Enhanced light extraction through the use of micro-LED arrays

• US 6,410,942 B1
• Filed: 11/14/2000
• Issued: 06/25/2002
• 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, DenBaars, Steven
• Primary Examiner(s): CRANE, SARA W
• Application Number:
  US09/713,576
• Time in Patent Office: 588 Days
• Field of Search: 257/88, 257/91, 257/93, 257/95, 257/98
• US Class Current: 257/88
• CPC Class Codes: H01L 33/08 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body H01L27/15 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 33/38 with a particular shape
• CPC Class Codes: H01L 33/42 Transparent materials

Abstract

This invention describes new LED structures that provide increased light extraction efficiency. The new LED structures include arrays of electrically interconnected micro-LEDs that have and active layer sandwiched between two oppositely doped layer. The micro-LEDs are formed on a first spreader layer with the bottom layer of the micro-LEDs in contact with the first spreader. A second spreader layer is formed over the micro-LEDs and in contact with their top layer. The first spreader layer is electrically isolated from the second spreader layer. Each of the spreader layers has a contact and when a bias is applied across the contacts, current spreads to the micro-LEDs and they emit light. The efficiency of the new LED is increased by the increased emission surface of the micro-LEDs. Light from each of the micro-LEDs active layer will reach a surface after travelling only a short distance, reducing total internal reflection of the light. Light extraction elements (LEEs) between the micro-LEDs can be included to further enhance light extraction. The new LEDs are fabricated with standard processing techniques making them highly manufacturable at costs similar to standard LEDs.

Claims

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

a conductive first spreader layer;

a plurality of micro light emitting diodes (micro-LEDs) separately disposed on a surface of said first spreader layer, each of said micro-LEDs comprising;

a p-type layer;

an n-type layer;

an active layer sandwiched 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 the bottom layer, current from said first spreader layer spreading into said bottom layer;

a second spreader layer over said micro-LEDs, current from said second spreader layer spreading into said top layer, a bias applied across said first and second spreader layers causing said micro-LEDs to emit light.

2. The LED of claim 1, wherein said first spreader layer is a conductive substrate.

3. The LED of claim 1, further comprising a substrate adjacent to the surface of said first spreader layer opposite said micro-LEDs.

4. The LED of claim 3, wherein said substrate is insulating and said first spreader layer is an epitaxially deposited semiconductor material.

5. The LED of claim 1, further comprising an insulating layer covering said micro-LEDs and the surface of said first spreader layer between said micro-LEDs, said insulating layer disposed between said second spreader and said micro-LEDs.

6. The LED of claim 5, wherein said insulating layer has holes over each of said micro-LEDs and said second spreader making contact with each said micro-LED through said holes.

7. The LED of claim 6, wherein said second spreading layer is a sheet of transparent conducting material.

8. The LED of claim 6, wherein said second spreader layer is an interconnected current spreading grid having a plurality of interconnected conductive paths, each of said micro-LEDs having one or more conductive paths over it and making contact with said top layer through said holes.

9. The LED of claim 6, wherein said second spreader is an electrically conductive material.

10. The LED of claim 1, further comprising light extraction elements (LEEs) integrated with said micro-LEDs to interact with light escaping from said micro-LEDs to further enhance light extraction from said LED.

11. The LED of claim 10, wherein said LEEs are disposed between said micro-LEDs.

12. The LED of claim 10, wherein said LEES are disposed on the surface of said first spreader layer, between said micro-LEDs.

13. The LED of claim 10, wherein said LEEs are integrated on the side surfaces of said micro-LEDs.

14. The LED of claim 10, wherein said LEEs are integrated on the sides surfaces of said micro-LEDs and are disposed between said micro-LEDs.

15. The LED of claim 10, wherein said LEEs have curved surfaces.

16. The LED of claim 10, wherein said LEEs have linear or piecewise linear surfaces.

17. The LED of claim 10, wherein said LEEs are randomly roughened surfaces.

18. The LED of claim 1, further comprising respective electrical contacts disposed on said first and second spreader layers, a bias applied across said contacts causing said active layer to emit light.

19. The LED of claim 6, wherein said second spreader layer is a reflective metal layer that is deposited over said micro-LEDs, said LED further comprising substrate adjacent to the surface of said first spreader opposite said micro-LEDs and a submount layer affixed to said metal layer, said substrate of said LED becoming the primary light emission surface.

20. The LED of claim 19, further comprising a conductive finger between said submount and said first spreader layer, a first contact on said submount connected to said conductive finger, and a second contact on said submount connected to said metal layer, said micro-LEDs emitting light when a bias is applied across said contacts.

21. The LED of claim 1, wherein said bottom layers of said micro-LEDs are connected and said active and top layers are disconnected.

22. The LED of claim 1, wherein said second spreader layer is an interconnected current spreading grid with conductive paths between said micro-LEDs, said LED further comprising semiconductor material under said conductive paths between micro-LEDs, said semiconductor material electrically isolating said first spreader layer from said conductive paths.

23. The LED of claim 22, wherein said semiconductor material comprises an active layer sandwiched between two oppositely doped layers.

24. A light emitting diode (LED), comprising:

a first spreader layer;

an array of light emitting elements disposed on said first spreader layer;

a second spreader layer disposed over said array of emitting elements, said first spreader layer electrically isolated from said second spreader layer; and

first and second contacts on said first and second spreader layer respectively, a bias applied across said contacts causing said array of emitting elements to emit light.

25. The LED of claim 24, wherein said emitting elements are micro-LEDs, each having an active layer sandwiched between two oppositely doped layers.

26. The LED of claim 24, wherein oppositely doped layers are p and n-type layers, wherein either said p-type or n-type layer is a bottom layer adjacent to said first spreader layer and the other said layer is the top layer adjacent to said second spreader, current from said first spreader flowing into said bottom layer and current from said second spreader flowing into said top layer.

27. The LED of claim 24, further comprising a substrate adjacent to the surface of said first spreader layer opposite said emitting elements.

28. The LED of claim 24, wherein said second spreader layer is an interconnected current spreading grid covering said emitting elements and having a plurality of interconnected conductive paths between said emitting elements.

29. The LED of claim 24, wherein said second spreading layer is a sheet of transparent conducting material.

30. The LED of claim 28, further comprising an insulating layer covering said emitting element and the surface of said first spreader layer between said emitting elements, said second layer disposed on said insulating layer, said insulating layer electrically isolating said first spreader layer from said second spreader layer.

31. The LED of claim 30, wherein said insulating layer has holes over each of said emitting elements and said second spreader making contact with each said emitting element through said holes.

32. The LED of claim 31, each of said emitting elements having one or more conductive paths over it and making contact with said emitting elements through said holes.

33. The LED of claim 28, further comprising semiconductor material under said conductive paths between emitting elements said semiconductor material electrically isolating said first spreader layer from said conductive paths.

34. The LED of claim 33, wherein said semiconductor material comprises an active layer surrounded by two oppositely doped layers.

35. The LED of claim 24, further comprising light extraction elements between said emitting elements to redirect light emitting from said emitting elements.

36. The LED of claim 24, further comprising light extraction elements on the side surfaces of said emitting elements to redirect light emitting from said emitting elements.

37. A light emitting diode (LED), comprising:

a first spreader layer;

an array of micro-LEDs disposed on said first spreader layer, a current applied to said first spreader layer spreading to said micro-LEDs;

an interconnected current spreading grid disposed over said micro-LEDs, said grid having conductive paths between said micro-LEDs, a current applied to said grid spreading to said micro-LEDS.

semiconductor material under said conductive paths between micro-LEDs, said semiconductor material electrically isolating said first spreader layer from said conductive paths.

first and second contacts on said first and second spreader layer respectively, a bias applied across said contacts causing said array of emitting elements to emit light.

38. The LED of claim 37, wherein said semiconductor material comprises an active layer sandwiched between two oppositely doped layers.