Distributed bragg reflector for reflecting light of multiple wavelengths from an LED
View Patent ↗A blue LED device has a transparent substrate and a reflector structure disposed on the backside of the substrate. The reflector structure includes a Distributed Bragg Reflector (DBR) structure having layers configured to reflect yellow light as well as blue light. In one example, the DBR structure includes a first portion where the thicknesses of the layers are larger, and also includes a second portion where the thicknesses of the layers are smaller. In addition to having a reflectance of more than 97.5 percent for light of a wavelength in a 440 nm-470 nm range, the overall reflector structure has a reflectance of more than 90 percent for light of a wavelength in a 500 nm-700 nm range.
1. A Light Emitting Diode (LED) device comprising:
a substrate; and
a reflector structure disposed below the substrate, the reflector structure comprising:
a low-index total internal reflection layer (TIR) disposed below the substrate;
a Distributed Bragg Reflector (DBR) disposed below the TIR; and
a reflective metal layer disposed below the DBR,
wherein the DBR comprises a first plurality of periods and a second plurality of periods, wherein each of the first plurality of periods includes a first layer of a high index dielectric material with a first thickness and a second layer of silicon dioxide with a second thickness, and wherein each of the second plurality of periods includes a first layer of the high index dielectric material with a third thickness and a second layer of silicon dioxide with a fourth thickness,
wherein the TIR is a single layer of silicon dioxide that is thicker than any silicon dioxide layer of the DBR.
2. The LED device of claim 1 , wherein the high index dielectric material is selected from the group consisting of: TiO2, ZnSe, Si3N4, Nb2O5 and Ta2O5.
3. The LED device of claim 1 , wherein the reflector structure has a reflectance greater than 90 percent for first light passing from the substrate to the reflector structure, and wherein the first light has a wavelength in a first range from 500 nm to 700 nm.
4. The LED device of claim 3 , wherein the reflector structure has a reflectance greater than 90 percent for second light passing from the substrate to the reflector structure, and wherein the second light has a wavelength in a second range from 440 nm to 470 nm.
5. The LED device of claim 1 , wherein the first layer of each of the first plurality of periods is titanium dioxide approximately 75 nm thick, wherein the second layer of each of the first plurality of periods is silicon dioxide approximately 138 nm thick, wherein the first layer of each of the second plurality of periods is titanium dioxide approximately 46 nm thick, and wherein the second layer of each of the second plurality of periods is silicon dioxide approximately 85 nm thick.
6. The LED device of claim 5 , wherein a titanium dioxide layer of the first plurality of periods of the DBR is in contact with the TIR.
7. The LED device of claim 5 , wherein a titanium dioxide layer of the second plurality of periods of the DBR is in contact with a silicon dioxide layer of the first plurality of periods.
8. The LED device of claim 1 , wherein the reflective metal layer is made of a metal taken from the group consisting of: aluminum, silver, rhodium, platinum and nickel.
9. The LED device of claim 1 , wherein the substrate is a transparent substrate.
10. The LED device of claim 1 ,
wherein the second thickness is greater than the first thickness, and wherein the fourth thickness is greater than the third thickness.
11. The LED device of claim 10 , wherein the first high index dielectric material is selected from the group consisting of: TiO2, ZnSe, Si3N4, Nb2O5 and Ta2O5; and wherein the second high index dielectric material is selected from the group consisting of: TiO2, ZnSe, Si3N4, Nb2O5 and Ta2O5.
12. The LED device of claim 1 , further comprising an active layer configured to emit a first light of a wavelength less than 500 nm, wherein the reflector structure has a reflectance greater than 90.0 percent for a second light passing from the substrate and to the reflector structure, and wherein the second light has a wavelength in a range from 500 nm to 700 nm.
13. The LED device of claim 1 , further comprising an active layer comprising indium and gallium and configured to emit light of a wavelength less than 500 nm, wherein an overall LED device exhibits a Photon Recycling Efficiency (PRE) of more than 85 percent for light having a wavelength in a range of 500-700 nm.
14. The LED device of claim 1 , further comprising an active layer configured to emit a first light of a wavelength of approximately 440-470 nm, wherein the reflector structure has a reflectance greater than 90.0 percent for a second light passing from the substrate to the reflector structure, and wherein the second light has a wavelength of approximately 500-700 nm.