Buried semiconductor laser and method for manufacturing the same

1. A buried semiconductor laser, comprising:

an n-type indium phosphide (InP) substrate; an active layer disposed on said n-type InP substrate;

block layers bilaterally provided over said active layer and said block layers;

a clad layer provided over said active layer and said block layers; and

a p-type gallium indium arsenide (InGaAs) contact layer provided over said clad layer,

wherein a predetermined portion of said p-type InGaAs contact layer has a compressive strain equal to or less than a critical strain,

wherein said predetermined portion of p-type InGaAs contact layer includes a flat portion remote from a portion thereof immediately above said active layer and an inclined portion immediately above said active layer, said flat portion of the p-type InGaAs contact layer has a compressive strain that is equal to or less than the critical strain, and said inclined portion of the p-type InGaAs contact layer has a tensile strain that is equal to or less than the critical strain.

2. The buried semiconductor laser according to claim 1 , wherein said flat portion of the p-type InGaAs contact layer includes a layer thickness of 0.3 μm, and the compressive strain of said flat portion is within a range of from 0.1% to 0.2%.

3. The buried semiconductor laser according to claim 2 , wherein said p-type InGaAs contact layer comprises a superlattice structure of a p-type indium arsenide (InAs) layer with a p-type gallium arsenide (GaAs) layer, and

wherein said p-type InAs layer and said p-type GaAs layer have average compressive strains within a range of from 0.1% to 0.2% in said flat portion.

4. A method for manufacturing a buried semiconductor laser, comprising:

forming an active layer on an n-type InP substrate;

forming block layers on both sides of said active layer;

forming a clad layer over said active layer and said block layer; and

forming a p-type InGaAs contact layer over said clad layer,

wherein said forming the p-type InGaAs contact layer includes forming a portion of the p-type InGaAs contact layer having a compressive strain equal to or less than a critical strain.

wherein said forming the portion of the p-type InGaAs contact layer includes forming a flat portion of the p-type InGaAs contact layer remote from a portion thereof immediately above said active layer and an inclined portion immediately above said active layer, said flat portion of the p-type InGaAs contact layer having a compressive strain that is not greater than the critical strain, and said inclined portion of the p-type InGaAs contact layer having a tensile strain that is not greater than the critical strain.

5. The method according to claim 4 , wherein said forming the p-type InGaAs contact layer includes forming the p-type InGaAs contact layer, in which said flat portion includes a layer thickness of 0.3 μm, and the compressive strain of said flat portion is within a range of from 0.1% to 0.2%.

6. The method according to claim 5 , wherein said forming the p-type InGaAs contact layer includes forming the p-type InGaAs contact layer-comprising of a superlattice structure of a p-type indium arsenide (InAs) layer and a p-type gallium arsenide (GaAs) layer, said p-type InAs layer and said p-type GaAs layer having average compressive strains within a range of from 0.1% to 0.2% in said flat portion.

7. The buried semiconductor laser according to claim 1 , wherein the portion of the p-type InGaAs contact layer includes a flat portion having a layer thickness of less than or equal to 0.3 μm, and the compressive strain of said flat portion is within a range of from 0.1% to 0.2%.

8. The buried semiconductor laser according to claim 1 , wherein the flat portion of the p-type InGaAs contact layer is remote by at least 50 μm from the active layer.

9. The buried semiconductor laser according to claim 1 , wherein a composition of the p-type InGaAs contact layer is within a range from In 0.546 Ga 0.454 As to In 0.56 Ga 0.439 As.

10. A buried semiconductor laser, comprising:

an n-type indium phosphide (InP) substrate;

an active layer disposed on said n-type InP substrate;

block lavers bilaterally provided on both sides of said active layer;

a clad layer provided over said active layer and said block layers; and

a p-type gallium indium arsenide (InGaAs) contact layer provided over said clad layer,

wherein a predetermined portion of said p-type InGaAs contact layer has a compressive strain equal to or less than a critical strain,

wherein the p-type InGaAs contact layer comprises a superlattice structure including a p-type indium arsenide (InAs) layer and a p-type gallium arsenide (GaAs) layer,

wherein a flat portion of the p-type InAs layer and a flat portion of the p-type GaAs layer have average compressive strains within a range from 0.1% to 0.2%, and

wherein said superlattice structure includes the flat portion and an inclined portion, each of which has a thickness that is not greater than a critical strain.

11. The buried semiconductor laser according to claim 1 , wherein the p-type InGaAs contact layer has an average compressive strain within a range from 0.1% to 0.2% in a flat portion.

12. The method according to claim 4 , wherein forming the p-type InGaAs comprises growing the p-type InGaAs contact layer to include a flat portion having a compressive strain of 0.1% to 0.2%, the flat portion of the p-type InGaAs contact layer being remote by at least 50 μm from the active layer.

13. The method according to claim 4 , wherein forming the p-type InGaAs contact layer comprises:

providing triethylgallium (TEGa) as a source material of Ga, and trimethylindium (TMIn) as a source material of In, and

controlling the flow rates of the source materials of TEGa and TMIn to provide a controlled strain of the InGaAs to have a compressive strain of 0.1 to 0.2%.

14. The method according to claim 13 , wherein said controlling the flow rates comprises adjusting the flow rates of triethylgallium and trimethylindium to provide the p-type InGaAs contact layer comprising In x Ga y As z , where x is within the range of 0.546 to 0.560, y is within the range of 0.454 to 0.439, and z is equal to 1.

15. A buried semiconductor laser, comprising:

an InP substrate having a first type conductivity;

an active layer disposed on said InP substrate;

block layers bilaterally provided on both sides of said active layer;

a clad layer over said active layer and said block layers; and

a contact layer comprising a second conductivity type indium gallium arsenide (InGaAs) material provided over the clad layer,

wherein said contact layer includes a flat portion remote from a portion thereof immediately above said active layer, and an inclined portion immediately above said active layer, and said contact layer has average compressive strain within a range of from 0.1% to 0.2% in said flat portion,

wherein said contact layer has a tensile strain in said inclined portion, and

wherein said tensile strain is within a range of from 0.1% to 0.2%.

16. The buried semiconductor laser according to claim 15 , wherein said contact layer comprises a superlattice structure of an InAs layer with a GaAs layer.