Semiconductor light emitting device and method for manufacturing the same

• US 20060056474A1
• Filed: 09/08/2005
• Published: 03/16/2006
• Est. Priority Date: 09/10/2004
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Asakawa, Koji, Ohashi, Kenichi, Fujimoto, Akira
• Granted Patent: US 7,476,910 B2
• Time in Patent Office: Days
• US Class Current: 372/43.10
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers

Abstract

In a semiconductor light emitting device, a semiconductor light emitting element has a light extracted surface on which a plurality of convex structures is formed. The convex structures each have a conical mesa portion constituting a refractive index gradient structure, a cylindrical portion constituting a diffraction grating structure, and a conical portion constituting a refractive index gradient structure. The mesa portion, cylindrical portion, and conical portion are arranged in this order from the light extracted surface. The period between the convex structures is longer than 1/(the refractive index of an external medium+the refractive index of the convex structures) of an emission wavelength and equal to or shorter than the emission wavelength. The circle-equivalent average diameter of the cylindrical portion is ⅓ to 9/10 of that of the bottom of the mesa portion.

Claims

1. A semiconductor light emitting device comprising:

a semiconductor light emitting element including a light extracted surface on which a plurality of convex structures are formed;

the convex structures each including a conical mesa portion, a cylindrical portion, and a conical portion configuring, the mesa portion, the cylindrical portion, and the conical portion being arranged in this order from the light extracted surface toward exterior,

an period between the convex structures being longer than 1/(a refractive index of an external medium+a refractive index of the convex structures) of an emission wavelength and equal to or shorter than the emission wavelength, and a circle-equivalent average diameter of the cylindrical portion being ⅓

to 9/10 of that of a bottom of the mesa portion.

2. The semiconductor light emitting device according to claim 1, wherein the circle-equivalent average diameter of a top of the mesa portion is equivalent to that of the cylindrical portion, the circle-equivalent average diameter of the bottom of the mesa portion is longer than 1/(the refractive index of the external medium+the refractive index of the convex structures) and equal to or shorter than the emission wavelength, and an average height of the mesa portion is 1/10 to ⅕

of the emission wavelength.

3. The semiconductor light emitting device according to claim 1, wherein a circle-equivalent average diameter of a bottom of the conical portion is equivalent to that of the cylindrical portion, and an average height of the conical portion is at least 1/10 of the emission wavelength and is equal to or smaller than the emission wavelength.

4. The semiconductor light emitting device according to claim 1, wherein an average height of each of the convex structures is 0.6 to 1.5 times as large as the emission wavelength.

5. The semiconductor light emitting device according to claim 1, wherein an average height of the cylindrical portion is at least 3/10 of the emission wavelength and is equal to or smaller than the emission wavelength.

6. The semiconductor light emitting device according to claim 1, wherein the light emitting element comprises (or is formed of) a light emitting diode, and an electrode is formed on a part of the light extracted surface, whereas the convex structures are formed on a part of the light extracted surface on which the electrode is not formed.

7. The semiconductor light emitting device according to claim 6, wherein the light emitting diode is formed by stacking a plurality of semiconductor layers configuring a hetero structure on a top surface of a substrate, and a bottom surface of the substrate forms the light extracted surface.

8. The semiconductor light emitting device according to claim 1, wherein a group of the mesa portions forms a refractive index gradient structure, a group of the cylindrical portion forms a diffraction grating structure, and a group of the conical portion forms a refractive index gradient structure.

9. A semiconductor light emitting device comprising:

a semiconductor light emitting element including a light extracted surface on which a plurality of convex structures are formed;

the convex structures each including a conical mesa portion, a cylindrical portion, and a conical portion, the mesa portion, the cylindrical portion, and the conical portion being arranged in this order from the light extracted surface toward exterior,

an period between the convex structures being longer than 1/(a refractive index of an external medium+a refractive index of the convex structures) of an emission wavelength and equal to or shorter than the emission wavelength, and an average height of the convex structures is 0.6 to 1.5 times as large as the emission wavelength,

a circle-equivalent average diameter of the cylindrical portion being ⅓

to 9/10 of that of a bottom of the mesa portion, and an average height of the cylindrical portion being at least 3/10 of the emission wavelength and is equal to or smaller than the emission wavelength,

a circle-equivalent average diameter of a top of the mesa portion being equivalent to that of the cylindrical portion, a circle-equivalent average diameter of a bottom of the mesa portion being longer than 1/(the refractive index of the external medium+the refractive index of the convex structures) and equal to or shorter than the emission wavelength, and an average height of the mesa portion being 1/10 to ⅕

of the emission wavelength, and

a circle-equivalent average diameter of a bottom of the conical portion being equivalent to that of the cylindrical portion, and an average height of the conical portion being at least 1/10 of the emission wavelength and being equal to or smaller than the emission wavelength.

10. The semiconductor light emitting device according to claim 9, wherein the light emitting element is formed of a light emitting diode, and an electrode is formed on a part Qf the light extracted surface, whereas the convex structures are formed on a part of the light extracted surface on which the electrode is not formed.

11. The semiconductor light emitting device according to claim 10, wherein the light emitting diode is formed by stacking a plurality of semiconductor layers configuring a hetero structure on a top surface of a substrate, and a bottom surface of the substrate forms the light extracted surface.

12. The semiconductor light emitting device according to claim 9, wherein a group of the mesa portions forms a refractive index gradient structure, a group of the cylindrical portion forms a diffraction grating structure, and a group of the conical portion forms a refractive index gradient structure.

13. A method for manufacturing a semiconductor light emitting device comprising a semiconductor light emitting element, the method comprising:

forming a mask on which circular patterns are periodically arranged, on a light extracted surface of a semiconductor light emitting element,

selectively etching the light extracted surface of the semiconductor light emitting element by a reactive ion etching technique using the mask to form convex structures each including a conical mesa portion, a cylindrical portion, and a conical portion, the mesa portion, the cylindrical portion, and the conical portion being arranged in this order from the light extracted surface, and an period between the convex structures is longer than 1/(a refractive index of an external medium+a refractive index of the convex structures) of an emission wavelength and equal to or shorter than the emission wavelength, and a circle-equivalent average diameter of the cylindrical portion is ⅓

to 9/10 of that of a bottom of the mesa portion.

14. The method according to claim 13, wherein the light extracted surface is formed of a light radiation side outermost layer or an inorganic light transmission layer of the semiconductor light emitting element.

15. The method according to claim 13, wherein in order to form the mask, a resist is formed on the light extracted surface and the circular patterns are drawn on the resist by a lithography technique using electron light or light.

16. The method according to claim 13, wherein in order to form the mask, a thin film formed of a resin composition which contains a block copolymer or graft copolymer and which forms a micro phase separation structure in a self-organizing manner is formed on the light extracted surface and at least one of phases of the micro phase separation structure of the thin film is selectively removed.

17. The method according to claim 13, wherein in order to form the mask, polymer beads or silica beads configured in a monolayer are formed on the light extracted surface.

18. A method for manufacturing a semiconductor light emitting device comprising a semiconductor light emitting element, the method comprising:

forming a mask on which circular patterns are periodically configured, on a light extracted surface of a semiconductor light emitting element;

selectively etching the light extracted surface by a reactive ion etching technique using the mask to form a cylindrical portion of each of convex structures configuring a diffraction grating structure and setting an period between the convex structures longer than 1/(a refractive index of an external medium+a refractive index of the convex structures) of an emission wavelength and equal to or shorter than the emission wavelength; and

etching the light extracted surface by a physical etching technique using an inert gas to form a conical mesa portion at a bottom of each of the cylindrical portions, forming a conical portion at a top of the cylindrical portion, and setting a circle-equivalent average diameter of the cylindrical portion ⅓

to 9/10 of that of a bottom of the mesa portion.

19. The method according to claim 18, wherein the light extracted surface is formed of a light radiation side outermost layer or an inorganic light transmission layer of the semiconductor light emitting element.

20. The method according to claim 18, wherein in order to form the mask, a resist is formed on the light extracted surface and the circular patterns are drawn on the resist by a lithography technique using electron light or light.

21. The method according to claim 18, wherein in order to form the mask, a thin film formed of a resin composition which contains a block copolymer or graft copolymer and which forms a micro phase separation structure in a self-organizing manner is formed on the light extracted surface and at least one of phases of the micro phase separation structure of the thin film is selectively removed.

22. The method according to claim 18, wherein in order to form the mask, polymer beads or silica beads configured in a monolayer are formed on the light extracted surface.