EMC/FDTD/MD for multiphysics characterization of semiconductors at THz frequencies

Doped semiconductors typically have characteristic scattering rates and plasma frequencies in the THz regime. As the stimulating frequency approaches the THz, otau ≈ 1, and the conductivity of doped semiconductors becomes complex and strongly frequency-dependent.;We have developed a multiphysics computational technique for semiconductor carrier transport at THz frequencies. The technique combines the ensemble Monte Carlo (EMC) simulation of carrier transport with the finite-difference time-domain (FDTD) solver of Maxwell's curl equations and the molecular dynamics (MD) technique for short-range Coulomb interaction. At each time step, electric and magnetic fields from FDTD and MD influence EMC carrier motion according to the Lorentz force. Likewise, microscopic currents from carrier motion in the EMC influence FDTD electric field updates according to Ampere's law, and EMC charge density defines MD fields according to Coulomb's law.;The strength of the EMC/FDTD solver was first established though characterization of silicon of low doping density. We demonstrated the necessity for rigorous enforcement of Gauss's law for FDTD solvers with charged particles. This work established new understanding of the capabilities of FDTD to accurately predict the diverging fields surrounding charges in semiconductors. The technique was extended to high carrier density materials through incorporation of MD. A new technique has been developed to combine electric fields from MD with electromagnetic fields from FDTD without double counting the fields. The complex conductivity calculated by EMC/FDTD/MD shows excellent agreement with experimental data for silicon of doping density n0 = 5.47 x 1014 and 3.15 x 1016 cm3 under THz-frequency stimulation.;The EMC/FDTD/MD technique was further extended to describe the exchange interaction between indistinguishable electrons, by assuming a finite electron radius. The addition of this description allows EMC/FDTD/MD to accurately describe carrier dynamics in materials with n0 ≥ 1018 cm-3. EMC/FDTD/MD was used to predict the complex conductivity of doped silicon at room temperature for n0 = 1014--1019 cm -3 and f = 0--2.5 THz. The results of this calculation are of immediate value to researchers in THz materials and device design. The prediction establishes the strength of EMC/FDTD/MD for THz-frequency characterization of high-conductivity materials.