External light efficiency of light emitting diodes

• US 8,395,167 B2
• Filed: 08/16/2007
• Issued: 03/12/2013
• Est. Priority Date: 08/16/2006
• Status: Active Grant

• Current Assignee: Tinggi Technologies Pte., Ltd.
• Original Assignee: Tinggi Technologies Pte., Ltd.
• Inventors: Kang, Xuejun, Chen, Zhen, Ng, Tien Khee, Lam, Jenny, Yuan, Shu
• Primary Examiner(s): Richards, N Drew
• Assistant Examiner(s): WITHERS, GRANT S
• Application Number:
  US12/377,380
• Publication Number:
  US 20100295014A1
• Time in Patent Office: 2,035 Days
• Field of Search: 257/95
• US Class Current: 257/95
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/405 Reflective materials

Abstract

A method to improve the external light efficiency of light emitting diodes, the method comprising etching an external surface of an n-type layer of the light emitting diode to form surface texturing, the surface texturing reducing internal light reflection to increase light output. A corresponding light emitting diode is also disclosed.

Claims

1. A method to improve the external light efficiency of a light emitting diode, the light emitting diode including an n-type layer, a p-type layer, an ohmic contact layer, and a contact layer, the method comprising:

etching an external surface of the n-type layer to form surface texturing, the surface texturing reducing internal light reflection to increase light output,

wherein the surface texturing is at least one selected from the group consisting of;

micro-lenses and surface roughened micro-lenses, and

wherein the surface texturing is over a part of the external surface of the n-type layer and is in light spaces formed between joining portions and an outer portion of a current dissipation array on the external surface of the n-type layer.

2. The method as claimed in claim 1, wherein the light emitting diode has an active layer between the n-type layer and the p-type layer and the active layer comprises at least one selected from the group consisting of:

a quantum well, quantum wells, quantum dots, and quantum wires.

3. The method as claimed in claim 1, wherein the surface texturing is formed by wet etching with an aqueous solution of potassium hydroxide at a temperature for a predetermined period.

4. The method as claimed in claim 1, further comprising:

agitating the light emitting diode with ultraviolet illumination during the etching.

5. The method as claimed in claim 1, wherein the etching is dry etching, the dry etching being at least one selected from the group consisting of:

plasma etching, plasma bombardment, or laser processing; and

the dry etching being performed before or after wet etching.

6. The method as claimed in claim 1, wherein the micro-lenses are selected from the group consisting of:

hemispherical, substantially hemispherical, hemispherical with a flat top, a segment of a sphere, pyramidical, cylindrical, and cuboid; and

the micro-lenses are of;

(a) a spacing between the micro-lenses in the range 2 to 3 μ

m;

(b) a pitch of substantially 6 μ

m; and

(c) a radius of substantially 2 μ

m.

7. The method as claimed in claim 2, wherein a first ohmic contact is formed on the external surface of the n-type layer and a second ohmic contact is formed on a surface of the p-type layer, the second ohmic contact configured to reflect light to enhance light emission of the light emitting diode and comprising a stack of multiple layers of metals and their alloys, at least one of the metals being a highly reflective metal including at least one of:

silver and aluminum, the highly reflective metal serving as a light reflection layer to enhance light reflection of the light emitting diode.

8. The method as claimed in claim 7, wherein the second ohmic contact covers the surface of the p-type layer entirely.

9. The method as claimed in claim 7, wherein the second ohmic contact covers a portion of the surface of the p-type layer, with the remainder of the surface of the p-type layer being at least partially covered with at least one reflective material, the at least one reflective material reflecting light to enhance light emission of the light emitting diode.

10. The method as claimed in claim 2, wherein the p-type layer, the active layer, and the n-type layer are at least one selected from the group consisting of:

a GaN-related material, GaN, InGaN, AlGaN, AlGaInN, InN and AlN.

11. The method as claimed in claim 1 further comprising:

forming surface texturing on at least one layer selected from the group consisting of;

the p-type layer, the ohmic contact layer, and the contact layer.

12. A light emitting diode comprising:

an n-type layer having surface texturing over a part of an external surface of the n-type layer to reduce internal light reflection and increasing light output and external light efficiency of the light emitting diode,

wherein the surface texturing is formed by etching and is at least one selected from the group consisting of;

micro-lenses and surface roughened micro-lenses, and

wherein the surface texturing is in light spaces formed between joining portions and an outer portion of a current dissipation array on the external surface of the n-type layer.

13. The light emitting diode as claimed in claim 12, further comprising:

a p-type layer; and

an active layer between the n-type layer and the p-type layer, the active layer comprising at least one selected from the group consisting of;

a quantum well, quantum wells, quantum dots, and quantum wires.

14. The light emitting diode as claimed in claim 12, wherein the micro-lenses are selected from the group consisting of:

hemispherical, substantially hemispherical, hemispherical with a flat top, a segment of a sphere, pyramidicial, cylindrical, and cuboid; and

the micro-lenses are of;

(a) a spacing between the micro-lenses in the range 2 to 3 μ

m;

(b) a pitch of substantially 6 μ

m; and

(c) a radius of substantially 2 μ

m.

15. The light emitting diode as claimed in claim 13, wherein a first ohmic contact is formed on the external surface of the n-type layer and a second ohmic contact is formed on a surface of the p-type layer, the second ohmic contact configured to reflect light to enhance light emission of the light emitting diode and comprising a stack of multiple layers of metals and their alloys, at least one of the metals being a highly reflective metal including at least one of:

silver and aluminum;

the highly reflective metal serving as a light reflection layer to enhance light reflection of the light emitting diode.

16. The light emitting diode as claimed in claim 15, wherein the second ohmic contact covers the surface of the p-type layer entirely.

17. The light emitting diode as claimed in claim 15, wherein the second ohmic contact covers a portion of the surface of the p-type layer, with the remainder of the surface of the p-type layer being at least partially covered with at least one reflective material, the at least one reflective material reflecting light to enhance light emission of the light emitting diode.

18. The light emitting diode as claimed in claim 13, wherein the p-type layer, the active layer, and the n-type layer are at least one selected from the group consisting of:

a GaN-related material, GaN, InGaN, AlGaN, AlGaInN, InN and AlN.

19. The light emitting diode as claimed in claim 13, further comprising:

surface texturing on at least one layer selected from the group consisting of;

the p-type layer, the ohmic contact layer, and the contact layer.