Aluminum nitride substrate removal for ultraviolet light-emitting devices

Patent metadata

Field	Value
Publication number	US-11355664-B2
Application number	US-202016929634-A
Country	US
Kind code	B2
Filing date	Jul 15, 2020
Priority date	May 12, 2017
Publication date	Jun 7, 2022
Grant date	Jun 7, 2022

Abstract

In various embodiments, extraction efficiency of light-emitting devices fabricated on aluminum nitride substrates is enhanced via removal of at least a portion of the substrate.

First claim

What is claimed is:

1. An illumination device comprising:
a first contact layer having a first polarity;
a second contact layer having a second polarity opposite the first polarity, at least a portion of the second contact layer defining a plurality of pillars separated by recesses disposed therebetween;
a light-emitting structure disposed between the first and second contact layers, the light-emitting structure comprising a multiple-quantum well layer comprising a plurality of periods each comprising a strained Al x Ga 1-x N barrier and a strained Al y Ga 1-y N quantum well, x and y being different by an amount facilitating confinement of charge carriers in the multiple-quantum well layer, and y being selected for emission of ultraviolet light by the light-emitting structure;
a plurality of single-crystalline aluminum nitride caps, each of the aluminum nitride caps being disposed on a top surface of one of the pillars defined by the second contact layer;
a first electrical contact disposed in direct mechanical contact with the first contact layer; and
a second electrical contact disposed in direct mechanical contact with the second contact layer.

2. The device of claim 1 , wherein each of the aluminum nitride caps has a curved top surface.

3. The device of claim 1 , wherein each of the aluminum nitride caps is substantially hemispherical.

4. The device of claim 1 , wherein each of the aluminum nitride caps is conical or pyramidal.

5. The device of claim 1 , wherein the first and second electrical contacts are metallic.

6. An illumination device comprising:
a first contact layer having a first polarity;
a second contact layer having a second polarity opposite the first polarity, at least a portion of the second contact layer defining a plurality of pillars separated by recesses disposed therebetween;
a light-emitting structure disposed between the first and second contact layers, the light-emitting structure comprising a multiple-quantum well layer comprising a plurality of periods each comprising a strained Al x Ga 1-x N barrier and a strained Al y Ga 1-y N quantum well, x and y being different by an amount facilitating confinement of charge carriers in the multiple-quantum well layer, and y being selected for emission of ultraviolet light by the light-emitting structure;
a plurality of single-crystalline aluminum nitride caps, each of the aluminum nitride caps being disposed on a top surface of one of the pillars defined by the second contact layer; and
an electrically insulating handle wafer affixed to the first contact layer.

7. The device of claim 6 , wherein the handle wafer comprises at least one of glass, sapphire, or quartz.

8. The device of claim 6 , wherein each of the aluminum nitride caps (i) has a curved top surface, (ii) is conical, or (iii) is pyramidal.

9. The device of claim 6 , wherein the first and second electrical contacts are metallic.

10. A method of forming an illumination device, the method comprising:
forming a crystalline release layer over or within an aluminum nitride substrate, the release layer (i) having an absorption band corresponding to a first wavelength of light and (ii) being strained at least in part due to lattice mismatch with the substrate;
forming an active light-emitting device structure over the release layer; and
exposing the release layer to light having the first wavelength, whereby absorption of the light by the release layer results in separation of at least a portion of the substrate from the active light-emitting device structure.

11. The method of claim 10 , wherein the lattice mismatch of the release layer with the substrate is greater than 0.1%.

12. The method of claim 10 , wherein the lattice mismatch of the release layer with the substrate is greater than 1%.

13. The method of claim 10 , wherein the release layer is tensilely strained.

14. The method of claim 10 , wherein the release layer is compressively strained.

15. The method of claim 10 , wherein forming the release layer comprises intentionally introducing one or more dopants into at least a portion of the release layer.

16. The method of claim 15 , wherein the one or more dopants are introduced during epitaxial growth of the at least a portion of the release layer.

17. The method of claim 15 , wherein the one or more dopants are introduced via ion implantation or diffusion.

18. The method of claim 10 , further comprising, before exposing the release layer to light, attaching the active light-emitting device structure to a handle wafer.

19. The method of claim 18 , wherein the release layer is exposed to light through the handle wafer.

20. The method of claim 10 , wherein the release layer is exposed to light through the aluminum nitride substrate.

21. A method of forming an illumination device, the method comprising:
forming a release layer over or within an aluminum nitride substrate, the release layer (i) having an absorption band corresponding to a first wavelength of light and (ii) being strained at least in part due to lattice mismatch with the substrate;
forming an active light-emitting device structure over the release layer; and
exposing the release layer to light having the first wavelength, and applying, to the aluminum nitride substrate, additional heat beyond any heat resulting from exposure of the release layer to light having the first wavelength, whereby absorption of the light by the release layer results in separation of at least a portion of the substrate from the active light-emitting device structure.

22. The method of claim 21 , wherein the lattice mismatch of the release layer with the substrate is greater than 0.1%.

23. The method of claim 21 , wherein the lattice mismatch of the release layer with the substrate is greater than 1%.

24. The method of claim 21 , wherein the release layer is tensilely strained.

25. The method of claim 21 , wherein the release layer is compressively strained.

26. The method of claim 21 , wherein forming the release layer comprises intentionally introducing one or more dopants into at least a portion of the release layer.

27. The method of claim 26 , wherein the one or more dopants are introduced during epitaxial growth of the at least a portion of the release layer.

28. The method of claim 26 , wherein the one or more dopants are introduced via ion implantation or diffusion.

29. The method of claim 21 , further comprising, before exposing the release layer to light, attaching the active light-emitting device structure to a handle wafer.

30. The method of claim 29 , wherein the release layer is exposed to light through the handle wafer.

31. The method of claim 21 , wherein the release layer is exposed to light through the aluminum nitride substrate.

32. A method of forming an illumination device, the method comprising:
providing a semiconductor structure comprising (i) an aluminum nitride substrate, (ii) a plurality of enclosed voids disposed over an entirety of the substrate and defined within a semiconductor material, and (ii) an active light-emitting device structure disposed over the substrate; and
applying radiation proximate the voids, whereby heating of the voids and/or material proximate the voids by the radiation results in separation of at least a portion of the substrate from the act

Assignees

• Grandusky James R
• Schowalter Leo J
• Moe Craig
• Crystal Is Inc

Inventors

• Grandusky James R
• Schowalter Leo J
• Moe Craig

Classifications

• H10P95/11 Primary

  Separation of active layers from substrates · CPC title

• H10H20/825

  containing nitrogen, e.g. GaN · CPC title

• H10H20/819

  characterised by their shape, e.g. curved or truncated substrates · CPC title

• H10H20/018 Primary

  Bonding of wafers · CPC title

• H01L33/0093 Primary

  Electricity · mapped topic