Group III nitride compound semiconductor light emitting device
In a group III nitride compound semiconductor light emitting device comprising an n-type semiconductor layer, a p-type semiconductor layer having a superlattice structure in which a first layer comprising at least Al and a second layer having a different composition from that of the first layer are laminated repetitively, and an active layer interposed between the n-type semiconductor layer and the p-type semiconductor layer, wherein an Al composition of the first layer which is the closest to the active layer is set to be lower than that of each of the other first layers, and wherein a doping amount of a p-type impurity in the first layer which is the closest to the active layer is set to be smaller than that of the p-type impurity of each of the other first layers or non-doped.
1. A group III nitride compound semiconductor light emitting device comprising:
an n-type semiconductor layer;
a p-type net conductivity semiconductor layer comprising a superlattice structure comprising a plurality of first and second layers, said first layers comprising at least Al and said second layers having a composition differing from a composition of the first layers, said plurality of first and second layers being laminated alternately and repetitively; and
an active layer interposed between the n-type semiconductor layer and the p-type net conductivity semiconductor layer,
wherein a layer of said first layers located closest to the active layer has an Al composition that is less than an Al composition of other layers of said first layers,
wherein said layer of said first layers located closest to the active layer comprises one of:
no doping; and
a doping amount of a p-type impurity that is less than a doping amount of a p-type impurity of said other layers of said first layers, and
wherein the first layers comprise AlGaN and the second layers comprise InGaN.
2. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein the active layer does not contain Al.
3. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein said layer of said first layers located closest to the active layer has a growth temperature that is greater than a growth temperature of said other layers of said first layers.
4. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein a thickness of the first layers and a thickness of the second layers is in a range from 1 nm to 6 nm.
5. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein a number of repetitions of the first layers and the second layers is in a range from four repetitions to eight repetitions.
6. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein said layer of the first layers located closest to the active layer is in contact with the active layer.
7. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein the Al composition of the layer of said first layers located closest to the active layer is in a range from 10% to 80% of said Al composition of the other layers of said first layers.
8. The group III nitride compound semiconductor light emitting device according to claim 7 , wherein the Al composition of the layer of said first layers located closest to the active layer is in a range from 30% to 60% of the Al composition of the other layers of said first layers.
9. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein the Al composition of the layer of said first layers located closest to the active layer is in a range from 5% to 25% of said layer of said first layers located closest to the active layer.
10. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein the active layer has a multiple quantum well structure, and
wherein a barrier layer located closest to the p-type net conductivity semiconductor layer in the multiple quantum well structure is in contact with said layer of said first layers.
11. The group III nitride compound semiconductor light emitting device according to claim 10 , wherein a well layer in the multiple quantum well structure comprises InGaN and the barrier layer comprises GaN.
12. The group III nitride compound semiconductor light emitting device according to claim 10 , wherein the thickness of the barrier layer located closest to the p-type net conductivity semiconductor layer is in a range from 10% to 80% of the thickness of the other barrier layers.
13. The group III nitride compound semiconductor light emitting device according to claim 12 , wherein the thickness of the barrier layer located closest to the p-type net conductivity semiconductor layer is in a range from 20% to 60% of the thickness of the other barrier layers.
14. The group III nitride compound semiconductor light emitting device according to claim 10 , wherein the thickness of the barrier layer is at least 3 nm.
15. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein the n-type semiconductor layer comprises a superlattice structure.
16. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein said p-type impurity comprises one of Mg, Zn, Be, Ca, Sr, and Ba.
17. The group III nitride compound semiconductor light emitting device according to claim 11 , wherein the active layer is devoid of Al.
18. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein a number of repetitions of the first layers and the second layers is in a range from six repetitions to thirty repetitions.
19. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein said first layers and said second layers comprise a general formula Al x In y Ga 1-x-y N, where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1.
20. The group III nitride compound semiconductor light emitting device according to claim 1 , wherein an uppermost layer of said active layer comprises GaN.
21. The group III nitride compound semiconductor light emitting device according to claim 1 , further comprising a barrier layer located closest to the p-type net conductivity semiconductor layer in a multiple quantum well structure of said active layer, said barrier layer being located next to said layer of said first layers.