Buried contact layer for UV emitting device
In some embodiments, a light emitting structure comprises a layered semiconductor stack comprising a first set of doped layers, a second layer, a light emitting layer positioned between the first set of doped layers and the second layer, and an electrical contact to the first set of doped layers. The first set of doped layers can comprise a first sub-layer, a second sub-layer, and a third sub-layer, wherein the third sub-layer is adjacent to the light emitting layer. The electrical contact can be coupled to the second sub-layer. The first, second and third sub-layers can be doped n-type, and an electrical conductivity of the second sub-layer can be higher than an electrical conductivity of the first and third sub-layers. The first, second and third sub-layers, and the light emitting layer can each comprise a superlattice. The second layer can comprise a chirped superlattice.
1. A light emitting structure, comprising:
a layered stack comprising a first set of doped layers, a second layer, a light emitting layer positioned between the first set of doped layers and the second layer, and a first electrical contact to the first set of doped layers, wherein:
the first set of doped layers, the second layer, and the light emitting layer comprise semiconductor materials;
the first set of doped layers comprises a first sub-layer, a second sub-layer, and a third sub-layer, wherein the third sub-layer is adjacent to the light emitting layer;
the first, second and third sub-layers comprise a first, second and third superlattice, respectively;
the first electrical contact is coupled to the second sub-layer;
the first, second and third sub-layers are doped n-type;
an electrical conductivity of the second sub-layer is higher than an electrical conductivity of the first and third sub-layers;
the light emitting layer comprises a fourth superlattice;
the second layer comprises a fifth superlattice; and
the fifth superlattice is a chirped superlattice comprising changing well layer thicknesses, changing barrier layer thicknesses, or changing well layer and barrier layer thicknesses through the fifth superlattice, wherein at least one of the first, second, third, fourth, and fifth superlattices comprise Al.sub.xGa.sub.1-xN, where 0≤x≤1.
2. The light emitting structure of claim 1 , wherein:
light with a wavelength shorter than 300 nm that is emitted from the light emitting layer passes through the first set of doped layers before being emitted from the light emitting structure; and
the second sub-layer absorbs from 10% to 60% of the light emitted from the light emitting layer that reaches the second sub-layer.
3. The light emitting structure of claim 1 , wherein the well layers of the second superlattice comprise materials with lower bandgaps than the well layers of the first and third superlattices.
4. The light emitting structure of claim 1 , wherein each of the first, second and third sub-layers comprises an effective bandgap that is constant throughout the sub-layer.
5. The light emitting structure of claim 1 , wherein each of the first, second and third sub-layers comprises an effective bandgap that varies throughout the sub-layer.
6. The light emitting structure of claim 1 , wherein each of the first, second and third sub-layers have a thickness from about 10 nm to 3000 nm.
7. The light emitting structure of claim 1 , wherein the first sub-layer comprises a thickness greater than 100 nm.
8. The light emitting structure of claim 1 , wherein the first, second, third, fourth, and fifth superlattices each comprise sets of GaN well layers and AlN barrier layers.
9. The light emitting structure of claim 1 , wherein the first, second, third, fourth, and fifth superlattices each comprise Al x Ga 1-x N, where 0≤x≤1.
10. The light emitting structure of claim 1 , wherein at least one of the first, second, third, fourth, and fifth superlattices comprise InAlGaN.
11. The light emitting structure of claim 1 , wherein the first, second, third, fourth, and fifth superlattices each comprise InAlGaN.
12. The light emitting structure of claim 1 , wherein at least one of the first, second, third, fourth, and fifth superlattices comprise tri-layered unit cells.
13. The light emitting structure of claim 12 , wherein the tri-layered unit cells comprise AlN, Al x Ga 1-x N, and GaN.
14. The light emitting structure of claim 12 , wherein the tri-layered unit cells comprise AlN, Al x Ga 1-x N, and Al y In z Ga 1-y-z N.
15. The light emitting structure of claim 1 , wherein the second layer comprises a thickness from 5 nm to 50 nm.
16. The light emitting structure of claim 1 , wherein the chirped superlattice is a p-type chirped superlattice.
17. The light emitting structure of claim 1 , further comprising a substrate coupled to the first set of doped layers, wherein the substrate comprises sapphire, SiC, AlN, GaN, silicon, or diamond.
18. The light emitting structure of claim 1 , further comprising a second electrical contact coupled to the second layer, wherein the second electrical contact comprises Ti, Al, Ta and/or Ni.
19. The light emitting structure of claim 1 , wherein the first electrical contact comprises Ti, Al, Ta and/or Ni.