Semiconductor laser device and method of manufacturing the same
A semiconductor laser device includes an N-type cladding layer, an active layer, and a P-type cladding layer. The active layer includes a well layer, a P-side first barrier layer above the well layer, and a P-side second barrier layer above the P-side first barrier layer. The P-side second barrier layer has an AI composition ratio higher than an AI composition ratio of the P-side first barrier layer. The P-side second barrier layer has band gap energy greater than band gap energy of the P-side first barrier layer. The semiconductor laser device has an end face window structure in which band gap energy of a portion of the well layer in a vicinity of an end face that emits the laser light is greater than band gap energy of a central portion of the well layer in a resonator length direction.
1 . A semiconductor laser device that emits laser light, the semiconductor laser device comprising:
a substrate;
an N-type cladding layer above the substrate;
an active layer above the N-type cladding layer; and
a P-type cladding layer above the active layer,
wherein the active layer includes:
a well layer;
a P-side first barrier layer above the well layer; and
a P-side second barrier layer above the P-side first barrier layer,
the P-side second barrier layer has an Al composition ratio higher than an Al composition ratio of the P-side first barrier layer,
the P-side second barrier layer has band gap energy greater than band gap energy of the P-side first barrier layer,
the semiconductor laser device further comprises:
a P-type guiding layer between the P-side second barrier layer and the P-type cladding layer; and
a P-side high Al composition layer between the well layer and the P-side first barrier layer,
the P-side high Al composition layer has an Al composition ratio higher than the Al composition ratio of the P-side first barrier layer,
the P-type guiding layer has band gap energy greater than the band gap energy of the P-side second barrier layer, and
the semiconductor laser device has an end face window structure in which band gap energy of a portion of the well layer in a vicinity of an end face that emits the laser light is greater than band gap energy of a central portion of the well layer in a resonator length direction.
2 . The semiconductor laser device according to claim 1 ,
wherein the P-type cladding layer has band gap energy greater than band gap energy of the N-type cladding layer.
3 . The semiconductor laser device according to claim 1 ,
wherein the well layer has a thickness of at least 6 nm.
4 . The semiconductor laser device according to claim 1 ,
wherein the well layer comprises a semiconductor material represented by a composition formula of Al X Ga 1-X-Y In Y As, where 0<X<1 and 0<Y<1.
5 . The semiconductor laser device according to claim 1 ,
wherein the band gap energy of the P-side second barrier layer gradually increases with distance from the well layer.
6 . The semiconductor laser device according to claim 1 ,
wherein the P-side first barrier layer includes an undoped region that is doped with no impurities, and
the undoped region has a thickness of at least 5 nm.
7 . The semiconductor laser device according to claim 1 ,
wherein the P-side second barrier layer is entirely doped with impurities, and
the P-side first barrier layer includes an undoped region that is doped with no impurities in a region on a side close to the well layer, and a doped region that is doped with impurities in a region on a side far from the well layer.
8 . The semiconductor laser device according to claim 1 ,
wherein a concentration of impurities with which the P-side second barrier layer is doped gradually increases with distance from the well layer.
9 . The semiconductor laser device according to claim 1 ,
wherein an Al composition ratio at least in an interface region between the P-type guiding layer and the P-type cladding layer gradually increases with distance from the well layer.
10 . The semiconductor laser device according to claim 1 ,
wherein a concentration of impurities with which the P-type guiding layer is doped gradually increases with distance from the well layer.
11 . The semiconductor laser device according to claim 1 ,
wherein the active layer further includes an N-side first barrier layer below the well layer, and an N-side second barrier layer below the N-side first barrier layer,
the N-side second barrier layer has an Al composition ratio higher than an Al composition ratio of the N-side first barrier layer, and
the N-side second barrier layer has band gap energy greater than band gap energy of the N-side first barrier layer.
12 . The semiconductor laser device according to claim 11 ,
wherein the band gap energy of the N-side second barrier layer gradually increases with distance from the well layer.
13 . The semiconductor laser device according to claim 11 ,
wherein the N-side second barrier layer is entirely doped with impurities, and
the N-side first barrier layer includes an undoped region that is doped with no impurities in a region on a side close to the well layer, and a doped region that is doped with impurities in a region on a side far from the well layer.
14 . The semiconductor laser device according to claim 11 ,
the P-side second barrier layer has the band gap energy greater than the band gap energy of the N-side second barrier layer.
15 . The semiconductor laser device according to claim 11 , further comprising:
an N-side high Al composition layer between the well layer and the N-side first barrier layer, the N-side high Al composition layer having an Al composition ratio higher than the Al composition ratio of the N-side first barrier.
16 . The semiconductor laser device according to claim 11 , further comprising:
an N-type guiding layer between the N-side second barrier layer and the N-type cladding layer.
17 . The semiconductor laser device according to claim 16 ,
wherein an Al composition ratio at least in an interface region between the N-type guiding layer and the N-type cladding layer gradually increases with distance from the well layer.
18 . The semiconductor laser device according to claim 16 ,
wherein a concentration of impurities with which each of the N-type cladding layer, the N-type guiding layer, the N-side second barrier layer, and the N-side first barrier is doped gradually increases with distance from the well layer or increases in stages.
19 . The semiconductor laser device according to claim 1 ,
wherein the active layer further includes an N-side first barrier layer below the well layer, and an N-side second barrier layer below the N-side first barrier layer,
the N-side second barrier layer has an Al composition ratio higher than an Al composition ratio of the N-side first barrier layer,
the N-side second barrier layer has band gap energy greater than band gap energy of the N-side first barrier layer,
the semiconductor laser device further comprises an N-type guiding layer between the N-side second barrier layer and the N-type cladding layer, and
the P-type guiding layer has band gap energy different from band gap energy of the N-type guiding layer.
20 . The semiconductor laser device according to claim 5 , further comprising:
an N-side first barrier layer and an N-side second barrier layer between the well layer and the N-type cladding layer, in a direction from the well layer to the N-type cladding layer,
the N-side second barrier layer has an Al composition ratio higher than an Al composition ratio of the N-side first barrier layer,
the N-side second barrier layer has band gap energy greater than band gap energy of the N-side first barrier layer,
the band gap energy of the N-side second barrier layer gradually increases with distance from the well layer, and
a maximum value of the band gap energy of the P-side second barrier layer is larger than a maximum value of the band gap energy of the N-side second barrier layer.
21 . The semiconductor laser device according to claim 1 ,
wherein the P-side second barrier layer is in direct contact with the P-side first barrier layer.
22 . The semiconductor laser device according to claim 1 ,
wherein the well layer has a single quantum well structure including a single quantum well layer.
23 . The semiconductor laser device according to claim 1 ,
wherein the active layer further includes an N-side first barrier layer below the well layer, and an N-side second barrier layer below the N-side first barrier layer, and
a total thickness of the P-side first barrier layer and the N-side first barrier layer is at least 20 nm and at most 80 nm.
24 . A method of manufacturing a semiconductor laser device that emits laser light, the method comprising:
disposing an N-type cladding layer above a substrate;
disposing a well layer above the N-type cladding layer;
depositing a P-side high Al composition layer above the well layer
depositing a P-side first barrier layer above the P-side high Al composition layer;
depositing a P-side second barrier layer above the P-side first barrier layer;
depositing a P-type guiding layer above the P-side second barrier layer; and
disposing a P-type cladding layer above the P-type guiding layer,
wherein
the P-side second barrier layer has an Al composition ratio higher than an Al composition ratio of the P-side first barrier layer,
the P-side second barrier layer has band gap energy greater than band gap energy of the P-side first barrier layer,
the P-side high Al composition layer has an Al composition ratio higher than the Al composition ratio of the P-side first barrier layer,
the P-type guiding layer has band gap energy greater than the band gap energy of the P-side second barrier layer, and
the semiconductor laser device has an end face window structure in which band gap energy of a portion of the well layer in a vicinity of an end face that emits the laser light is greater than band gap energy of a central portion of the well layer in a resonator length direction.