LED system and method

• US 20080080166A1
• Filed: 10/01/2007
• Published: 04/03/2008
• Est. Priority Date: 10/02/2006
• Status: Active Grant

• Current Assignee: illumitex, Inc.
• Original Assignee: illumitex, Inc.
• Inventors: Thomas, Matthew, Winberg, Paul, Duong, Dung
• Granted Patent: US 7,789,531 B2
• Time in Patent Office: Days
• US Class Current: 362/84
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• 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

Embodiments provide an LED comprising a quantum well region operable to generate light and a substrate having an interface with the quantum well region, wherein light generated by the quantum well region traverses the interface to enter the substrate and exit the LED through an exit face of the substrate. The exit face may be opposite from and a distance from the interface, with some portion or all of this LED being shaped to optimize the light extraction efficiency of the device. The exit face can have at least 70% of a minimum area necessary to conserve brightness for a desired half-angle of light. Sidewalls of the LED may be positioned and shaped so that rays incident on a sidewall reflect to the exit face with an angle of incidence at the exit face at less than or equal to a critical angle at the exit face.

Claims

1. An LED comprising:

a quantum well region operable to generate light; and

a shaped substrate having an interface with the quantum well region, wherein light generated by the quantum well region traverses the interface, the shaped substrate comprising;

an exit face opposite from and a distance from the interface, wherein the substrate is shaped so that a portion of the light entering the shaped substrate through the interface will exit the shaped substrate through the exit face and wherein the exit face has at least 70% of a minimum area necessary to conserve radiance for a desired half-angle of light projected from the shaped substrate; and

a set of sidewalls, wherein each sidewall is positioned and shaped so that at least a majority of rays having a straight transmission path from the interface to that sidewall reflect to the exit face with an angle of incidence at the exit face at less than or equal to a critical angle at the exit face.

2. The LED of claim 1, wherein the quantum well region is shaped in conformance with the substrate.

3. The LED of claim 1, wherein the exit face has at least the minimum area necessary to conserve radiance.

4. The LED of claim 1, wherein the interface is rectangular in shape and wherein the effective solid angle whereby light leaves the exit surface is determined to account for the shape of the interface.

5. The LED of claim 1 wherein the distance is within 50% of a minimum distance so that all rays with a straight transmission path from the interface to the exit face have an angle of incidence that is less than or equal to the critical angle at the exit face.

6. The LED of claim 1, wherein each sidewall is positioned and shaped so that at least 80% of rays with a straight transmission path from the interface to the sidewall are reflected to the exit face with an angle of incidence on the exit face at less than or equal to the critical angle at the exit face.

7. The LED of claim 1, wherein the shapes of the sidewall are selected to create a desired light output profile.

8. The LED of claim 1, wherein the exit face is parallel to and rotationally aligned with the interface and wherein the exit face has the same shape and aspect ratio as a shape of the interface.

9. The LED of claim 1, further comprising a layer of photo-luminescent material capable of emitting desired wavelengths to create white light.

10. An LED comprising:

a quantum well region operable to generate light;

a shaped substrate having an interface with the quantum well region, the shaped substrate comprising;

an exit face opposite from and a distance from the interface, wherein the substrate is shaped so that a portion of the light entering the shaped substrate through the interface will exit the shaped substrate through the exit face and wherein the exit face has at least 70% of a minimum area necessary to conserve radiance for a desired solid angle of light projected from the shaped substrate;

a set of sidewalls, wherein each sidewall is positioned and shaped so that at least a portion of rays having a straight transmission path from the interface to that sidewall reflect to the exit face with an angle of incidence at the exit face at less than or equal to a critical angle at the exit face;

wherein the area of the exit face, distance and sidewall shapes are selected to project light with a half angle of between 10 to 60 degrees.

11. The LED of claim 10, wherein the interface has a rectangular shape and wherein the effective solid angle whereby light leaves the exit face is determined to account for the area of the shape of the interface.

12. The LED of claim 10, wherein the distance is within 50% of a minimum distance so that all rays with a straight transmission path from the interface to the exit face have an angle of incidence that is less than or equal to the critical angle at the exit face.

13. The LED of claim 10, wherein each sidewall is positioned and shaped so that at least 80% of rays with a straight transmission path from the interface to the sidewall are reflected to the exit surface with an angle of incidence on the exit surface at less than or equal to the critical angle at the exit surface.

14. The LED of claim 10, wherein the exit face has the same shape and aspect ratio as a shape of the interface and wherein the exit face is parallel to and rotationally aligned with the interface.

15. The LED of claim 10, further comprising a layer of photo-luminescent material capable of emitting desired wavelengths to create white light.

16. The LED of claim 10, wherein the quantum well region is shaped in conformance with the substrate.

17. The LED of claim 10, wherein the shapes of the sidewall are selected to create a desired light output profile.

18. The LED of claim 10, wherein the exit face has at least the minimum area necessary to conserve radiance.

19. An LED comprising:

a quantum well region operable to generate light;

a shaped substrate having an interface with the quantum well region, the shaped substrate comprising;

an exit face opposite from and a distance from the interface, wherein;

the substrate is shaped so that a portion of the light entering the shaped substrate through the interface will exit the shaped substrate through the exit face;

the exit face has an area that is within 30% of a minimum area defined by

$\frac{{\mathrm{\Phi <br><br>}}_2<br><br>n_1^2<br><br>A_1<br><br>{\mathrm{\Omega <br><br>}}_1}{{\mathrm{\Phi <br><br>}}_1<br><br>n_2^2<br><br>{\mathrm{\Omega <br><br>}}_2}$

 

D₂n²¹

 

wherein Φ

₁ is the light flux traversing the interface;

Φ

₂ is the light flux exiting the exit face and is equal to Φ

₁;

Ω

₁ is the effective solid angle whereby light traverses the interface and Ω

₂ is the effective solid angle whereby light leaves the exit face;

A₁ is the area of the interface;

n₁ is the refractive index of the shaped substrate and n₂ is the refractive index of the medium external to the shaped substrate;

the distance is at least a minimum distance so that all rays with a straight transmission path from the interface to the exit face have an angle of incidence that is less than or equal to a critical angle at the exit face; and

a set of sidewalls, wherein each sidewall is positioned and shaped so that at least a portion of rays having a straight transmission path from the interface to that sidewall reflect to the exit face with an angle of incidence at the exit face at less than or equal to the critical angle at the exit face.

20. The LED of claim 19, wherein the area of the exit face, distance and sidewall shapes are selected to project light with a half angle of between 10 to 60 degrees with at least 70% efficiency and a desired light output profile.

21. The LED of claim 19, wherein the quantum well region is shaped in conformance with the substrate.

22. The LED of claim 19, wherein the interface has a rectangular shape and wherein the effective solid angle whereby light leaves the exit surface is determined to account for the square shape of the interface.

23. The LED of claim 19, further comprising a layer of photo-luminescent material capable of emitting desired wavelengths to create white light.

24. The LED of claim 19, wherein the shapes of the sidewall are selected to create a desired light output profile.

25. An LED comprising:

a quantum well region operable to generate light; and

a shaped substrate having an interface with the quantum well region, wherein light generated by the quantum well region traverses the interface, the shaped substrate comprising;

at least two exit faces, wherein the substrate is shaped so that a portion of the light entering the shaped substrate through the interface will exit the shaped substrate through the at least two exit faces and wherein the at least two exit faces have a combined area that is at least 70% of a minimum area necessary to conserve radiance; and

a set of sidewalls, wherein each sidewall is positioned and shaped so that at least a majority of rays having a straight transmission path from the interface to that sidewall reflect to an exit face of the two or more exit faces with an angle of incidence at that exit face at less than or equal to a critical angle at that exit face.