Co/GeTe interfacial reactions and Co-Ge-Te phase equilibria

Abstract

BackgroundGeTe is an important medium-temperature thermoelectric material, and Co is often used as a diffusion barrier layer. This study examines the interfacial reactions between Co and GeTe to verify the suitability of Co as a barrier layer. This study also determines the phase diagram of the Co-Ge-Te ternary system to provide basic material system knowledge and for better understanding the interfacial reactions. MethodsThe Co-Ge-Te phase diagram is determined based on the experimental results of this study, those related in the literature, and the phase diagrams of its three binary constituent systems. The Co/GeTe couples are prepared by plating Co layer on the GeTe substrate, and then reacted at 500 °C and 400 °C. Significant findingsIt is found the Ge0.5Te0.5 is of rhombohedral structure at 500 °C, gradually transforms to a cubic structure with increasing Te content, and the results differ from those in the literature. There are 15 single phases at 500 °C and 400 °C in the Co-Ge-Te ternary system, including two ternary compounds, Co2Ge3Te3 and CoGeTe. In the Co/GeTe couples reacting at 500 °C for 14 days, Co2Te3, Co5Ge3, CoGe and CoGeTe are formed, and the thickness of the reaction layer is about 80 μm. At 400 °C for 50 days, CoGe2, Co5Ge3 and Co2Te3 are formed, and the thickness of the reaction layer is about 12 μm. At both 500 °C and 400 °C, Co is the primary diffusion species in the Co/GeTe reaction couples. The results suggest Co is not a suitable barrier layer for GeTe at 500℃.