Semiconductor device

1. A semiconductor device, comprising:

an active layer;

a first semiconductor layer of first conductive type;

an overflow prevention layer disposed between the active layer and the first semiconductor layer, which is doped with impurities of first conductive type and which prevents overflow of electrons or holes;

a second semiconductor layer of first conductive type which is disposed either of between the active layer and the overflow prevention layer or between the overflow prevention layer and the first semiconductor layer; and

an impurity diffusion prevention layer disposed between the overflow prevention layer and the second semiconductor layer, which has a band gap smaller than those of the overflow prevention layer, the first semiconductor layer and the second semiconductor layer and which prevents diffusion of impurities of first conductive type,

wherein each of the active layer, the overflow prevention layer, the first semiconductor layer, the second semiconductor layer and the impurity diffusion prevention layer are formed of GaN-based compound semiconductor.

2. The semiconductor device according to claim 1 ,

wherein the second semiconductor layer is disposed between the active layer and the overflow prevention layer; and

the impurity diffusion prevention layer is disposed between the second semiconductor layer and the overflow prevention layer.

3. The semiconductor device according to claim 1 ,

wherein the impurity diffusion prevention layer includes In; and

a composition ratio of In in the impurity diffusion prevention layer is higher than those of the overflow prevention layer, the first semiconductor layer and the second semiconductor layer.

4. The semiconductor device according to claim 1 ,

wherein the active layer emits a light with a predetermined wavelength;

the first conductive type is p-type;

the first semiconductor layer is used as a p-type clad layer;

the second semiconductor layer is used as a p-type guide layer; and

the overflow prevention layer prevents overflow of electrons.

5. The semiconductor device according to claim 4 , further comprising:

an n-type guide layer disposed on a side of the active layer opposite from the p-type guide layer, which includes GaN or In x1 Ga 1-x1 N (0<x1<1);

wherein the active layer includes a single or multiple quantum well structure having In x2 Ga 1-x2 N (0<x2≦1) and a barrier layer having In x3 Ga 1-x3 N (0≦x3<1, x2>x3); and

the p-guide layer has In x4 Ga 1-x4 N (0≦x4<1, x3>x4).

6. The semiconductor device according to claim 1 ,

wherein the overflow prevention layer has a Ga 1-y Al y N layer (0<y≦1).

7. A semiconductor device, comprising:

an active layer;

a first semiconductor layer of first conductive type;

an overflow prevention layer disposed between the active layer and the first semiconductor layer, which is doped with impurities of first conductive type and which prevents overflow of electrons or holes;

a second semiconductor layer of first conductive type disposed between the overflow prevention layer and the first semiconductor layer;

a third semiconductor layer of first conductive type disposed between the active layer and the overflow prevention layer; and

an impurity diffusion prevention layer disposed at least one of between the overflow prevention layer and the second semiconductor layer and between the overflow prevention layer and the third semiconductor layer, which has a band gap smaller than those of the overflow prevention layer, the first semiconductor layer, the second semiconductor layer and the third semiconductor layer and which prevents diffusion of impurities of first conductive type,

wherein each of the active layer, the overflow prevention layer, the first semiconductor layer, the second semiconductor layer, the third semiconductor layer and the impurity diffusion prevention layer are formed of GaN-based compound semiconductor.

8. The semiconductor device according to claim 7 ,

wherein the impurity diffusion prevention layer is disposed between the second semiconductor layer and the overflow prevention layer.

9. The semiconductor device according to claim 7 ,

wherein the impurity diffusion prevention layer is disposed between the third semiconductor layer and the overflow prevention layer.

10. The semiconductor device according to claim 7 ,

wherein the impurity diffusion prevention layer includes In; and

a composition ratio of In in the impurity diffusion prevention layer is higher than of those of the overflow prevention layer, the first semiconductor layer, the second semiconductor layer and the third semiconductor layer.

11. The semiconductor device according to claim 7 ,

wherein the active layer emits a light with a predetermined wavelength;

the first conductive type is p-type;

the first semiconductor layer is used as a p-type clad layer;

each of the second and third semiconductor layers is used as a p-type guide layer; and

the overflow prevention layer prevents overflow of electrons.

12. The semiconductor device according to claim 7 , further comprising:

an n-type guide layer disposed on a side of the active layer opposite from the p-type guide layer, which includes GaN or In x1 Ga 1-x1 N (0<x1<1);

wherein the active layer includes a single or multiple quantum well structure having In x2 Ga 1-x2 N (0<x2≦1) and a barrier layer having In x3 Ga 1-x3 N (0≦x3<1, x2>x3); and

the p-guide layer has In x4 Ga 1-x4 N (0≦x4<1, x3>x4).

13. The semiconductor device according to claim 7 ,

wherein the overflow prevention layer has a Ga 1-y Al y N layer (0<y≦1).