Processes occurring during the formation of graded ZnSe/ZnTe contacts on p-ZnSe

We show that the formation of ohmic contacts to p-ZnSe does not mainly depend on the exact design of the applied ZnSe/ZnTe grading, but rather on the temperature during contact growth and the thickness of the ZnTe cap layer on top of the grading. These facts demonstrate that a diffusion process dominates the contact formation. From the activation energy of the diffusion process we conclude that the diffusing species is nitrogen, which diffuses from the ZnTe cap into the underlying p-ZnSe. The nitrogen excess leads to an overcompensation in the ZnSe. Such an overcompensation process can be quantitatively described by the formation of compensating complexes involving two nitrogen atoms.