Photo-induced carrier dynamics in InSb probed with broadband THz spectroscopy based on BNA crystals

We report an optical pump-terahertz (THz) probe study of the photo-induced transient carrier dynamics in the low bandgap semiconductor indium antimonide (InSb). Using an organic N-benzyl-2-methyl-nitroaniline crystal as a broadband THz source, we access the full spectral response over more than 5 THz, for varying pump-probe delay following the optical excitation. Using the Drude-Lorentz model accounting for differences between the excited length in the material and the penetration depth of the THz beam in pumped InSb, we extract the absolute carrier density as a function of the pump-probe delay and provide insights on the diffusion length at given carrier densities, for different pump fluences. The mismatch between the THz penetration depth and the actual excited sample depth after carrier diffusion is discussed, since their evolutions with time and pump fluence are not intuitive as both quantities depend on carrier density.