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

TL;DR

This study investigates ultrafast carrier dynamics in thin Bi2Se3 films, revealing how carrier recombination is influenced by film thickness and surface defect charge trapping, with implications for optoelectronic applications.

Contribution

It demonstrates the impact of film thickness and surface defect charge trapping on carrier recombination dynamics in Bi2Se3 topological insulator films.

Findings

Recombination involves radiative and non-radiative processes between Dirac surface states.

Recombination is enhanced in films below approximately 20 nm due to bulk electron depletion.

Charge trapping on surface defects influences ultrafast carrier dynamics.

Abstract

Transient reflectivity (TR) from thin films (6 - 40 nm thick) of the topological insulator Bi2Se3 reveal ultrafast carrier dynamics, which suggest the existence of both radiative and non-radiative recombination between electrons residing in the upper cone of initially unoccupied high energy Dirac surface states (SS) and holes residing in the lower cone of occupied low energy Dirac SS. The modeling of measured TR traces allowed us to conclude that recombination is induced by the depletion of bulk electrons in films below ~20 nm thick due to the charge captured on the surface defects. We predict that such recombination processes can be observed using time-resolved photoluminescence techniques.