Nitride semiconductor laser device and optical information reproduction apparatus using the same

1. A nitride semiconductor laser device, comprising:

a first-conductivity-type cladding layer formed of a nitride semiconductor material;

an active layer formed of a nitride semiconductor material; and

a second-conductivity-type cladding layer formed of a nitride semiconductor material,

wherein:

the first-conductivity-type cladding layer includes a layer having a total thickness having a range larger than 0.4 μm and less than 1.15 μm and formed of a material having a refractive index lower than at least an effective refractive index of a laser oscillation mode,

the layer having a total thickness having a range larger than 0.4 μm and less than 1.15 μm in the first-conductivity-type cladding layer includes at least a first-conductivity-type first cladding layer and a first-conductivity-type second cladding layer which have different compositions from each other, and

the first-conductivity-type first cladding layer has a refractive index lower than the refractive index of the first-conductivity-type second cladding layer.

2. A nitride semiconductor laser device according to claim 1 , wherein a distance between the first-conductivity-type first cladding layer and the active layer is 0.05 μm or more and 0.24 μm or less in a thickness direction of the nitride semiconductor laser device.

3. A nitride semiconductor laser device according to claim 2 , further comprising a first-conductivity-type contact layer formed of a nitride semiconductor material provided on the second main surface of the first-conductivity-type cladding layer, wherein the first-conductivity-type contact layer has a refractive index higher than the effective refractive index of the laser oscillation mode and is formed of a material which is transmissive with respect to light having a laser oscillation wavelength of the laser oscillation mode.

4. A nitride semiconductor laser device according to claim 2 , wherein a distance between the first-conductivity-type second cladding layer and the active layer is 0.34 μm or less in a thickness direction of the nitride semiconductor laser device.

5. A nitride semiconductor laser device according to claim 2 , wherein the first-conductivity-type first cladding layer has a thickness of 0.02 μm or more and 0.15 μm or less.

6. A nitride semiconductor laser device according to claim 2 , wherein the first-conductivity-type second cladding layer has an Al content which is 0.03 or more and 0.10 or less.

7. A nitride semiconductor laser device according to claim 2 , comprising a horizontal direction light confinement ridge structure on the side of the first-conductivity-type cladding layer with respect to the active layer.

8. A nitride semiconductor laser device according to claim 7 , wherein the first-conductivity-type first cladding layer has a flat portion and a stripe convex portion, and at least the first-conductivity-type second cladding layer is provided substantially on the entirety of a top surface of the stripe convex portion.

9. A nitride semiconductor laser device according to claim 8 , further comprising a buried layer of a second conductivity type or of a high resistance so as to cover a top surface of the flat portion, side surfaces of the stripe convex portion and side surfaces of the first-conductivity-type second cladding layer, wherein the buried layer has a refractive index which is substantially equal to that of the first-conductivity-type first cladding layer.

10. A nitride semiconductor laser device according to claim 9 , wherein the buried layer is formed of InGaAlN or AlGaN having substantially an equal composition of that of the first-conductivity-type first cladding layer.

11. A nitride semiconductor laser device according to claim 10 , wherein the first-conductivity-type first cladding layer and first-conductivity-type second cladding layer each contain at least AlGaN.

12. A nitride semiconductor laser device according to claim 11 , wherein an Al content of the first-conductivity-type first cladding layer y 1 , an Al content of the first-conductivity-type second cladding layer y 2 , and a thickness of the first-conductivity-type first cladding layer d [μm] are in the ranges of:

0.02≦d≦0.05; and

−0.557+11.128 ×y 1 −75.583 ×y 1 2 +224.67 ×y 1 3 −246.67 ×y 1 4 ≦y 2 ≦0.0036+0.90169 ×y 1 ; and

y 2 <y 1 ≦0.30; and

0.04≦y 2 ≦0.15,

or

0.05≦d≦0.10; and

y 2 ≦0.0086+0.89 ×y 1 ; and

y 2 <y 1 ≦0.30; and

0.04≦y 2 ≦0.15,

or

0.10≦d≦0.15; and

y 2 ≦0.017974+0.90169 ×y 1 ; and

y 2 <y 1 ≦0.30; and

0.04≦y 2 ≦0.15.

13. A nitride semiconductor laser device according to claim 12 , wherein an Al content of the first-conductivity-type first cladding layer y 1 , an Al content of the first-conductivity-type second cladding layer y 2 , and a thickness of the first-conductivity-type first cladding layer d [μm] are in the ranges of:

0.02≦d≦0.05; and

0.030851 ×y 1 (−0.27442) ≦y 2 ; and

y 2 <y 1 ≦0.30; and

 0.04≦y 2 ≦0.15,

or

0.05≦d≦0.10, and

0.016137 ×y 1 (−0.52323) ≦y 2 ≦0.094234 ×y 1 (−0.35119) ; and

y 2 <y 1 ≦0.30; and

0.04≦y 2 ≦0.15,

or

0.10≦d≦0.15; and

y 2 ≦0.031792 ×y 1 (−0.95084) ; and

y 2 <y 1 ≦0.30; and

0.04≦y 2 ≦0.15.

14. A nitride semiconductor laser device according to claim 12 , wherein an Al content of the first-conductivity-type first cladding layer y 1 , an Al content of the first-conductivity-type second cladding layer y 2 , and a thickness of the first-conductivity-type first cladding layer d are in the ranges of:

0.05≦d≦0.15; and

0.04≦y 1 ≦0.08; and

0.10≦y 2 ≦0.20.

15. A nitride semiconductor laser device according to claim 2 , wherein:

the second-conductivity-type cladding layer has a third main surface and a fourth main surface, the third main surface being closer to the active layer than the fourth main surface, and includes a second-conductivity-type first cladding layer and a second-conductivity-type second cladding layer having a different composition from that of the second-conductivity-type first cladding layer, which are provided in this order from the third main surface of the second-conductivity-type cladding layer, and

the second-conductivity-type first cladding layer has a refractive index lower than that of the second-conductivity-type second cladding layer.

16. A nitride semiconductor laser device according to claim 15 , wherein a distance between the second-conductivity-type first cladding layer and the active layer is 0.05 μm or more and 0.24 μm or less in a thickness direction of the nitride semiconductor laser device.

17. A nitride semiconductor laser device according to claim 16 , wherein a distance between the second-conductivity-type second cladding layer and the active layer is 0.34 μm or less in a thickness direction of the nitride semiconductor laser device.

18. A nitride semiconductor laser device according to claim 16 , wherein the second-conductivity-type first cladding layer has a thickness of 0.02 μm or more and 0.15 μm or less.

19. A nitride semiconductor laser device according to claim 16 , wherein the second-conductivity-type first cladding layer and the second-conductivity-type second cladding layer each contain at least AlGaN.

20. A nitride semiconductor laser device according to claim 19 , wherein an Al content of the second-conductivity-type first cladding layer x 1 , an Al content of the second-conductivity-type second cladding layer x 2 , and a thickness of the second-conductivity-type first cladding layer d′ are in the ranges of:

0.02≦d′≦0.05; and

−0.557+11.128×x 1 −75.583×x 1 2 ; and

+224.67 ×x 1 3 −246.67 ×x 1 4 ≦x 2 ≦0.0036+0.90169 ×x 1 ; and

x 2 < x 1 ×0.30; and

0.04≦x 2 ≦0.15,

or

0.05≦d′≦0.10; and

x 2 ≦0.0086+0.89 ×x 1 ; and

x 2 <x 1 ≦0.30; and

0.04≦x 2 ≦0.15,

or

0.10≦d′≦0.15; and

x 2 ≦0.017974+0.90169 ×x 1 ; and

x 2 <x 1 ≦0.30; and

0.04≦x 2 ≦0.15.

21. A nitride semiconductor laser device according to claim 20 , wherein an Al content of the second-conductivity-type first cladding layer x 1 , an Al content of the second-conductivity-type second cladding layer x 2 , and a thickness of the second-conductivity-type first cladding layer d′ are in the ranges of:

0.02≦d′≦0.05; and

0.030851×x 1 (−0.27442) ×x 2 ; and

x 2 <x 1 ≦0.30; and

0.04≦x 2 ≦0.15,

or

0.05≦d′≦0.10; and

0.016137 ×x 1 (−0.52323) ≦x 2 ≦0.094234 ×x 1 (−0.35119) ; and

x 2 <x 1 ≦0.30; and

0.04≦x 2 ≦0.15,

or

0.10≦d′≦0.15; and

x 2 ≦0.031792 ×x 1 (−0.95084) ; and

x 2 <x 1 ≦0.30; and

0.04≦x 2 ≦0.15.

22. A nitride semiconductor laser device according to claim 20 , wherein an Al content of the second-conductivity-type first cladding layer x 1 , an Al content of the second-conductivity-type second cladding layer x 2 , and a thickness of the second-conductivity-type first cladding layer d′ are in the ranges of:

0.05≦d′≦0.15; and

 0.04≦x 1 ≦0.08; and

0.10≦x 2 ≦0.20.

23. An optical information reproduction apparatus for reproducing information recorded on an optical disc having an information recording surface, by converting light which is emitted by a light source to the optical disc and then reflected by the optical disc, the optical information reproduction apparatus comprising a nitride semiconductor laser device according to claim 1 as a light source.

24. A nitride semiconductor laser device, comprising:

a first-conductivity-type cladding layer formed of a nitride semiconductor material;

an active layer formed of a nitride semiconductor material; and

a second-conductivity-type cladding layer formed of a nitride semiconductor material,

wherein:

the first-conductivity-type cladding layer includes a layer having a total thickness having a range larger than 0.4 μm and less than 1.15 μm and formed of a material having a refractive index lower than at least an effective refractive index of a laser oscillation mode, and

the second-conductivity-type cladding layer includes an area having a refractive index which decreases continuously towards the active layer.

25. A nitride semiconductor laser device, comprising:

a first-conductivity-type cladding layer formed of a nitride semiconductor material;

an active layer formed of a nitride semiconductor material; and

a second-conductivity-type cladding layer formed of a nitride semiconductor material,

wherein:

the first-conductivity-type cladding layer includes a layer having a total thickness having a range larger than 0.4 μm and less than 1.15 μm and formed of a material having a refractive index lower than at least an effective refractive index of a laser oscillation mode, and

a portion disposed within the first-conductivity-type cladding layer or the whole portion of the first-conductivity-type cladding layer is formed as a super-lattice construction, and within boundary planes of multi-layer films constituting the super-lattice construction, there exists a combination of two planes in which a first plane has an average value of refractive index of upper and lower layers disposed in the boundary planes which is smaller than a refractive index of a second plane which is farther from the active layer than the first plane.