Study of Mg2Si Thin Film and Ultra-Thin Film Formation for Thermoelectric Applications

Mg2Si thin and ultra-thin films are grown on silicon (Si) substrates by performing heat treatments of Magnesium (Mg) layers deposited on Si (100), using radio frequency (RF)-sputtering and molecular beam epitaxy (MBE) techniques. In order to investigate the effect of annealing parameters on the formation of Mg2Si thin films, we conducted heat treatments under vacuum for some samples and in an argon gas atmosphere for others. X-ray diffraction (XRD) analysis of the thin films annealed in both environments confirms the formation of polycrystalline Mg2Si. This characterization also reveals that the formation of this compound depends on duration and pressure for the vacuum annealing and on temperature for the argon gas atmosphere annealing. Here, we report that the vacuum annealing is a good choice for Mg2Si thin film formation because the low temperature of the process is condusive to silicon technology. Some optimum parameters for obtaining Mg2Si thin films are proposed in this paper. Auger electron spectroscopy (AES) characterization technique confirms the formation of Mg2Si ultra-thin films at an annealing temperature of 200°C and under an ultra-high vacuum (UHV). In addition, scanning tunneling microscopy (STM) characterization indicates a nanosized grain formation of this compound with average size of approximately 20–40 nm.