High efficiency light emitting diode (LED) with optimized photonic crystal extractor

• US 20060192217A1
• Filed: 02/28/2005
• Published: 08/31/2006
• Est. Priority Date: 02/28/2005
• 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., David, Aurelien J.F., Weisbuch, Claude C.A.
• Granted Patent: US 7,582,910 B2
• Time in Patent Office: Days
• US Class Current: 257/94
• CPC Class Codes: H01L 2933/0083 Periodic patterns for optical field-shaping in or on the semiconductor body or semiconductor body package, e.g. photonic bandgap structures
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/382 the electrode extending partially in or entirely through the semiconductor body

Abstract

A high efficiency, and possibly highly directional, light emitting diode (LED) with an optimized photonic crystal extractor. The LED is comprised of a substrate, a buffer layer grown on the substrate (if needed), an active layer including emitting species, one or more optical confinement layers that tailor the structure of the guided modes in the LED, and one or more diffraction gratings, wherein the diffraction gratings are two-dimensional photonic crystal extractors. The substrate may be removed and metal layers may be deposited on the buffer layer, photonic crystal and active layer, wherein the metal layers may function as a mirror, an electrical contact, and/or an efficient diffraction grating.

Claims

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

(a) a substrate;

(b) an active layer formed on the substrate, wherein the active layer includes one or more light emitting species;

(c) one or more optical confinement layers formed under or around the active layer, wherein the optical confinement layers tailor a structure of guided modes within the LED; and

(d) one or more diffraction gratings formed on the optical confinement layers, wherein the diffraction gratings are two-dimensional photonic crystals that extract light from the LED.

2. The LED of claim 1, further comprising a buffer layer formed on the substrate, wherein the active layer is formed on the buffer layer.

3. The LED of claim 1, wherein the diffraction gratings direct emissions outside the LED and convert guided modes into extracted light.

4. The LED of claim 1, further comprising one or more layers deposited on one or both sides of the LED, wherein the layers function as a mirror, electrical contact and/or diffraction grating

5. The LED of claim 1, where the optical confinement layers enhance light extraction by the photonic crystals.

6. The LED of claim 5, wherein the optical confinement layers help to excite those modes localized above the optical confinement layers.

7. The LED of claim 1, wherein light is primarily emitted into modes that interact with the photonic crystals, so that guided modes that are usually lost are diffracted outside the LED.

8. The LED of claim 1, wherein the photonic crystals cross the light emitting species in the active layer.

9. The LED of claim 1, wherein the photonic crystals are situated within one or a few optical lengths from the light emitting species in the active layer.

10. The LED of claim 1, wherein the LED retains a planar single layer structure.

11. The LED of claim 1, wherein the photonic crystals include a taper comprised of variable hole lines.

12. The LED of claim 11, wherein the taper comprises one or more periods of modified holes, and the modified holes have a variable hole depth, variable hole period, or variable hole diameter.

13. The LED of claim 1, wherein characteristics of the photonic crystals are varied along its structure, so as to modify properties of the photonic crystals.

14. The LED of claim 1, wherein a light generation region coincides or overlaps with the photonic crystals, so that guided light does not suffer from reflexion or scattering at an interface to the photonic crystals region.

15. The LED of claim 1, wherein a position of the light emitting species is finely tuned, so as to precisely control its emission properties.

16. The LED of claim 1, wherein, by suitable tailoring of a guided modes structure, light diffraction by the photonic crystals occurs in a given range of directions, thereby forming a highly directional light source.

17. A method of fabricating a light emitting diode (LED), comprising:

(a) forming an active layer on a substrate, wherein the active layer includes of one or more light emitting species;

(b) forming one or more optical confinement layers under or around the active layer, wherein the optical confinement layers tailor a structure of guided modes within the LED; and

(c) forming one or more diffraction gratings on the optical confinement layers, wherein the diffraction gratings are two-dimensional photonic crystals that extract light from the LED.

18. The method of claim 17, further comprising forming a buffer layer on the substrate, wherein the active layer is formed on the buffer layer.

19. The method of claim 17, wherein the diffraction gratings direct emissions outside the LED and convert guided modes into extracted light.

20. The method of claim 17, further comprising depositing one or more layers on one or both sides of the LED, wherein the layers function as a mirror, electrical contact and/or diffraction grating

21. The method of claim 17, where the optical confinement layers enhance light extraction by the photonic crystals.

22. The method of claim 21, wherein the optical confinement layers help to excite those modes localized above the optical confinement layers.

23. The method of claim 17, wherein light is primarily emitted into modes that interact with the photonic crystals, so that guided modes that are usually lost are diffracted outside the LED.

24. The method of claim 17, wherein the photonic crystals cross the light emitting species in the active layer.

25. The method of claim 17, wherein the photonic crystals are situated within one or a few optical lengths from the light emitting species in the active layer.

26. The method of claim 17, wherein the LED retains a planar single layer structure.

27. The method of claim 17, wherein the photonic crystals include a taper comprised of variable hole lines.

28. The method of claim 27, wherein the taper comprises one or more periods of modified holes, and the modified holes have a variable hole depth, variable hole period, or variable hole diameter.

29. The method of claim 17, wherein characteristics of the photonic crystals are varied along its structure, so as to modify properties of the photonic crystals.

30. The method of claim 17, wherein a light generation region coincides or overlaps with the photonic crystals, so that guided light does not suffer from reflexion or scattering at an interface to the photonic crystals region.

31. The method of claim 17, where a position of the light emitting species is finely tuned, so as to precisely control its emission properties.

32. The method of claim 17, wherein, by suitable tailoring of a guided modes structure, light diffraction by the photonic crystals occurs in a given range of directions, thereby forming a highly directional light source.

33. A device fabricated according to the method of claim 17.