Estimation of external quantum efficiency of Ge rich Si1-x-yGexCy on Si photodetectors at 1.3 μm

In this paper, we have calculated the external quantum efficiency of Ge rich Si_1-x-yGe_xC_y on Si photodetectors at 1.3 mum assuming a large absorption coefficient of 2000 cm^-1 and 5000 cm^-1. For this purpose, the existing theory of band gap and band offset of ternary SiGeC alloy grown on Si as well as the reported absorption data for the Si_0.11Ge_0.88C_0.01 alloy has been used. The work involves the determination of the composition (values of x and y) of the alloy satisfying the band gap and absorption requirements. An iteration technique is employed to make this estimation from the experimental data to take into account the changes due to altered alloy composition and other effects. The external quantum efficiency for the photodetector with estimated composition is then calculated and its variation with detection length is shown for different values of detection layer thickness as parameters.