Electron dynamics in Ge crystals studied by terahertz emission from photoexcited surfaces

Abstract

A systematic study of terahertz (THz) emission from Ge surfaces excited by femtosecond laser pulses was accomplished. THz transients emitted by differently doped Ge crystals were investigated both experimentally and theoretically by using Monte Carlo modelling. The dependences of the radiation spectra on the crystal doping level have indicated that the main mechanism leading to the THz emission is cold plasma oscillation; the same polarity of the transients emitted from n- and p-type Ge suggests that this oscillation was activated by the photo-Dember effect at the semiconductor surface. The optical pump–THz probe experiment and corresponding numerical calculation had revealed the details of the photoexcited electron redistribution among different conduction band valleys.