Method of Fabricating Light Emitting Device and Thus-Fabricated Light Emitting Device

• US 20080061307A1
• Filed: 04/13/2005
• Published: 03/13/2008
• Est. Priority Date: 04/27/2004
• Status: Active Grant

• Current Assignee: Shin-Etsu Handotai Co., Ltd. (Shin-Etsu Chemical Company Limited)
• Original Assignee: Shin-Etsu Handotai Co., Ltd. (Shin-Etsu Chemical Company Limited)
• Inventors: Ikeda, Hitoshi, Nakamura, Akio, Suzuki, Kingo
• Granted Patent: US 7,579,205 B2
• Time in Patent Office: Days
• US Class Current: 257/94
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 24/03 Manufacturing methods
• CPC Class Codes: H01L 24/05 of an individual bonding area
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/30 containing only elements of Group III and Group V of the Periodic Table
• CPC Class Codes: Y10S 438/964 Roughened surface

Abstract

A light emitting device wafer having a light emitting layer section 24 having an AlGaInP-base double heterostructure, and a GaP light extraction layer 20 disposed on the light emitting layer section so as to allow a first main surface thereof to compose a first main surface of the wafer is fabricated so that the first main surface of the GaP light extraction layer appears as the (100) surface. The first main surface of the GaP light extraction layer 20 composed of the (100) surface is etched using an etching solution for surface roughening to thereby form surface roughening projections 40f. Accordingly, there can be provided a method of fabricating a light emitting device having the GaP light extraction layer agreed with the (100) main surface, capable of readily subjecting the (100) main surface to surface roughening.

Claims

1. A method of fabricating a light emitting device comprising:

a light emitting device wafer fabricating step fabricating a light emitting device wafer having a light emitting layer section based on a double heterostructure in which a first-conductivity-type cladding layer, an active layer and an second-conductivity-type cladding layer, each of which being composed of a compound semiconductor having a composition allowing lattice matching with GaAs, out of compound semiconductors expressed by formula (Al_xGa_1-x)_yIn_1-yP (where, 0≦

x≦

1, 0≦

y≦

1), are stacked in this order, and a GaP light extraction layer disposed on said light emitting layer section so as to allow a first main surface thereof to compose a first main surface of the wafer, so that the first main surface of said GaP light extraction layer appears as the (100) surface;

a main light extraction area roughening step forming surface roughening projections on the first main surface of said GaP light extraction layer composed of said (100) surface, by etching said surface using an etching solution for surface roughening containing acetic acid, hydrofluoric acid, nitric acid, iodine and water up to a total content of 90% by mass or more, and having a total content by mass of acetic acid, hydrofluoric acid, nitric acid and iodine larger than the content by mass of water; and

a dicing step dicing said light emitting device wafer to thereby fabricate light emitting device chips each having said surface roughening projections on the first main surface of said GaP light extraction layer.

2. The method of fabricating a light emitting device as claimed in claim 1, wherein said etching solution for surface roughening contains:

acetic acid (on CH₃COOH basis);

37.4% by mass or more and 94.8% by mass or less;

hydrofluoric acid (on HF basis);

0.4% by mass or more and 14.8% by mass or less;

nitric acid (on HNO₃ basis);

1.3% by mass or more and 14.7% by mass or less; and

iodine (on I₂ basis);

0.12% by mass or more and 0.84% by mass or less,

and has a water content of 2.4% by mass or more and 45% by mass or less.

3. The method of fabricating a light emitting device as claimed in claim 1, wherein said etching solution for surface roughening contains:

acetic acid (on CH₃COOH basis);

45.8% by mass or more and 94.8% by mass or less;

hydrofluoric acid (on HF basis);

0.5% by mass or more and 14.8% by mass or less;

nitric acid (on HNO₃ basis);

1.6% by mass or more and 14.7% by mass or less; and

iodine (on I₂ basis);

0.15% by mass or more and 0.84% by mass or less,

and has a water content of 2.4% by mass or more and 32.7% by mass or less.

4. The method of fabricating a light emitting device as claimed in claim 1, wherein said GaP light extraction layer is formed to as thick as 10 μ

m or more on said light emitting device wafer, and

further comprising a side-face light extraction area roughening step forming surface roughening projections on the side-face light extraction areas of said GaP light extraction layer composed of the side faces of the chips formed by said dicing, by etching said areas using said etching solution for surface roughening.

5. The method of fabricating a light emitting device as claimed in claim 4, wherein said dicing is carried out so that the {100} surface appears on the side faces of the chip.

6. The method of fabricating a light emitting device as claimed in claim 4, wherein said surface roughening projections are formed by removing, after said dicing step, a process-induced damage layer formed in said side-face light extraction areas of said GaP light extraction layer using an etching solution for removing damage composed of an aqueous sulfuric acid/hydrogen peroxide solution, and then by etching the exposed surface by said etching solution for surface roughening.

7. The method of fabricating a light emitting device as claimed in claim 6, wherein said GaP light extraction layer is formed to be as thick as 40 μ

m or more.

8. The method of fabricating a light emitting device as claimed in claim 1, wherein said GaP light extraction layer is formed to be thinner than 40 μ

m, and said surface roughening projections are not formed on the side faces of said GaP light extraction layer.

9. The method of fabricating a light emitting device as claimed in claim 1, wherein said surface roughening projections formed by the anisotropic etching using said etching solution for surface roughening are further rounded by etching using an isotropic etching solution.

10. A light emitting device comprising:

a light emitting layer section based on a double heterostructure in which a first-conductivity-type cladding layer, an active layer and an second-conductivity-type cladding layer, each of which being composed of a compound semiconductor having a composition allowing lattice matching with GaAs, out of compound semiconductors expressed by formula (Al_xGa_1-x)_yIn_1-yP (where, 0≦

x≦

1, 0≦

y≦

1), stacked in this order; and

a GaP light extraction layer having a thickness of 10 μ

m or more, formed on the first main surface side of said light emitting layer section, having a part of a first main surface thereof covered with a light-extraction-side electrode, allowing an area of said first main surface not covered by said light-extraction-side electrode to function as a main light extraction area, and allowing the side face areas to similarly function as side-face light extraction areas,

wherein said GaP light extraction layer is a GaP single crystal layer having the (100) surface as said first main surface, and has surface roughening projections formed by etching on both of said main light extraction area and said side-face light extraction areas.

11. The light emitting device as claimed in claim 10, wherein outer surfaces of said surface roughening projections are formed mainly as having the {111} surfaces by chemical anisotropic etching of GaP single crystal.

12. The light emitting device as claimed in claim 10, wherein said surface roughening projections in said main light extraction area of said GaP light extraction layer are formed by immersing the entire surface of a flat crystalline main surface, composed of the (100) surface, of the GaP single crystal into an etching solution for surface roughening.

13. The light emitting device as claimed in claim 11, wherein said surface roughening projections in said side-face light extraction area of said GaP light extraction layer are formed by immersing the side faces of the layer into an etching solution for surface roughening.

14. The light emitting device as claimed in claim 10, wherein said surface roughening projections formed in said side-face light extraction areas of said GaP light extraction layer satisfy at least either one of conditions that they have a smaller mean height, and that they have a larger mean interval of formation, as compared with those of the surface roughening projections formed in said main light extraction area.

15. The light emitting device as claimed in claim 13, wherein said side-face light extraction areas of said GaP light extraction layer are composed of the {100} surface of GaP single crystal.

16. The light emitting device as claimed in claim 10, wherein said surface roughening projections are rounded to have curved surfaces on the end portion side thereof.

17. The light emitting device as claimed in claim 16, wherein each of said surface roughening projections has a main body composing the projection base and thinned towards the end side thereof, and a swelled tip portion integrated with said main body, as being swelled out in a ball form on the end side thereof.

18. The light emitting device as claimed in claim 10, wherein a plurality of said surface roughening projections formed as being distributed on said main light extraction area show a polyhedral form having a plurality of planes surrounding the outer surface of at least the projection bases, and the majority of said projections are formed as having both of φ

1 and φ

2 of 30°

or more, satisfying φ

1>

φ

2, where φ

1 and φ

2 are acute angles respectively held between each of two opposing surfaces of the same projection and the first main surface of said GaP light extraction layer in a predetermined direction on said main light extraction area.

19. The light emitting device as claimed in claim 18, wherein said light emitting layer section is obtained as being epitaxially grown on a GaAs substrate having the principal crystal axis with an off-angle of 1°

to 25°

, both ends inclusive, away from the <

100>

direction, and the crystal orientation of said GaP light extraction layer is agreed with said off-angled light emitting layer section.

20. The light emitting device as claimed in claim 10, wherein said surface roughening projections are such as those having a basic geometry obtained by anisotropic etching, and further rounded using an isotropic etching solution.