Light emitting diode structures

• US 7,509,012 B2
• Filed: 09/22/2004
• Issued: 03/24/2009
• Est. Priority Date: 09/22/2004
• Status: Active Grant

• Current Assignee: Quantum NIL Limited, Quantum NIL Limited Taiwan Branch
• Original Assignee: Luxtaltek Corporation
• Inventors: Zoorob, Majd, Lincoln, John
• Primary Examiner(s): Pak; Sung H
• Assistant Examiner(s): TRAN, HOANG Q
• Application Number:
  US10/946,747
• Publication Number:
  US 20060062540A1
• Time in Patent Office: 1,644 Days
• Field of Search: None
• US Class Current: 385/129
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• 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 33/24 of the light emitting region, e.g. non-planar junction

Abstract

According to one aspect of the present invention, a light emitting diode (LED) structure including an active core layer and at least one substrate layer having a first refractive index, comprises a 2-dimensional photonic quasicrystal in the structure, the photonic quasicrystal comprising an array of regions having a second refractive index, the array exhibiting long range order but short range disorder. The long range order is associated with diffractive properties of the structure and gives rise to uniform-far field diffraction patterns from the LED. The present invention enjoys the benefit of improved light extraction from LEDs without undesirable far field illumination patterns.

Claims

1. A light emitting diode (LED) structure comprising a first layer, a second layer, and a light-generating layer disposed between the first and second layers, the first layer having an upper surface distal the light-generating layer and a lower surface proximate the light-generating layer, wherein light generated in the light-generating layer by spontaneous emission emerges from the LED structure through the upper surface of the first layer, the first layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein the first region comprises a p-doped semiconductor material and the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index.

2. A light emitting diode (LED) structure according to claim 1, wherein the sub-regions do not extend to the upper surface of the first layer.

3. A light emitting diode (LED) structure according to claim 1, wherein the photonic quasicrystal extends into the light-generating layer.

4. A light emitting diode (LED) structure according to claim 1, wherein the second layer comprises a first region having a first refractive index and further comprises a 2-dimensional photonic quasicrystal, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index.

5. A light emitting diode (LED) structure according to claim 1, wherein the Fourier transform of the array has a degree of rotational symmetry n, where n>

6.

6. A light emitting diode (LED) structure according to claim 1, wherein the photonic quasicrystal is designed to have a bandgap that overlaps with the emission spectrum of the active layer in the LED.

7. A light emitting diode (LED) structure according to claim 6, wherein the bandgap extends in all directions and for all polarisations.

8. A light emitting diode (LED) structure according to claim 1, wherein the array is in the form of a Fibonacci spiral pattern.

9. A light emitting diode (LED) structure according to claim 1, wherein the array is in a Penrose tiling pattern.

10. A light emitting diode (LED) structure according to claim 1, wherein a section of the photonic quasicrystal is repeated periodically.

11. A light emitting diode (LED) structure according to claim 1, wherein the sub regions comprise a tunable material.

12. A light emitting diode (LED) structure comprising a first layer, a second layer, and a light-generating layer disposed between the first and second layers, the first layer having an upper surface distal the light-generating layer and a lower surface proximate the light-generating layer, wherein light generated in the light-generating layer by spontaneous emission emerges from the LED structure through the upper surface of the first layer, the second layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index.

13. A light emitting diode (LED) structure according to claim 12, wherein the second layer has an upper surface proximate the light-generating layer and a lower surface distal the light-generating layer and wherein the sub regions in the second layer do not extend to the lower surface of the second layer.

14. A light emitting diode (LED) structure according to claim 12, wherein the second layer has an upper surface proximate the light-generating layer and a lower surface distal the light-generating layer and wherein the sub regions in the second layer do not extend to the upper surface of the second layer.

15. A light emitting diode (LED) structure according to claim 12, wherein the second layer has an upper surface proximate the light-generating layer and a lower surface distal the light-generating layer and wherein the sub regions in the second layer do not extend to the upper surface or the lower surface of the second layer.

16. A light emitting diode (LED) structure according to claim 12, wherein the first layer comprises a first region having a first refractive index and further comprises a 2-dimensional photonic quasicrystal, wherein the photonic quasicrystal of the first layer comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index.

17. A light emitting diode (LED) structure comprising a first layer, a second layer, and a light-generating layer disposed between the first and second layers, the first layer having an upper surface distal the light-generating layer and a lower surface proximate the light-generating layer, wherein light generated in the light-generating layer by spontaneous emission emerges from the LED structure through the upper surface of the first layer, the first layer comprising a first region having a first refractive index and further comprising a periodically-repeated section of a 2-dimensional photonic quasicrystal, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index.

18. A light emitting diode (LED) structure comprising a first layer and a light-generating layer, the first layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein light generated in the light-generating layer by spontaneous emission is extracted by the photonic quasicrystal and coupled out of the LED structure, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index, wherein the photonic quasicrystal is configured to have a bandgap that does not overlap with an emission spectrum of the light-generating layer.

19. A light emitting diode (LED) structure comprising a first layer and a light-generating layer, the first layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein light generated in the light-generating layer by spontaneous emission is extracted by the photonic quasicrystal and coupled out of the LED structure, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index, wherein the photonic quasicrystal is configured to have a bandgap that overlaps with an emission spectrum of the light-generating layer.

20. A light emitting diode (LED) structure comprising a first layer, a second layer, and a light-generating layer, the first layer having an upper surface distal the light-generating layer and a lower surface proximate the light-generating layer, wherein light generated in the light-generating layer by spontaneous emission emerges from the LED structure through the upper surface of the first layer, the second layer disposed in a part of the LED structure closer to the lower surface of the first layer than the upper surface of the first layer, the second layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index, wherein the first region of the second layer comprises a metallic material.

21. A light emitting diode (LED) structure according to claim 20, wherein the metallic material comprises silver.

22. A light emitting diode (LED) structure comprising a first layer and a light-generating layer, the first layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein light generated in the light-generating layer by spontaneous emission is extracted by the photonic quasicrystal and coupled out of the LED structure, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index, wherein each sub-region comprises a material other than air.

23. A light emitting diode (LED) structure according to claim 22, wherein the refractive index of the material forming each sub-region is tunable.

24. A light emitting diode (LED) structure comprising a first layer, a second layer, and a light-generating layer disposed between the first and second layers, the first layer having an upper surface distal the light-generating layer and a lower surface proximate the light-generating layer, wherein light generated in the light-generating layer by spontaneous emission emerges from the LED structure through the upper surface of the first layer, the first layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, each sub-region having a refractive index different to the first refractive index, and wherein at least one parameter of the sub-regions varies across the array, the parameter selected from a group which includes a geometrical property and a material property of the sub-regions.

25. A light emitting diode (LED) structure comprising a first layer, a second layer, and a light-generating layer disposed between the first and second layers, the first layer having an upper surface distal the light-generating layer and a lower surface proximate the light-generating layer, wherein light generated in the light-generating layer by spontaneous emission emerges from the LED structure through the upper surface of the first layer, the first layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein the photonic quasicrystal comprises an array of sub-regions exhibiting long range order but short range disorder, wherein the shape sub-regions have a substantially square cross-section in a plane parallel to the upper surface of the first layer.

26. A light emitting diode (LED) structure comprising a first layer, a second layer, and a light-generating layer disposed between the first and second layers, the first layer having an upper surface distal the light-generating layer and a lower surface proximate the light-generating layer, wherein light generated in the light-generating layer by spontaneous emission emerges from the LED structure through the upper surface of the first layer, the first layer comprising a first region having a first refractive index and further comprising a 2-dimensional photonic quasicrystal, wherein the photonic quasicrystal comprises an array of sub-regions arranged in a pattern which exhibits long range order but short range disorder, each sub-region having a second refractive index different to the first refractive index, the pattern comprising either a Fibonacci spiral pattern or a Penrose tiling pattern or a square-triangle tiling pattern.

27. A light emitting diode (LED) structure according to claim 26, wherein the pattern includes defects.