Band Gap Renormalization, Carrier Multiplication, and Stark Broadening in Photoexcited Black Phosphorus.
basic_science · Level V
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- Record sourced from PubMed, PMID 30525684.
- Also identified by DOI 10.1021/acs.nanolett.8b04344.
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Abstract
We investigate black phosphorus by time- and angle-resolved photoelectron spectroscopy. The electrons excited by 1.57 eV photons relax down to a conduction band minimum within 1 ps. Despite the low band gap value, no relevant amount of carrier multiplication could be detected at an excitation density 3-6 × 10<sup>19</sup> cm<sup>-3</sup>. In the thermalized state, the band gap renormalization is negligible up to a photoexcitation density that fills the conduction band by 150 meV. Astonishingly, a Stark broadening of the valence band takes place at an early delay time. We argue that electrons and holes with a high excess energy lead to inhomogeneous screening of near surface fields. As a consequence, the chemical potential is no longer pinned in a narrow impurity band.