Formation of Mg₂Si_1−xSn_x Thin Films by Co-sputtering and Investigation of their p-type Electrical Conduction

Abstract

We obtained Mg₂Si_1−xSn_x films on the c-plane sapphire and the (100) CaF₂ substrates using the radio frequency (RF) magnetron co-sputtering method under various sputtering area ratio of Mg chips to Mg₂Si (Sn) target and a subsequent two-step annealing process up to 400 °C. The X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDS) analysis of the samples confirmed that the obtained films were ternary Mg₂Si_1−xSn_x films with a composition of x ≈ 0.31. Optical microscopy and EDS mapping images of Mg₂Si and Mg₂Si_1−xSn_x (x = 0.31) films after annealing at 400 °C showed remarkable Mg desorption from Mg₂Si_1−xSn_x films, but not from Mg₂Si films. The Hall effect measurements revealed that all Mg₂Si_1−xSn_x films annealed at 400 °C had a p-type conductivity. The first-principles calculations suggested that a combination of two different types of defects, Sn substitution at Si site (Sn_Si) and Mg vacancy (V_Mg), which acts as an acceptor, could be the origin of the p-type conductivity of Mg₂Si_1−xSn_x films.