Ambipolar diffusion of photo-excited carriers in bulk GaAs

TL;DR

This study investigates how photo-excited carriers diffuse in bulk GaAs across different temperatures using ultrafast pump-probe techniques, revealing temperature-dependent ambipolar diffusion coefficients that align with mobility data.

Contribution

It provides new measurements of ambipolar diffusion coefficients in bulk GaAs over a range of temperatures using a high-resolution ultrafast optical method.

Findings

Diffusion coefficients decrease from 170 to 20 cm²/s as temperature rises.

Results are consistent with previous mobility-based measurements.

Carrier dynamics are effectively monitored with spatial and temporal resolution.

Abstract

The ambipolar carrier diffusion in bulk GaAs is studied by using an ultrafast pump-probe technique with a high spatial resolution. Carriers with a point-like spatial profile are excited by a tightly focused pump laser pulse. The spatiotemporal dynamics of the carriers are monitored by a time-delayed and spatially scanned probe pulse. Ambipolar diffusion coefficients are deduced from linear fits to the expansion of the area of the profiles, and are found to decrease from about 170~$\mathrm{cm}^2 \mathrm{s}^{-1}$ at 10 K to about 20~$\mathrm{cm}^2 \mathrm{s}^{-1}$ at room temperature. Our results are consistent with those deduced from the previously measured mobilities.