Forming an optical element on the surface of a light emitting device for improved light extraction

• US 20020141006A1
• Filed: 03/30/2001
• Published: 10/03/2002
• Est. Priority Date: 03/30/2001
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: Camras, Michael D., Hofler, Gloria E., Pocius, Douglas W.
• Granted Patent: US 6,987,613 B2
• Time in Patent Office: Days
• US Class Current: 359/15
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating

Abstract

Provided is a light emitting device including a Fresnel lens and/or a holographic diffuser formed on a surface of a semiconductor light emitter for improved light extraction, and a method for forming such light emitting device. Also provided is a light emitting device including an optical element stamped on a surface for improved light extraction and the stamping method used to form such device. An optical element formed on the surface of a semiconductor light emitter reduces reflective loss and loss due to total internal reflection, thereby improving light extraction efficiency. A Fresnel lens or a holographic diffuser may be formed on a surface by wet chemical etching or dry etching techniques, such as plasma etching, reactive ion etching, and chemically-assisted ion beam etching, optionally in conjunction with a lithographic technique. In addition, a Fresnel lens or a holographic diffuser may be milled, scribed, or ablated into the surface. Stamping, an alternative method for forming an optical element, can also be used to form a Fresnel lens or a holographic diffuser on the surface of a semiconductor light emitter. Stamping includes pressing a stamping block against the surface of a light emitting diode. The stamping block has a shape and pattern that are the inverse of the desired optical element. Optionally, stamping can be done before, after, or concurrently with wafer-bonding. Alternatively, a material can be stamped and later bonded to the semiconductor light emitter.

Claims

1. A method of forming a light emitting device, said method comprising:

forming at least one of Fresnel lens and holographic diffuser on at least one surface of a semiconductor light emitter to affect light emitted by said semiconductor light emitter.

2. The method of claim 1 wherein said semiconductor light emitter has at least one light extraction surface from where light is intended to be extracted, and wherein said forming is done on at least one extraction surface of said semiconductor light emitter.

3. The method of claim 1 wherein said forming comprises pressing a stamping block against at least one surface of said semiconductor light emitter.

4. The method of claim 1 wherein said forming is executed concurrently with a wafer-bonding process, said wafer-bonding process comprising:

removing a first substrate of said semiconductor light emitter; and

bonding a second substrate to said semiconductor light emitter.

5. The method of claim 1 wherein said forming comprises at least one method selected from etching, milling, ablation, machining, scribing, electron discharge machining, and stamping.

6. The method of claim 1 further comprising:

beveling one or more sides of said semiconductor light emitter.

7. The method of claim 1 wherein said semiconductor light emitter has a light emitting layer, said method further comprising:

confining light emission to a preselected section of said light emitting layer.

8. The method of claim 7 wherein said confining comprises at least one method selected from applying the Holonyak process, using selective area growth, using selective area bonding, using diffusion, and using ion implantation.

9. The method of claim 1 further comprising:

coating one or more surfaces of said semiconductor light emitter with a reflective material.

10. The method of claim 1 further comprising:

coating said Fresnel lens or said holographic diffuser with a reflective material.

11. The method of claim 2 further comprising:

forming an optical element on the surface opposite of said extraction surface.

13. The device of claim 12 further comprising:

a reflective material coating at least one surface of said device.

14. The device of claim 12 wherein a light emitting layer of said semiconductor light emitter is made to emit photons primarily toward a preselected section of said first optical element.

15. The device of claim 12 wherein at least one surface of light emitting device is beveled.

16. The device of claim 12 wherein said semiconductor light emitter is a confined-emission spot light emitting diode.

17. The device of claim 12 wherein said semiconductor light emitter and said first optical element comprise (Al_xGa₁₋

x)_yIn<sub>1−

y</sub>P where0≦

×

≦

1 and 0≦

y≦

1.

18. The device of claim 12 wherein said light-emitting diode comprises a III-nitride semiconductor alloy and said first optical element comprises one of silicon carbide and sapphire.

19. The device of claim 12 wherein said semiconductor light emitter and said first optical element comprise aluminum gallium arsenide semiconductor alloy.

20. The device of claim 12, wherein said semiconductor light emitter has a flip-chip configuration.

21. The device of claim 12, wherein said semiconductor light emitter has a configuration in which a light emitting layer of said semiconductor light emitter is substantially perpendicular to said Fresnel lens.

22. The device of claim 12, wherein the radiation pattern of said device is controlled by the ratio of the focal length of said first optical element to the distance between said first optical element and a light-emitting layer of said semiconductor light emitter.

23. The device of claim 12, wherein said first optical element is designed to achieve one of light focusing, light collimating, and light diverging.

24. The device of claim 12 wherein said first optical element is designed to direct light in a preselected direction.

25. The device of claim 12 further comprising:

a second optical element on a surface of said semiconductor light emitter opposite the surface having said first optical element.

26. The device of claim 25 wherein at least one of said first Fresnel lens and said second Fresnel lens is designed to focus light.

28. The method of claim 27 further comprising:

coating a surface of said light emitting device with a reflective layer.

29. The method of claim 27 wherein said stamping is done on at least one of a semiconductor layer and a substrate layer of said semiconductor light emitter.

30. The method of claim 29 wherein said semiconductor layer comprises a transparent aluminum-bearing compound.

31. The method of claim 27, wherein said pressing is executed at an elevated temperature, said elevated temperature being higher than room temperature.

32. The method of claim 31, further comprising lowering said elevated temperature to facilitate the separation of said stamping block from said semiconductor light emitter after said pressing.

33. The method of claim 32, wherein said elevated temperature is higher than the ductile transition temperature of the material constituting said at least one surface on which said Fresnel lens is formed.

35. The device of claim 34 wherein a light emitting layer of said semiconductor light emitter is made to emit photons primarily toward a preselected section of said first optical element.

36. The device of claim 34 wherein said light-emitting and said first optical element comprise (Al_xGa₁₋

x)_yIn<sub>1−

y</sub>P where 0≦

×

≦

1 and 0≦

y≦

1.

37. The device of claim 34 wherein said semiconductor light emitter comprises a III-nitride semiconductor alloy and said first optical element comprises one of silicon carbide and sapphire.

38. The device of claim 34 wherein said semiconductor light emitter and said first optical element comprise aluminum gallium arsenide semiconductor alloy.

39. The device of claim 34 wherein said light emitting diode has a flip-chip configuration.

40. The device of claim 34 wherein said light emitting diode has a configuration in which the light emitting layer of said light emitting diode is substantially perpendicular to said Fresnel lens.

12. A light emitting device comprising:

a semiconductor light emitter; and

a first optical element forming at least one surface of said semiconductor light emitter, said first optical element comprising one of Fresnel lens and holographic diffuser.

27. A method of forming a light emitting device, said method comprising:

Stamping at least one optical element on at least one surface of a semiconductor light emitter to affect the light emitted by said semiconductor light emitter.

34. A light emitting device comprising:

a semiconductor light emitter; and

at least one optical element stamped on at least one surface of semiconductor light emitter, wherein said optical element is a first optical element.

41. A light emitting diode array comprising a plurality of light emitting devices, a light emitting device comprising:

a semiconductor light emitter; and

one of a Fresnel lens and a holographic diffuser formed on a surface of said semiconductor light emitter.

42. A light emitting array comprising a plurality of light emitting devices, a light emitting device comprising:

a semiconductor light emitter; and

an optical element stamped on a surface of said semiconductor light emitter.

43. A display device comprising at least one blue light emitting device, at least one green light emitting device, and at least one red light emitting device, wherein at least one of said blue light emitting device, green light emitting device, and red light emitting device comprises:

a semiconductor light emitter; and

one of a Fresnel lens and a holographic diffuser formed on a surface of said semiconductor light emitter.

44. A display device comprising at least one blue light emitting device, at least one green light emitting device, and at least one red light emitting device, wherein at least one of said blue light emitting device, green light emitting device, and red light emitting device comprises:

a semiconductor light emitter; and

one optical element stamped on a surface of said semiconductor light emitter.

45. A method for forming a light emitting device, said method comprising:

stamping an optical element in a material, said material being transparent to light emitted from said light emitting device; and

bonding said optical element to a semiconductor light emitter.