High power semiconductor laser device

1. A semiconductor laser device, comprising:

a semiconductor substrate;

a lower clad layer formed on the semiconductor substrate;

a lower guide layer formed on the lower clad layer;

an active layer formed on the lower guide layer;

an upper guide layer formed on the active layer; and

an upper clad layer formed on the upper guide layer,

wherein the lower and upper clad layers have the same refractivity, and the lower clad layer includes a high refractivity layer, which is spaced from the lower guide layer by a constant distance and has a refractivity higher than that of the upper clad layer; and

wherein the high refractivity layer has an Al content (wt %) of approximately 0.85 to approximately 0.97 times as much as an Al content of the lower clad layer.

2. The semiconductor laser device as set forth in claim 1 ,

wherein the high refractivity layer is spaced from the lower guide layer toward the side of the substrate by at least a distance corresponding to half of the total thickness of the upper and lower guide layers and the active layer.

3. The semiconductor laser device as set forth in claim 1 ,

wherein the upper and lower guide layers have the same thickness.

4. The semiconductor laser device as set forth in claim 1 ,

wherein the upper and lower guide layers have the same refractivity.

5. The semiconductor laser device as set forth in claim 1 ,

wherein the high refractivity layer is disposed between the lower clad layer and the semiconductor substrate.

6. The semiconductor laser device as set forth in claim 1 ,

wherein the distance of the high refractivity layer spaced from the lower guide layer toward the side of the semiconductor substrate is less than 3 times as large as the total thickness of the upper and lower guide layers and the active layer.

7. The semiconductor laser device as set forth in claim 1 ,

wherein the high refractivity layer is disposed in the lower clad layer.

8. The semiconductor laser device as set forth in claim 1 ,

wherein the active layer is made of an i-GaAs based material, the upper and lower guide layers are made of an i-AlGaAs based material, the upper clad layer is made of a p-type AlGaAs based material, and the lower clad layer is made of an n-type AlGaAs based material.

9. The semiconductor laser device as set forth in claim 1 ,

wherein the active layer is made of an i-AlGaAs based material, the upper and lower guide layers are made of an i-AlGaAs based material, the upper clad layer is made of a p-type AlGaAs based material, and the lower clad layer is made of an n-type AlGaAs based material.

10. A semiconductor laser device, comprising:

a semiconductor substrate;

a lower clad layer formed on the semiconductor substrate;

a lower guide layer formed on the lower clad layer;

an active layer formed on the lower guide layer;

an upper guide layer formed on the active layer; and

an upper clad layer formed on the upper guide layer,

wherein

the lower clad layer includes a low refractivity layer, wherein said low refractivity layer and said upper clad layer have the same refractivity;

the lower clad layer further includes a high refractivity layer, which is spaced from the lower guide layer by a constant distance and has a refractivity higher than that of the upper clad layer; and

the high refractivity layer has an Al content (wt %) of approximately 1.3 to approximately 2.5 times as much as an Al content of the lower guide layer.

11. A semiconductor laser device, comprising:

a semiconductor substrate;

a lower clad structure formed on the semiconductor substrate;

a lower guide layer formed on the lower clad structure;

an active layer formed on the lower guide layer;

an upper guide layer formed on the active layer; and

an upper clad layer formed on the upper guide layer;

wherein

the lower clad structure comprises first and second lower clad layers;

the first lower clad layer and the upper clad layer have the same first refractivity;

the second lower clad layer is spaced from the lower guide layer by a constant distance and has a second refractivity higher than the first refractivity; and

the second lower clad layer has an Al content (wt %) of approximately 0.85 to approximately 0.97 times as much as an Al content of the first lower clad layer.

12. The semiconductor laser device as set forth in claim 11 . wherein the lower clad structure further comprises a third lower clad layer.

13. The semiconductor laser device as set forth in claim 12 , wherein the first lower clad layer has the same refractivity as that of the third lower clad layer.

14. The semiconductor laser device as set forth in claim 13 , wherein

the third lower clad layer is formed on the semiconductor substrate;

the second lower clad layer is formed on the third lower clad layer;

the first lower clad layer is formed on the second lower clad layer; and

the lower guide layer is fanned on the first lower clad layer.

15. The semiconductor laser device as set forth in claim 11 , wherein

the second lower clad layer is formed on the semiconductor substrate;

the first lower clad layer is formed on the second lower clad layer; and

the lower guide layer is formed on the first lower clad layer.

16. The semiconductor laser device as set forth in claim 11 , wherein said distance is at least half of a total thickness of the upper and lower guide layers and the active layer.

17. The semiconductor laser device as set forth in claim 11 , wherein the upper and lower guide layers have the same thickness or the same refractivity.

18. The semiconductor laser device as set forth in claim 11 , wherein said distance is less than 3 times as much as a total thickness of the upper and lower guide layers and the active layer.

19. The semiconductor laser device as set forth in claim 11 , wherein

the active layer is made of one selected from the group consisting of an i-GaAs based material and an i-AlGaAs based material;

the upper and lower guide layers are made of an i-AlGaAs based material;

the upper clad layer is made of a p-type AlGaAs based material; and

the lower clad structure is made of an n-type AlGaAs based material.