1. A semiconductor structure for light emitting devices that can emit in the red to ultraviolet portion of the electromagnetic spectrum, said structure comprising: a first n-type cladding layer of Al x In y Ga 1−x−y N, where 0≦x≦1 and 0≦y<1 and (x+y)≦1; a second n-type cladding layer of Al x In y Ga 1−x−y N where 0≦x≦1 and 0≦y<1 and (x+y)≦1, wherein said second n-type cladding layer is further characterized by the substantial absence of magnesium , and wherein a composition of said second n-type cladding layer is graded ; an active portion between said first and second cladding layers in the form of a multiple quantum well having a plurality of In x Ga 1−x N well layers where 0<x<1 separated by a corresponding plurality of Al x In y Ga 1−x−y N barrier layers where 0≦x≦1 and 0≦y≦1; a p-type layer of a Group III nitride, wherein said second n-type cladding layer is positioned between said p-type layer and said multiple quantum well; wherein said first and second n-type cladding layers have respective bandgaps that are each larger than the bandgap of said well layers , wherein a p-n junction is defined between said second n-type cladding layer and said p-type layer .