Controllable preparation and superconducting properties of tantalum films with different orientations

Abstract

Transmon qubits based on $\alpha$-Ta films have been demonstrated to possess long lifetimes, sparking significant interests among researchers in this material. In this study, we systematically investigated the growth conditions of $\alpha$-Ta films on sapphire substrates. By controlling the growth temperature and power, we successfully prepared films with two distinct crystal orientations: $\alpha$-Ta [110] and $\alpha$-Ta [111]. We found that the growth conditions with low power and low temperature, as well as that with high power and high temperature, are conducive to the growth of $\alpha$-Ta [110], while the low power combined with high temperature favors the growth of $\alpha$-Ta [111]. The critical transition temperature $T_c$ of the [111]-oriented film increases more gently with the increase of residual resistance ratio (RRR) compared to the [110]-oriented film. Additionally, our result indicates that as the thickness of the $\alpha$-Ta [111] film increases, the values of both $T_c$ and RRR rise, with the highest RRR value of 24.6. Our results provide important references for the preparation of high-quality $\alpha$-Ta thin films.