The role of interfacial reactions in Pt/CdTe contact formation
The reactions at the interface between CdTe and the contact metal platinum have been studied using various approaches including theoretical and experimental ternary phase diagram determination, bulk and thin film diffusion couples and electrical characterization of elemental and compound contacts on p- and n-Cd0.95Zn0.05Te (CZT). At the interface of Pt/CdTe diffusion couples a non-planar reaction layer of the intermetallics PtCd and PtTe is formed. This is consistent with the studied ternary phase diagram. Additional compounds which are stable in direct contact to CdTe can also be identified using these data. The contact barrier heights of pure Pt and of alloys with Cd or Te on CZT substrates and their variation after various annealing procedures were determined both on etched (Te-rich) and on virtually stoichiometric CZT surfaces. All the Pt-based contacts on the etched CZT surface showed a similar behaviour, determined by the Te excess and the ensuing formation of PtTe in direct contact to CZT. In contrast to that, a wide range of electrical properties can be achieved on the stoichiometric surface by deposition of Pt with or without additional Cd or Te interlayers due to the variety of phases forming in direct contact to CZT after deposition and annealing.