Current transport and structural model for Li-diffused CdTe low-resistance contacts

Abstract

Low-resistance contacts to p-type CdTe have been made by diffusing Li into the CdTe surface before evaporation of Au as the contact metal. The best contact showed a contact resistivity of 2.1×10−3 Ω cm2 at room temperature, and 3.7×10−2 Ω cm2 at liquid N2 temperature, the lowest values reported to date for p-type CdTe. Surface analysis of the Li-diffused surface indicates that the crystalline structure of the CdTe surface has been greatly disturbed and a Te-rich surface layer is produced. Te tends to out-diffuse with time through the Au layer to restore the stoichiometric Te/Cd ratio in the CdTe. A metal-insulator-semiconductor tunnel diode model qualitatively explains the observed current-voltage characteristics of the contacts. Numerical analysis shows good agreement between the calculated contact resistivities and the experimental data. Surface states and fixed charges in the insulator play an important role in the current-voltage characteristics through the modification of metal work function and the distribution of the applied voltage. Contact resistivity increases with decreasing hole concentration, but the effect is small if a high enough density of interface states dominates the properties of the contact.