Semiconductor device and method for fabricating the same

1. A semiconductor device comprising:

a substrate and a semiconductor layer formed on the substrate,

wherein the substrate includes:

a first indentation region provided in a main surface thereof and formed with first recesses or protrusions;

a second indentation region provided to adjoin the first indentation region, formed with second recesses or protrusions; and

a flat region provided in a portion of the main surface located on the side of the second indentation region opposite from the first indentation region,

the second indentation region has a lower probability of occurrence of growth nuclei than the first indentation region, and has a higher probability of occurrence of growth nuclei than the flat region, in the case where a crystal of a semiconductor is grown on the main surface, and

the semiconductor layer is made flat at a boundary between the first indentation region and the second indentation region, and at a boundary between the second indentation region and the flat region.

2. The device of claim 1 , wherein the density of the second recesses or protrusions in the second indentation region is lower than the density of the first recesses or protrusions in the first indentation region.

3. The device of claim 2 , wherein in the second indentation region, the density of the second recesses or protrusions is higher in an area located on the side thereof in contact with the first indentation region than in an area located on the opposite side from that area.

4. The device of claim 1 , wherein the first recesses or protrusions are arranged in a lattice pattern, and the second recesses or protrusions are arranged in a lattice pattern having a longer arrangement period than the lattice pattern with the first recesses or protrusions arranged therein.

5. The device of claim 1 , wherein the first recesses or protrusions are arranged in a first lattice pattern, and the second recesses or protrusions are arranged at lattice points of a second lattice pattern other than randomly-selected lattice points, respectively, the second lattice pattern having the same period as the first lattice pattern.

6. The device of claim 1 , wherein the diameters of the second recesses or protrusions are smaller than the diameters of the first recesses or protrusions.

7. The device of claim 6 , wherein the diameters of the second recesses or protrusions are larger in an area of the second indentation region located on the side thereof in contact with the first indentation region than in an area located on the opposite side from that area.

8. The device of claim 1 , wherein the first recesses or protrusions are first recesses, the second recesses or protrusions are second recesses, and the depths of the second recesses are equal to or smaller than the depths of the first recesses, and in the second indentation region, the depths of the second recesses are smaller in an area located on the side thereof in contact with the first indentation region than in an area located on the opposite side from that area.

9. The device of claim 8 , wherein the second recesses have tapered shapes in which the upper diameters are larger than the bottom diameters, respectively.

10. The device of claim 1 , wherein the first recesses or protrusions are first protrusions, the second recesses or protrusions are second protrusions, and the heights of the second protrusions are equal to or smaller than the heights of the first protrusions, and in the second indentation region, the heights of the second protrusions are smaller in an area located on the side thereof in contact with the first indentation region than in an area located on the opposite side from that area.

11. The device of claim 10 , wherein the second protrusions have tapered shapes in which the upper diameters are smaller than the bottom diameters, respectively.

12. A method for fabricating a semiconductor device, comprising

the step (a) of forming a substrate and

the step (b) of growing a crystal of a semiconductor layer on the substrate,

wherein the substrate includes:

a first indentation region provided in a main surface thereof and formed with first recesses or protrusions;

a second indentation region provided to adjoin the first indentation region, formed with second recesses or protrusions; and

a flat region provided in a portion of the main surface located on the side of the second indentation region opposite from the first indentation region,

the second indentation region has a lower probability of occurrence of growth nuclei than the first indentation region, and has a higher probability of occurrence of growth nuclei than the flat region, in the case where a crystal of a semiconductor is grown on the main surface.

13. The method of claim 12 ,

wherein the step (a) is the step of etching the first indentation region and the second indentation region using different masks to form the first recesses or protrusions and the second recesses or protrusions, respectively, and

the first recesses or protrusions and the second recesses or protrusions are formed so that the density of the second recesses or protrusions in the second indentation region is lower than the density of the first recesses or protrusions in the first indentation region.

14. The method of claim 12 ,

wherein the step (a) is the step of etching the first indentation region and the second indentation region using different masks to form first recesses and second recesses, respectively, and

the second recesses are formed so that the depths of the second recesses are equal to or smaller than the depths of the first recesses and that in the second indentation region, the depths of the second recesses are smaller in an area located on the side thereof in contact with the first indentation region than in an area located on the side thereof in contact with the flat region.

15. The method of claim 12 ,

wherein the step (a) is the step of etching the first indentation region and the second indentation region using different masks to form first protrusions and second protrusions, respectively, and

the second protrusions are formed so that the heights of the second protrusions are equal to or smaller than the heights of the first protrusions and that in the second indentation region, the heights of the second protrusions are smaller in an area located on the side thereof in contact with the first indentation region than in an area located on the side thereof in contact with the flat region.

16. The method of claim 12 , further comprising, after the step (b), the step of removing the substrate.

17. The method of claim 12 , further comprising, after the step (b), the step of removing the flat region in the substrate.