Optimization of Si1-xGex/Si waveguide photodetectors operating at λ=1.3 μm

This paper analyzes the influence of various design parameters in the external quantum efficiency (QE) of waveguide detectors based on Si/Si_1-xGe_x strained-layer superlattices (SLSs), for use in optical communications at λ=1.3 μm. The study presents an algorithm that automatically generates structurally stable SLSs. This generation is completed by intensive simulation of the generated SLSs to calculate the external QE. The simulation embraces optical waveguiding, absorption, quantum size effect, as well as thermodynamics of the strained layers. Two sets of data were created using two different models for the SiGe layer critical thickness, h_c(x). A conservative model for h_c, corresponding to the equilibrium regime, yielded discrete maximum values for QE (around 12%) that were mainly dependent on the alloy absorption. A second model for h_c, corresponding to the metastable regime, produced considerably higher QEs (around 60%), and shows the great importance of fiber-to-waveguide coupling efficiency. The importance of the passive-waveguide coupler geometry is investigated using the beam propagation method