Light-emitting element comprising a reflective structure with high efficiency

• US 9,240,519 B2
• Filed: 01/23/2014
• Issued: 01/19/2016
• Est. Priority Date: 01/25/2013
• Status: Active Grant

• Current Assignee: Epistar Corporation
• Original Assignee: Epistar Corporation
• Inventors: Tseng, Chun-Lung, Shen, Ching-Hsing, Chuang, Keng-Lin, Su, Chih-Tsung, Liu, Chih-Hui Alston, Kun, Yu-Ming
• Primary Examiner(s): Maldonado, Julio J
• Assistant Examiner(s): Hossain, Moazzam
• Application Number:
  US14/162,614
• Publication Number:
  US 20140209949A1
• Time in Patent Office: 726 Days
• Field of Search: 257/98, 257/E33.069
• US Class Current: 1/1
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

A light-emitting element, comprises: a substrate; a light-emitting semiconductor stack over the substrate and comprising an active layer; and a Distributed Bragg reflective unit under the substrate comprising a first Distributed Bragg reflective structure under the substrate and comprising a first number of pairs of alternately stacked first sub-layers and second sub-layers, and a second Distributed Bragg reflective structure under the first Distributed Bragg reflective structure and comprising a second number of pairs of alternately stacked third sub-layers and fourth sub-layers, wherein the first number is different from the second number.

Claims

1. A light-emitting element, comprising:

a substrate, comprising a first portion and a second portion surrounding the first portion, wherein the second portion has a vertical thickness smaller than a vertical thickness of the first portion, and the first portion comprises a textured surface comprising alternate concave structures and convex structures;

a light-emitting semiconductor stack over the substrate and comprising an active layer; and

a Distributed Bragg reflective unit under the substrate and comprising a first Distributed Bragg reflective structure conformably formed on the textured surface of the substrate and comprising a first number of pairs of alternately stacked first sub-layers and second sub-layers, and

a second Distributed Bragg reflective structure conformably formed on the first Distributed Bragg reflective structure and comprising a second number of pairs of alternately stacked third sub-layers and fourth sub-layers, wherein the first number is different from the second number.

2. The light-emitting element according to claim 1, further comprising a metal reflective layer under the second Distributed Bragg reflective structure.

3. The light-emitting element according to claim 1, wherein the light-emitting semiconductor stack comprises III-nitride material, III-phosphide material, or III-arsenide material.

4. The light-emitting element according to claim 1, wherein a total thickness of the first Distributed Bragg reflective structure is larger than a total thickness of the second Distributed Bragg reflective structure.

5. The light-emitting element according to claim 1, wherein each first sub-layer is closer to the substrate than the second sub-layer in a same pair of the first Distributed Bragg reflective structure, wherein a thickness of the first sub-layer is smaller than a thickness of the second sub-layer.

6. The light-emitting element according to claim 5, wherein a refractive index of the first sub-layer is larger than that of the second sub-layer.

7. The light-emitting element according to claim 1, wherein each third sub-layer of is closer to the substrate than the fourth sub-layer in a same pair of the second Distributed Bragg reflective structure, wherein a thickness of the third sub-layer is smaller than a thickness of the fourth sub-layer.

8. The light-emitting element according to claim 7, wherein a refractive index of the third sub-layer is larger than that of the fourth sub-layer.

9. The light-emitting element according to claim 1, wherein each first sub-layer of is closer to the substrate than the second sub-layer in a same pair of the first Distributed Bragg reflective structure, and each third sub-layer of the pairs is closer to the substrate than the fourth sub-layer in a same pair of the second Distributed Bragg reflective structure, wherein a thickness of the first sub-layer is larger than a thickness of the third sub-layer, and a thickness of the second sub-layer is larger than a thickness of the fourth sub-layer.

10. The light-emitting element according to claim 9, wherein a refractive index of the first sub-layer or a refractive index of the third sub-layer is larger than 2.

11. The light-emitting element according to claim 1, wherein the second portion is devoid of any textured surfaces.

12. The light-emitting element according to claim 9, wherein a material of the second sub-layer or a material of the fourth sub-layer comprises SiO₂, LaF₃, MgF₂, NaF, Na₃AlF₆, CaF₂, or the combinations thereof.

13. The light-emitting element according to claim 1, further comprising a window layer between the substrate and the first Distributed Bragg reflective structure.

14. The light-emitting element according to claim 1, wherein a distance between two adjacent concave structures ranges from 2 μ

m to 10 μ

m.

15. The light-emitting element according to claim 1, wherein the second portion comprises a minimum thickness not more than 80% of a maximum thickness of the first portion.

16. The light-emitting element according to claim 15, wherein a perpendicular height taken to the top surface of the substrate, of one of the convex structures is not more than 20% of the thickness of the maximum thickness of the first portion.

17. The light-emitting element according to claim 16, wherein the perpendicular height is not less than 8 μ

m.

18. The light-emitting element according to claim 1, further comprising a metal reflective layer conformably formed on the second Distributed Bragg reflective structure.

19. The light-emitting element according to claim 18, wherein the metal reflective layer covers the textured surface of the substrate.