First Principle Study of Si and Ge Band Structure for UTB MOSFETs Applications

Ab initio study of the band structures of Si and Ge thin film is conducted for all common surface orientations with film thickness ranging from 4nm to 1nm. The ab initio calculation predicts features not captured by the conventional effective mass approximation such as the deviation from isotropic energy dispersion for one of the two-fold degenerate Delta valleys at G for Ge<100> and shifting of Delta valley minima towards G as film thickness decreases for Ge<110>.It also offers more reliable insights into the problem of L and Delta valleys competition for carrier occupation in Ge<100> and Ge<110>. Our study predicts that Ge thin film band structure at <110> surface with [110] channel direction has the highest average hole/electron carrier velocity down to a body thickness of 1nm, making it a promising candidate for aggressively scaled UTB MOSFETs