Numerical investigation of subpicosecond electrical pulse generation by edge illumination of silicon transmission-line gaps

The phenomena involved in the subpicosecond electrical pulses generated by edge illumination of a charged coplanar transmission line on silicon substrate are investigated theoretically using a two-dimensional numerical model. The calculated terminal current, which is related to the observed electrical signal, is interpreted as being due to the dielectric relaxation of the spacecharge field based on an equivalent circuit model. The pulse dependence (including amplitude, delay, rise time, and shape) on the wavelength of the laser source is investigated in terms of light penetration and the generated photocarriers. The frequency limit of the laser pulse train is determined theoretically for different carrier lifetimes. The simulation results are in qualitative agreement with experimental observations, and the dielectric relaxation interpretation is consistent with other theories based on the full-wave analysis and the Monte Carlo model.