III-Nitride light emitting diodes having improved performance are provided. In one embodiment, a light emitting device includes a substrate, a nucleation layer disposed on the substrate, a defect reduction structure disposed above the nucleation layer, and an n-type III-Nitride semiconductor layer disposed above the defect reduction structure. The n-type layer has, for example, a thickness greater than about one micron and a silicon dopant concentration greater than or equal to about 1019 cm−3. In another embodiment, a light emitting device includes a III-Nitride semiconductor active region that includes at least one barrier layer either uniformly doped with an impurity or doped with an impurity having a concentration graded in a direction substantially perpendicular to the active region.