Highly reflective mounting arrangement for LEDs

• US 7,622,746 B1
• Filed: 03/17/2006
• Issued: 11/24/2009
• Est. Priority Date: 03/17/2006
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Bridgelux Incorporated
• Inventors: Lester, Steven D., Lin, Chao-Kun, Shum, Frank, So, William, Mo, Qingwei
• Primary Examiner(s): Monbleau; Davienne
• Assistant Examiner(s): Rodela; Eduardo A
• Application Number:
  US11/378,763
• Time in Patent Office: 1,348 Days
• Field of Search: 257/79, 257/98, 257/99, 257/E33.068, 257/E33.072, 257/E33.064
• US Class Current: 257/98
• CPC Class Codes: H01L 33/387 with a plurality of electrode regions in direct contact with the semiconductor body and being electrically interconnected by another electrode layer
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

A semiconductor device emitting light about a predetermined wavelength comprising a structure comprising a plurality of layers, sometimes referred to as a stack, providing low resistance, high reflectivity and ohmic contacts to at least one semiconductor material.

Claims

1. A device capable of emitting light about a predetermined nominal wavelength in response to an applied electric current comprising:

a light emitting portion comprising at least one semiconductor material;

first optically transmissive, ohmic contact layer coupled to the light emitting portion;

second optically transmissive, dielectric layer with a refractive index less than the at least one semiconductor material and of a thickness greater than one-quarter wavelength of the predetermined nominal wavelength divided by the index of refraction of the second optically transmissive, dielectric layer coupled to the first optically transmissive, ohmic contact layer;

one or more third layers wherein each one or more third layers comprises a first dielectric layer of high-index of refraction and a second dielectric layer of low-index of refraction wherein the first dielectric layer is of a thickness about mλ

/4n_H, and the second dielectric layer is of a thickness about kλ

/4n_L; and

a metallic layer coupled to the one or more third layers and in contact with the second optically transmissive, dielectric layer and to the first optically transmissive, ohmic contact layer by more than one via through the one or more third layers and the second optically transmissive dielectric layer;

wherein the reflectivity of the metallic layer to the predetermined nominal wavelength is greater than about 50 percent.

2. The device of claim 1 wherein said metallic layer comprises at least three layers comprising:

a first layer comprising said metallic layer;

a second layer comprising a diffusion barrier; and

a third layer of a solderable material;

wherein elements of the solderable material are prevented from reaching said metallic layer by the second layer.

3. The device of claim 1 wherein said optically transmissive, dielectric layer is chosen from a group comprising silicon dioxide, silicon monoxide, MgF₂ and siloxane polymers.

4. The device of claim 1 wherein said first dielectric layer of high-index of refraction of said one or more second layers is chosen from a group comprising titanium dioxide (TiO₂), Ti₃O₅, Ti₂O₃, TiO, ZrO₂+TiO₂ZrO₂Nb₂O₅, CeO₂, ZnS, Al₂O₃, niobium pentoxide (Nb₂O₅), tantalum pentoxide (Ta₂O₅) and siloxane polymers and said second dielectric layer of low-index of refraction of said one or more second layers is chosen from a group comprising SiO, SiO₂, MgF₂ and siloxane polymers.

5. The device of claim 1 wherein said optically transmissive, ohmic contact layer is chosen from a group comprising indium-tin oxide, nickel/gold alloys and ruthenium dioxide, RuO₂.

6. The device of claim 1 wherein said metallic layer is chosen from a group comprising Al, Ag, Rh, Pd, Cu, Au, Cr, Ti, Ni, nickel/gold alloys, chrome/gold alloys, silver/aluminum mixtures and combinations thereof.

7. A device capable of emitting light about a predetermined nominal wavelength in response to an applied electric current comprising:

a light emitting portion comprising at least one semiconductor material and a first and second surface wherein the light is emitted from the first and second surfaces and the second surface is substantially coupled to an optically transmissive, ohmic contact layer;

first optically transmissive dielectric layer with a refractive index less than the at least one semiconductor material and of a thickness greater than one-quarter wavelength of the predetermined nominal wavelength divided by the index of refraction of the first optically transmissive, dielectric layer coupled to the optically transmissive, ohmic contact layer

one or more second layers coupled to the first optically transmissive dielectric layer comprising a first dielectric layer of high-index of refraction and a second dielectric layer of low-index of refraction wherein the first dielectric layer is of a thickness about mλ

/4n_H, and the second dielectric layer is of a thickness about kλ

/4n_L, where m and k are odd integers, λ

is the predetermined nominal wavelength, n_H is the refractive index of the high-index of refraction dielectric layer and n_L is the refractive index of the low-index of refraction dielectric layer;

a metallic layer coupled to the one or more second layers and in contact with the first optically transmissive dielectric layer and to the optically transmissive, ohmic contact layer by more than one via through the one or more second layers and the first optically transmissive dielectric layer;

wherein the reflectivity of the metallic layer to the predetermined wavelength is greater than 50 percent; and

a means for mounting the light emitting device;

wherein the metallic layer is thermally coupled to the means for mounting and makes at least one electrical contact to the means for mounting.

8. The device of claim 7 wherein said metallic layer comprises at least three layers comprising:

a first layer comprising said metallic layer;

a second layer comprising a diffusion barrier; and

a third layer of a solderable material;

wherein elements of the solderable material are prevented from reaching said metallic layer by the second layer.

9. The device of claim 7 wherein said optically transmissive, dielectric layer is chosen from a group comprising silicon dioxide, silicon monoxide, MgF₂ and siloxane polymers.

10. The device of claim 7 wherein said first dielectric layer of high-index of refraction of said one or more second layers is chosen from a group comprising titanium dioxide (TiO₂), Ti₃O₅, Ti₂O₃, TiO, ZrO₂+TiO₂ZrO₂Nb₂O₅, CeO₂, ZnS, Al₂O₃, niobium pentoxide (Nb₂O₅), tantalum pentoxide (Ta₂O₅) and siloxane polymers and said second dielectric layer of low-index of refraction of said one or more second layers is chosen from a group comprising SiO, SiO₂, MgF₂ and siloxane polymers.

11. The device of claim 7 wherein said optically transmissive, ohmic contact layer is chosen from a group comprising indium-tin oxide, nickel/gold alloys and ruthenium dioxide, RuO₂.

12. The device of claim 7 wherein said metallic layer is chosen from a group comprising Al, Ag, Rh, Pd, Cu, Au, Cr, Ti, Ni, nickel/gold alloys, chrome/gold alloys, silver/aluminum mixtures and combinations thereof.

13. The device of claim 7 further comprising a metal-oxide layer coupled to said first surface of said light emitting portion wherein the metal-oxide layer comprises one or more layers wherein at least the first layer has an index of refraction greater than 2 and an optical extinction coefficient less than 0.2.

14. The light emitting device of claim 13 wherein said metal-oxide layer is chosen from a group comprising metal oxides, silicon dioxide, silicon carbide, GaN, Ta₂O₅, Nb₂O₅, TiO₂, AlInGaN based solid solutions and their non-stoichiometric mixtures, and wherein said metal-oxide layer portion has a predetermined shape and pattern.

15. A device capable of emitting light about a predetermined wavelength in response to an applied electric current comprising:

a light emitting portion comprising at least one semiconductor material and a first and second surface wherein the light is emitted from the first and second surfaces and the second surface is substantially coupled to an optically transmissive, ohmic contact layer;

at least one electrical contact on the first surface of the light emitting portion comprising an ohmic contact layer and patterned metallization suitable for at least one external electrical connection over at least one portion of the ohmic contact layer;

first optically transmissive, dielectric layer with a refractive index less than the at least one semiconductor material and of a thickness greater than one-quarter wavelength of the predetermined wavelength divided by the index of refraction of the optically transmissive dielectric layer coupled to the optically transmissive, ohmic contact layer

one or more second layers coupled to the first optically transmissive dielectric layer wherein each one or more second layers comprises a first dielectric layer of high-index of refraction and a second dielectric layer of low-index of refraction wherein the first dielectric layer is of a thickness about mλ

/4n_H, and the second dielectric layer is of a thickness about kλ

/4n_L, where m and k are odd integers, λ

is the predetermined nominal wavelength, n_H is the refractive index of the high-index of refraction dielectric layer and n_L is the refractive index of the low-index of refraction dielectric layer;

a metallic layer coupled to the one or more second layers and in contact with the optically transmissive, dielectric layer and to the first optically transmissive, ohmic contact layer by more than one via through the one or more second layers, and the first optically transmissive dielectric layer;

wherein the reflectivity of the metallic layer to the predetermined wavelength is greater than 50 percent; and

a means for mounting the device;

wherein the metallic layer is at least thermally coupled to the means for mounting.

16. The device of claim 15 wherein said metallic layer comprises at least three layers comprising:

a first layer comprising said metallic layer;

a second layer comprising a diffusion barrier; and

a third layer of a solderable material;

wherein elements of the solderable material are prevented from reaching said metallic layer by the second layer.

17. The device of claim 15 wherein said optically transmissive, dielectric layer is chosen from a group comprising silicon dioxide, silicon monoxide, MgF₂ and siloxane polymers.

18. The device of claim 15 wherein said first dielectric layer of high-index of refraction of said one or more second layers is chosen from a group comprising titanium dioxide (TiO₂), Ti₃O₅, Ti₂O₃, TiO, ZrO₂+TiO₂ZrO₂Nb₂O₅, CeO₂, ZnS, Al₂O₃, niobium pentoxide (Nb₂O₅), tantalum pentoxide (Ta₂O₅) and siloxane polymers and said second dielectric layer of low-index of refraction of said one or more second layers is chosen from a group comprising SiO, SiO₂, MgF₂ and siloxane polymers.

19. The device of claim 15 wherein said optically transmissive, ohmic contact layer is chosen from a group comprising indium-tin oxide, nickel/gold alloys and ruthenium dioxide, RuO₂.

20. The device of claim 15 wherein said metallic layer is chosen from a group comprising Al, Ag, Rh, Pd, Cu, Au, Cr, Ti, Ni, nickel/gold alloys, chrome/gold alloys, silver/aluminum mixtures and combinations thereof.

21. The device of claim 15 further comprising a metal-oxide layer coupled to said ohmic contact layer wherein the metal-oxide layer comprises one or more layers wherein at least the first layer has an index of refraction greater than 2 and an optical extinction coefficient less than 0.2.

22. The light emitting device of claim 21 wherein said metal-oxide layer is chosen from a group comprising metal oxides, silicon dioxide, silicon carbide, GaN, Ta₂O₅, Nb₂O₅, TiO₂, AlInGaN based solid solutions and their non-stoichiometric mixtures, and wherein said metal-oxide layer portion has a predetermined shape and pattern.

23. A method of improving light extraction efficiency of a device capable of emitting light about a predetermined wavelength in response to an applied electric current comprising the steps:

coupling an optically transmissive, ohmic contact layer to a light emitting portion of the device;

coupling first surface of an optically transmissive, dielectric layer of a thickness greater than one-quarter wavelength of the predetermined wavelength divided by the index of refraction of the optically transmissive dielectric layer to the optically transmissive, ohmic contact layer; and

coupling a first surface of one or more second layers to a second surface of the optically transmissive, dielectric layer wherein each one or more second layers comprises a first dielectric layer of high-index of refraction and a second dielectric layer of low-index of refraction wherein the first dielectric layer is of a thickness about mλ

/4n_H, and the second dielectric layer is of a thickness about kλ

/4n_L, where m and k are odd integers, λ

is the predetermined nominal wavelength in air, n_H is the refractive index of the high-index of refraction dielectric layer and n_L is the refractive index of the low-index of refraction dielectric layer; and

coupling a metallic layer to a second surface of the one or more second layers and in contact with the optically transmissive, dielectric layer and to the optically transmissive, ohmic contact layer by more than one via through the one or more second layers and the optically transmissive, dielectric layer;

wherein the reflectivity of the metallic layer to the predetermined wavelength is greater than 50 percent.