研究目的
Investigating the bandgap renormalization, carrier multiplication, and Stark broadening in photoexcited black phosphorus using time and angle resolved photoelectron spectroscopy.
研究成果
The study concludes that in photoexcited black phosphorus, electrons relax to the conduction band minimum within 1 ps with negligible carrier multiplication and bandgap renormalization. A Stark broadening of the valence band occurs due to inhomogeneous screening of near surface fields, altering the chemical potential pinning.
研究不足
The study is limited by the moderate photoexcitation density and the 3D screening of the Coulomb interaction, which may affect the detection of bandgap renormalization and carrier multiplication.
Time-resolved ARPES experiments are performed on the femto-ARPES setup, using a Ti:sapphire laser system delivering 50 fs pulses at 1.57 eV (790 nm) with a 250 kHz repetition rate. Part of the laser beam is used to generate 6.3 eV photons through cascade frequency mixing in BaB2O4 (BBO) crystals. The 1.57 and 6.3 eV beams are employed to photoexcite the sample and induce photoemission, respectively. The overall energy resolution of the experiment is ~30 meV whereas the cross correlation between pump and probe pulse has Full Width Half Maximum FWHM of 0.16 ps. All data have been acquired with p polarized probe at an incident angle of 45°. Single crystals of black phosphorous grown from ‘HQgraphene’ have been cleaved and measured at the base pressure of 7 × 10?11 mbar.
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