Diffusion-free ultrafast carrier dynamics in silicon nano-pillars

TL;DR

This study investigates ultrafast carrier dynamics in silicon nano-pillars using pump-probe reflectivity, revealing high carrier densities, rapid electron-phonon interactions, and recombination times up to 10 ns, with diffusion effects eliminated by structure design.

Contribution

The paper demonstrates a method to study ultrafast carrier dynamics in silicon nano-pillars without diffusion influence, providing new insights into recombination and electron-phonon interactions.

Findings

Recombination time up to 10 ns at high carrier density

Electron-phonon interaction occurs within 350-400 fs

Reflectivity change up to 8% at strong pumping

Abstract

We have investigated ultrafast carriers dynamics in crystalline silicon nano-pillars structure using a pump-probe reflectivity method with 800 nm, 150 fs laser pulses and fluence in the range of {17 - 170} mJ/cm^2. Dimensions of the structure allow us to eliminate contribution from the diffusion process to the relaxation dynamics of the excited carriers. Strong intensity-dependent time-resolved reflectivity change, \Delta R(\tau_d), was monitored in the submelting regime. At strong pumping \Delta R(\tau_d) can reach up to 8%, a several times higher than for a bulk silicon. From the measurements we deduced recombination time of up to 10 ns at carriers density of ~1 x 10^20 cm^-3, while electron-phonon interaction occurs during 350-400 fs and it is independent of the concentration.