Exploration of Free Carrier Relaxation Dynamics in Bulk Gallium Arsenide

Multidimensional coherent spectroscopy (MDCS) is an ultrafast spectroscopic measurement that spreads coherent information across multiple dimensions, disentangling congested spectral features. Both coherent and incoherent transport processes, as well as their dynamics, can be easily separated and measured with MDCS. These attributes make MDCS ideal for studying complex material behaviors such as carrier-carrier scattering and exciton formation in semiconductors.

Here, we present MDCS spectra of bulk gallium arsenide (GaAs) showing strain-induced separation of the heavy-hole and light-hole exciton states¹, exciton formation from free carriers across a broad energy distribution, and relaxation from GaAs quantum wells in the same sample. The spectra clearly show the Sommerfeld enhancement of the free carrier absorption at long times, while early times show a transient feature related to the fast relaxation of states near the band-edge. We suspect that this transient feature is caused by correlated free carrier pairs or higher-lying excitonic states that form a quasi-continuum near the band edge.

[1] Wilmer et. al., Phys. Rev. B, 94, 2016.