Spectroscopy of buried states in black phosphorus with surface doping

Abstract

Electrostatic gating or alkali metal evaporation can be successfully employed to tune the interface of layered black phosphorus (BP) from a semiconductor to a 2D Dirac semimetal. Although Angle Resolved Photoelectron Spectroscopy (ARPES) experiments have captured the collapse of the band gap in the inversion layer, a quantitative estimation of band structure evolution has been hindered by the short escape depth and matrix elements of the probed photoelectrons. Here, we precisely monitor the evolution of electronic states using time-resolved ARPES at a photon energy of 6.3 eV. The probing depth of laser -based ARPES is long enough to observe the buried electronic states originating from the valence band maximum. Our data shows that the band gap has a maximal value of 0.32 eV in the pristine sample, and that it shrinks down monotonically by increasing the carrier concentration in the topmost layer. Most interestingly, the band velocity of the valence band increases by a factor of two along the armchair direction, surpassing the value reported in graphene on silicon carbide (SiC). This control of band structure via external gating will be of interest with regard to the design of optoelectronic devices.

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

“…At positive delay, we now probe the photoexcited system at a pump fluence of 160 μJ/cm 2 . At this fluence, the SPV is saturated [36] and we recover a flat band regime for the VB: surface and bulk contributions of the VB are now aligned [see Fig. 3(b)].…”

“…In recent works [36,37], it has been shown that φ BB in alkali-doped BP at this critical coverage equals a few hundreds of meV and can be compensated via the illumination of the surface. Under the preexisting electric field, photogenerated electrons and holes are redistributed in the SCR and create a compensating field called surface photovoltage (SPV).…”

Ultrafast Dynamics of the Surface Photovoltage in Potassium Doped Black Phosphorus

“…At positive delay, we now probe the photoexcited system at a pump fluence of 160 µJ/cm 2 . At this fluence, the SPV is saturated 36 and we recover a flat band regime for the VB: surface and bulk contributions of the VB are now aligned (see Fig. 3(b)).…”

“…In recent works 36,37 , it has been shown that φ BB in alkali doped BP at this critical coverage equals a few hundreds of meV and can be compensated via the illumination of the surface. Under the preexisting electric field, photo-generated electrons-holes are redistributed in the SCR and create a compensating field called surface photovoltage (SPV).…”

Extremely low-energy ARPES of quantum well states in cubic-GaN/AlN and GaAs/AlGaAs heterostructures

“…The most important limitation here is that the probed states are accessed in limited windows of energy (~ 1.5 eV below the Fermi level) and momentum (~ 0.2 Å 1 near the center of the first Brillouin zone). Hence, ELE-ARPES is usually applied for specific materials that show interesting physics at the center of the Brillouin zone (BZ) such as the Dirac cone in 3D topological insulators 20 , 21 , kinks in some strongly correlated materials 22 , 23 and the electronic structure in direct-band gap materials 24 . Interestingly, combining ARPES with two femtosecond laser pulses in a pump-probe configuration, where the probe is in the DUV energy range 25 , 26 , can provide direct visualization of the photoexcited band structure of both occupied and unoccupied states as well as their ultrafast dynamics in the time domain 20 , 21 , 25 .…”