Ultraviolet light-emitting devices incorporating graded layers and compositional offsets
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.
1. A semiconductor device comprising:
a substrate;
an Al v Ga 1-v N layer disposed over the substrate;
a graded Al z Ga 1-z N layer disposed over the Al v Ga 1-v N layer, a composition of the graded Al z Ga 1-z N layer being graded in Al concentration z from a bottom portion to a top portion, such that the Al concentration z monotonically decreases, in a continuous or stepwise fashion, from the bottom portion, in a direction away from the Al v Ga 1-v N layer, to the top portion;
an Al w Ga 1-w N cap layer disposed over the graded Al z Ga 1-z N layer; and
a metallic contact disposed over the Al w Ga 1-w N cap layer and comprising at least one metal,
wherein the Al concentration z of the bottom portion of the graded Al z Ga 1-z N layer is less than an Al concentration v of the Al v Ga 1-v N layer.
2. The device of claim 1 , wherein the substrate has an Al u Ga 1-u N top surface, wherein 0≤u≤1.0.
3. The device of claim 1 , wherein the substrate comprises at least one of silicon carbide, silicon, MgO, Ga 2 O 3 , alumina, ZnO, GaN, InN, or sapphire.
4. The device of claim 1 , wherein 0≤w≤0.4.
5. The device of claim 1 , wherein the Al concentration z of the bottom portion of the graded Al z Ga 1-z N layer is less than an Al concentration v of the Al v Ga 1-v N layer by an amount no less than 0.03.
6. The device of claim 1 , wherein the Al concentration z of the bottom portion of the graded Al z Ga 1-z N layer is less than an Al concentration v of the Al v Ga 1-v N layer by an amount no more than 0.85.
7. The device of claim 1 , wherein the Al concentration z of the bottom portion of the graded Al z Ga 1-z N layer is less than an Al concentration v of the Al v Ga 1-v N layer by an amount no less than 0.03 and by an amount no more than 0.85.
8. The device of claim 1 , wherein the graded Al z Ga 1-z N layer is undoped.
9. 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 .
10. The device of claim 1 , wherein the graded Al z Ga 1-z N layer is strained.
11. The device of claim 1 , wherein the Al concentration z of the top portion of the graded Al z Ga 1-z N layer is approximately equal to the Al concentration w of the Al w Ga 1-w N cap layer.
12. The device of claim 1 , wherein the Al concentration w of the Al w Ga 1-w N cap layer is approximately 0.
13. The device of claim 1 , wherein a thickness of the Al w Ga 1-w N cap layer is no less than 1 nm and no greater than 50 nm.
14. The device of claim 1 , wherein the Al w Ga 1-w N cap layer is p-type doped.
15. The device of claim 1 , further comprising a Al m Ga 1-m N layer disposed below the Al v Ga 1-v N layer, wherein an Al concentration m of the Al m Ga 1-m N layer is less than the Al concentration z of the bottom portion of the graded Al z Ga 1-z N layer.
16. The device of claim 15 , wherein the Al m Ga 1-m N layer is a portion of a light-emitting device structure.
17. A semiconductor device comprising:
a substrate;
an Al v Ga 1-v N layer disposed over the substrate;
a graded Al z Ga 1-z N layer disposed over the Al v Ga 1-v N layer, a composition of the graded Al z Ga 1-z N layer being graded in Al concentration z from a bottom portion to a top portion, such that the Al concentration z decreases from the bottom portion, in a direction away from the Al v Ga 1-v N layer, to the top portion;
an Al w Ga 1-w N cap layer disposed over the graded Al z Ga 1-z N layer; and
a metallic contact disposed over the Al w Ga 1-w N cap layer and comprising at least one metal,
wherein an Al concentration w of the Al w Ga 1-w N cap layer is less than the Al concentration z of the top portion of the graded Al z Ga 1-z N layer, and
wherein the graded Al z Ga 1-z N layer is undoped or p-type doped with a p-type dopant concentration of less than 10 13 cm −3 .
18. The device of claim 17 , wherein the substrate has an Al u Ga 1-u N top surface, wherein 0≤u≤1.0.
19. The device of claim 17 , wherein the substrate comprises at least one of silicon carbide, silicon, MgO, Ga 2 O 3 , alumina, ZnO, GaN, InN, or sapphire.
20. The device of claim 17 , wherein 0≤w≤0.4.
21. The device of claim 17 , wherein the Al concentration w of the Al w Ga 1-w N cap layer is less than the Al concentration z of the top portion of the graded Al z Ga 1-z N layer by an amount no less than 0.03.
22. The device of claim 17 , wherein the Al concentration w of the Al w Ga 1-w N cap layer is less than the Al concentration z of the top portion of the graded Al z Ga 1-z N layer by an amount no more than 0.85.
23. The device of claim 17 , wherein the Al concentration w of the Al w Ga 1-w N cap layer is less than the Al concentration z of the top portion 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 17 , wherein the graded Al z Ga 1-z N layer is undoped.
25. The device of claim 17 , wherein the p-type dopant concentration within the graded Al z Ga 1-z N layer is less than 10 13 cm −3 .
26. The device of claim 17 , wherein the graded Al z Ga 1-z N layer is strained.
27. The device of claim 17 , wherein the Al concentration z of the bottom portion of the graded Al z Ga 1-z N layer is approximately equal to the Al concentration v of the Al v Ga 1-v N layer.
28. The device of claim 17 , wherein the Al concentration w of the Al w Ga 1-w N cap layer is approximately 0.
29. The device of claim 17 , wherein a thickness of the Al w Ga 1-w N cap layer is no less than 1 nm and no greater than 50 nm.
30. The device of claim 17 , wherein the Al w Ga 1-w N cap layer is p-type doped.