Ultrafast Dynamics of the Surface Photovoltage in Potassium Doped Black Phosphorus

TL;DR

This study investigates the ultrafast dynamics of surface photovoltage in potassium-doped black phosphorus, revealing how photoinduced effects influence band structure and surface dipoles over picosecond to nanosecond timescales.

Contribution

It provides detailed experimental and simulation insights into the transient behavior of surface photovoltage and band structure evolution in doped black phosphorus.

Findings

Surface photovoltage rises quickly and plateaus for tens of picoseconds.

The photovoltage decays over nanoseconds, indicating partial screening effects.

Simulations match experimental dynamics, confirming drift-diffusion processes.

Abstract

Black phosphorus is a quasi-two-dimensional layered semiconductor with a narrow direct band gap of 0.3 eV. A giant surface Stark effect can be produced by the potassium doping of black phosphorus, leading to a semiconductor to semimetal phase transition originating from the creation of a strong surface dipole and associated band bending. By using time- and angle-resolved photoemission spectroscopy, we report the partial photoinduced screening of this band bending by the creation of a compensating surface photovoltage. We further resolve the detailed dynamics of this effect at the pertinent timescales and the related evolution of the band structure near the Fermi level. We demonstrate that after a fast rise time, the surface photovoltage exhibits a plateau over a few tens of picoseconds before decaying on the nanosecond timescale. We support our experimental results with simulations based on drift-diffusion equations.