Effect of Mn doping on ultrafast carrier dynamics in thin films of the topological insulator Bi2Se3

TL;DR

This study investigates how manganese doping affects ultrafast carrier dynamics in Bi2Se3 topological insulator films, revealing doping-dependent scattering mechanisms and potential for high-speed optoelectronic applications.

Contribution

It demonstrates that Mn doping alters carrier relaxation pathways and enhances electron-phonon interactions in Bi2Se3 films, introducing a new approach to control ultrafast dynamics in topological insulators.

Findings

Carrier dynamics depend on Mn content and photoexcited carrier density.

Mn doping introduces electron trapping by Mn2+ acceptors.

Shortest decay time (~0.75 ps) observed at highest Mn doping.

Abstract

Transient reflectivity (TR) measured at laser photon energy 1.51 eV from the indirectly intersurface coupled topological insulator Bi2-xMnxSe3 films (12 nm thick) revealed a strong dependence of the rise-time and initial decay-time constants on photoexcited carrier density and Mn content. In undoped samples (x = 0), these time constants are exclusively governed by electron-electron and electron-phonon scattering, respectively, whereas in films with x = 0.013 - 0.27 ultrafast carrier dynamics are completely controlled by photoexcited electron trapping by ionized Mn2+ acceptors and their dimers. The shortest decay-time (~0.75 ps) measured for the film with x = 0.27 suggests a great potential of Mn-doped Bi2Se3 films for applications in high-speed optoelectronic devices. Using Raman spectroscopy exploiting similar laser photon energy (1.58 eV), we demonstrate that due to indirect intersurface coupling in the films, the photoexcited electron trapping in the bulk enhances the electron-phonon interaction strength in Dirac surface states.