Nitride semiconductor laser element
A nitride semiconductor laser element has a first nitride semiconductor layer, an active layer, a second nitride semiconductor layer, and a first protective film in contact with a cavity end face of the nitride semiconductor layer, wherein the first protective film in contact with at least the active layer of the cavity end face has a region thinner than the maximum thickness of the first protective film.
1. An edge emitting nitride semiconductor laser element having
nitride semiconductor layers including a first nitride semiconductor layer, an active layer and a second nitride semiconductor layer laminated in a lamination direction, and
a first protective film continuously covering a cavity end face of the nitride semiconductor layers with the cavity end face extending in a direction parallel to the lamination direction,
the first protective film having a thin film region in which a film thickness of the first protective film, which is defined as a distance from the cavity end face to a top surface of the first protective film measured in a direction perpendicular to the lamination direction of the nitride semiconductor layers, increases with increasing distance from a position corresponding to the active layer in the direction parallel to the lamination direction of the nitride semiconductor layers, wherein a ridge is formed on a surface of the second nitride semiconductor layer to form an optical waveguide region, and the thin film region of the first protective film has a width that is larger than a width of the ridge as measured in the direction perpendicular to the lamination direction of the nitride semiconductor layers on a plane parallel to the cavity end face.
2. The laser element according to claim 1 , wherein a ridge is formed on a surface of the second nitride semiconductor layer, and the first protective film has the thin film region under the ridge and nearby.
3. The laser element according to claim 1 , wherein the first protective film is formed of a material having a hexagonal system crystal structure.
4. The laser element according to claim 1 , wherein the first protective film is composed of nitride material.
5. The laser element according to claim 1 , wherein the first protective film has the maximum thickness of 50 Å to 1000 Å.
6. The laser element according to claim 1 , wherein the first protective film has a crystal structure that has the same axial orientation as that of the nitride semiconductor layers constituting the cavity end face.
7. The laser element according to claim 1 , wherein the cavity end face is the M-plane(1-100), A-plane(11-20), C-plane(0001) or R-plane(1-102).
8. The laser element according to claim 1 , wherein a second protective film is further formed on the first protective film.
9. The laser element according to claim 1 , wherein the thin film region of the first protective film has a minimum thickness which is at least 5% thinner than a maximum thickness of the first protective film.
10. The laser element according to claim 1 , wherein the thin film region of the first protective film corresponds to an optical waveguide region of the cavity end face.
11. The laser element according to claim 1 , wherein the thin film region of the first protective film has a horizontally elliptical shape on the cavity end face.
12. The laser element according to claim 1 , further comprising
a second protective film formed on the first protective film,
wherein the second protective film has a thick part protruding from a face on the cavity end face side and from a face opposite the cavity end face with the thick part being disposed in a position corresponding to the thin film region of the first protective film.
13. The laser element according to claim 12 , wherein the thick part of the second protective film is formed on an optical waveguide region of the cavity end face and nearby.
14. The laser element according to claim 12 , wherein a ridge is formed on a surface of the second nitride semiconductor layer, and the second protective film has the thick part under the ridge and nearby.
15. The laser element according to claim 12 , wherein the thick part has a horizontally elliptical shape on the cavity end face.
16. The laser element according to claim 12 , wherein the thick part has a thickness which is at least 5% thicker than the other part of the second protective film.
17. The laser element according to claim 12 , wherein the thick part of the second protective film has the thickness of 1000 Å to 3000 Å.
18. The laser element according to claim 12 , wherein the second protective film is composed of oxide material.
19. The laser element according to claim 12 , wherein the surface area of the thick part formed on a face on the cavity end face side is smaller than the surface area of the thick part formed on the opposite face.
20. The laser element according to claim 12 , wherein the first protective film is formed of a material having a hexagonal system crystal structure.
21. The laser element according to claim 12 , wherein the first protective film has a crystal structure that has the same axial orientation as that of the nitride semiconductor layers constituting the cavity end face.
22. The laser element according to claim 12 , wherein the end face of the cavity is the M-plane(1-100), A-plane(11-20), C-plane(0001) or R-plane(1-102).