Electrode structures for LEDs with increased active area

• US 8,080,879 B2
• Filed: 05/03/2010
• Issued: 12/20/2011
• Est. Priority Date: 05/19/2006
• Status: Expired

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Bridgelux Incorporated
• Inventors: Shum, Frank T.
• Primary Examiner(s): Tran, Minh-Loan T
• Assistant Examiner(s): Lopez, Fei Fei Yeung
• Application Number:
  US12/772,767
• Publication Number:
  US 20100213495A1
• Time in Patent Office: 596 Days
• Field of Search: None
• US Class Current: 257/767
• 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 33/405 Reflective materials
• CPC Class Codes: H01L 33/42 Transparent materials
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

An electrode structure is disclosed for enhancing the brightness and/or efficiency of an LED. The electrode structure can have a metal electrode and an optically transmissive thick dielectric material formed intermediate the electrode and a light emitting semiconductor material. The electrode and the thick dielectric cooperate to reflect light from the semiconductor material back into the semiconductor so as to enhance the likelihood of the light ultimately being transmitted from the semiconductor material. Such LED can have enhanced utility and can be suitable for uses such as general illumination. The semiconductor material can have a cutout formed therein and a portion of the electrode can be formed outside of the cutout and a portion of the electrode can be formed inside of the cutout. The portion of the electrode outside the cutout can be electrically isolated from the semiconductor material by the dielectric material.

Claims

1. An electrode structure for an LED, the electrode structure comprising:

a semiconductor material having a cutout formed therein;

an electrically insulating porous dielectric material;

a metal electrode;

at least one pair of dielectric layers configured so as to define a DBR structure and disposed between a portion of the metal electrode and a portion of the dielectric material, wherein each pair of dielectric layers of the DBR structure is substantially optically transmissive, is comprised of layers of materials of different indices of refraction, and is a multiple of approximately ¼

λ

thick;

and

wherein a portion of the electrode is formed outside of the cutout and a portion of the electrode is formed inside of the cutout,

wherein the portion of the electrode outside the cutout is electrically isolated from the semiconductor material by the dielectric material, and

wherein the portion of the electrode inside the cutout is in electrical contact with the semiconductor material.

2. The electrode structure as recited in claim 1, wherein the dielectric material is optically transmissive, having an index of refraction greater than or equal to one and less than that of a semiconductor upon which the dielectric material is formed, and having a thickness greater than ½

λ

, the dielectric material being formed to the electrode so as to enhance reflection of light.

3. The electrode structure as recited in claim 1, wherein the dielectric material has a thickness of approximately 1.75 λ

.

4. The electrode structure as recited in claim 1, wherein:

the electrode is formed upon the semiconductor material;

the dielectric material is formed intermediate at least a portion of the electrode and the semiconductor material; and

the semiconductor material comprises at least one material selected from the group consisting of;

AlGaAs;

AlInGaP;

AlInGaN; and

GaAsP.

5. The electrode structure as recited in claim 1, wherein the dielectric material comprises at least one material selected from the group consisting of:

silicon dioxide;

silicon monoxide;

MgF₂;

siloxane polymers; and

air.

6. The electrode structure as recited in claim 1, further comprising an ohmic contact layer formed between the electrode and a semiconductor.

7. The electrode structure as recited in claim 1, wherein the dielectric material comprises porous ITO.

8. The electrode structure as recited in claim 1, wherein the dielectric material comprises porous SiO₂.

9. The electrode structure as recited in claim 1, wherein the dielectric material is porous enough to reduce its effective index of refraction such that total internal reflection occurs within the semiconductor material.

10. An electrode structure for an LED, the electrode structure comprising:

a semiconductor material having a cutout formed therein;

an electrically insulating porous dielectric material layer comprising ITO; and

a metal electrode, wherein

a portion of the electrode is formed outside of the cutout and a portion of the electrode is formed inside of the cutout,

the portion of the electrode outside the cutout is electrically isolated from the semiconductor material by the dielectric material layer, and

the portion of the electrode inside the cutout is in electrical contact with the semiconductor material.

11. The electrode structure as recited in claim 10, wherein the dielectric material is optically transmissive, having an index of refraction greater than or equal to one and less than that of a semiconductor upon which the dielectric material is formed, and having a thickness greater than ½

λ

, the dielectric material being formed to the electrode so as to enhance reflection of light.

12. The electrode structure as recited in claim 10, wherein the dielectric material has a thickness of approximately 1.75 λ

.

13. The electrode structure as recited in claim 10, wherein:

the electrode is formed upon the semiconductor material;

the dielectric material is formed intermediate at least a portion of the electrode and the semiconductor material; and

the semiconductor material comprises at least one material selected from the group consisting of;

AlGaAs;

AlInGaP;

AlInGaN; and

GaAsP.

14. The electrode structure as recited in claim 10, wherein the dielectric material comprises at least one material selected from the group consisting of:

silicon dioxide;

silicon monoxide;

MgF₂;

siloxane polymers; and

air.

15. The electrode structure as recited in claim 10, further comprising an ohmic contact layer formed between the electrode and a semiconductor.

16. The electrode structure as recited in claim 10, wherein the dielectric material further comprises porous SiO₂.

17. The electrode structure as recited in claim 10, wherein the dielectric material is porous enough to reduce its effective index of refraction such that total internal reflection occurs within the semiconductor material.

18. The electrode structure as recited in claim 10, further comprising at least one pair of dielectric layers configured so as to define a DBR structure and disposed between a portion of the electrode and a portion of the dielectric, wherein each pair of dielectric layers of the DBR structure is substantially optically transmissive, is comprised of layers of materials of different indices of refraction, and is a multiple of approximately ¼

λ

thick.