Enhanced light extraction in LEDs through the use of internal and external optical elements

• US 6,657,236 B1
• Filed: 11/28/2000
• Issued: 12/02/2003
• Est. Priority Date: 12/03/1999
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Cree Lighting Company (Ideal Industries Incorporated)
• Inventors: Thibeault, Brian, Mack, Michael, DenBaars, Steven
• Primary Examiner(s): Flynn, Nathan J.
• Assistant Examiner(s): FORDE, REMMON R
• Application Number:
  US09/727,803
• Time in Patent Office: 1,099 Days
• Field of Search: 257/98, 257/95, 257/96, 257/97, 257/99, 257/81, 257/94
• US Class Current: 257/98
• CPC Class Codes: H01L 2933/0091 Scattering means in or on the semiconductor body or semiconductor body package H01L33/22 takes precedence
• 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 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: Y10S 977/712 formed from plural layers of nanosized material, e.g. stacked structures
• CPC Class Codes: Y10S 977/834 Optical properties of nanomaterial, e.g. specified transparency, opacity, or index of refraction

Abstract

This invention describes new LEDs having light extraction structures on or within the LED to increase its efficiency. The new light extraction structures provide surfaces for reflecting, refracting or scattering light into directions that are more favorable for the light to escape into the package. The structures can be arrays of light extraction elements or disperser layers. The light extraction elements can have many different shapes and are placed in many locations to increase the efficiency of the LED over conventional LEDs. The disperser layers provide scattering centers for light and can be placed in many locations as well. The new LEDs with arrays of light extraction elements are fabricated with standard processing techniques making them highly manufacturable at costs similar to standard LEDs. The new LEDs with disperser layers are manufactured using new methods and are also highly manufacturable.

Claims

1. A light emitting diode (LED) with enhanced light extraction structures, comprising:

an LED structure having;

an epitaxially grown p-type layer;

an epitaxially grown n-type layer; and

an epitaxially grown active layer between said p-type and n-type layers;

a first spreader layer adjacent to said LED structure;

a second spreader layer adjacent to said LED structure, opposite said first spreader layer; and

light extraction structures disposed integral with said LED, said light extraction structures providing surfaces to allow light trapped within said LED to disperse, reflect and/or refract out of said LED.

2. The LED of claim 1, further comprising a substrate adjacent to said first spreader layer, opposite said LED structure.

3. The LED of claim 1, wherein said substrate is electrically conductive and serves as a spreader layer.

4. The LED of claim 1, wherein said light extraction structures are disposed in a plane parallel to said layers and substantially covering the area of said LED.

5. The LED of claim 4, wherein said light extraction structures comprise an array of light extraction elements.

6. The LED of claim 5, wherein said LEEs have curved surfaces.

7. The LED of claim 5, wherein said LEEs have piecewise linear surfaces.

8. The LED of claim 1, wherein said light extraction structures comprise a disperser layer.

9. The LED of claim 8, wherein said disperser layer comprises a layer of microspheres.

10. The LED of claim 9, said microspheres have a different index of refraction than said LED layers.

11. The LED of claim 8, wherein said disperser layer comprises a roughened layer of material within said LED.

12. The LED of claim 11, wherein said roughened layer has a different index of refraction than said LED.

13. The LED of claim 1, wherein said light extraction structures are disposed on said second spreader layer, opposite said LED structure.

14. The LED of claim 2, wherein said light extraction structures are disposed on the surface of said substrate, opposite said first spreader layer.

15. The LED of claim 1, wherein said light extraction structures are disposed internal to said LED.

16. The LED of claim 15, wherein said light extraction structures have a different index of refraction than said LED layers.

17. The LED of claim 2, wherein said light extraction structures are disposed on the interface between said substrate and said first spreader layer, said structures substantially within said first spreader layer.

18. The LED of claim 2, wherein said light extraction structures are disposed within said first spreader layer.

19. The LED of claim 2, wherein said light extraction structures are disposed on the interface between said substrate and said first spreader layer, said structures substantially within said substrate.

20. The LED of claim 1, further comprising a first contact on said first spreader layer and a second contact on said second spreader layer, a bias applied across said contacts causing said LED to emit light.

21. The LED of claim 2, wherein said substrate is conductive and said LED further comprises a first contact on said substrate and a second contact on said second spreader layer, a bias applied across said contacts causing said active layer to emit light.

22. The light emitting diode of claim 2, further comprising:

a submount;

a reflective layer disposed on said LED structure; and

a second spreader layer on said submount and affixed to said reflective layer opposite said LED structure;

a bias applied across said first and second conductive layers causing said active layer to emit light, said substrate being the primary emission surface.

23. A light emitting diode with enhanced light extraction, comprising

a p-type layer;

an n-type layer;

an active layer between said p-type and n-type layers wherein either said p-type or n-type layer is a top layer and the other said layer is a bottom layer;

a first spreader layer adjacent to said bottom layer;

a second spreader layer on said top layer;

respective electrical contacts on said spreader layers so that a bias applied across said contacts causes said active layer to emit light;

a substrate adjacent to said first spreader layer; and

light extraction structures integral with said layers, running parallel to said layers and substantially covering said LED, said light extraction structures providing surfaces to allow light trapped within said LED to disperse, reflect and/or refract out of said LED.

24. The LED of claim 23, wherein said light extraction structures comprise an array of light extraction elements (LEEs) having curved or piecewise linear surfaces.

25. The LED of claim 23, wherein said light extraction structures comprise a disperser layer.

26. The LED of claim 25, wherein said disperser layer comprises a roughened layer of material within said LED.

27. The LED of claim 23, wherein said light extraction structures are disposed on said second spreader layer, opposite said top layer.

28. The LED of claim 23, wherein said light extraction structures are disposed on the surface of said substrate, opposite said first spreader layer.

29. The LED of claim 23, wherein said light extraction structures are disposed internal to said LED layers.

30. The LED of claim 23, wherein said light extraction structures are disposed on the interface between said substrate and said first spreader layer, said structures substantially within said first spreader layer.

31. The LED of claim 23, wherein said light extraction structures are disposed within said first spreader layer.

32. The LED of claim 23, wherein said light extraction structures are disposed on the interface between said substrate and said first spreader layer, said structures substantially within said substrate.

33. A light emitting diode (LED) with enhanced light extraction, comprising:

an LED structure having;

an epitaxially grown p-type layer;

an epitaxially grown n-type layer; and

an epitaxially grown active layer between said p-type and n-type layers;

a reflective layer deposited on said LED structure;

a second spreader layer on said reflective layer;

a submount on said second spreader layer;

a first spreader layer adjacent said LED structure, opposite said reflective layer;

a bias applied across said first and second spreader layers causing said active layer to emit light, said substrate becoming the primary light emission surface; and

light extraction structures integral with said LED, said light extraction structures running parallel to said LED structure and substantially covering the area of said LED.

34. The LED of claim 33, wherein said light extraction structures comprise an array of light extraction elements (LEEs) having curved or piecewise linear surfaces.

35. The. LED of claim 33, wherein said light extraction structures comprise a disperser layer.

36. The LED of claim 33, further comprising a p-contact on said submount and adjacent to said second spreader, a conductive media between said submount and said first spreader layer, and an n-contact on said submount and adjacent said conducting media, a bias applied across said p- and n-contacts causing said LED structure to emit light.