Identifying incoherent mixing effects in the coherent two-dimensional photocurrent excitation spectra of semiconductors

TL;DR

This paper investigates incoherent mixing effects in 2D coherent photocurrent spectra of semiconductors, demonstrating how such effects can be identified and distinguished from coherent signals in experimental data.

Contribution

The study simulates incoherent population mixing in photocurrent signals and proposes a strategy to detect its presence in 2D spectroscopy data.

Findings

Incoherent mixing causes cross-talk between linear amplitudes at different delays.

No strict phase correlation is observed between coherent and incoherent signals.

A method to recognize incoherent effects in 2D spectra is identified.

Abstract

We have previously demonstrated that in the context of two-dimensional (2D) coherent electronic spectroscopy measured by phase modulation and phase-sensitive detection, an \emph{incoherent} nonlinear response, due to pairs of photoexcitations produced via linear excitation pathways, contribute to the measured signal as unexpected background [Gr\'egoire et al., J.\ Chem.\ Phys. \textbf{147}, 114201 (2017)]. Here, we simulate the effect of such incoherent population mixing in the photocurrent signal collected from a GaAs solar cell by acting externally on the transimpedance amplifier circuit used for phase-sensitive detection, and we identify an effective strategy to recognize the presence of incoherent population mixing in 2D data. While we find that incoherent mixing is reflected by cross-talk between the linear amplitude at the two time-delay variables in the four-pulse excitation sequence, we do not observe any strict phase correlations between the coherent and incoherent contributions, as expected from modelling of a simple system.