Electrical Contacts to p‐ZnSe Based on HgSe and ZnTe

Low resistance ohmic contacts to p‐ZnSe involving the use of HgSe are studied in detail. HgSe does not form an ohmic contact with p‐ZnSe because of a residual valence band offset at the heterojunction of 0.5 to 0.6 eV. Annealing of HgSe/ZnSe:N does not result in an ohmic contact because a large miscibility gap in Hg 1− x Zn x Se prevents a HgZn interdiffusion and therefore the formation of a graded heterojunction. The molecular beam epitaxial (MBE) growth of Hg 1− x Zn x Se does not circumvent this problem because these epitaxial layers suffer from a compositional phase separation due to spinodal demixing during MBE growth. A significant improvement of HgSe based contacts could be achieved by the use of ZnSe 1− x Te x :N transition layers between HgSe and ZnSe:N. Either by abrupt, graded, or multilayer heterojunctions, very low contact resistivities are obtained. The growth of ZnSe 1− x Te x :N layers on top of ZnSe:N is shown to reduce the carrier concentration in ZnSe:N by several orders of magnitude. A nitrogen diffusion process is believed to be responsible for this effect.