High light extraction efficiency light emitting diode (LED) with emitters within structured materials
View Patent ↗Light Emitting Diodes (LEDs) where the emission region, usually a (Al,In,Ga)N layer, is structured for efficient light extraction, are disclosed. The structuring is designed for light extraction from thin films, such as a photonic crystal acting as a diffraction grating. In addition, the structuring controls the in-plane emission and allows new modes into which light will be emitted. Various electrode designs are proposed, including ZnO structures which are known to lead to both excellent electrical properties, such as good carrier injection, and high transparency. Alternatively, the (Al,In,Ga)N layer can be replaced by structures with other materials compositions, in order to achieve efficient light extraction.
1. A light emitting diode (LED), comprising:
a structured emitting region including one or more light emitting active layers embedded in a plurality of index modulation layers, wherein the index modulation layers are structured as a photonic crystal with the active layers embedded within the photonic crystal, the index modulation layers include a low index layer and a high index layer, the low index layer has a lower refractive index than the high index layer, and the active layer is positioned inside the lower index layer.
2. The LED of claim 1 , wherein the LED has an emission rate 60% to 80% of an emission rate for a non structured emitting region comprised of the higher index layer.
3. The LED of claim 1 , further comprising a p-type contact and an n-type contact for applying a bias across the contacts, wherein the p-type contact or the n-type contact is a transparent electrode on or above the structured emitting region.
4. The LED of claim 3 , wherein the transparent electrode comprises zinc oxide, silicon carbide or indium tin oxide.
5. The LED of claim 1 , further comprising a p-type contact and an n-type contact for applying a bias across the contacts, wherein the p-type contact or the n-type contact is a reflective contact on or above the structured emitting region.
6. The LED of claim 1 , wherein the structured emitting region comprises (Al,Ga,In)N.
7. The LED of claim 1 , further comprising a backside mirror positioned on a surface of the LED.
8. The LED of claim 1 , further comprising a regrown GaN layer between the structured emitting region and the p-type contact or the n-type contact for improving electrical contact, optical properties or both.
9. The LED of claim 1 , further comprising a structured lateral epitaxial grown region below or on top of the structured emitting region.
10. The LED of claim 1 , further comprising one or more materials filling holes in the photonic crystal, wherein the materials filling the holes are dielectric, metal, semiconductor, or optically active materials.
11. The LED of claim 10 , wherein the optically active materials are light emitting polymers dyes, dye impregnated polymers, phosphors, or species used to obtain overall white light emission from the LED.
12. The LED of claim 1 , wherein the photonic crystal has a non-regular pattern.
13. The LED of claim 1 , wherein the photonic crystal has a periodic pattern.
14. The LED of claim 1 , wherein the photonic crystal has a pattern optimised for directional light emission.
15. A method for fabricating a light emitting diode (LED) having efficient light extraction, comprising
forming a structured emitting region including one or more light emitting active layers embedded in a plurality of index modulation layers, wherein the index modulation layers are structured as a photonic crystal with the active layers embedded within the photonic crystal, the index modulation layers include a low index layer and a high index layer, and the low index layer has a lower refractive index than the high index layer, and the active layer is positioned inside the lower index layer.
16. The method of claim 15 , wherein the structured emitting region is formed by etching or direct organized growth.
17. The method of claim 15 , further comprising forming a reflective contact on top of the structured emitting region.
18. The method of claim 15 , further comprising forming a transparent contact by direct deposition or attachment of a thin conductive and transparent layer on top of the structured emitting region.
19. The method of claim 15 , further comprising removing the LED from a substrate.
20. The method of claim 15 , further comprising thinning the structured emitting region.
21. The method of claim 15 , further comprising growing or regrowing GaN on top of the structured emitting region.
22. The method of claim 15 , further comprising growing an additional lateral epitaxial overgrowth (LEO) grown structured layer below or on top of the structured emitting region.
23. The method of claim 15 , wherein the structured emitting region provides for light extraction from thin films, such as the photonic crystal acting as a diffraction grating.
24. The method of claim 15 , wherein the structured emitting region controls in-plane emissions and allows new modes into which light will be emitted.
25. The LED of claim 1 , wherein the light emitting active layers and index modulation layers are (Al,In,Ga)N layers.
26. The method of claim 15 , wherein the light emitting active layers and index modulation layers are (Al,In,Ga)N layers.