Light emitting diode structures
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.
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.