Ultraviolet light emitting diodes

• US 10,361,343 B2
• Filed: 07/02/2015
• Issued: 07/23/2019
• Est. Priority Date: 07/02/2014
• Status: Active Grant

• Current Assignee: Trustees of Boston University
• Original Assignee: Boston University
• Inventors: Brummer, Gordon C., Nothern, Denis M., Moustakas, Theodore D.
• Primary Examiner(s): Tornow, Mark W
• Application Number:
  US15/321,507
• Publication Number:
  US 20170200865A1
• Time in Patent Office: 1,482 Days
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/145 with a current-blocking structure
• CPC Class Codes: H01L 33/24 of the light emitting region, e.g. non-planar junction
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/58 Optical field-shaping elements

Abstract

The invention provides ultraviolet (UV) light-emitting diodes (LEDs). The UV LEDs can comprise abase layer including p-type SiC or p-type AlGaN, an active layer, and an n-AlGaN layer, wherein the active layer is disposed between the base layer and the n-AlGaN layer. In some embodiments, the absorption losses in p-SiC can be decreased or prevented by incorporating a conductive AlGaN Distributed Bragg Reflector (DBR) between the p-type SiC layer and the active layer. In some embodiments, the n-AlGaN layer can be textured to increase the extraction efficiency (EE). In some embodiments, the external quantum efficiency of the LEDs can be 20-30% or more.

Claims

1. A deep ultraviolet light-emitting diode comprising:

a base layer including a p-type material forming a first side of the diode;

an active layer grown on the base layer, whereby radiative recombination of carriers in the active layer produces ultraviolet light in response to an applied electric field;

a light reflecting layer disposed between the base layer and the active layer, wherein the light reflecting layer reflects the ultraviolet light away from the base layer, and

an n-AlGaN layer grown on the active layer, wherein the n-AlGaN is on a second side of the diode which is opposite to the first side, and wherein the active layer is disposed between the base layer and the n-AlGaN layer and wherein the n-AlGaN layer includes a textured surface, whereby ultraviolet light is emitted from the textured surface.

2. The ultraviolet light-emitting diode of claim 1, wherein the p-type material is SiC or AlGaN.

3. The ultraviolet light-emitting diode of claim 1, wherein the light-reflecting layer includes at least one p-type electrically conductive AlGaN distributed Bragg reflector (DBR), whereby the p-type DBR effectively reflects the ultraviolet light away from the base layer.

4. The ultraviolet light-emitting diode of claim 3, wherein the p-type DBR has a peak reflectance substantially similar to the wavelength of the ultraviolet light produced by the active layer.

5. The ultraviolet light-emitting diode of claim 3, wherein the p-type DBR comprises a plurality of alternating first layers and second layers having different refractive indices, wherein the first layer and the second layer each comprises a plurality of alternating layers having different spontaneous polarizations.

6. The ultraviolet light-emitting diode of claim 3, wherein the p-type DBR comprises a plurality of repeating layers, wherein each layer is graded in composition between at least two materials with different spontaneous polarizations.

7. The ultraviolet light-emitting diode of claim 1, further comprising an electron-blocking layer disposed between the light-reflecting layer and the active layer.

8. The ultraviolet light-emitting diode of claim 7, wherein the electron blocking layer is p-doped or undoped.

9. The ultraviolet light-emitting diode of claim 1, wherein the active layer substantially comprises AlGaN, InAlN, or InAlGaN.

10. The ultraviolet light-emitting diode of claim 1, wherein the active layer comprises a single quantum well.

11. The ultraviolet light-emitting diode of claim 1, wherein the active layer comprises a plurality of quantum wells.

12. The ultraviolet light-emitting diode of claim 1, wherein the active layer comprises a plurality of quantum dots.

13. The ultraviolet light-emitting diode of claim 1, wherein the textured surface has a random texture.

14. The ultraviolet light-emitting diode of claim 1, wherein the textured surface has a patterned texture.

15. The ultraviolet light-emitting diode of claim 14, wherein the patterned texture comprises a micro lens array.

16. The ultraviolet light-emitting diode of claim 14, wherein the patterned texture comprises a photonic crystal.

17. The ultraviolet light-emitting diode of claim 1, further comprising an n-type electrically conductive anti-reflective coating layer in contact with the n-AlGaN layer, such that the n-AlGaN layer is disposed in between the active layer and the anti-reflective coating layer.

18. The ultraviolet light-emitting diode of claim 1, wherein the diode produces ultraviolet light in the range of 210 nm to 365 nm.

19. The ultraviolet light-emitting diode of claim 1, wherein the diode produces ultraviolet light in the range of 250 nm to 300 nm.