ELECTRICAL-PROPERTIES AT P-ZNSE METAL INTERFACES/

In order to prepare low resistance ohmic contacts to p-ZnSe by the ''d eposition and annealing (DA)'' technique which has been extensively us ed for GaAs and Si-based devices, formation of a heavily doped layer b y the p-ZnSe/metal reaction is required. For p-ZnSe/Ni contacts, Ni an d Se reacted preferentially at the ZnSe/Ni interface upon annealing at temperatures higher than 250 degrees C. However, capacitance-voltage measurements showed that the net acceptor concentration (N-A - N-D) cl ose to the p-ZnSe/Ni interface was reduced upon the Ni/ZnSe reaction, resulting in high contact resistance. For p-ZnSe/Au contacts, neither Au/ZnSe reaction nor reduction of the acceptor concentration were obse rved after annealing at temperatures lower than 300 degrees C. This in dicates that although the metal/p-ZnSe reaction is mandatory to prepar e a heavily doped layer, the reaction induced an increase in the compe nsation donors in the p-ZnSe substrate. In order to increase the accep tor concentration in the vicinity of the p-ZnSe/metal interface throug h diffusion from the contact materials, Li or O which was reported to play the role of an acceptor in ZnSe was deposited with a contact meta l and annealed at elevated temperatures. Ni or Ag was selected as the contact metal, because these metals were expected to enhance Li or O d oping by reacting with ZnSe. However, the current density-voltage char acteristics of the Li(N)/Ni and Ag(O) contacts exhibited rectifying be havior, and the contact resistances increased with increasing annealin g temperature. The present results indicated that, even though the acc eptor concentration in the p-ZnSe substrate increased by diffusion of the dopants from the contact elements, an increment of the compensatio n donors was larger than that of the accepters. The present experiment s indicated that preparation of low resistance ohmic contacts by formi ng a heavily doped intermediate layer between p-ZnSe and metal is extr emely difficult by the DA technique.