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

TL;DR

This study investigates the ultrafast carrier dynamics in InSb using broadband THz spectroscopy with BNA crystals, revealing how photoexcited carriers diffuse and affect the material's spectral response over time.

Contribution

It introduces a broadband THz spectroscopy method with BNA crystals to analyze carrier dynamics in InSb, providing new insights into diffusion and density effects.

Findings

Carrier density as a function of pump-probe delay was extracted.

Diffusion length varies with carrier density and pump fluence.

Mismatch between THz penetration depth and excited sample depth was analyzed.

Abstract

We report an optical pump - terahertz (THz) probe study of the photoinduced transient carrier dynamics in the low bandgap semiconductor Indium Antimonide (InSb). Using an organic N-benzyl-2-methyl-nitroaniline (BNA) 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 material and the penetration depth of 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.