Understanding interfacial compounds induced by Ag diffusion on improving interface electrical contact resistivity between the Cu electrode and Bi2Te3 thin film

It has been reported that introducing Ag interlayer at the Cu/Bi ₂Te ₃ interface can achieve ultra-low electrical contact resistivity. However, there is no consensus on the influence of Ag diffusion induced by Ag interlayer on electrical contact. Thus, the impact of Ag diffusion on electrical contact conductivity for Cu/Ag/Bi ₂Te ₃ multilayers was investigated. The generation of interfacial compounds induced by Ag diffusion was analyzed and the contact resistivity was measured in Cu/Ag/Bi ₂Te ₃ multilayers with different Ag interlayer thickness before and after annealing. It was found that Ag diffusion induced interfacial compounds Cu ₄Ag ₃Te ₄ at the Cu/Ag interface before annealing, which could decrease contact resistivity to 3.728×10 ⁻¹² Ω∙m ². After annealing, the relative amount of Cu ₄Ag ₃Te ₄ at the Cu/Ag interface slightly decreased, and the Ag ₂Te was found to appear at the Ag/Bi ₂Te ₃ interface, which could further decrease contact resistivity to 3.187×10 ⁻¹² Ω∙m ². With Ag interlayer thickness increasing from 50 nm to 300 nm, the contact resistivity decreased from 3.726×10 ⁻¹⁰ Ω∙m ² to 3.728×10 ⁻¹² Ω∙m ² before annealing because the relative amount of Cu ₄Ag ₃Te ₄ increased about 5 times, after annealing the contact resistivity further decreased by 10.27∼41.7 % because the relative amount of Ag ₂Te increased about 1.1 times. In addition, we had optimized the ultra-low contact resistivity test method by redesigning the structure of test samples and modifying the formula of contact resistivity to eliminate two errors. One is caused by Cu electrode short-circuit resistance due to the test current being short-circuited by the middle electrode between two test electrodes. The other is caused by the increased electrical resistance of Bi ₂Te ₃ thin film due to Te atom volatilization after annealing. The results showed that the errors of the test results were reduced by at least 21.50 %. Our work provides guidance for further optimizing electrical contact of thin-film thermoelectric devices.