Light-emitting element array

1. A light-emitting element array comprising a plurality of light-emitting elements configured to emit light in a direction perpendicular to the surface of a substrate, each of the light-emitting elements including:

the substrate;

a first nitride semiconductor layer on the substrate, having a mesa portion;

an active layer made of a nitride semiconductor disposed on the mesa portion of the first semiconductor layer opposite the substrate, the active layer having a light-emitting region;

a second nitride semiconductor layer on the active layer; and

a heat radiation layer disposed in such a manner that the surface formed by projecting the heat radiation layer on a plane perpendicular to the optical axis of the light-emitting element does not overlap with the surface formed by projecting the mesa portion on the same plane when viewed in the optical axis direction,

wherein when the light-emitting element is projected on a plane perpendicular to the optical axis, the surface of the projection of the heat radiation layer has an area S T satisfying the inequality: 0<S T ≦390×(S O /S M ) 0.65 , and

wherein S M represents the area of the surface of the projection of the mesa portion on the plane, S O represents the area of the surface of the projection of the light-emitting region of the active layer on the plane.

2. The light-emitting element array according to claim 1 , wherein the mesa portion and the light-emitting region satisfy the inequality: 0.64≦S O /S M <1.

3. The light-emitting element array according to claim 1 , wherein the mesa portion and the heat radiation layer satisfy the inequality: 0<S T /S M ≦0.64.

4. The light-emitting element array according to claim 1 , wherein the heat radiation layer is disposed on a surface of the first semiconductor layer other than the surface of the mesa portion, opposite the substrate.

5. The light-emitting element array according to claim 1 , wherein the heat radiation layer has a higher thermal conductivity than the thermal conductivities of the first semiconductor layer, the active layer and the second semiconductor layer.

6. The light-emitting element array according to claim 1 , wherein the heat radiation layer functions as an electrode that injects current to the active layer.

7. The light-emitting element array according to claim 1 , further comprising a heat sink on the heat radiation layer.

8. The light-emitting element array according to claim 1 , wherein the mesa portion is formed in a protruding shape by removing at least the second semiconductor layer and part of the active layer to expose the first semiconductor layer.

9. The light-emitting element array according to claim 1 , wherein the mesa portion is formed in a protruding shape by removing at least part of the substrate to expose the first semiconductor layer.

10. The light-emitting element array according to claim 1 , wherein the light-emitting elements are surface emitting lasers.

11. The light-emitting element array according to claim 10 , wherein the light-emitting elements further includes a current confinement layer defining a region of the active layer to which current is injected.

12. The light-emitting element array according to claim 1 , wherein the light emitting elements are light-emitting diodes.

13. A solid-state laser comprising the light-emitting element array as set forth in claim 1 .