Distributed bragg reflector for reflecting light of multiple wavelengths from an LED

• US 8,981,410 B1
• Filed: 10/16/2013
• Issued: 03/17/2015
• Est. Priority Date: 09/01/2011
• Status: Active Grant

• Current Assignee: Seoul Semiconductor Co., Ltd.
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Lin, Chao-Kun
• Primary Examiner(s): Kebede, Brook
• Application Number:
  US14/055,596
• Publication Number:
  US 20150069434A1
• Time in Patent Office: 517 Days
• Field of Search: 257 95-100
• US Class Current: 257/98
• CPC Class Codes: G02B 5/0833 comprising inorganic materials only
• CPC Class Codes: H01L 2224/49107 on the semiconductor or solid-state body
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

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.

Claims

1. A Light Emitting Diode (LED) device comprising:

a substrate;

an active layer formed above the substrate; and

a reflector structure disposed below the substrate, the reflector structure comprising;

a low-index total internal reflection layer (TIR); and

a Distributed Bragg Reflector (DBR) disposed below the substrate,

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 a low index dielectric material 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 the low index dielectric material with a fourth thickness, and

wherein the TIR is disposed between the substrate and 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; and

wherein the low index dielectric material is selected from the group consisting of;

SiO₂, MgF₂ and CaF₂.

3. The LED device of claim 1, wherein the reflector structure has a reflectance greater than 90 percent for first light having a wavelength in a first range from 500 nm to 700 nm and passing from the substrate to the reflector structure.

4. The LED device of claim 3, wherein the reflector structure has a reflectance greater than 90 percent for second light having a wavelength in a second range from 440 nm to 470 nm and passing from the substrate to the reflector structure.

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 TIR is a single layer of silicon dioxide.

9. The LED device of claim 5, wherein the TIR is a single layer of silicon dioxide that is thicker than any silicon dioxide layer of the DBR.

10. The LED device of claim 1, wherein the substrate is a transparent substrate.

11. The LED device of claim 1, wherein the second thickness is larger than the first thickness, and wherein the fourth thickness is larger than the third thickness.

12. The LED device of claim 11, wherein the high index dielectric material is TiO₂, and the low index dielectric material is SiO₂.

13. The LED device of claim 1, wherein:

the active layer is configured to emit a first light of a wavelength less than 500 nm; and

the reflector structure has a reflectance greater than 90.0 percent for a second light having a wavelength in a range from 500 nm to 700 nm and passing from the substrate to the reflector structure.

14. 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.

15. 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 having a wavelength of approximately 500-700 nm and passing from the substrate to the reflector structure.

16. The LED device of claim 1, further comprising a reflective metal layer disposed below the DBR.

17. The LED device of claim 16, wherein the reflective metal layer is made of a metal taken from the group consisting of:

aluminum, silver, rhodium, platinum and nickel.

18. The LED device of claim 1, wherein:

the active layer is configured to emit a light of a first wavelength less than 500 nm;

the first layer of the first plurality of periods has a first quarter-wave optical thickness (QWOT) value with respect to the light of the first wavelength;

the first layer of the second plurality of periods has a second QWOT value with respect to the light of the first wavelength; and

the second QWOT is closer to one than the first QWOT.

19. The LED device of claim 1, wherein:

the active layer is configured to emit a light of a first wavelength less than 500 nm;

the second layer of the first plurality of periods has a third quarter-wave optical thickness (QWOT) value with respect to the light of the first wavelength;

the second layer of the second plurality of periods has a fourth QWOT value with respect to the light of the first wavelength; and

the fourth QWOT is closer to one than the third QWOT.

20. The LED device of claim 1, wherein:

the active layer is configured to emit a light of a first wavelength less than 500 nm;

the TIR has a first quarter-wave optical thickness (QWOT) value with respect to the light of the first wavelength;

the first layer of the first plurality of periods has a second quarter-wave optical thickness (QWOT) value with respect to the light of the first wavelength;

the first layer of the second plurality of periods has a third QWOT value with respect to the light of the first wavelength;

the first QWOT is larger than the second QWOT; and

the second QWOT is larger than the third QWOT.

21. The LED device of claim 1, wherein:

the active layer is configured to emit a light of a first wavelength less than 500 nm;

the TIR has a first quarter-wave optical thickness (QWOT) value with respect to the light of the first wavelength;

the second layer of the first plurality of periods has a fourth quarter-wave optical thickness (QWOT) value with respect to the light of the first wavelength;

the second layer of the second plurality of periods has a fifth QWOT value with respect to the light of the first wavelength;

the first QWOT is larger than the fourth QWOT; and

the fourth QWOT is larger than the fifth QWOT.

22. An LED assembly comprising:

the LED device of claim 1; and

a printed circuit board (PCB) formed below the reflector structure.

23. The LED assembly of claim 22, wherein the PCB is formed of aluminum.

24. The LED assembly of claim 22, further comprising a phosphor covering the LED device of claim 1,

wherein the active layer emits a light of a first wavelength less than 500 nm, and the phosphor converts the light of the first wavelength to a light of a second wavelength in a range of 500-700 nm.

25. The LED assembly of claim 24, wherein the LED assembly is configured to emit white light.

26. A Light Emitting Diode (LED) device comprising:

a substrate;

an active layer formed on the substrate and configured to emit second light of a wavelength less than 500 nm, wherein the active layer comprises indium and gallium; and

a reflector structure formed on an opposite side of the substrate from the active layer, the reflector structure comprising a low-index total internal reflection (TIR) layer and a Distributed Bragg Reflector (DBR),

wherein the reflector structure has a first reflectance greater than 90 percent for first light having a wavelength in a range of 500 nm to 700 nm and passing from the substrate to the reflector structure and a second reflectance greater than 90 percent for the second light, and

the TIR is disposed between the substrate and the DBR.

27. The LED device of claim 26, wherein the DBR comprises:

a first plurality of periods, wherein each of the first plurality of periods includes a first layer of a first material of a first thickness and a second layer of a second material of a second thickness; and

a second plurality of periods, wherein each of the second plurality of periods includes a third layer of the first material of a third thickness and a fourth layer of the second material of a fourth thickness.