Characteristic timescales of carrier dynamics in sulfur-hyperdoped silicon probed by femtosecond laser optical pump/THz probe pulses

Non-invasive local time-resolved THz transmission studies probe structural effects of free carrier-lattice interactions in crystalline microelectronic nanostructures with elaborate fabrication history. In our study, this method was utilized for structural and electronic characterization of 450-nm thick surface nanolayers of crystalline silicon Si(100) wafers, implanted by sulfur (S) at variable S-concentrations (C S ∼ 10 19 -10 21 cm −3 ) and post-annealed by a nanosecond laser (pulsed laser annealing, PLA). 800-nm 40-fs laser pulses linearly excited moderate electron-hole plasma densities ∼10 19 -10 20 cm −3 at low variable fluence of 10–10 2 μJ/cm 2 in the reference c-Si sample over the indirect absorption depth of 10 μm, and probed such plasma in a transmission mode by time-delayed fs-laser generated THz pulses to reveal its sub-picosecond carrier scattering times within the probe pulse (underdamped plasma), and carrier lifetimes on the multi-nanosecond timescale. Likewise, moderately hyperdoped (C S ∼ 10 19 -10 20 cm −3 ) Si samples with the deep S-donor centers follow the trends for c-Si due to the minor contributions of their thin hyperdoped layers to THz absorption. In contrast, in the heavily hyperdoped (C S ∼ 10 21 cm −3 ) Si samples the THz absorption coefficients drop for the much shorter damage defect/impurity-driven carrier scattering times for both such (un)annealed hyperdoped samples. The fs-laser optical pump/THz probe studies enlightened the structural features of the hyperdoped samples, which affect their key electronic characteristics – carrier mobility and lifetimes – as a function of implanted S-concentrations and post-implantation laser annealing.