DESIGN OF OHMIC CONTACTS TO P-ZNSE

First-principle density functional calculations are used to design improved ohmic contacts to p-ZnSe. Two design strategies are applied: the use of a graded semiconductor epilayer with a large valence band offset, and the imposition of an interlayer to reduce the metal/p-ZnSe Schottky barrier. In the former strategy we study BeTe because it is lattice matched to ZnSe. We find the BeTe/ZnSe valence band offset is nearly the same as the ZnTe/ZnSe offset, so that if BeTe can be sufficiently p doped, its grading with ZnSe should lead to an ohmic contact comparable to a ZnTe-grading contact, but without the deleterious presence of misfit dislocations. For the latter strategy we consider the use of a thin As-Si interlayer between the II-VI material and metal. The As effects an extra microscopic dipole at the interface that lowers the Fermi level 1 eV in the II-VI band gap, leading to greatly decreased rectification at p-type contacts. Applying both strategies simultaneously suggests that a metal/Si-As/BeTe/ZnSe multilayer structure would afford a nearly ideal ohmic contact to p-ZnSe.