Effects of post-annealing on crystalline and transport properties of Bi_(2)Te_(3) thin films

A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to obtain high-quality Bi_(2) Te_(3) films with the carrier density down to 4.0 × 10^(13) cm^(-2). In contrast to the most-used method of high substrate temperature growth, we firstly sputtered Bi_(2) Te_(3) thin films at room temperature and then applied post-annealing. It enables the growth of highly-oriented Bi_(2) Te_(3) thin films with larger grain size and smoother interface. The results of electrical transport show that it has a lower carrier density as well as a larger coherent length(~ 228 nm, 2 K). Our studies pave the way toward large-scale, cost-effective production of Bi_(2) Te_(3) thin films to be integrated with other materials in wafer-level scale for electronic and spintronic applications.

Correlation between pass-through flux of cobalt target and microstructure and magnetic properties of sputtered thin films

Cobalt thin films were deposited on silicon substrates by magnetron sputtering two commercial cobalt targets with different pass-through fluxes(PTFs).The influences of PTF on the magnetic properties of sputtered thin films were investigated.The results indicate that under the same sputtering conditions,cobalt thin film deposited by Co target with high PTF(84.21%) has lower remanence ratio(0.65),while cobalt thin film prepared by Co target with low PTF(69.13%) has higher remanence ratio(0.87).Through introducing an external magnetic field parallel to the film surface during sputtering processes,both the remanence ratios of cobalt thin films prepared by the two targets can be enhanced to approach 1.High-resolution transmission electron microscopy(HRTEM) images show that in the absence of the external magnetic field during sputtering,cobalt thin film deposited by the target with high PTF is randomly oriented in crystallographic orientations,which is due to that Co atoms have no enough time to migrate and diffuse on substrate and the atomic stacking is disordered.It is worth mentioning that crystallographic orientations of cobalt thin film deposited by target with low PTF are relatively consistent,resulting in relatively higher remanence ratio.In addition,HRTEM analysis indicates that the external magnetic field during sputtering drives the Co grains to arrange in a regular order with(002) orientation,leading to the improvement in remanence ratios.