Semiconductor light emitting device

1. A semiconductor light emitting device, comprising:

an n-type semiconductor layer including a nitride semiconductor;

a p-type semiconductor layer of a nitride semiconductor;

a light emitting portion provided between the n-type semiconductor layer and the p-type semiconductor layer and including a plurality of quantum well layers, each of the quantum well layers including a nitride semiconductor;

a first intermediate region provided between the light emitting portion and the p-type semiconductor layer, the first intermediate region including:

a first region including Al x1 Ga 1-x1 N, wherein in the first region a first Al composition ratio x 1 is an atomic ratio of Al among group III elements, the first Al composition ratio x 1 being not lower than 0.001 and not higher than 0.05, the first region having a thickness not thinner than 0.5 nanometer, and

a second region provided between the first region and the p-type semiconductor layer, the second region contacting the p-type semiconductor layer, the second region including Al x2 Ga 1-x2 N, wherein in the second region a second Al composition ratio x 2 is an atomic ratio of Al among group III elements, the second Al composition ratio x 2 being not lower than 0.1 and not higher than 0.2, a concentration of a p-type impurity in the second region being higher than a concentration of a p-type impurity in the first region; and

a second intermediate region provided between the first region and the light emitting portion, the second intermediate region contacting one of the quantum well layers, the second intermediate region having a thickness not thinner than 3 nanometers and not thicker than 8 nanometers and including In z1 Ga 1-z1 N, wherein in the second intermediate region an In composition ratio z 1 is an atomic ratio of In among group III elements, the In composition ratio z 1 being not lower than 0 and lower than 1.

2. The device according to claim 1 , further comprising a third region provided between the first region and the second region, the third region including Al x3 Ga 1-x3 N, wherein in the third region a third Al composition ratio x 3 is an atomic ratio of Al among group III elements, the third Al composition being between the first Al composition ratio x 1 and the second Al composition ratio x 2 .

3. The device according to claim 2 , further comprising:

a fourth region provided between the third region and the second region, the fourth region including Al x4 Ga 1-x4 N, wherein in the fourth region a fourth Al composition ratio x 4 is an atomic ratio of Al among group III elements, the fourth Al composition ratio x 4 being between the third Al composition ratio x 3 and the second Al composition ratio x 2 .

4. The device according to claim 2 , wherein the third Al composition ratio x 3 in the third region increases along a direction from the light emitting portion toward the p-type semiconductor layer.

5. The device according to claim 4 , wherein the third region includes a plurality of layers.

6. The device according to claim 1 , wherein an Al composition ratio increases from the first region toward the second region.

7. The device according to claim 1 , wherein the first Al composition ratio x 1 is substantially 0.05 and a thickness of the first region is substantially 5 nanometers.

8. The device according to claim 1 , wherein the second Al composition ratio x 2 is substantially 0.20 and a thickness of the second region is substantially 5 nanometers.

9. The device according to claim 1 , wherein the second intermediate region includes substantially no Al.

10. The device according to claim 1 , wherein the second intermediate region is made of one of GaN and InGaN.

11. The device according to claim 1 , wherein the light emitting portion includes a plurality of barrier layers, the barrier layers and the quantum well layers being alternately stacked along a direction from the n-type semiconductor layer toward the p-type semiconductor layer.

12. The device according to claim 11 , wherein one of the plurality of barrier layers is in contact with the n-type semiconductor layer.

13. The device according to claim 1 , wherein the p-type semiconductor layer is of made of GaN.

14. The device according to claim 1 , wherein

the n-type semiconductor layer includes an n-type GaN layer and a n-type guide layer,

the n-type guide layer is provided between the n-type GaN layer and the light emitting portion, and

the n-type guide layer is made of one of GaN including Si and InGaN including Si.

15. The device according to claim 1 , wherein

the p-type semiconductor layer includes a p-type GaN contact layer and a p-type GaN layer provided between the p-type GaN contact layer and the second region, and

a concentration of a p-type impurity included in the p-type GaN layer is lower than a concentration of a p-type impurity included in the p-type GaN contact layer.

16. The device according to claim 1 , further comprising:

a substrate made of sapphire, the n-type semiconductor layer being provided between the substrate and the light emitting portion; and

a buffer layer provided between the substrate and the n-type semiconductor layer.

17. The device according to claim 1 , further comprising:

an n-side electrode provided in contact with the n-type semiconductor layer; and

a p-side electrode provided in contact with the p-type semiconductor layer.