Ultraviolet light-emitting devices incorporating graded layers and compositional offsets

Patent metadata

Field	Value
Publication number	US-10211368-B2
Application number	US-201715587879-A
Country	US
Kind code	B2
Filing date	May 5, 2017
Priority date	Sep 17, 2015
Publication date	Feb 19, 2019
Grant date	Feb 19, 2019

Abstract

In various embodiments, light-emitting devices incorporate graded layers with compositional offsets at one or both end points of the graded layer to promote formation of two-dimensional carrier gases and polarization doping, thereby enhancing device performance.

First claim

What is claimed is:

1. An ultraviolet (UV) light-emitting device comprising:
a substrate having an Al u Ga 1-u N top surface, wherein 0≤u≤1.0;
an active, light-emitting device structure disposed over the substrate, the light-emitting device 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;
an electron blocking layer disposed over the multiple-quantum well layer, the electron blocking layer comprising Al v Ga 1-x N, wherein v>y and v>x;
a graded Al z Ga 1-z N layer disposed over the electron blocking layer, a composition of the graded Al z Ga 1-z N layer being graded in Al concentration z such that the Al concentration z decreases in a direction away from the light-emitting device structure;
a p-doped Al w Ga 1-w N cap layer disposed over the graded Al z Ga 1-z N layer, wherein 0≤w≤0.4; and
a metallic contact disposed over the p-doped Al w Ga 1-w N cap layer and comprising at least one metal,
wherein at an interface between the graded Al z Ga 1-z N layer and the electron blocking layer, the Al concentration z of the graded Al z Ga 1-z N layer is less than the Al concentration v of the electron blocking layer.

2. The device of claim 1 , wherein, at the interface between the graded Al z Ga 1-z N layer and the electron blocking layer, the Al concentration z of the graded Al z Ga 1-z N layer is less than the Al concentration v of the electron blocking layer by an amount no less than 0.03.

3. The device of claim 1 , wherein, at the interface between the graded Al z Ga 1-z N layer and the electron blocking layer, the Al concentration z of the graded Al z Ga 1-z N layer is less than the Al concentration v of the electron blocking layer by an amount no more than 0.85.

4. The device of claim 1 , wherein, at the interface between the graded Al z Ga 1-z N layer and the electron blocking layer, the Al concentration z of the graded Al z Ga 1-z N layer is less than the Al concentration v of the electron blocking layer by an amount no less than 0.03 and by an amount no more than 0.85.

5. The device of claim 1 , wherein 0.4≤u≤1.0.

6. The device of claim 1 , wherein 0≤w≤0.2.

7. The device of claim 1 , wherein the graded Al z Ga 1-z N layer is undoped.

8. The device of claim 1 , wherein a p-type dopant concentration within the graded Al z Ga 1-z N layer is less than 10 13 cm −3 .

9. The device of claim 1 , wherein the Al concentration z of the graded Al z Ga 1-z N layer at an interface between the graded Al z Ga 1-z N layer and the p-doped Al w Ga 1-w N cap layer is approximately equal to the Al concentration w of the p-doped Al w Ga 1-w N cap layer.

10. The device of claim 1 , wherein the Al concentration w of the p-doped Al w Ga 1-w N cap layer is approximately 0.

11. The device of claim 1 , wherein the substrate comprises doped or undoped AlN.

12. The device of claim 1 , wherein the UV light-emitting device comprises a light-emitting diode.

13. The device of claim 1 , wherein the UV light-emitting device comprises a laser.

14. The device of claim 1 , wherein a thickness of the p-doped Al w Ga 1-w N cap layer is no less than 1 nm and no greater than 50 nm.

15. The device of claim 1 , further comprising an n-doped Al n Ga 1-n N bottom contact layer disposed between the substrate and the multiple-quantum well layer, wherein y<n<x.

16. The device of claim 1 , further comprising a reflection layer disposed over at least a portion of the p-doped Al w Ga 1-w N cap layer, the reflection layer having a reflectivity to light emitted by the light-emitting device structure larger than a reflectivity to light emitted by the light-emitting device structure of the metallic contact.

17. The device of claim 16 , wherein the reflection layer comprises Al.

18. The device of claim 16 , further comprising a transmissive layer disposed between at least a portion of the reflection layer and the p-doped Al w Ga 1-w N cap layer, the transmissive layer having a transmissivity to light emitted by the light-emitting structure larger than a transmissivity to light emitted by the light-emitting structure of the metallic contact.

19. The device of claim 18 , wherein the transmissive layer comprises at least one of silicon oxide, silicon nitride, aluminum oxide, or gallium oxide.

20. An ultraviolet (UV) light-emitting device comprising:
a substrate having an Al u Ga 1-u N top surface, wherein 0≤u≤1.0;
an active, light-emitting device structure disposed over the substrate, the light-emitting device 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;
a graded Al z Ga 1-z N layer disposed over the multiple-quantum well layer, a composition of the graded Al z Ga 1-z N layer being graded in Al concentration z such that the Al concentration z decreases in a direction away from the light-emitting device structure;
a p-doped Al w Ga 1-w N cap layer disposed over the graded Al z Ga 1-z N layer, wherein 0≤w≤0.4; and
a metallic contact disposed over the p-doped Al w Ga 1-w N cap layer and comprising at least one metal,
wherein at an interface between the graded Al z Ga 1-z N layer and the p-doped Al w Ga 1-w N cap layer, the Al concentration w of the p-doped Al w Ga 1-w N cap layer is less than the Al concentration z of the graded Al z Ga 1-z N layer.

21. The device of claim 20 , wherein, at the interface between the graded Al z Ga 1-z N layer and the p-doped Al w Ga 1-w N cap layer, the Al concentration w of the p-doped Al w Ga 1-w N cap layer is less than the Al concentration z of the graded Al z Ga 1-z N layer by an amount no less than 0.03.

22. The device of claim 20 , wherein, at the interface between the graded Al z Ga 1-z N layer and the p-doped Al w Ga 1-w N cap layer, the Al concentration w of the p-doped Al w Ga 1-w N cap layer is less than the Al concentration z of the graded Al z Ga 1-z N layer by an amount no more than 0.85.

23. The device of claim 20 , wherein, at the interface between the graded Al z Ga 1-z N layer and the p-doped Al w Ga 1-w N cap layer, the Al concentration w of the p-doped Al w Ga 1-w N cap layer is less than the Al concentration z of the graded Al z Ga 1-z N layer by an amount no less than 0.03 and by an amount no more than 0.85.

24. The device of claim 20 , wherein 0.4≤u≤1.0.

25. The device of claim 20 , wherein 0≤w≤0.2.

26. The device of claim 20 , wherein the graded Al z Ga 1-z N layer is undoped.

27. The device of claim 20 , wherein a p-type dopant concentration within the graded Al z Ga 1-z N layer is less than 10 13 cm −3 .

28. The device of claim 20 , further comprising, disposed between the multiple-quantum well layer and the graded Al z Ga 1-z N layer, an electron blocking layer comprising Al v Ga 1-v N, wherein v>y and v>x.

29. The device of claim 28 , wherein the Al concentration z of the graded Al z Ga 1-z N layer at an interface between the graded Al z Ga 1-z N layer and the electron blocking layer is approximately equal to the Al concentration v of the electron

Assignees

• Moe Craig
• Grandusky James R
• Gibb Shawn R
• Schowalter Leo J
• Sato Kosuke
• Morishita Tomohiro
• Crystal Is Inc

Inventors

• Moe Craig
• Grandusky James R
• Gibb Shawn R
• Schowalter Leo J
• Sato Kosuke
• Morishita Tomohiro

Classifications

• H01L33/145

  Electricity · mapped topic

• H01L33/46

  Electricity · mapped topic

• H01L33/405

  Electricity · mapped topic

• H01L33/32

  Electricity · mapped topic

• H01L33/36

  Electricity · mapped topic