Effect of surface states and in-plane deformation on transport properties of charge carriers in bismuth films

Abstract

Since the energy spectrum of bismuth charge carriers is highly sensitive to mechanical deformations, studying their influence, leading to an increase or decrease in the overlap of actual extrema, on the transport properties of charge carriers in ultrathin bismuth films makes it possible to investigate the combination of manifestations of the quantum size effect and metallic surface states. In this work, the temperature dependencies of the electrical and galvanomagnetic properties of thin bismuth films (10–1250 nm) are studied under conditions of in-plane tensile and compressive deformation. Deformations are created as a result of the difference in the coefficients of thermal expansion of the film and substrate materials. Silicon with an oxidized surface, mica, and polished cleavage (111) CaF2 are used in order to create either tensile and compressive deformations. The presence of film deformations is confirmed by XRD. The magnitude of deformation is calculated based on the CTEs of the materials. The absence of mechanical stress relaxation or the formation of additional defects during temperature measurements is confirmed by the absence of hysteresis of properties in the range of 77–300 K. Based on the experimental results, the mobilities and concentration of charge carriers are calculated within the framework of the two-band model. As the film thickness decreases to less than 100 nm, an increase in the charge carrier concentration is observed, which is associated with metallic surface states. It is shown that the magnitude of the effect of deformation on the concentration of charge carriers in films of all thicknesses remains unchanged.