Nitride semiconductor light-emitting element and method for producing same

1. A nitride semiconductor light-emitting element comprising:

an n-type nitride semiconductor layer;

a nitride semiconductor active layer provided on said n-type nitride semiconductor layer; and

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

said p-type nitride semiconductor layer includes a first p-type nitride semiconductor layer, a second p-type nitride semiconductor layer and a third p-type nitride semiconductor layer in this order from the side of said nitride semiconductor active layer,

said first p-type nitride semiconductor layer- and said second p-type nitride semiconductor layer contain Al respectively,

an average Al composition in said first p-type nitride semiconductor layer and an average Al composition in said second p-type nitride semiconductor layer are equivalent to each other,

said third p-type nitride semiconductor layer has a smaller band gap than said second p-type nitride semiconductor layer, and

the p-type impurity concentration in said second p-type nitride semiconductor layer and the p-type impurity concentration in said third p-type nitride semiconductor layer are lower than the p-type impurity concentration in said first p-type nitride semiconductor layer respectively.

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

said p-type nitride semiconductor layer further includes a fourth p-type nitride semiconductor layer on a side of said third p-type nitride semiconductor layer opposite to the side where said nitride semiconductor active layer is set,

said fourth p-type nitride semiconductor layer has a smaller band gap than said second p-type nitride semiconductor layer, and

the p-type impurity concentration in said fourth p-type nitride semiconductor layer is higher than the p-type impurity concentration in said third p-type nitride semiconductor layer.

3. The nitride semiconductor light-emitting element according to claim 1 , wherein

said nitride semiconductor active layer has a multiple quantum well structure including a plurality of nitride semiconductor quantum well layers and a plurality of nitride semiconductor barrier layers, and

a nitride semiconductor barrier layer, included in said plurality of nitride semiconductor barrier layers, other than a nitride semiconductor barrier layer in contact with said p-type nitride semiconductor layer contains an n-type impurity.

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

said n-type nitride semiconductor layer includes an n-type nitride semiconductor contact layer and an n-type nitride semiconductor superlattice layer,

said n-type nitride semiconductor superlattice layer is positioned between said n-type nitride semiconductor contact layer and said nitride semiconductor active layer, and

an average n-type impurity concentration in said n-type nitride semiconductor superlattice layer is at least 1×10 18 atoms/cm 3 .

5. A method for producing a nitride semiconductor light-emitting element, comprising the steps of:

vapor-phase-growing a nitride semiconductor active layer on an n-type nitride semiconductor layer;

vapor-phase-growing a first p-type nitride semiconductor layer containing Al on said nitride semiconductor active layer;

vapor-phase-growing a second p-type nitride semiconductor layer, containing Al, having an equivalent average Al composition to said first p-type nitride semiconductor layer on said first p-type nitride semiconductor layer; and

vapor-phase-growing a third p-type nitride semiconductor layer having a smaller average Al composition than said first p-type nitride semiconductor layer on said second p-type nitride semiconductor layer, wherein

said second p-type nitride semiconductor layer and said third p-type nitride semiconductor layer are doped with a p-type impurity in lower concentrations than said first p-type nitride semiconductor layer respectively.

6. The method for producing a nitride semiconductor light-emitting element according to claim 5 , wherein

the vapor phase growth is interrupted after the step of vapor-phase-growing said second p-type nitride semiconductor layer and before the step of vapor-phase-growing said third p-type nitride semiconductor layer.

7. The method for producing a nitride semiconductor light-emitting element according to claim 6 , wherein

the pressure of the vapor phase is changed in the interruption of said vapor phase growth.

8. The method for producing a nitride semiconductor light-emitting element according to claim 5 , further comprising a step of vapor-phase-growing a fourth nitride semiconductor layer doped with the p-type impurity in a higher concentration than said third p-type nitride semiconductor layer on said third p-type nitride semiconductor layer after the step of vapor-phase-growing said third p-type nitride semiconductor layer.

9. The nitride semiconductor light-emitting element according to claim 1 , further comprising a nitride semiconductor layer containing Al between said nitride semiconductor active layer and said first p-type nitride semiconductor layer.