Gallium nitride-based compound semiconductor light-emitting device with an electrode covered by an over-coating layer
A gallium nitride-based compound semiconductor light-emitting device includes an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer of gallium nitride-based compound semiconductors which are formed in this order on a substrate, the negative electrode and the positive electrode being provided in contact with the n-type semiconductor layer and the p-type semiconductor layer, respectively. The positive electrode includes a first electrode and an over-coating layer covering the side surfaces and upper surface of the first electrode, and the area where the over-coating layer comes into contact with the p-type semiconductor layer is greater at the corner portions of the positive electrode than at the side portions thereof, per unit length of the outer edge of the first electrode.
1. A gallium nitride-based compound semiconductor light-emitting device comprising an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer of gallium nitride-based compound semiconductors which are formed in this order on a substrate, a negative electrode and a positive electrode being provided in contact with the n-type semiconductor layer and the p-type semiconductor layer, respectively, wherein the positive electrode comprises at least a first electrode having a side surface and an over-coating layer having a side surface and covering side surfaces and an upper surface of the first electrode, and an area where the over-coating layer comes into contact with the p-type semiconductor layer is greater at corner portions of the positive electrode than at side portions thereof, per unit length of an outer edge of the first electrode,
wherein an angle of corner portions in a plane projected shape of the first electrode or of the over-coating layer is selected to be an obtuse angle, or corner portions in a plane projected shape of the first electrode or of the over-coating layer are formed in an arcuate shape, so that the area where the over-coating layer comes into contact with the p-type semiconductor layer becomes greater at the corner portions of the positive electrode than at the side portions thereof.
2. The gallium nitride-based compound semiconductor light-emitting device according to claim 1 , wherein when a gap between a side surface of the first electrode and a side surface of the over-coating layer on a side portion is denoted by A, a gap between a side surface of the first electrode and a side surface of the over-coating layer at corner portions is not smaller than 2 1/2 ×A.
3. The gallium nitride-based compound semiconductor light-emitting device according to claim 1 , wherein a gap between the side surface of the first electrode and the side surface of the over-coating layer is 0.1 to 50 μm.
4. The gallium nitride-based compound semiconductor light-emitting device according to claim 1 , wherein the first electrode is a reflecting electrode.
5. The gallium nitride-based compound semiconductor light-emitting device according to claim 4 , wherein the first electrode is a reflecting electrode containing Ag or Al.
6. The gallium nitride-based compound semiconductor light-emitting device according to claim 4 , wherein the over-coating layer is at least one of metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt and Au, or an alloy thereof.
7. A lamp comprising the gallium nitride-based compound semiconductor light-emitting device according to claim 1 .