Semiconductor laser and fabricating method therefor
View Patent ↗At least a lower cladding layer, an active layer for generating laser light, a first upper cladding layer, an etching stopper layer and a second upper cladding layer are stacked on a substrate. An impurity for restraining laser light absorption is diffused into the second upper cladding layer along a region where a light-emitting end surface is to be formed, under a condition that allows the etching stopper layer to maintain a function of stopping etching for the second upper cladding layer (First annealing process). Etching is performed until the etching stopper layer is reached such that the second upper cladding layer is left in a ridge shape. The impurity in the second upper cladding layer is re-diffused into the active layer to thereby cause local intermixing of the active layer in a portion extending along the light-emitting end surface and located just under the ridge (Second annealing process).
1. A semiconductor laser, which emits laser light through a light-emitting end surface, comprising:
a lower cladding layer, an active layer for generating laser light, a first upper cladding layer and an etching stopper layer stacked in this order on a substrate;
a second upper cladding layer formed in a shape of a ridge on the etching stopper layer, the ridge extending perpendicularly to the light-emitting end surface;
a current blocking layer disposed in regions on both sides of the second upper cladding layer; and
an impurity diffused in a portion extending along the light-emitting end surface from the etching stopper layer to the active layer and located at least under the ridge for local intermixing in this portion to restrain laser light absorption, wherein
in a region along the light-emitting end surface, the etching stopper layer has a bandgap smaller in portions thereof disposed in positions corresponding to both sides of the ridge than in a portion thereof located just under the ridge.
2. The semiconductor laser as claimed in claim 1 , wherein
in the region along the light-emitting end surface, the active layer has a bandgap larger in a portion thereof located just under the ridge than in portions thereof disposed in positions corresponding to both sides of the ridge.
3. The semiconductor laser as claimed in claim 2 , wherein
in the region along the light-emitting end surface, a photoluminescence wavelength shift to a shorter wavelength side due to the local intermixing of the active layer in the portion located just under the ridge is 18 nm or more, and a photoluminescence wavelength shift to the shorter wavelength side due to the local intermixing of the active layer in the portions corresponding to both sides of the ridge is not larger than 15 nm.
4. The semiconductor laser as claimed in claim 1 , wherein
the first upper cladding layer contains a diffused impurity of Be or C, and
the impurity diffused in said portion extending along the light-emitting end surface from the etching stopper layer to the active layer is Zn.
5. The semiconductor laser as claimed in claim 4 , wherein
the second upper cladding layer contains a diffused impurity of Be or C.
6. The semiconductor laser as claimed in claim 1 , wherein
the active layer comprises at least one quantum well layer and barrier layers alternating with the quantum well layer;
the at least one quantum well layer is constructed of (Al x Ga 1-x ) y In 1-y P (0≦x≦1 and 0≦y≦1); and
the barrier layers are constructed of (Al x Ga 1-x ) y In 1-y P (0≦x≦1 and 0≦y≦1) whose Al content (x) is greater than that of the quantum well layer.
7. The semiconductor laser as claimed in claim 6 , wherein
the etching stopper layer is constructed of Ga y In 1-y P (0≦y≦1); and
the first and second upper cladding layers are each constructed of (Al x Ga 1-x ) y In 1-y P (0≦x≦1 and 0≦y≦1).
8. The semiconductor laser as claimed in claim 1 , wherein
the active layer comprises at least one quantum well layer and barrier layers alternating with the quantum well layer;
the at least one quantum well layer is constructed of In z Ga 1-z As (0≦z≦1) or Al x Ga 1-x As (0≦x≦1); and
the barrier layers are constructed of Al x Ga 1-x As (0≦x≦1) whose Al content (x) is greater than that of the quantum well layer when the latter is constructed of Al x Ga 1-x As (0≦x≦1).
9. The semiconductor laser as claimed in claim 8 , wherein
the etching stopper layer is constructed of Al x Ga 1-x As (0≦x≦0.3), and
the first and second upper cladding layers are each constructed of Al y Ga 1-y As (x<y≦1).