Light emitting diode

1. A light emitting diode (LED), comprising:

an n-type semiconductor layer, an active layer, a p-type semiconductor layer, and a transparent electrode layer arranged on a substrate;

a tunnel layer interposed between the p-type semiconductor layer and the transparent electrode layer;

an opening arranged in the transparent electrode layer so that the tunnel layer or the p-type semiconductor layer under the tunnel layer is exposed upward;

a distributed Bragg reflector (DBR) arranged in the opening; and

an electrode pad arranged on the transparent electrode layer to cover the DBR in the opening.

2. The LED of claim 1 , wherein a side surface of the electrode pad contacts an inner side surface of the opening, and a lower surface of the electrode pad contacts the DBR.

3. The LED of claim 1 , wherein the tunnel layer is an n-type tunnel layer (n++) doped with a highly concentrated n-type impurity.

4. The LED of claim 1 , wherein the transparent electrode layer is an indium tin oxide (ITO) layer.

5. The LED of claim 1 , further comprising a lower DBR arranged under the active layer.

6. The LED of claim 1 , wherein the LED is a GaN-based LED.

7. The LED of claim 1 , wherein the DBR comprises low refractive index layers and high refractive index layers alternately laminated.

8. The LED of claim 7 , wherein the low refractive index layers comprise SiO 2 or Al 2 O 3 .

9. The LED of claim 7 , wherein the high refractive index layers comprise Si 3 N 4 , TiO 2 , or Si—H.

10. A light emitting diode (LED), comprising:

an n-type semiconductor layer, an active layer, a p-type semiconductor layer, and a transparent electrode layer arranged on a substrate;

an opening arranged in the transparent electrode layer;

an electrode pad arranged to partially fill the opening; and

an n++ or undoped layer arranged on the transparent electrode layer and contacting the electrode pad.