Linear Optical Response of Si_(1-x)Ge_x Compounds

摘要

Si_(1-x)Ge_x is a good candidate as a substitute material for Si in a low-power and high-speed semiconductor device technologies. Optical devices, such as heterojunction bipolar transistors, are already in industrial production. The samples are grown on Si(00l) with both n-and p-type impurities and with different Ge concentrations. The linear optical response of Si_(1-x)Ge_x is investigated theoretically using a full-potential linearized augmented plane wave method with respect to composition x. The calculated real and imaginary parts of the dielectric function ε(ω) = ε_1 (ω) + iε_2(ω) were found to be in good agreement with recent spectroscopic ellipsometry measurements performed by Bahng et al., J. Phys.: Condens. Matter 13, 777 (2001). We also perform absorption measurements for different type of samples showing the variation of energy gaps as a function of Ge concentrations.