Sapphire substrate having triangular projections with portions extending in direction of substrate crystal axis

• US 9,012,936 B2
• Filed: 08/05/2011
• Issued: 04/21/2015
• Est. Priority Date: 08/06/2010
• Status: Active Grant

• Current Assignee: Nichia Corporation
• Original Assignee: Nichia Corporation
• Inventors: Narita, Junya, Okada, Takuya, Wakai, Yohei, Inoue, Yoshiki, Sako, Naoya, Kadan, Katsuyoshi
• Primary Examiner(s): Bradford, Peter
• Application Number:
  US13/204,317
• Publication Number:
  US 20120074431A1
• Time in Patent Office: 1,355 Days
• Field of Search: 257/98, 257/E33.067, 257/E51.021, 257/E33.074, 257/79
• US Class Current: 257/96
• CPC Class Codes: H01L 21/0242 Crystalline insulating materials
• CPC Class Codes: H01L 21/0243 Surface structure
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: Y10T 428/24 Structurally defined web or sheet [e.g., overall dimension, etc.]
• CPC Class Codes: Y10T 428/24479 including variation in thickness

Abstract

The sapphire substrate has a principal surface for growing a nitride semiconductor to form a nitride semiconductor light emitting device and comprising a plurality of projections of the principal surface, wherein an outer periphery of a bottom surface of each of the projections has at least one depression. This depression is in the horizontal direction. The plurality of projections are arranged so that a straight line passes through the inside of at least any one of projections when the straight line is drawn at any position in any direction in a plane including the bottom surfaces of the plurality of projections.

Claims

1. A sapphire substrate having a principal surface for growing a nitride semiconductor to form a nitride semiconductor light emitting device, the sapphire substrate comprising a plurality of projections on the principal surface,

wherein each projection of the plurality of projections is separated from each adjacent projection of the plurality of projections,

wherein each of the projections has a bottom that has a substantially triangular shape,

wherein each side of the bottom of the projections has a depression in its center,

wherein extended portions of the bottoms of the respective projections extend in a direction that is within a range of ±

10 degrees of a crystal axis “

a”

of the sapphire substrate, and

wherein the plurality of projections are arranged so that any straight line that is drawn at any position in any direction in a plane including the bottoms of the plurality of projections passes through a geometric area of the bottom of at least one of projections.

2. The sapphire substrate according to claim 1, wherein each of the projections has a substantially pyramidal shape or substantially truncated pyramidal shape.

3. The sapphire substrate according to claim 1, wherein the plurality of projections are arranged so that a vertex of a bottom of a first projection among neighboring projections is located in a region defined by an imaginary triangle formed between points of two vertexes of a bottom of a second projection among the neighboring projections, and a deepest point of the depression in a corresponding side of the second projection.

4. The sapphire substrate according to claim 3, wherein said first projection of the neighboring projections is arranged so that the deepest portion of the depression of the second projection is located on a line that bisects an angle of a vertex of said first projection.

5. The sapphire substrate according to claim 3, wherein said first projection of the neighboring projections is arranged so that the deepest portion of the depression of the second projection is located on a line that bisects an angle of a vertex of a triangle formed by joining vertexes of said first projection.

6. The sapphire substrate according to claim 3, wherein the projections have a side surface that is inclined from the principal surface of said sapphire substrate, and wherein, in a plan view, a width of the side surface at a first side of the crystal axis “

a”

of said sapphire substrate is larger than a width of the side surface at a second side of the crystal axis “

a”

of said sapphire substrate.

7. The sapphire substrate according to claim 1, wherein each of the projections has a shape with linear symmetry over a straight line that connects a depression to a vertex opposite to a side including the depression.

8. The sapphire substrate according to claim 1, wherein each of the projections has a top surface that has a shape substantially similar to that of its bottom.

9. The sapphire substrate according to claim 1, wherein the plurality of projections are arranged so as to form a plurality of rows, and wherein the plurality of projections are arranged so that bisectors that bisect angles of vertexes of projections arranged in the same row are located on a straight line.

10. The sapphire substrate according to claim 9, wherein an orientation of projections forming a first row among neighboring rows is opposite to an orientation of projections forming a second row among the neighboring rows.

11. The sapphire substrate according to claim 1, wherein the plurality of projections are arranged in a plurality of groups of projections, each group of (n+1) projections being arranged at group vertexes and a group center of a substantially regular n-sided polygon.

12. The sapphire substrate according to claim 11, wherein at least one of the groups shares at least one projection with a neighboring group.

13. A nitride semiconductor light emitting device formed by growing a nitride semiconductor on the principal surface of the sapphire substrate according to claim 1.

14. The semiconductor light emitting device according to claim 13, wherein said nitride semiconductor layer grown on the principal surface of the sapphire substrate has a flat surface.

15. The semiconductor light emitting device according to claim 13, wherein said semiconductor light emitting device has a structure in which a base layer, an n-type layer, an active layer and a p-type layer are sequentially laminated, and wherein the projections of said sapphire substrate are buried in said base layer.

16. The sapphire substrate according to claim 1, wherein each of the extended portions has a rounded distal end.

17. The sapphire substrate according to claim 1, wherein the depressions are curved depressions.

18. The sapphire substrate according to claim 1, wherein the projections have extended portions extending in three directions from a center toward respective tips of the projections.

19. The sapphire substrate according to claim 1, wherein the plurality of projections includes a plurality of adjacent projections that are all oriented in the same direction.

20. A nitride semiconductor light emitting device formed by growing a nitride semiconductor on the principal surface of the sapphire substrate according to claim 19.

21. A sapphire substrate having a principal surface for growing a nitride semiconductor to form a nitride semiconductor light emitting device, the sapphire substrate comprising a plurality of projections on the principal surface,

wherein each of the projections has a bottom that has a substantially triangular shape,

wherein each side of the bottom of the projections has a depression in its center,

wherein extended portions of the bottoms of the respective projections extend in a direction that is within a range of ±

10 degrees of a crystal axis “

a”

of the sapphire substrate, and

wherein the plurality of projections includes a plurality of adjacent projections that are all oriented in the same direction.

22. A nitride semiconductor light emitting device formed by growing a nitride semiconductor on the principal surface of the sapphire substrate according to claim 21.

23. A sapphire substrate having a principal surface for growing a nitride semiconductor to form a nitride semiconductor light emitting device, the sapphire substrate comprising a plurality of projections on the principal surface,

wherein each of the projections has a bottom that has a substantially triangular shape,

wherein each side of the bottom of the projections has a depression in its center,

wherein extended portions of the bottoms of the respective projections extend in a direction that is within a range of ±

10 degrees of a crystal axis “

a”

of the sapphire substrate, and

wherein the plurality of projections are arranged so that a vertex of a bottom of a first projection among neighboring projections is located in a region defined by an imaginary triangle formed between points of two vertexes of a bottom of a second projection among the neighboring projections, and a deepest point of the depression in a corresponding side of the second projection.

24. The sapphire substrate according to claim 23, wherein said first projection of the neighboring projections is arranged so that the deepest portion of the depression of the second projection is located on a line that bisects an angle of a vertex of said first projection.

25. The sapphire substrate according to claim 23, wherein said first projection of the neighboring projections is arranged so that the deepest portion of the depression of the second projection is located on a line that bisects an angle of a vertex of a triangle formed by joining vertexes of said first projection.

26. The sapphire substrate according to claim 23, wherein the projections have a side surface that is inclined from the principal surface of said sapphire substrate, and wherein, in a plan view, a width of the side surface at a first side of the crystal axis “

a”

of said sapphire substrate is larger than a width of the side surface at a second side of the crystal axis “

a”

of said sapphire substrate.