Dielectric function of Si1-xGex films grown on silicon-on-insulator substrates

Abstract

The dielectric functions of undoped and P-doped Si1-xGex (SiGe) films with a compressive strain on silicon-on-insulator (SOI) substrates are obtained by using spectroscopic ellipsometry. The respective Kato-Adachi and Tauc-Lorentz models are best fitted to the undoped and P-doped SiGe films to obtain their complex dielectric functions. The undoped SiGe films are characterized by multimodal peaks in the dielectric function, whereas the P-doped SiGe films exhibit only a broad peak. Further, the E-0 and E-1 critical points (CPs) of the undoped SiGe films are strongly dependent on the Ge concentration, whereas the E-2 CPs are independent of concentration. The E-0 and E-2 CPs in the undoped SiGe films on an SOI substrate are lower than those of SiGe on a bulk-Si substrate owing to the higher strain. For P doping in SiGe, its dose causes non-monotonic variations in E-g and E-0.