Formation and Optical Properties of Thin Mg<sub>2</sub>Ge Films on Si(001) Substrate

Abstract

Thin Mg2Ge films were grown using two methods: a co-deposition of Ge and Mg on Si substrate kept at room temperature followed by annealing at 200 °C (solid phase epitaxy – SPE) and reactive deposition epitaxy (RDE) of Ge and Mg on Si at 200 °C. Optical properties of these structures were investigated in the photon energy range of 0.02–6.2 eV. Based on optical functions calculation, it was shown that SPE growth results in formation of a crystalline layer of Mg2Si, which exhibits a strong optical phonon originated from the substrate-film interface. In the case of RDE growth, the amount of Mg2Si is sufficiently lower, but Mg‑Si-Ge compound phonon appears. The estimate of a fundamental indirect transition value in the film is 0.72 eV for SPE growth method and 0.56 eV for RDE due to the ternary compound Mg-Ge-Si at the film-substrate interface.