Semiconductor light-emitting element

1. A semiconductor light-emitting element having an emission wavelength band with a peak wavelength in an ultraviolet region from 200 nm to 365 nm, the semiconductor light-emitting element comprising:

an n-type semiconductor layer that has a composition of AlGaN or AlInGaN;

an active layer formed on the n-type semiconductor layer, the active layer containing an AlGaN semiconductor or an AlInGaN semiconductor;

a p-type semiconductor layer formed on the active layer, the p-type semiconductor layer having a composition of AlN, AlGaN, or AlInGaN; and

a p-electrode formed on the p-type semiconductor layer, the p-electrode being made of metal or metal oxide,

wherein:

the p-type semiconductor layer includes a contact layer formed near an interface between the p-type semiconductor layer and the p-electrode, and the contact layer is an AlGaN layer or an AlInGaN layer in which an Al composition decreases toward the interface between the p-type semiconductor layer and the p-electrode so that a band gap of the contact layer decreases continuously toward the interface between the p-type semiconductor layer and the p-electrode,

the contact layer includes a tunneling contact layer in contact with the p-electrode, and the tunneling contact layer is connected to the p-electrode by a tunnel junction,

a decrease rate of the Al composition in the contact layer toward the interface between the p-type semiconductor layer and the p-electrode is 0.0008 nm −1 to 0.05 nm −1 ,

the active layer has a quantum well structure that includes a well layer and a barrier layer,

a band gap of the barrier layer is larger than a band gap of the well layer,

the well layer consists of an AlGaN layer having a composition of Al x1 Ga 1−x1 N, and an Al composition of the well layer is 0.5 or greater than 0.5, and

the band gap of the contact layer varies in a band gap range greater than the band gap of the well layer.

2. The semiconductor light-emitting element according to claim 1 , wherein the p-electrode includes a laminate of a Ni layer and an Au layer, a laminate of a Pt layer and an Au layer, a laminate of a Pd layer and an Au layer, a laminate of Al on ITO, a Rh layer, or a Ru layer.

3. The semiconductor light-emitting element according to claim 1 , wherein a band gap of the p-type semiconductor layer is larger than the band gap of the well layer.

4. The semiconductor light-emitting element according to claim 1 , wherein the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are semiconductor layers epitaxially grown on a single crystal AlN substrate.

5. The semiconductor light-emitting element according to claim 1 , wherein:

the p-type semiconductor layer includes a p-type cladding layer formed in an active layer side with respect to the contact layer, and

the contact layer has a higher dopant concentration than the p-type cladding layer in a proximity of the interface between the p-type semiconductor layer and the p-electrode.

6. The semiconductor light-emitting element according to claim 1 , wherein the decrease rate of the Al composition in the contact layer decreases toward the interface between the p-type semiconductor layer and the p-electrode.

7. The semiconductor light-emitting element according to claim 1 , wherein the decrease rate of the Al composition in the contact layer increases toward the interface between the p-type semiconductor layer and the p-electrode.

8. The semiconductor light-emitting element according to claim 1 , wherein the contact layer has a layer thickness of 20 nm to 60 nm.

9. The semiconductor light-emitting element according to claim 1 , wherein the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are in a pseudomorphic state.

10. The semiconductor light-emitting element according to claim 1 , wherein the contact layer has a composition of Al y Ga 1−y N, where 0.6≤y≤0.8.