Semiconductor light-emitting device
A semiconductor laser, having an active layer with a double-quantum-well structure, includes two InGaN well layers, each of which has a thickness of 5 nm. The threshold current deteriorates to a relatively small degree while differential efficiency is improved considerably in a region having a light confinement coefficient Γ of 3.0% or less. The light confinement coefficient indicates the proportion of light in the well layers with respect to light in the light emitting device, during light emission. When the light confinement coefficient Γ is less than 1.5%, the threshold current increases considerably and the improvement in differential efficiency becomes small. It is therefore preferable that the lower limit of the light confinement coefficient Γ be about 1.5%. A differential efficiency of 1.6 W/A or more is obtained when light the confinement coefficient Γ is 3.0% or less, and a differential efficiency of 1.7 W/A or more is obtained when the light confinement coefficient Γ is 2.6% or less.
1. A semiconductor light-emitting device comprising:
a substrate; and
a plurality of III-V compound semiconductor layers supported by said substrate, each layer containing at least Ga and N as principal constituents, wherein said plurality of compound semiconductor layers include, sequentially arranged,
a first cladding layer of a first conductivity type, said first cladding layer including a plurality Al x Ga 1-x N (0≦x≦1) layers in which x increases toward said substrate, each of said Al x Ga 1-x N layers having a respective refractive index,
an active layer with a multi-quantum-well structure that includes at least two InGaN well layers, said first cladding layer being interposed between said substrate and said active layer, and
a second cladding layer of a second conductivity type, opposite the first conductivity type and disposed on an opposite side of said active layer from said first cladding layer, said second cladding layer having a refractive index, wherein said light-emitting device has a light confinement coefficient in a range from 1.5% to 2.0%, the light confinement coefficient indicating proportion of light in said at least two InGaN well layers to overall waveguide light in said light-emitting device during light emission by said light-emitting device.
2. The semiconductor light-emitting device according to claim 1 , wherein at least one Al x Ga 1-x N layer included in said first cladding layer has an Al composition ratio in a range from 0.005 to 0.08.
3. The semiconductor light-emitting device according to claim 1 , wherein at least one Al x Ga 1-x N layer included in said first cladding layer has an Al composition ratio in a range from 0.005 to 0.06.
4. The semiconductor light-emitting device according to claim 1 , wherein at least one Al x Ga 1-x N layer included in said first cladding layer has an Al composition ratio in a range from 0.005 to 0.04.
5. The semiconductor light-emitting device according to claim 1 wherein the refractive indices of said layers of said first cladding layer, excluding the layer of said first cladding layer closest to said substrate, are higher than the refractive index of said second cladding layer.