Growth, morphology and crystal structure of electrodeposited Bi2Se3 films: Influence of the substrate

Abstract

In this study, we investigated the growth, morphology and crystal structure of electrodeposited Bi2Se3 films on n-Si, Au and Ru substrates. The range of potentials at which films with good quality and stoichiometry can be grown have been identified. Scanning electron micrographs of the early stages of nucleation and growth suggests the film formation on all three substrates follow the Volmer-Weber growth mode. In the case of Si substrate, a pure orthorhombic phase of Bi2Se3 could be grown which is influenced by the epitaxy of the Si substrate. The Faradaic efficiency of film growth on Si substrate was found to be around 90%. However, on Au and Ru substrates, growth of mainly the rhombohedral phase could be achieved having relatively lower Faradaic efficiencies of 68% and 78%, respectively. The Bi2Se3 films grown on Au at more negative potentials were found to exhibit improvements in the rhombohedral crystal phase. Low temperature annealing was found to transform the orthorhombic or mixed phase crystal structure to that of pure rhombohedral. The onset of phase transformation in the mixed phase Bi2Se3 films (on Au) was found to be around 125 °C, determined using in-situ Raman spectroscopy. Aside from the temperature, the duration of heat treatment is identified to play a crucial role in this phase transformation. Based on our findings on room temperature deposition, we conclude that the growth of pure orthorhombic phase is favored on Si, while on Au and Ru, growth of the rhombohedral or mixed phase of Bi2Se3 could be achieved.