Semiconductor laser device, semiconductor laser module, and laser light source system for welding

1. A semiconductor laser device, comprising:

a first semiconductor layer on an n side;

a second semiconductor layer on the n side, the second semiconductor layer having band gap energy higher than band gap energy of the first semiconductor layer;

an active layer;

a third semiconductor layer on a p side;

a fourth semiconductor layer on the p side, the fourth semiconductor layer having band gap energy lower than band gap energy of the third semiconductor layer;

an n-type cladding layer; and

a p-type cladding layer, wherein

Eg2<Eg3 is satisfied, where Eg2 denotes a maximum value of the band gap energy of the second semiconductor layer, and Eg3 denotes a maximum value of the band gap energy of the third semiconductor layer,

the third semiconductor layer includes a first region layer in which band gap energy monotonically decreases toward the fourth semiconductor layer,

N2>N3 is satisfied, where N2 denotes an impurity concentration of the second semiconductor layer, and N3 denotes an impurity concentration of the third semiconductor layer,

the first semiconductor layer, the second semiconductor layer, the third semiconductor layer, and the fourth semiconductor layer are between the n-type cladding layer and the p-type cladding layer,

the n-type cladding layer is adjacent to the first semiconductor layer,

the p-type cladding layer is adjacent to the fourth semiconductor layer,

Eg1<Eg4 is satisfied, where Eg1 denotes a maximum value of the band gap energy of the first semiconductor layer, and Eg4 denotes a maximum value of the band gap energy of the fourth semiconductor layer,

the first semiconductor layer is a first waveguide layer,

the fourth semiconductor layer is a second waveguide layer,

light is generated in the active layer, and

a center position of an intensity of the light is located closer to the first semiconductor layer than to the active layer.

2. The semiconductor laser device according to claim 1 , wherein a minimum value of the band gap energy of the third semiconductor layer is greater than Eg2.

3. The semiconductor laser device according to claim 1 , wherein the third semiconductor layer has a thickness greater than a thickness of the second semiconductor layer.

4. The semiconductor laser device according to claim 1 , wherein the third semiconductor layer includes, between the first region layer and the active layer, a second region layer in which band gap energy monotonically increases toward the first region layer.

5. The semiconductor laser device according to claim 4 , wherein a maximum value of the band gap energy of the first region layer and a maximum value of the band gap energy of the second region layer are equal.

6. The semiconductor laser device according to claim 4 , wherein the second region layer has a thickness of 20 nm or more.

7. The semiconductor laser device according to claim 1 , wherein the first region layer has a thickness of 20 nm or more.

8. The semiconductor laser device according to claim 1 , wherein the third semiconductor layer includes an indirect band gap semiconductor layer.

9. The semiconductor laser device according to claim 1 , wherein

the third semiconductor layer includes a group III-V compound semiconductor containing Al, and

an Al ratio in the first region layer has a gradient.

10. The semiconductor laser device according to claim 9 , wherein the first region layer includes an AlGaAs based crystal or an AlGaInP based crystal.

11. The semiconductor laser device according to claim 1 , wherein the first region layer includes a direct band gap semiconductor layer.

12. The semiconductor laser device according to claim 1 , wherein N2−N1≥N3−N4 is satisfied, where N1 denotes an impurity concentration of the first semiconductor layer, and N4 denotes an impurity concentration of the fourth semiconductor layer.

13. The semiconductor laser device according to claim 1 , wherein N2 which denotes the impurity concentration of the second semiconductor layer is 7×10 17 cm −3 or less.

14. The semiconductor laser device according to claim 1 , wherein Eg1≤Eg3 min is satisfied, where Eg1 denotes a maximum value of the band gap energy of the first semiconductor layer, and Eg3 min denotes band gap energy in a portion of the first region layer adjacent to the fourth semiconductor layer.

15. The semiconductor laser device according to claim 1 , wherein

the first semiconductor layer and the second semiconductor layer are in contact with each other, and

the third semiconductor layer and the fourth semiconductor layer are in contact with each other.

16. The semiconductor laser device according to claim 1 , wherein

the second semiconductor layer is an n-type carrier blocking layer, and

the third semiconductor layer is a p-type carrier blocking layer.

17. The semiconductor laser device according to claim 16 , wherein

the active layer includes a barrier layer, and

a value obtained by subtracting an average Al ratio of the barrier layer from an average Al ratio of the p-type carrier blocking layer is 0.31 or more.

18. A semiconductor laser module, comprising:

the semiconductor laser device according to claim 1 .

19. A laser light source system for welding, comprising:

the semiconductor laser module according to claim 18 .

20. The semiconductor laser device according to claim 1 , wherein

the first waveguide layer is an n-type waveguide layer, and

the second waveguide layer is a p-type waveguide layer.