IMPROVEMENTS IN EXTERNAL LIGHT EFFICIENCY OF LIGHT EMITTING DIODES

• US 20100295014A1
• Filed: 08/16/2007
• Published: 11/25/2010
• Est. Priority Date: 08/16/2006
• Status: Active Grant

• Current Assignee: Tinggi Technologies Pte., Ltd.
• Original Assignee: Tinggi Technologies Pte., Ltd.
• Inventors: Chen, Zhen, Lam, Jenny, Ng, Tien Khee, Kang, Xuejun, Yuan, Shu
• Granted Patent: US 8,395,167 B2
• Time in Patent Office: Days
• US Class Current: 257/13
• 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

1-45. -45. (canceled)

46. 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, wherein the surface texturing is at least one selected from the group consisting of:

micro-lenses and surface roughened micro-lenses.

47. A method as claimed in claim 46, wherein the light emitting diode has a layer of p-type material and 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.

48. A method as claimed in claim 46, wherein the surface texturing is by wet etching with a chemical solution;

the chemical solution being an aqueous solution of potassium hydroxide and etching is at a temperature for a predetermined period.

49. A method as claimed in claim 46, wherein agitation of the light emitting diode is performed during the etching;

the agitation being by ultraviolet illumination.

50. A method as claimed in claim 46, wherein the etching is by 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 before or after the wet etching.

51. A method as claimed in claim 46, 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.

52. A method as claimed in claim 51, wherein the micro-lenses are substantially pyramidical and have facets at an angle of substantially 58°

.

53. A method as claimed in claim 46, wherein the surface texturing is over a part of the external surface and is in light spaces formed between joining portions and an outer portion of a current dissipation array on the external surface.

54. A method as claimed in claim 47, wherein a first ohmic contact is formed on the external surface of the n-type layer and a second ohmic contact is formed on p-type layer external surface;

the second ohmic contact being able to reflect light for enhancing light emission of the light emitting diode and comprises 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 being for a light reflection layer for enhancing light reflection of the light emitting diode.

55. A method as claimed in claim 54, wherein the second ohmic contact covers the entire p-type layer external surface.

56. A method as claimed in claim 54, wherein the second ohmic contact covers a portion of the p-type layer external surface, with the remainder of the p-type layer external surface being at least partially covered with at least one reflective material for reflecting light for enhancing light emission of the light emitting diode.

57. A method as claimed in claim 47, 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.

58. A method as claimed in claim 46 further comprising surface texturing on the p-type side by surface texturing at least one layer selected from the group consisting of:

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

59. A light emitting diode comprising an external surface of an n-type layer of the light emitting diode having surface texturing formed by etching, the surface texturing being for reducing internal light reflection for increasing light output and external light efficiency of the light emitting diode, wherein the surface texturing is at least one selected from the group consisting of:

micro-lenses and surface roughened micro-lenses.

60. A light emitting diode as claimed in claim 59, wherein the light emitting diode has a layer of p-type material 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.

61. A light emitting diode as claimed in claim 59, 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.

62. A light emitting diode as claimed in claim 61, wherein the micro-lenses are substantially pyramidical and have facets at an angle of substantially 58′

.

63. A light emitting diode as claimed in claim 59, wherein the surface texturing is over a part of the external surface and is in light spaces foil led between joining portions and an outer portion of a current dissipation array on the external surface.

64. A light emitting diode as claimed in claim 60, wherein a first ohmic contact is formed on the external surface of the n-type layer and a second ohmic contact is formed on p-type layer external surface;

the second ohmic contact being able to reflect light for enhancing light emission of the light emitting diode and comprises 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 being for a light reflection layer for enhancing light reflection of the light emitting diode.

65. A light emitting diode as claimed in claim 64, wherein the second ohmic contact covers the entire p-type layer external surface.

66. A light emitting diode as claimed in claim 64, wherein the second ohmic contact covers a portion of the p-type layer external surface, with the remainder of the p-type layer external surface being at least partially covered with at least one reflective material for reflecting light for enhancing light emission of the light emitting diode.

67. A light emitting diode as claimed in claim 60, 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.

68. A light emitting diode as claimed in claim 60 further comprising surface texturing on the p-type side, the surface texturing on the p-type side being on at least one layer selected from the group consisting of:

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