Berlin 2024 – scientific programme
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O: Fachverband Oberflächenphysik
O 23: Ultrafast Electron Dynamics at Surfaces and Interfaces III
O 23.8: Talk
Tuesday, March 19, 2024, 12:15–12:30, MA 041
Efficient carrier multiplication in the topological insulator Bi2Se3 — •Michael Herb1, Leonard Weigl1, Niklas Hofmann1, Johannes Gradl1, Jason Khoury2, Leslie Schoop2, and Isabella Gierz1 — 1University of Regensburg — 2Princeton University
Carrier multiplication, where the absorption of a single photon results in the formation of multiple electron-hole pairs, significantly increases the quantum yield of photodetectors and solar cells. It commonly occurs in semiconductors for incident photon energies that significantly exceed the size of the band gap. This makes the topological insulator Bi2Se3 with a bulk band gap of only ~300meV a promising candidate for efficient carrier multiplication in the visible spectral range. Previous investigations of the non-equilibrium carrier dynamics in Bi2Se3 mainly focused on the topological surface state [1] and photovoltage effects [2]. We use time- and angle-resolved photoemission spectroscopy with visible 2eV pump pulses to investigate carrier dynamics inside the bulk bands. We find that the both the hole concentration in the valence band and the electron concentration in the conduction band keep increasing after the pump pulse is gone, providing direct evidence for the occurrence of carrier multiplication.
[1] Y. H. Wang et al., Phys. Rev. Lett. 2012
[2] M. Neupane et al., Phys. Rev. Lett. 2015
Keywords: carrier multiplication; topological insulator; impact ionization; ultrafast; photoemission