Atomic ordering effect on SiGe electronic structure

In this paper, a realistic atomic model is used to study the atomic ordering effect on electronic structures of Si_0.5Ge_0.5. The hybrid density functional theory (DFT), HSE06, is chosen as the methodology. The calculated bandgap and effective masses of Si and Ge at various symmetry points are first validated by the reported experimental data and empirical pseudo-potential method (EPM) calculations. The study of two different Si_0.5Ge_0.5 atomic configurations shows that the SiSi-GeGe case is more stable than SiGe-SiGe (RS2 structure). In addition, the electron effective masses of the former one are larger than those of the latter one, and those calculated by EPM with virtual crystal approximation (VCA). This large electron effective mass is attributed to the localized electron orbital of the lowest anti-bonding state in the SiSi-GeGe case which leads to a flat E-k curve. However, no obvious ordering effect on hole effective mass is found.