Investigation of the relationship between Fe2VAl-based thin films sputtered of silicon and their bulk analogon with respect to the thermoelectric properties

Abstract

In this work, the thermoelectric properties of Heusler substrate-film systems are investigatedbased on (Fe2/3V1/3)75+xAl25–x compounds with x = {-4-;3; 3; 4} and comparedwith their bulk analogons. Seebeck measurements of bulk samples show absolute values of up to 100 μV/K, whereas annealed films on silicon substrates exhibit absolute values exceeding 600 μV/K. To investigate this rise of S, measurements of silicon wafers are performed to quantify the influence of the substrate on the total Seebeck coefficient. Silicon wafers, which were produced using the Czochralski method,show a drop in resistivity after annealing, due to oxygen contamination during productionof the wafers. Together with silicon’s Seebeck coefficient, this leads to aconsiderable contribution to the total measured Seebeck coefficient. For simplification purposes, aluminium, chromium and stoichiometric Fe2VAl films are manufactured to showcase their behavior on silicon substrates. High absolute values of the Seebeck coefficients of about 500 μV/K are achieved, when using very thin films, which have no relevant Seebeck coefficient themselves. For the purpose of subsequently reducing the film’s thickness, a sputter etching module is introduced into the sputtering device. Furthermore, a mathematical model to describe the angle- and distance-dependentsputtering rate is developed to increase the homogeneity of the film by optimization of the distance between sputter target and substrate