Electronic structure of epitaxial half-Heusler Co1-xNixTiSb across the semiconductor to metal transition

Abstract

Here, we report on the growth, electronic, and surface properties of the electron-doped half-Heusler series Co1-xNixTiSb (001) grown by molecular beam epitaxy. High-quality epitaxial growth of thin films is achieved on InP (001) substrates using an InAlAs buffer layer for all nickel concentrations. The semiconductor to metal transition as a function of substitutional alloying was examined using electrical transport, Seebeck measurements, and angle-resolved photoemission spectroscopy (ARPES). Temperature-dependent electrical transport measurements of films with composition x ≤ 0.1 exhibit thermally activated behavior while x > 0.1 exhibit metallic behavior. Smooth, highly ordered film surfaces can be achieved following ex-situ transfer of the films and subsequent desorption of a sacrificial, protective antimony capping layer. Using this transfer technique, ARPES experiments were performed to investigate the effects of nickel alloying on the electronic band structure. An electron pocket is observed below the Fermi level at the bulk X point for compositions x > 0.1, in accordance with the crossover from semiconducting to metallic behavior observed in the transport measurements.