Study of ohmic multilayer metal contacts to p-type ZnSe

A novel approach for making ohmic contacts to p-type ZnSe has been introduced. This approach includes growth of p-ZnSe at low temperature by a variant of molecular beam epitaxy, then treating the surface with KOH solution, followed by deposition of a Te/Pd/Pt/Au metal layer and annealing at 200–250 °C for 5 min. As a result, a stable ohmic contact up to a current density of 2 kA cm⁻² was obtained. Using this contact fabrication procedure, a ZnSe-based quantum-well laser was demonstrated in continuous wave mode of operation at room temperature. The formation of the ohmic contact is suggested to be due to the presence of oxygen on the ZnSe surface, the creation of TeO₂ at the metal/ZnSe interface, and the diffusion of Pd into ZnSe.