Light emitting diode with embedded saw-tooth multilayer having a photonic crystal structure and process for fabricating the same

• US 7,663,153 B2
• Filed: 01/25/2008
• Issued: 02/16/2010
• Est. Priority Date: 11/07/2007
• Status: Active Grant

• Current Assignee: National Tsing Hua University
• Original Assignee: Industrial Technology Research Institute, National Tsing Hua University
• Inventors: Huang, Chen-Yang, Xuan, Rong, Ku, Hao-Min, Chao, Chu-Li, Chao, Shiuh
• Primary Examiner(s): Pert; Evan
• Assistant Examiner(s): Wilson; Scott R
• Application Number:
  US12/011,304
• Publication Number:
  US 20090114935A1
• Time in Patent Office: 753 Days
• Field of Search: 257/98, 257/13, 257 79-103, 257/918, 257/E33.068, 257/E33.069, 257/E51.021, 438/22, 438 25- 27, 438/29
• US Class Current: 257/98
• CPC Class Codes: H01L 2933/0083 Periodic patterns for optical field-shaping in or on the semiconductor body or semiconductor body package, e.g. photonic bandgap structures
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/12 with a stress relaxation structure, e.g. buffer layer
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

A light emitting diode (LED) is provided. The LED at least includes a substrate, a saw-toothed multilayer, a first type semiconductor layer, an active emitting layer and a second type semiconductor layer. In the LED, the saw-tooth multilayer is formed opposite the active emitting layer below the first type semiconductor layer by an auto-cloning photonic crystal process. Due to the presence of the saw-tooth multilayer on the substrate of the LED, the scattered light form a back of the active emitting layer can be reused by reflecting and recycling through the saw-tooth multilayer. Thus, all light is focused to radiate forward so as to improve the light extraction efficiency of the LED. Moreover, the saw-tooth multilayer does not peel off or be cracked after any high temperature process because the saw-tooth multilayer has the performance of releasing thermal stress and reducing elastic deformation between it and the substrate.

Claims

1. A light emitting diode (LED), at least comprising:

a substrate;

a first type semiconductor layer disposed on the substrate;

an active emitting layer, disposed on the first type semiconductor layer;

a second type semiconductor layer, disposed on the active emitting layer; and

a saw-toothed multilayer, disposed below the first type semiconductor layer opposite the active emitting layer, wherein the saw-toothed multilayer is a photonic crystal.

2. The LED as claimed in claim 1, wherein the saw-toothed multilayer is disposed below the substrate.

3. The LED as claimed in claim 1, wherein the saw-toothed multilayer is disposed between the substrate and the first type semiconductor layer.

4. The LED as claimed in claim 3, wherein the saw-toothed multilayer has a lattice structure.

5. The LED as claimed in claim 4, wherein the lattice structure comprises a one-dimensional, two-dimensional or three-dimensional structure.

6. The LED as claimed in claim 4, wherein an arrangement of the lattice structure comprises a triangular, a hexagonal, a square or a combination array.

7. The LED as claimed in claim 4, wherein an outward shape of the lattice structure comprises a rectangle, a strip, a triangle or a half circle.

8. The LED as claimed in claim 4, wherein a period and/or a height of the lattice structure is determined by a luminescent wavelength range thereof suitable for the LED.

9. The LED as claimed in claim 1, wherein the saw-toothed multilayer is periodically and alternately stacked by two or more than two materials with different reflectivities.

10. The LED as claimed in claim 1, wherein a luminescent wavelength of the saw-toothed multilayer suitable for the LED is determined by at least one of a period of the saw-toothed multilayer, a thickness of stacked thin layers in the saw-toothed multilayer, a layer number of the stacked thin layers, and a refractive index of a material of the stacked thin layers.

11. The LED as claimed in claim 1, wherein stacked thin layers in the saw-toothed multilayer are fabricated by using two materials selected from a group consisting of TiO₂, Ta₂O₅, Nb₂O₅, CeO₂, ZnS, ZnO, GaN, SiN_X, AlN, Al₂O₃, SiO₂ and MgF₂.

12. The LED as claimed in claim 1, wherein a material of the substrate comprises sapphire, SiC, Si, GaAs, LiAlO₂, LiGaO₂ or AlN.

13. The LED as claimed in claim 1, wherein the saw-toothed multilayer is stacked on the substrate and an initial outward shape of the substrate comprises a triangular cone, a cube, a half circle or a strip with a cross-sectional view as a triangle, a rectangle or a half circle.

14. A process for fabricating an LED, comprising:

fabricating a saw-toothed multilayer on a substrate by an auto-cloning photonic crystal process to let the saw-toothed multilayer be an auto-cloning photonic crystal;

patterning the saw-toothed multilayer to form a lattice structure;

forming a first type semiconductor layer on the substrate to cover the lattice structure;

forming an active emitting layer on the first type semiconductor layer; and

forming a second type semiconductor layer on active emitting layer.

15. The process for fabricating the LED as claimed in claim 14, wherein stacked thin layers in the saw-toothed multilayer are fabricated by using two materials selected from a group consisting of TiO₂, Ta₂O₅, Nb₂O₅, CeO₂, ZnS, ZnO, GaN, SiN_X, AlN, Al₂O₃, SiO₂ and MgF₂.

16. The process for fabricating the LED as claimed in claim 14, wherein a material of the substrate comprises sapphire, SiC, Si, GaAs, LiAlO₂, LiGaO₂ or AlN.

17. A process for fabricating an LED, comprising:

a) forming a first type semiconductor layer on a substrate;

b) forming an active emitting layer on the first type semiconductor layer;

c) forming a second type semiconductor layer on the active emitting layer; and

forming a saw-toothed multilayer optionally either before the step a) or after the step c) by an auto-cloning photonic crystal process to let the saw-toothed multilayer be an auto-cloning photonic crystal.

18. The process for fabricating the LED as claimed in claim 17, wherein stacked thin layers in the saw-toothed multilayer are fabricated by using two materials selected from a group consisting of TiO₂, Ta₂O₅, Nb₂O₅, CeO₂, ZnS, ZnO, GaN, SiN_X, AlN, Al₂O₃, SiO₂ and MgF₂.

19. The process for fabricating the LED as claimed in claim 17, wherein a material of the substrate comprises sapphire, SiC, Si, GaAs, LiAlO₂, LiGaO₂ or AlN.