Effective mass anomalies in strained-Si thin films and crystals

Using first-principles calculations, effective mass for silicon channel region is investigated as a function of strain and substrate thickness. In {111} and {110} biaxially strained-Si, it is found that the longitudinal effective mass is extraordinarily enhanced for both thin films and crystals. This mass enhancement is caused by the change of the band structure with double minima into that with a single minimum due to strain and confinement. It is analytically shown that the effective mass diverges at the transition point. Further, we suggest the parameter regions of the strain, thickness, and confinement direction, which are most suitable for the experimental observation of the anomalies.