FORMATION OF A STABLE OHMIC CONTACT TO CDTE THIN-FILMS THROUGH THE DIFFUSION OF P FROM NI-P

Thin films of CdTe used in electronic devices often have problems with electrical contacts. This is due to the non-availability of a contacting material with a large work function for proper matching with p-CdTe. Moreover, the method of doping the thin film is the real problem. There are several possible solutions in this connection, one of which is the formation of a p+ layer on the CdTe surface by the reaction or indiffusion of dopant materials. Another approach is to engineer the barrier height prior to the metal contact deposition by depositing a layer of Cu-doped ZnTe onto the CdTe. However, all of the above methods have their own limitations. In this paper a method is presented which can overcome these limitations. Using an autocatalytic reduction process, Ni-P composite material has been deposited successfully on the p-CdTe surface. On annealing at an optimum temperature of 250-degrees-C, the contact resistivity comes down to 0.1-0.08 OMEGA cm2. XRD and EDAX studies reveal that the lowering of the contact resistance is due to the diffusion of P into the CdTe with the formation of a p+ layer. A model for this has also been presented in the text.