The first principle study of the electronic structure of SixGe(1−x) alloy films

Highlights: • The band gap of SiGe alloy film is related to the thickness of the film and the content of silicon. • Band gap maps are given in different films thicknesses and Si content. • The change maps of direct band gap and indirect band gap of SiGe alloy films are given. - Abstract: First principles calculation based on density functional theory (DFT) with the generalized gradient approximation (GGA) are carried out to investigate the electronic band structures of ${\text{Si}}_x{\text{Ge}}_{(1-x)}$ alloys nanofilms. The calculation results show that the band gaps of (100), (110) and (111) surfaces ${\text{Si}}_x{\text{Ge}}_{(1-x)}$ alloy films with different thickness first increase with the increase of Si content, then flatten out, and finally decrease. At the same time, the transformation of direct band gap and indirect band gap occurs when the thickness of films and Si content of the three surface ${\text{Si}}_x{\text{Ge}}_{(1-x)}$ alloy films changes to a certain critical condition. It will be a good way to obtain direct-gap band emission in ${\text{Si}}_x{\text{Ge}}_{(1-x)}$ alloys materials.