Optical designs for high-efficacy white-light emitting diodes

• US 7,868,341 B2
• Filed: 06/27/2008
• Issued: 01/11/2011
• Est. Priority Date: 06/27/2007
• Status: Expired due to Fees

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Diana, Frederic S., DenBaars, Steven P., Nakamura, Shuji
• Primary Examiner(s): CHAUDHARI, CHANDRA P
• Application Number:
  US12/163,510
• Publication Number:
  US 20090001399A1
• Time in Patent Office: 928 Days
• Field of Search: 257/98, 257/E33.061, 438/35
• US Class Current: 257/98
• CPC Class Codes: F21K 9/64 using wavelength conversion means distinct or spaced from the light-generating element, e.g. a remote phosphor layer
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/48091 Arched
• 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 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/19107 off-chip wires
• CPC Class Codes: H01L 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 2933/0058 relating to optical field-shaping elements
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/483 Containers
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H01L 33/504 Elements with two or more wavelength conversion materials
• CPC Class Codes: H01L 33/505 characterised by the shape, e.g. plate or foil
• CPC Class Codes: H01L 33/507 the elements being in intimate contact with parts other than the semiconductor body or integrated with parts other than the semiconductor body
• CPC Class Codes: H01L 33/58 Optical field-shaping elements
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

A method for increasing the luminous efficacy of a white light emitting diode (WLED), comprising introducing optically functional interfaces between an LED die and a phosphor, and between the phosphor and an outer medium, wherein at least one of the interfaces between the phosphor and the LED die provides a reflectance for light emitted by the phosphor away from the outer medium and a transmittance for light emitted by the LED die. Thus, a WLED may comprise a first material which surrounds an LED die, a phosphor layer, and at least one additional layer or material which is transparent for direct LED emission and reflective for the phosphor emission, placed between the phosphor layer and the first material which surrounds the LED die.

Claims

1. A white light emitting diode (WLED), comprising:

a light emitting diode (LED) for emitting primary light;

a secondary emitting species, optically coupled to the LED, for emitting secondary light having a wavelength different than a wavelength of the primary light; and

a plurality of optically functional or modified interfaces positioned between the secondary emitting species and the LED, wherein each of the optically functional or modified interfaces is at least partially transparent for the primary light and each of the optically functional or modified interfaces is at least partially reflective for the secondary light.

2. The WLED of claim 1, wherein at least one of the optically functional interfaces is positioned at a distance from the LED at least equal to a lateral extent of the LED.

3. The WLED of claim 1, wherein one of the optically functional interfaces comprises a surface of a first material and the first material is positioned such that its refractive index increases total internal reflection of the secondary light inside the secondary emitting species at the optically functional interface.

4. The WLED of claim 3, wherein:

the secondary emitting species is a phosphor layer emitting the secondary light when optically pumped by the primary light;

a second material at least partially surrounds the LED and is positioned such that the second material'"'"'s refractive index reduces the primary light'"'"'s total internal reflection inside the LED at an interface between the LED and the second material; and

the first material is positioned between the secondary emitting species and the second material.

5. The WLED of claim 4, wherein the first material'"'"'s refractive index is smaller than the phosphor layer'"'"'s refractive index.

6. The WLED of claim 4, wherein:

the LED comprises an LED die on a header or cup;

the second material comprises a dome shaped outer surface, wherein the LED die is encapsulated by the second material and the header or cup; and

the first material caps the outer surface and the phosphor layer caps the first material.

7. The WLED of claim 6, wherein the first material is an air gap having a thickness larger than a wavelength of the primary light.

8. The WLED of claim 7, wherein the second material is resin, epoxy, silicon or glass.

9. The WLED of claim 8, wherein the LED header resides on a mounting fixture, and the phosphor layer is attached to the mounting fixture via a reflective material.

10. The WLED of claim 4, wherein one of the optically functional interfaces comprises a third material that is positioned between at least some of the second material and the first material.

11. The WLED of claim 10, wherein:

the LED comprises an LED die on a header or cup;

the LED die is encapsulated by the second material and the header or cup;

the third material comprises a dome shaped outer surface;

the first material caps the outer surface and the phosphor layer caps the first material; and

the LED is positioned in the LED cup such that the LED'"'"'s field of view comprises an entirety of the outer surface of the third material and the LED cup reflects the primary light towards the phosphor.

12. The WLED of claim 1, wherein each of the optically functional or modified interfaces reflects the secondary light emitted by the secondary emitting species away from the LED.

13. The WLED of claim 1, wherein emission from the secondary emitting species is a yellow light emission and the LED die is a III-nitride-based LED die emitting blue light.

14. The WLED of claim 1, wherein the WLED emits white light with an overall luminous efficacy of 100 lm/W and a packaging efficacy of 100 lm/W greater.

15. The WLED of claim 1, wherein the WLED emits white light with a color rendering index of at least 60.

16. A method for fabricating a white light emitting diode (WLED), comprising:

providing a light emitting diode (LED) for emitting primary light;

providing a secondary emitting species, optically coupled to the LED, for emitting secondary light having a wavelength different than a wavelength of the primary light; and

providing a plurality of optically functional or modified interfaces between the secondary emitting species and the LED, wherein each of the optically functional or modified interfaces is at least partially transparent for the primary light and each of the optically functional or modified interfaces is at least partially reflective for the secondary light.

18. The method of claim 16, wherein at least one of the optically functional interfaces is positioned at a distance from the LED at least equal to a lateral extent of the LED.

19. The method of claim 16, wherein one of the optically functional interfaces comprises a surface of a first material and the first material is positioned such that its refractive index increases total internal reflection of the secondary light inside the secondary emitting species at the optically functional interface.

20. The method of claim 19, wherein:

the secondary emitting species is a phosphor layer emitting the secondary light when optically pumped by the primary light;

a second material at least partially surrounds the LED and is positioned such that the second material'"'"'s refractive index reduces the primary light'"'"'s total internal reflection inside the LED at an interface between the LED and the second material; and

the first material is positioned between the secondary emitting species and the second material.

21. The method of claim 20, wherein the first material'"'"'s refractive index is smaller than the phosphor layer'"'"'s refractive index.

22. The method of claim 20, wherein:

the LED comprises an LED die on a header or cup;

the second material comprises a dome shaped outer surface, wherein the LED die is encapsulated by the second material and the header or cup; and

the first material caps the outer surface and the phosphor layer caps the first material.

23. The method of claim 22, wherein the first material is an air gap having a thickness larger than a wavelength of the primary light.

24. The method of claim 23, wherein the second material is resin, epoxy, silicon or glass.

25. The method of claim 24, wherein the LED header resides on a mounting fixture, and the phosphor layer is attached to the mounting fixture via a reflective material.

26. The method of claim 20, wherein one of the optically functional interfaces comprises a third material that is positioned between at least some of the second material and the first material.

27. The method of claim 26, wherein:

the LED comprises an LED die on a header or cup;

the LED die is encapsulated by the second material and the header or cup;

the third material comprises a dome shaped outer surface;

the first material caps the outer surface and the phosphor layer caps the first material; and

the LED is positioned in the LED cup such that the LED'"'"'s field of view comprises an entirety of the outer surface of the third material and the LED cup reflects the primary light towards the phosphor.

28. The method of claim 16, wherein the optically functional interface reflects the secondary light emitted by the secondary emitting species away from the LED.

29. The method of claim 16, wherein emission from the phosphor layer is a yellow light emission and the LED die is a III-nitride-based LED die emitting blue light.

17. A method for emitting white light, comprising:

emitting primary light from a light emitting diode (LED);

emitting secondary light from a secondary emitting species optically coupled to the LED, wherein the secondary light has a wavelength different than a wavelength of the primary light; and

transmitting the primary light through, and reflecting the secondary light from, a plurality of optically functional or modified interfaces positioned between the secondary emitting species and the LED, wherein each of the optically functional or modified interfaces is at least partially transparent for the primary light and each of the optically functional or modified interfaces is at least partially reflective for the secondary light.