Theory of carrier dynamics and time resolved reflectivity in InMnAs/GaSb heterostructures

TL;DR

This paper presents a comprehensive theoretical model of time-resolved pump-probe reflectivity in InMnAs/GaSb heterostructures, accounting for carrier dynamics, phonon interactions, and various many-body effects, matching experimental observations.

Contribution

The work introduces a detailed Boltzmann equation-based model that includes carrier generation, relaxation, phonon emission, and trapping effects to explain pump-probe reflectivity signals.

Findings

Oscillations from coherent acoustic phonons are confirmed to be independent of ferromagnetism.

Background signals are explained by photoexcited carrier effects and many-body interactions.

Model successfully reproduces experimental differential reflectivity spectra.

Abstract

We present detailed theoretical calculations of two color, time-resolved pump-probe differential reflectivity measurements. The experiments modeled were performed on InMnAs/GaSb heterostructures and showed pronounced oscillations in the differential reflectivity as well as a time-dependent background signal. Previously, we showed that the oscillations resulted from generation of coherent acoustic phonon wavepackets in the epilayer and were not associated with the ferromagnetism. Now we take into account not only the oscillations, but also the background signal which arises from photoexcited carrier effects. The two color pump-probe reflectivity experiments are modeled using a Boltzmann equation formalism. We include photogeneration of hot carriers in the InMnAs quantum well by a pump laser and their subsequent cooling and relaxation by emission of confined LO phonons. Recombination of electron-hole pairs via the Schockley-Read carrier trapping mechanism is included in a simple relaxation time approximation. The time resolved differential reflectivity in the heterostructure is obtained by solving Maxwell's equations and compared with experiment. Phase space filling, carrier capture and trapping, band-gap renormalization and induced absorption are all shown to influence the spectra.