Nitride semiconductor laser device and method of producing the same

Abstract

A method of producing a nitride semiconductor laser device includes: forming a wafer including a nitride semiconductor layer of a first conductivity type, an active layer of a nitride semiconductor, a nitride semiconductor layer of a second conductivity type, and an electrode pad for the second conductivity type stacked in this order on a main surface of a conductive substrate and also including stripe-like waveguide structures parallel to the active layer; cutting the wafer to obtain a first type and a second type of laser device chips; and distinguishing between the first type and the second type of chips by automatic image recognition. The first type and the second type of chips are different from each other in position of the stripe-like waveguide structure with respect to a width direction of each chip and also in area ratio of the electrode pad to the main surface of the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing nitride semiconductor laser devices in a state of a laser bar in accordance with an embodiment of the present invention.

FIG. 2 is a schematic plan view illustrating a shape of a p-side electrode pad of a chip (B) in FIG. 1 in more detail.

FIG. 3 is a schematic plan view illustrating a shape of a p-side electrode pad of a chip (A) in FIG. 1 in more detail.

FIG. 4 is a conceptual block diagram showing a general constitution of an automatic chip inspection apparatus.

FIG. 5 is a schematic plan view illustrating a shape of a p-side electrode pad of a chip regarding a nitride semiconductor laser device according to another embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view showing a main part of a layered structure in a nitride semiconductor laser device according to still another embodiment of the present invention.

FIG. 7 is a schematic block diagram illustrating an optical system and a propagation path of light for reproduction in an optical information reproducing apparatus according to still another embodiment of the present invention.

FIG. 8 is a schematic cross-sectional view showing a main part of a layered structure in the nitride semiconductor laser device shown in FIG. 1.

FIG. 9 is a schematic cross-sectional view exemplarily showing a main part of a conventional nitride semiconductor laser device.

FIG. 10 is a schematic plan view of the nitride semiconductor laser device of FIG. 9 seen from above.

FIG. 11 is a schematic plan view exemplarily showing an upper surface of a laser bar according to the prior art just before division into individual chips.

Claims

1. A method of producing a nitride semiconductor laser device, comprising the steps of: forming a wafer including a nitride semiconductor layer of a first conductivity type, an active layer of a nitride semiconductor, a nitride semiconductor layer of a second conductivity type, and an electrode pad for the second conductivity type stacked in this order on a main surface of a conductive substrate and also including a plurality of stripe-like waveguide structures parallel to said active layer;cutting said wafer to obtain a first type of nitride semiconductor laser device chip and a second type of nitride semiconductor laser device chip; anddistinguishing between said first type and said second type of laser device chips by automatic image recognition,wherein said first type and said second type of laser device chips are different from each other in position of said stripe-like waveguide structure with respect to a width direction of each chip and also in area ratio of said electrode pad for the second conductivity type to said main surface of said substrate.

2. The method of producing a nitride semiconductor laser device according to claim 1, wherein the area ratio of said electrode pad for the second conductivity type in said first type of laser device chip is less than 60% of the area ratio of said electrode pad for the second conductivity type in said second type of laser device chip.

3. The method of producing a nitride semiconductor laser device according to claim 1, wherein, in each of said first type and said second type of laser device chips, a metal layer of less than 0.1 μm thickness is present or not present in an area not having said electrode pad for the second conductivity type on an upper surface of said semiconductor layer of the second conductivity type.

4. The method of producing a nitride semiconductor laser device according to claim 1, wherein, in each of said first type and said second type of laser device chips, said electrode pad for the second conductivity type includes a circular area of 80 μm diameter.

5. The method of producing a nitride semiconductor laser device according to claim 4, wherein said circular area is spaced by a distance of more than 10 μm from said stripe-like waveguide structure.

6. The method of producing a nitride semiconductor laser device according to claim 1, wherein, in each of said first type and said second type of laser device chips, said main surface of said substrate is a rectangle having two sides parallel to and the other two sides perpendicular to said stripe-like waveguide structure, and each of said other two sides has a length of more than 50 μm and less than 250 μm.

7. The method of producing a nitride semiconductor laser device according to claim 1, wherein, in each of said first type and said second type of laser device chips, an area not having said electrode pad for the second conductivity type on an upper surface of said semiconductor layer of the second conductivity type is lower by more than 10% in reflectance with respect to almost the entire wavelength range of incident illumination light vertical to said chip as compared to the other area having said electrode pad for the second conductivity type during said automatic image recognition.

8. The method of producing a nitride semiconductor laser device according to claim 7, wherein, in each of said first type and said second type of laser device chips, the area not having said electrode pad for the second conductivity type on the upper surface of said semiconductor layer of the second conductivity type has a layer of more than 10 nm thickness made of an absorbing material having an absorption coefficient of more than 10000 cm−1 with respect to almost the entire wavelength range of incident illumination light vertical to said chip during said automatic image recognition.

9. The method of producing a nitride semiconductor laser device according to claim 8, wherein said absorbing material is insulator or semiconductor.

10. The method of producing a nitride semiconductor laser device according to claim 9, wherein said absorbing material includes silicon, germanium, or TiO2.

11. The method of producing a nitride semiconductor laser device according to claim 7, wherein, in each of said first type and said second type of laser device chips, the area not having said electrode pad for the second conductivity type on the upper surface of said semiconductor layer of the second conductivity type has minute surface unevenness, and a root mean square roughness over a length of 5 μm in a direction parallel to the uneven surface is more than 1 nm and less than 200 nm.

12. A nitride semiconductor laser device, comprising a nitride semiconductor layer of a first conductivity type, an active layer of a nitride semiconductor, a nitride semiconductor layer of a second conductivity type, and an electrode pad for the second conductivity type stacked in this order on a main surface of a conductive substrate, wherein a stripe-like waveguide structure parallel to said active layer is formed, andan area of said electrode pad for the second conductivity type is more than 2% and less than 60% of an area of said main surface of said substrate.

13. The nitride semiconductor laser device according to claim 12, wherein a metal layer of less than 0.1 μm thickness is present or not present in an area not having said electrode pad for the second conductivity type on an upper surface of said semiconductor layer of the second conductivity type.

14. The nitride semiconductor laser device according to claim 12, wherein said electrode pad for the second conductivity type includes a circular area of 80 μm diameter.

15. The nitride semiconductor laser device according to claim 14, wherein said circular area is spaced by a distance of more than 10 μm from said stripe-like waveguide structure.

16. The nitride semiconductor laser device according to claim 12, wherein said main surface of said substrate is a rectangle having two sides parallel to and the other two sides perpendicular to said stripe-like waveguide structure, and each of said other two sides has a length of more than 50 μm and less than 250 μm.

17. The nitride semiconductor laser device according to claim 12, wherein an area not having said electrode pad for the second conductivity type on an upper surface of said semiconductor layer of the second conductivity type is lower by more than 10% in reflectance with respect to almost the entire wavelength range of incident illumination light vertical to said chip as compared to the other area having said electrode pad for the second conductivity type during said automatic image recognition.

18. The nitride semiconductor laser device according to claim 17, wherein the area not having said electrode pad for the second conductivity type on the upper surface of said semiconductor layer of the second conductivity type has a layer of more than 10 nm thickness made of an absorbing material having an absorption coefficient of more than 10000 cm−1 with respect to almost the entire wavelength range of incident illumination light vertical to said chip during said automatic image recognition.

19. The nitride semiconductor laser device according to claim 18, wherein said absorbing material is insulator or semiconductor.

20. The nitride semiconductor laser device according to claim 19, wherein said absorbing material includes silicon, germanium, or TiO2.

21. The nitride semiconductor laser device according to claim 17, wherein the area not having said electrode pad for the second conductivity type on the upper surface of said semiconductor layer of the second conductivity type has minute surface unevenness, and a root mean square roughness over a length of 5 μm in a direction parallel to the uneven surface is more than 1 nm and less than 200 nm.

22. An optical information reproducing apparatus comprising the nitride semiconductor laser device of claim 12.