Nitride semiconductor light-emitting device and method for producing the same

1. A nitride semiconductor light-emitting device comprising:

a first conductive-type nitride semiconductor layer;

a superlattice layer provided on said first conductive-type nitride semiconductor layer;

an active layer provided on said superlattice layer; and

a second conductive-type nitride semiconductor layer provided on said active layer, wherein

an average carrier concentration of said superlattice layer is higher than an average carrier concentration of said active layer,

said superlattice layer is formed of alternate lamination of a doped layer containing a first conductive-type impurity and an undoped layer not containing said first conductive-type impurity,

thickness per one layer of said doped layer is greater than or equal to 1.5 nm and less than or equal to 15 nm,

thickness per one layer of said undoped layer is greater than or equal to 0.5 nm and less than or equal to 5 nm,

each of said doped layer and said undoped layer of the superlattice layer contains In, and

said active layer generates light, and

the average carrier concentration of said superlattice layer is greater than or equal to 1.2 and smaller than 5 times the average carrier concentration of said active layer.

2. The nitride semiconductor light-emitting device according to claim 1 , wherein

said active layer has a barrier layer, and

a proportion of thickness per one layer of said doper layer to thickness per one period of said superlattice layer is greater than or equal to a proportion of thickness per one layer of said barrier layer to thickness per one period of said active layer.

3. The nitride semiconductor light-emitting device according to claim 1 , wherein a concentration of the first conductive-type impurity in said doped layer is greater than or equal to a concentration of the first conductive-type impurity in said barrier layer.

4. The nitride semiconductor light-emitting device according to claim 1 , wherein

said active layer has a well layer not containing said first conductive-type impurity, and

a proportion of thickness per one layer of said undoped layer to thickness per one period of said superlattice layer is less than or equal to a proportion of thickness per one layer of said well layer to thickness per one period of said active layer.

5. The nitride semiconductor light-emitting device according to claim 1 , wherein said undoped layer is in contact with a lower face of said active layer.

6. The nitride semiconductor light-emitting device according to claim 1 , wherein said superlattice layer has two or more layers of said doped layer.

7. The nitride semiconductor light-emitting device according to claim 1 , wherein concentration of the first conductive-type impurity in said doped layer is greater than or equal to 1×10 17 cm −3 .

8. The nitride semiconductor light-emitting device according to claim 2 , wherein said barrier layer does not contain said first conductive-type impurity, or concentration of the first conductive-type impurity in said barrier layer is less than or equal to 8×10 17 cm −3 .

9. The nitride semiconductor light-emitting device according to claim 4 , wherein said active layer has two or more layers of said well layer.

10. The nitride semiconductor light-emitting device according to claim 2 , wherein thickness per one layer of said barrier layer is less than or equal to 7 nm.

11. The nitride semiconductor light-emitting device according to claim 1 , wherein

between said first conductive-type nitride semiconductor layer and said superlattice layer, a short-period superlattice layer having a thickness per one period that is smaller than thickness per one period of said superlattice layer is provided, and

concentration of the first conductive-type impurity in said short-period superlattice layer is greater than or equal to 1×10 18 cm −3 and less than or equal to 5×10 19 cm −3 .

12. The nitride semiconductor light-emitting device according to claim 1 , wherein

said doped layer contains said first conductive-type impurity and Al a Ga b In (1-a-b) N (0≦a<1, 0<b≦1), and

said undoped layer is formed of In c Ga (1-c) N (0<c≦1).

13. The nitride semiconductor light-emitting device according to claim 4 , wherein

said active layer is formed of lamination of said barrier layer and said well layer,

said barrier layer contains said first conductive-type impurity and Al x Ga y In (1-x-y) N (0≦x<1, 0<y≦1), and

said well layer is formed of In z Ga (1-z) N (0<z≦1).

14. The nitride semiconductor light-emitting device according to claim 1 , wherein

said active layer contains In, and

wavelength of light emitted by said superlattice layer by photoluminescence is less than or equal to wavelength of light emitted by said active layer.

15. A method for producing a nitride semiconductor light-emitting device comprising the steps of:

growing a first conductive-type nitride semiconductor layer on a substrate;

growing a superlattice layer on said first conductive-type nitride semiconductor layer;

growing an active layer on said superlattice layer; and

providing a second conductive-type nitride semiconductor layer on said active layer, wherein

a growth rate of said superlattice layer is greater than or equal to a growth rate of a well layer which is a part of said active layer,

the step of growing said superlattice layer includes the step of alternately laminating a doped layer containing a first conductive-type impurity and an undoped layer not containing said first conductive-type impurity and growing said superlattice layer having higher average carrier concentration than that of said active layer,

thickness per one layer of said doped layer is greater than or equal to 1.5 nm and less than or equal to 15 nm,

thickness per one layer of said undoped layer is greater than or equal to 0.5 nm and less than or equal to 5 nm,

each of said doped layer and said undoped layer of the superlattice layer contains In, and said active layer generates light, and

a growth rate of said undoped layer is greater than or equal to the growth rate of said well layer.

16. The method for producing the nitride semiconductor light-emitting device according to claim 15 , wherein

said doped layer is grown by using a first source gas and a first carrier gas, and

said first carrier gas contains greater than or equal to 0.3% by volume and less than or equal to 30% by volume of hydrogen gas.

17. The method for producing the nitride semiconductor light-emitting device according to claim 15 , wherein a growth temperature of said superlattice layer is equal to a growth temperature of said active layer, or higher than the growth temperature of said active layer.

18. The method for producing the nitride semiconductor light-emitting device according to claim 15 , wherein the growth rate of said well layer is greater than or equal to 10 nm/hour and less than or equal to 150 nm/hour.