Structure and resistivity of bismuth thin films deposited by pulsed DC sputtering

Abstract

Bismuth thin films have been deposited using pulsed DC magnetron sputter deposition under four deposition conditions, combining powers of 50 and 100 W and argon gas pressures, 2 and 10 mTorr. Estimated deposition rates were between 0.08 and 3.5 nm s⁻¹. The films were examined using scanning electron microscopy, cross-sectioning using a focussed ion beam (FIB), X-ray diffraction and sheet resistance and Hall effect measurement. Room temperature deposition gave a predominant orientational texture of (111) rhombohedral. However, higher film thickness, low sputtering power, high sputtering gas pressure and deposition onto a heated substrate above 125 °C increase the fraction of (110) orientation. FIB cross-sectioning indicates that films deposited at room temperature have an irregular crystalline structure with voids, but those grown at 160 °C are denser with a better polycrystalline structure. Transport measurements indicate a dominance of conduction by electrons, with films deposited at room temperature having high sheet resistance, low sheet resistance being favoured by low sputtering pressure. Deposition at higher temperatures improves the conductivity but increases the Hall coefficient.