LED Including Photonic Crystal Structure

• US 20080070334A1
• Filed: 10/08/2007
• Published: 03/20/2008
• Est. Priority Date: 01/28/2002
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.), Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Inventors: Wierer, Jonathan, Sigalas, Mihail, Krames, Michael
• Granted Patent: US 7,642,108 B2
• Time in Patent Office: Days
• US Class Current: 438/32
• CPC Class Codes: H01L 2224/48091 Arched
• 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 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 33/08 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body H01L27/15 takes precedence
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: Y10S 438/943 Movable

Abstract

A photonic crystal light emitting diode (“PXLED”) is provided. The PXLED includes a periodic structure, such as a lattice of holes, formed in the semiconductor layers of an LED. The parameters of the periodic structure are such that the energy of the photons, emitted by the PXLED, lies close to a band edge of the band structure of the periodic structure. Metal electrode layers have a strong influence on the efficiency of the PXLEDs. Also, PXLEDs formed from GaN have a low surface recombination velocity and hence a high efficiency. The PXLEDs are formed with novel fabrication techniques, such as the epitaxial lateral overgrowth technique over a patterned masking layer, yielding semiconductor layers with low defect density. Inverting the PXLED to expose the pattern of the masking layer or using the Talbot effect to create an aligned second patterned masking layer allows the formation of PXLEDs with low defect density.

Claims

1. A method of making a light emitting diode, the method comprising:

providing a semiconductor structure comprising a plurality of semiconductor layers, the semiconductor structure being capable of emitting light;

providing a photosensitive layer overlying said semiconductor structure, the photosensitive layer having a planar lattice of openings, wherein a ratio of a period of said planar lattice of openings to a wavelength of said emitted light in air is greater than about 0.1 and less than about 5; and

forming a planar lattice of holes by at least partially removing said plurality of semiconductor layers at regions corresponding to said planar lattice of openings.

2. The method of claim 1, wherein a top electrode layer is disposed between said semiconductor structure and said photosensitive layer, the method further comprising removing said top electrode layer at regions corresponding to said planar lattice of openings.

3. The method of claim 2, wherein said top electrode layer is reflective.

4. The method of claim 1, wherein said semiconductor structure comprises a plurality of III-nitride layers.

5. The method of claim 1, wherein the semiconductor structure comprises:

forming a first semiconductor layer doped with a first dopant, overlying a substrate;

forming an active layer, capable of emitting said light, overlying said first semiconductor layer;

forming a second semiconductor layer doped with a second dopant, said first and second dopant being of opposite type, overlying said active layer.

6. The method of claim 5, wherein forming a planar lattice of holes comprises forming a planar lattice of holes in at least said active layer and said second semiconductor layer.

7. The method of claim 5, wherein providing a semiconductor structure comprises:

removing said second semiconductor layer and said active layer over a region of said first semiconductor layer, displaced from said planar lattice of holes;

forming an electrode layer overlying at least a portion of said displaced region of said first semiconductor layer.

8. The method of claim 1, wherein providing a photosensitive layer having a planar lattice of openings comprises removing portions of said photosensitive layer in a planar lattice of openings with a high resolution lithographic technique.

9. The method of claim 8, wherein removing portions of said photosensitive layer comprises removing said portions of said photosensitive layer with one of electron beam lithography, nano-imprint lithography, deep X-ray lithography, interferometric lithography, hot embossing, and microcontact printing.

10. The method of claim 1, wherein forming a planar lattice of holes comprises forming said planar lattice of holes by a dry etch process.

11. The method of claim 1, further comprising:

removing the photosensitive layer;

filling said planar lattice of holes with a dielectric to form an approximately flat surface with a surface of said second semiconductor layer; and

forming an electrode layer overlying said approximately flat surface.

12. A method of making a light emitting diode, the method comprising:

providing a structure comprising;

a first substrate;

a masking layer with a first planar lattice of openings, the masking layer overlying said first substrate; and

a plurality of semiconductor layers overlying said first substrate, the plurality of semiconductor layers including an active region capable of emitting light sandwiched between a layer of first conductivity type and a layer of second conductivity type, the plurality of semiconductor layers overlying said first substrate;

wherein a ratio of a period of said planar lattice of openings to a wavelength of said emitted light in air is greater than about 0.1 and less than about 5; and

forming a planar lattice of holes in said plurality of semiconductor layers by at least partially removing said plurality of semiconductor layers in regions corresponding to said first planar lattice of openings of said masking layer.

13. The method of claim 12, wherein providing a structure comprising a plurality of semiconductor layers overlying said first substrate comprises growing said plurality of semiconductor layers by epitaxial lateral overgrowth.

14. The method of claim 12, further comprising:

forming a bonding layer overlying said plurality of semiconductor layers;

disposing a second substrate over said bonding layer; and

removing said first substrate.

15. The method of claim 14, further comprising:

removing said masking layer;

forming a first electrode layer overlying said layer of first conductivity type by depositing said first electrode layer at an angle such that there is no substantial electrical contact between said first electrode layer and said layer of second conductivity type; and

forming a second electrode layer overlying a region of said layer of second conductivity type displaced from said planar lattice of holes.

16. The method of claim 14, wherein said forming a planar lattice of holes comprises:

forming a photosensitive layer overlying said masking layer;

exposing said photosensitive layer at regions corresponding to said first lattice of openings of said masking layer by shining a light from the direction of said second substrate.

17. The method of claim 16, wherein forming a planar lattice of holes comprises forming a lattice of aligned mask-layers corresponding to said first planar lattice of openings of said first masking layer by removing a portion of said photosensitive layer, overlying said first masking layer, leaving said exposed regions of said photosensitive layer and removing said first masking layer from said layer of first conductivity type.

18. The method of claim 17, further comprising:

forming a first electrode layer overlying said layer of first conductivity type and said aligned mask-layers;

forming a second planar lattice of openings in said first electrode layer by removing said lattice of aligned mask-layers and portions of said first electrode layer overlying said aligned mask-layers with a lift-off technique; and

forming a planar lattice of holes by at least partially removing said plurality of semiconductor layers in regions corresponding to said second planar lattice of openings in said first electrode layer.

19. The method of claim 12, further comprising:

filling said lattice of holes with a dielectric to form an approximately flat surface with a surface of said first semiconductor layer; and

forming a first electrode layer overlying said approximately flat surface.

20. A method of making a light emitting diode, the method comprising:

providing a structure comprising;

a substrate;

a masking layer with a first planar lattice of openings overlying said substrate;

a plurality of semiconductor layers overlying said masking layer, said plurality of semiconductor layers including an active layer capable of emitting light sandwiched between a first semiconductor layer doped with a first dopant and a second semiconductor layer doped with a second dopant; and

a photosensitive layer overlying said plurality of semiconductor layers;

shining light at said first planar lattice of openings from the direction of said substrate; and

creating images of said openings of said first planar lattice of openings on said photosensitive layer by causing the diffraction of said shined light.

21. The method of claim 20 wherein a ratio of a period of said planar lattice of openings and a wavelength of said emitted light in air is greater than about 0.1 and less than about 5.

22. The method of claim 20, wherein providing a structure comprising a plurality of semiconductor layers comprises growing said plurality of semiconductor layers over the substrate by epitaxial lateral overgrowth.

23. The method of claim 20, wherein said plurality of semiconductor layers have a total thickness proportional to a square of a lattice spacing of said first planar lattice of openings, and proportional to an inverse of a wavelength of said emitted light in said plurality of semiconductor layers.

24. The method of claim 20, further comprising:

forming a second planar lattice of openings in said photosensitive layer by removing said photosensitive layer at regions corresponding to said images of said openings of said first planar lattice of openings;

forming a planar lattice of holes in said plurality of semiconductor layers by at least partially removing said plurality of semiconductor layers in regions corresponding to said second planar lattice of openings; and

removing said photosensitive layer, exposing a surface of said second semiconductor layer.

25. The method of claim 24, further comprising:

filling said planar lattice of holes with a dielectric to form an approximately flat surface with said exposed surface of said second semiconductor layer; and

forming an electrode layer overlying said approximately flat surface.