The electronic structure dependence of silicon composition in SiGe alloy: A DFT study on meta-GGA level

The density functional theory (DFT) study on two variation of SiGe alloy (Si_0.50Ge_0.50 representing 50:50 ratio; Si_0.25Ge_0.75 representing 25:75 ratio) are reported in this study by utilizing a parameter-free functional named SCAN (strongly-constrained and appropriately normed). The SCAN functional is within meta-generalized gradient approximation (meta-GGA) level of accuracy. It was known from previous DFT studies based on LDA/GGA functional, germanium (Ge) system is predicted to be a metal instead of insulator, limiting the understanding on SiGe alloy without any parameterization included. By using the SCAN functional, we observed that the lattice parameter of SiGe alloy will increased with the reduction of Si-content inside the system. From the density of states figure we obtain an insulating gap value of 0.89 eV, while Si_0.25Ge_0.75 alloy shows a lower value of 0.75 eV. Our results indicate that the reduction gap effects caused by the increasing of Ge-content is captured properly and well-matched with the known experimental data.