A light-emitting diode or laser diode comprises a sapphire substrate and,
grown on the substrate, a GaN buffer layer, an n-doped GaN contact layer,
an n-doped (AlGa)N cladding layer, a Zn-doped (InGa)N active layer, a
p-doped (AlGa)N cladding layer and a p-doped GaN contact layer. Graded
layers are introduced at the interfaces between the cladding layers and
both the contact layers and the active layer. The constituency of each
graded layer is graded from one side to the other of the layer such that
the layer is lattice matched with the adjacent layer on each side with the
result that the strain at the interfaces between the layers is reduced and
the possibility of deleterious dislocations being introduced at the
interfaces is minimised. By removing or reducing such dislocations, the
efficiency of the operation of the device is increased.
