Ultrafast dynamics of the surface photovoltage in potassium-doped black phosphorus

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.

Field-induced ultrafast modulation of Rashba coupling at room temperature in ferroelectric $α$-GeTe(111)

“…The SPV build up typically takes a few tens to a few hundreds of fs. 25,26 We performed drift-diffusion calculations on a GeTe surface (see Fig. S7), demonstrating that the pump-pulses completely suppress the initial BB after a few tens of fs, in excellent agreement with our experimental findings.…”

“…Drift-diffusion calculations -The drift-diffusion equations have been solved with a custom code as described in Ref. 26 using the parameters listed in the Extended data. Second derivative of static α-GeTe(111) ARPES spectrum Thermal surface state population ps, as fitted with an exponential decay.…”

“…builds up and modifies the electronic energy level diagram of the system. SPV is a well known phenomenon in semiconductors physics: 25,26 it corresponds to a photoinduced spatial redistribution of charge carriers and to a compensation of the pre-existing band bending (BB) in the surface charge region (SCR). Evidence of a positive SPV in our case is given in Fig.…”

Optical manipulation of Rashba-split 2-dimensional electron gas

“…More complex simulations of the PV effect such as those recently developed in ref. 40 might further improve quantitative accuracy. Nevertheless, the model captures the fundamental observations of the experiment and provides a clear explanation of the underlying mechanisms.…”

Driving ultrafast spin and energy modulation in quantum well states via photo-induced electric fields

“…The SPV photo-gating method can be extended to other semiconductor systems with 2D electron gases. In fact, a similar gating method to the one presented here has been utilized successfully in black phosphorous to drive gap renormalization at the surface 68,69 . An example of a future application is a heterojunction system in which an exfoliated or MBE-grown 2D material is placed on top of an SPV substrate separated by a thin insulating layer.…”