Linear optical response of Si1-xGex compounds

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(001) 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 e(ω) = e 1 (ω) + i e 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.