Contact etching and metallization for improved LED device performance and reliability
A light emitting device includes a vertical via through the P-type semiconductor layer and the active layer. Using a vertical via reduces quantum well damage, allows shortening of P-N spacing, and allows increased reflective area. A dielectric structure is formed in the via to provide a sloped wall that extends to an upper surface of the device. Another dielectric layer covers the upper surface and the sloped wall, and provides select contacts to the semiconductor layers. A metal layer is subsequently applied. Because the dielectric layers provide a continuous slope from the surface of the device, the metal layer does not include a vertical drop. Because the active layer does not extend into the via, the contact to the N-type semiconductor layer may be situated closer to the wall of the via, increasing the area available for a reflective layer.
1. A light emitting device comprising:
a semiconductor structure comprising an active layer between a first-type semiconductor layer and a second-type semiconductor layer;
a reflective layer over the semiconductor structure;
a via in the reflective layer, the second-type semiconductor layer and the active layer, the via having walls within the semiconductor structure that are substantially orthogonal to a surface of the active layer;
a dielectric structure comprising, within the via, a first surface facing a center of the via that extends from a top surface of the reflective layer to the first-type semiconductor layer to form an acute angle with the first-type semiconductor layer, a second surface facing the walls of the via that is substantially orthogonal to the surface of the active layer and a third surface facing the first-type semiconductor layer that is parallel to the surface of the active layer; and
a metal layer on the dielectric structure and contacting the first-type semiconductor layer.
2. The light emitting device of claim 1 , wherein the dielectric structure includes a first dielectric structure that provides a slope within the via formed by the acute angle, and a second dielectric structure that extends over the reflective layer and onto the slope within the via.
3. The light emitting device of claim 1 , wherein the metal layer includes one or more of: Al, Ti, Au, and Ni.
4. The light emitting device of claim 1 , wherein the reflective layer includes silver.
5. The light emitting device of claim 4 , including a barrier layer that controls migration of the silver.
6. The light emitting device of claim 5 , wherein the barrier layer includes one or more of: TiW, TiWN and TiN.
7. The light emitting device of claim 1 , wherein the dielectric structure includes one or more of: SiN x , SiO x , and Si-oxy-nitride.
8. The light emitting device of claim 1 , wherein the reflective layer includes a combination of two or more of: Ag, SiO x , NbO x , ZnO, TiO x and indium tin oxide (ITO).
9. The light emitting device of claim 1 , wherein the metal layer is in electrical contact with the second-type semiconductor layer via the reflective layer.
10. The light emitting device of claim 1 , wherein the via having walls within the semiconductor structure comprises walls created by at least one surface of the semiconductor structure.