Light Emitting Diodes with Light Filters

• US 20090236619A1
• Filed: 03/19/2008
• Published: 09/24/2009
• Est. Priority Date: 03/19/2008
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Chakroborty, Arpan
• Granted Patent: US 8,916,890 B2
• Time in Patent Office: Days
• US Class Current: 257/89
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H01L 33/508 having a non-uniform spatial arrangement or non-uniform concentration, e.g. patterned wavelength conversion layer, wavelength conversion layer with a concentration gradient of the wavelength conversion material

Abstract

LED chips including an LED layer or layers capable of emitting light of a first wavelength, a light conversion layer on the LED capable of converting at least a portion of the light of a first wavelength to light of a second wavelength, and a filter layer therebetween that is transmissive to light of a first wavelength and reflective to light of a second wavelength. The filter layer may prevent at least some of the light of a second wavelength from entering the LED layer or layers, where it may be subject to various optical losses, such as internal reflection and absorption. LED chips may also include multiple filter and light conversion layers. Methods of fabrication are also disclosed.

Claims

1. A light emitting diode (LED) chip comprising:

an LED layer capable of emitting light of a first wavelength;

a reflector layer on a first side of the LED layer,

a light conversion layer on a second side the LED layer, opposite the first side, capable of converting at least a portion of the light of a first wavelength to light of a second wavelength; and

a filter layer between the LED layer and the light conversion layer that is transmissive to the light of a first wavelength and reflective to the light of a second wavelength, the filter layer being directly on at least a portion of the LED layer.

2. The LED chip of claim 1 wherein the light conversion layer is directly on at least a portion of the filter layer.

3. The LED chip of claim 1 further comprising a pedestal in electrical contact with the LED wherein the pedestal extends through both the filter layer and the light conversion layer and is exposed at the surface of the light conversion layer.

4. The LED chip of claim 1 that is configured to emit white light.

5. The LED chip of claim 1 wherein the LED is on a substrate.

6. The LED chip of claim 3 further comprising a contact on the LED layer wherein the pedestal is on the contact.

7. The LED chip of claim 1 wherein the light conversion layer comprises a phosphor material.

8. The LED chip of claim 1 wherein the LED layer comprises one or more layers of materials from the Group III-nitride material system.

9. The LED chip of claim 5 wherein the substrate comprises a growth substrate.

10. The LED chip of claim 5 wherein the substrate comprises a carrier substrate.

11. The LED chip of claim 10 wherein the LED layer is flip-chip mounted to the carrier substrate.

12. The LED chip of claim 10 wherein the reflector layer is between the carrier substrate and the LED layer.

13. The LED chip of claim 1 wherein the filter layer is transmissive to light between and including 400 nm and 500 nm and is reflective to light below 400 nm and above 500 nm.

14. The LED chip of claim 1 wherein the filter layer is transmissive to light below and including 500 nm and is reflective to light above 500 nm

15. The LED chip of claim 1 wherein the LED layer has a first index of refraction and the light conversion layer and the filter layer have the same second index of refraction.

16. The LED chip of claim 1 wherein the LED layer has a first index of refraction, the light conversion layer has a second index of refraction, and the filter layer has a third index of refraction that is intermediate the first index of refraction and the second index of refraction.

17. The LED chip of claim 1 wherein a surface of the LED layer is non-planar, patterned, or textured.

18. The LED chip of claim 17 further comprising a spacer layer on the non-planar, patterned, or textured surface of the LED layer.

19. The LED chip of claim 1 further comprising multiple light filter layers and multiple light conversion layers on the LED layer.

20. The light emitting device of claim 1, further comprising a light scattering layer.

21. A light emitting diode (LED) chip comprising:

an LED layer capable of emitting light of a first wavelength, wherein the LED layer comprises an n-type layer and a p-type layer on opposing sides of an active layer;

a reflector layer on a first side of the LED layer closest to the p-type layer,

a light conversion layer on a second side the LED layer, opposite the first side, capable of converting at least a portion of the light of a first wavelength to light of a second wavelength; and

a filter layer between the LED layer and the light conversion layer that is transmissive to the light of a first wavelength and reflective to the light of a second wavelength, the filter layer being directly on at least a portion of the LED layer.

22. A method for wafer-level fabricating a light emitting diode (LED) chip comprising;

forming a reflector layer on a substrate;

providing a plurality of LEDs on the substrate, each of the LEDs capable of emitting light of a first wavelength;

forming a light conversion layer over the LEDs capable of converting at least a portion of the light of a first wavelength to light of a second wavelength; and

forming a filter layer between the LEDs and the light conversion layer that is transmissive to the light of a first wavelength and reflective to the light of a second wavelength.

23. The method of claim 22 further comprising;

forming pedestals on the LEDs prior to forming the filter layer and light conversion layer, each of the pedestals in electrical contact with one of the LEDs wherein the filter layer and the light conversion layer bury at least some of the pedestals.

24. The method of claim 23 further comprising;

planarizing the filter layer and the light conversion layer leaving at least some of the filter layer and the light conversion layer on the LEDs while exposing at least some of the buried pedestals.

25. The method of claim 22 wherein the LED chips are configured to emit white light.

26. The method of claim 22 further comprising depositing a contact on each of the LEDs and depositing a pedestal on each of the contacts.

27. The method of claim 22 wherein the light conversion layer comprises a phosphor material.

28. The method of claim 22 wherein the LEDs comprise materials from the Group III-nitride material system.

29. The method of claim 22 wherein the substrate comprises a growth substrate.

30. The method of claim 22 wherein the substrate comprises a carrier substrate.

31. The method of claim 30 further comprising flip-chip bonding the LEDs to the carrier substrate.

32. The method of claim 24 further comprising singulating the LEDs.

33. The method of claim 22 wherein the filter layer is transmissive to light between and including 400 nm and 500 nm and is reflective to light below 400 nm and above 500 nm.

34. The method of claim 22 wherein the filter layer is transmissive to light below and including 500 nm and is reflective to light above 500 nm

35. The method of claim 22 wherein each of the LEDs have a first index of refraction and the light conversion layer and the filter layer have the same second index of refraction.

36. The method of claim 22 wherein each of the LEDs have a first index of refraction, the light conversion layer has a second index of refraction, and the filter layer has a third index of refraction that is intermediate the first index of refraction and the second index of refraction.

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

an LED layer capable of emitting light of a first wavelength;

a light conversion layer on the LED layer capable of converting at least a portion of the light of a first wavelength to light of a second wavelength;

a filter layer between the LED layer and the light conversion layer that is transmissive to the light of a first wavelength and reflective to the light of a second wavelength, the filter layer being directly on at least a portion of the LED layer; and

an encapsulation layer on the filter layer wherein the encapsulation layer includes at least one flat surface

38. A light emitting diode (LED) package comprising:

a first LED chip capable of emitting light of a first wavelength;

a second LED chip capable of emitting light of a second wavelength, different than the first wavelength; and

a filter layer on the first LED chip that is transmissive to light of a first wavelength and reflective to light of a second wavelength.

39. The LED package of claim 38 further comprising;

a second filter layer on the second LED chip that is transmissive to light of a second wavelength and reflective to light of a first wavelength.

40. The LED package of claim 38 wherein the light of a first wavelength is one of red, green, or blue.

41. The LED package of claim 38 wherein the light of a second wavelength is one of red, green, or blue.

42. The LED package of claim 38 wherein at least one of the first and second LED chips further comprises a light conversion layer.

43. The LED package of claim 38 further comprising an encapsulation layer that is on both the first LED chip and the second LED chip.

44. The LED package of claim 43 wherein the encapsulation layer includes at least one flat surface.

45. The LED package of claim 43 wherein the encapsulation layer contains light scatterers.

46. The LED package of claim 38 further comprising;

a submount wherein the first and second LED chips are on the submount; and

a reflector layer is between at least one of the first and second LEDs and the submount.

47. The LED package of claim 39 further comprising;

a third LED chip capable of emitting light of a third wavelength, different than the first wavelength and the second wavelength; and

a third filter layer on the third LED chip that is transmissive to light of a third wavelength and reflective to light of a first and second wavelength.

48. The LED package of claim 38 further comprising multiple LED chips of capable of emitting light of the first wavelength and multiple LED chips capable of emitting light of a second wavelength.