on the semiconductor substrate and having a cascade structure formed by alternately laminating quantum well emission layers and injection layers by multistage-laminating unit laminate structures each including the quantum well emission layer and the injection layer, wherein the unit laminate structure included in the active layer has, in its subband level structure, a first upper level, a second upper level as an energy level higher than the first upper level, and a lower level which are formed in the quantum well emission layer, and an injection level which is formed in the injection layer, the quantum well emission layer has, in order from the unit laminate structure side of the preceding stage, first to n-th barrier layers (n is an integer of 2 or more) and first to n-th well layers, where the first barrier layer is an injection barrier layer for electrons from the injection layer of the preceding stage to the quantum well emission layer, the injection layer has, in order from the quantum well emission layer side, first to m-th barrier layers (m is an integer of 2 or more) and first to m-th well layers, where the first barrier layer is an exit barrier layer for electrons from the quantum well emission layer to the injection layer, an energy interval between the first upper level and the second upper level is smaller than the energy of a longitudinal optical phonon, the injection barrier layer has a layer thickness thicker than layer thicknesses of the second to n-th barrier layers in the quantum well emission layer and layer thicknesses of the second to m-th barrier layers in the injection layer; the exit barrier layer has a layer thickness thicker than layer thicknesses of the second to n-th barrier layers in the quantum well emission layer and layer thicknesses of the second to m-th barrier layers in the injection layer; and the layer thickness of the exit barrier layer is set in a range not less than 70% and not more than 150% of the layer thickness of the injection barrier layer, and light is generated by emission transition using the subband level structure formed by the first upper level, the second upper level, and the lower level in the quantum well emission layer, and electrons after the emission transition are injected from the lower level into the second upper level in the quantum well emission layer of the subsequent stage via the injection level in the injection layer.