Nitride semiconductor laser device and method for fabricating the same

Abstract

A nitride semiconductor laser device has a buried type structure including an active layer sandwiched between an n-type cladding layer and a p-type cladding layer; and a current blocking layer having an opening for confining a current flowing to the active layer. In the buried type structure, a regrown layer made of a nitride semiconductor layer including In (such as an InGaN layer or an AlInGaN layer) and doped with a p-type impurity is formed on the current blocking layer so as to cover the opening of the current blocking layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C and 1D are electron micrographs and schematic diagrams thereof for explaining a problem to be solved by a nitride semiconductor laser device of this invention;

FIG. 2 is a graph of a laser oscillation threshold current concerned with the problem to be solved by the invention;

FIG. 3 is a schematic diagram for showing a phenomenon of a change to the n-type conductivity concerned with the problem to be solved by the invention;

FIG. 4 is a cross-sectional view for schematically showing the architecture of a nitride semiconductor laser device according to Embodiment 1 of the invention;

FIG. 5 is a cross-sectional view for showing a specific architecture of the nitride semiconductor laser device of Embodiment 1;

FIG. 6 is a graph of a laser oscillation threshold current in the invention;

FIGS. 7A, 7B, 7C and 7D are cross-sectional views for schematically showing procedures in a method for fabricating a nitride semiconductor laser device according to Embodiment 2 of the invention;

FIG. 8 is a cross-sectional view for showing the architecture of a conventional nitride semiconductor laser device having a ridge structure; and

FIG. 9 is a cross-sectional view for showing the architecture of a conventional nitride semiconductor laser device having a buried type structure.

Claims

1. A nitride semiconductor laser device comprising: an active layer sandwiched between cladding layers; anda current blocking layer having an opening for confining a current flowing to said active layer,wherein a regrown layer is formed on said current blocking layer for covering said opening of said current blocking layer, andsaid regrown layer is made of a nitride semiconductor layer including In and doped with a p-type impurity.

2. The nitride semiconductor laser device of claim 1, wherein said nitride semiconductor layer including In is made of InGaN or AlInGaN.

3. The nitride semiconductor laser device of claim 1, wherein said regrown layer is made of a multilayered film including said nitride semiconductor layer including In and a thin film of GaN or AlGaN formed below said nitride semiconductor layer including In.

4. The nitride semiconductor laser device of claim 1, wherein said current blocking layer is made of GaN or AlGaN doped with an n-type impurity.

5. The nitride semiconductor laser device of claim 1, wherein said current blocking layer has a lower refractive index than said regrown layer.

6. The nitride semiconductor laser device of claim 1, wherein said regrown layer corresponds to a part of said cladding layers.

7. The nitride semiconductor laser device of claim 1, wherein a region adjacent to the side face of said opening in said regrown layer buried in said opening of said current blocking layer is changed to an n-type conductivity, andthe width of said n-type conductivity changed region is 10% or lower of the width of a region where said n-type conductivity is not changed in said regrown layer buried in the opening.

8. A nitride semiconductor laser device comprising: an active layer sandwiched between cladding layers; anda current blocking layer having an opening for confining a current flowing to said active layer,wherein a regrown layer made of a nitride semiconductor doped with a p-type impurity is formed on said current blocking layer for covering said opening of said current blocking layer,a portion of said regrown layer buried in said opening of said current blocking layer and adjacent to a side face of said opening is changed to have an n-type conductivity, andsaid portion changed to have an n-type conductivity has a width of 0.15 μm or less.

9. A method for fabricating a nitride semiconductor laser device including an active layer sandwiched between cladding layers and a current blocking layer having an opening for confining a current flowing to said active layer, comprising the steps of: forming said active layer sandwiched between said cladding layers on a substrate;forming said current blocking layer on one of said cladding layers;forming said opening for confining the current flowing to said active layer by etching a part of said current blocking layer; andforming a regrown layer on said current blocking layer for covering said opening of said current blocking layer,wherein said regrown layer is made of a nitride semiconductor layer including In and doped with a p-type impurity.

10. The method for fabricating a nitride semiconductor laser device of claim 9, wherein the step of forming a regrown layer includes: a first sub-step of forming a thin film of GaN or AlGaN on said current blocking layer for covering said opening of said current blocking layer; anda second sub-step of forming said nitride semiconductor layer including In and doped with a p-type impurity on said thin film.

11. The method for fabricating a nitride semiconductor laser device of claim 9, wherein said nitride semiconductor layer including In is made of InGaN or AlInGaN.

12. A method for fabricating a nitride semiconductor laser device including an active layer sandwiched between cladding layers and a current blocking layer having an opening for confining a current flowing to said active layer, comprising the steps of: forming said active layer sandwiched between said cladding layers on a substrate;forming said current blocking layer on one of said cladding layers;forming said opening for confining the current flowing to said active layer by etching a part of said current blocking layer; andforming a regrown layer made of a nitride semiconductor layer doped with a p-type impurity on said current blocking layer for covering said opening of said current blocking layer,wherein the step of forming a regrown layer includes: a first sub-step of depositing said nitride semiconductor layer at a first growth temperature where lateral growth of said nitride semiconductor layer is slow; anda second sub-step of depositing said nitride semiconductor layer at a second growth temperature where said nitride semiconductor layer is grown with high crystallinity.

13. The method for fabricating a nitride semiconductor laser device of claim 12, wherein said first growth temperature is lower than said second growth temperature.

14. The method for fabricating a nitride semiconductor laser device of claim 9 or 12, wherein a region adjacent to the side face of said opening in said regrown layer buried in said opening of said current blocking layer is changed to an n-type conductivity, andthe width of said n-type conductivity changed region is 10% or lower of the width of a region where said n-type conductivity is not changed in said regrown layer buried in the opening.