White, single or multi-color light emitting diodes by recycling guided modes

• US 20060054905A1
• Filed: 09/10/2004
• Published: 03/16/2006
• Est. Priority Date: 09/10/2004
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: DenBaars, Steven P., Nakamura, Shuji, Benisty, Henri, Schwach, Carole, Weisbuch, Claude Charles Aime
• Granted Patent: US 7,223,998 B2
• Time in Patent Office: Days
• US Class Current: 257/89
• 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 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• 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 33/32 containing nitrogen
• CPC Class Codes: H01L 33/405 Reflective materials
• CPC Class Codes: H01L 33/505 characterised by the shape, e.g. plate or foil

Abstract

A white, single or multi-color light emitting diode (LED) includes a mirror for reflecting photons within the LED; a first active region, adjacent the mirror, including one or more current-injected layers for emitting photons when electrically biased in a forward direction; a second active region, adjacent the first active region, including one or more optically-pumped layers for emitting photons, wherein the optically-pumped layers are optically excited by the photons emitted by the current-injected layers, thereby recycling guided modes; and an output interface, adjacent the second active region, for allowing the photons emitted by the optically-pumped layers to escape the LED as emitted light.

Claims

1. A light emitting diode (LED) comprising:

a first active region comprised of one or more current-injected layers for emitting photons when electrically biased in a forward direction; and

a second active region, adjacent the first active region, comprised of one or more optically-pumped layers for emitting photons, wherein the optically-pumped layers are optically excited by the photons emitted by the current-injected layers, thereby recycling guided modes.

2. The LED of claim 1, wherein the LED comprises a white, single or multi-color LED.

3. The LED of claim 1, wherein the first active region is comprised of doped materials and the second active region is comprised of undoped materials.

4. The LED of claim 1, wherein the current-injected layers are comprised of emitters such as quantum wells (QWs) or quantum dots (QDs).

5. The LED of claim 1, wherein the optically-pumped layers comprise electrically-passive layers.

6. The LED of claim 1, wherein the optically-pumped layers are comprised of emitters such as quantum wells (QWs), quantum dots (QDs), phosphors, dyes, light emitting polymers, or other light emitting molecules.

7. The LED of claim 1, wherein any color of light is achieved by combining emitters at desired wavelengths.

8. The LED of claim 1, wherein the optically-pumped layers are optically-pumped by the guided modes of the current-injected layers, absorb the guided modes and re-emit the absorbed guided modes at the same or different wavelengths.

9. The LED of claim 1, wherein the optically-pumped layers emit photons at the same or different wavelengths as the current-injected layers.

10. The LED of claim 1, wherein the photons emitted by the optically-pumped layers escape the LED as emitted light through an output interface comprising a textured surface, a distributed Bragg reflector (DBR), an epoxy structure, or other structure.

11. The LED of claim 10, further comprising an epoxy added on the output interface to increase an escape cone for the emitted light.

12. The LED of claim 1, wherein the first and second active regions are close and are not separated by a substrate in order to achieve an efficient recycling.

13. The LED of claim 1, further comprising a mirror, adjacent the first active region, that reflects an energy flux from the first active region and thus multiplies the photons emitted from the current-injected layers that optically excite the optically-pumped layers in the second active region.

14. The LED of claim 13, wherein the mirror is a contact layer.

15. The LED of claim 13, wherein the current-injected layer lies at an antinode of an electric field of an optical wave to the mirror to enhance coupling effects.

16. The LED of claim 13, wherein a value d represents a distance between the mirror and the first active region, such that:

d=λ

/4 or λ

/4+n λ

/2 approximately for a metallic mirror, or
d=λ

/2 or λ

/2+n λ

/2 for a distributed Bragg reflector (DBR) mirror,

where λ

is the wavelength of the optical wave.

17. The LED of claim 13, wherein a thickness of the first region is adjusted so as to obtain a micro-cavity enhancement effect due to reflections at the mirror and at an interface between the first and second regions.

18. The LED of claim 1, wherein current injection is used in the optically-pumped layers to increase intensity.

19. A method of creating a light emitting diode (LED), comprising:

creating a first active region comprised of one or more current-injected layers for emitting photons when electrically biased in the forward direction; and

creating a second active region, adjacent the first active region, comprised of one or more optically-pumped layers for emitting photons, wherein the optically-pumped layers are optically excited by the photons emitted by the current-injected layers, thereby recycling guided modes within the LED.

20. The method of claim 19, wherein the LED comprises a white, single or multi-color LED.

21. The method of claim 19, wherein the first active region is comprised of doped materials and the second active region is comprised of undoped materials.

22. The method of claim 19, wherein the current-injected layers are comprised of emitters such as quantum wells (QWs) or quantum dots (QDs).

23. The method of claim 19, wherein the optically-pumped layers comprise electrically-passive layers.

24. The method of claim 19, wherein the optically-pumped layers are comprised of emitters such as quantum wells (QWs), quantum dots (QDs), phosphors, dyes, light emitting polymers, or other light emitting molecules.

25. The method of claim 19, wherein any color of light is achieved by combining emitters at desired wavelengths.

26. The method of claim 19, wherein the optically-pumped layers are optically-pumped by the guided modes of the current-injected layers, absorb the guided modes and re-emit the absorbed guided modes at the same or different wavelengths.

27. The method of claim 19, wherein the optically-pumped layers emit photons at the same or different wavelengths as the current-injected layers.

28. The method of claim 19, wherein the photons emitted by the optically-pumped layers escape the LED as emitted light through an output interface comprising a textured surface, a distributed Bragg reflector (DBR), an epoxy structure, or other structure.

29. The method of claim 28, further comprising adding epoxy on the output interface to increase an escape cone for the emitted light.

30. The method of claim 19, wherein the first and second active regions are close and are not separated by a substrate in order to achieve an efficient recycling.

31. The method of claim 19, further comprising creating a mirror, adjacent the first active region, that reflects an energy flux from the first active region and thus multiplies the photons emitted from the current-injected layers that optically excite the optically-pumped layers in the second active region.

32. The method of claim 31, wherein the mirror is a contact layer.

33. The method of claim 31, wherein the current-injected layer lies at an antinode of an electric field of an optical wave to the mirror to enhance coupling effects.

34. The method of claim 31, wherein a value d represents a distance between the mirror and the first active region, such that:

d=λ

/4 or λ

/4+n λ

/2 approximately for a metallic mirror, or
d=λ

/2 or λ

/2+n λ

/2 for a distributed Bragg reflector (DBR) mirror,

where λ

is the wavelength of the optical wave.

35. The method of claim 31, wherein a thickness of the first region is adjusted so as to obtain a micro-cavity enhancement effect due to reflections at the mirror and at an interface between the first and second regions.

36. The method of claim 19, wherein current injection is used in the optically-pumped layers to increase intensity.

37. A white, single or multi-color light emitting diode (LED) comprising:

a mirror for reflecting photons within the LED;

a first active region, adjacent the mirror, comprised of one or more current-injected layers for emitting photons when electrically biased in the forward direction;

a second active region, adjacent the first active region, comprised of one or more optically-pumped layers for emitting photons, wherein the optically-pumped layers are optically excited by the photons emitted by the current-injected layers, thereby recycling guided modes within the LED; and

an output interface, adjacent the second active region, for allowing the photons emitted by the optically-pumped layers to escape the LED.

38. The LED of claim 37, wherein the first active region is comprised of doped materials and the second active region is comprised of undoped materials.

39. The LED of claim 37, wherein the current-injected layers are comprised of emitters such as quantum wells (QWs) or quantum dots (QDs).

40. The LED of claim 37, wherein the optically-pumped layers comprise electrically-passive layers.

41. The LED of claim 37, wherein the optically-pumped layers are comprised of emitters such as quantum wells (QWs), quantum dots (QDs), phosphors, dyes, light emitting polymers, or other light emitting molecules.

42. The LED of claim 37, wherein any color of light is achieved by combining emitters at desired wavelengths.

43. The LED of claim 37, wherein the optically-pumped layers are optically-pumped by the guided modes of the current-injected layers, absorb the guided modes and re-emit the absorbed guided modes at the same or different wavelengths.

44. The LED of claim 37, wherein the optically-pumped layers emit photons at the same or different wavelengths as the current-injected layers.

45. The LED of claim 37, wherein the output interface comprises a textured surface, a distributed Bragg reflector (DBR), an epoxy structure, or other structure.

46. The LED of claim 37, wherein the first and second active regions are close and are not separated by a substrate in order to achieve an efficient recycling.

47. The LED of claim 37, wherein the mirror reflects an energy flux from the first active region and thus multiplies the photons emitted from the current-injected layers that optically excite the optically-pumped layers in the second active region.

48. The LED of claim 37, wherein the mirror is a contact layer.

49. The LED of claim 37, wherein the current-injected layer lies at an antinode of an electric field of an optical wave to the mirror to enhance coupling effects.

50. The LED of claim 37, wherein a value d represents a distance between the mirror and the first active region, such that:

d=λ

/4 or λ

/4+n λ

/2 approximately for a metallic mirror, or
d=λ

/2 or λ

/2+n λ

/2 for a distributed Bragg reflector (DBR) mirror,

where λ

is the wavelength of the optical wave.

51. The LED of claim 37, wherein a thickness of the first region is adjusted so as to obtain a micro-cavity enhancement effect due to reflections at the mirror and at an interface between the first and second regions.

52. The LED of claim 37, wherein current injection is used in the optically-pumped layers to increase intensity.