Ultrafast Excitonic Behavior in Two-Dimensional Metal–Semiconductor Heterostructure

Abstract

The excitonic behavior in two-dimensional (2D) heterostructures of transition metal dichalcogenide atomic layers has attracted much attention. Here, we report, for the first time, the ultrafast behavior of charge carriers in heterostructure of metal (NbSe2) and semiconductor (WSe2) atomic layers via ultrafast spectroscopy. We observe a blue-shift of the excited-state absorption peak in time-resolved absorption spectra with time delays in both the as-grown semiconducting WSe2 and the metal–semiconductor heterostructure. However, the heterostructure shows a clear difference in the peak position and relaxation time of its electrons. This result indicates higher excited energy states in WSe2 in the presence of the NbSe2 metallic layer contact and implies the existence of interlayer electron quenching from WSe2 to NbSe2 layers. The heterostructure shows a shorter time scale in the peak rise time compared to bare WSe2, due to interfacial defects between WSe2 and NbSe2 layers. The results offer a better understanding of the optoelectronic properties of 2D heterostructure interfaces.

Metal doping in topological insulators- a key for tunable generation of terahertz

“…The wellcharacterized sample has used to investigate the kinetic decay profile from a few femtoseconds to nanoseconds with the help of TRUS in reflection geometry. The HELIOS femtosecond transient absorption spectrometer has been used from dynamic measurements [35,36]. The ZnTPP (soon released as BND TM ) reference material calibrates its spectra in NPL.…”

Excited-state dynamics of structurally characterized crystal of SnxSb1-x

“…There is an increase in the differential reflection signal with average power. The physical reason for this upsurge in differential reflectance is the band filling phenomenon [31,[34][35][36][37][38]. It resembles that after photoexcitation, the excited population of carriers is accumulated in the allowed optical transitions.…”

“…The Helios ultrafast spectroscopy system (from ultrafast systems) in the reflectance geometry has been used for evaluating the excited state carrier dynamics of the flakes of SnxSb1-x crystal. The whole spectroscopy system consists of a mode-locked laser, an amplifier, TOPAS (Optical parametric amplifier), delay stage, and spectrometer [18,31,32]. Mode-locked laser (Micra form Coherent) produces a laser pulse of ~35 fs with an average power of ~280-400 mW.…”

Ultrafast Interfacial Carrier Dynamics and Persistent Topological Surface States in VSe2/Bi2Se3 Van Der Waals Heterojunctions

“…Previous ultrafast spectroscopic studies show that the interesting features in MSJ are determined by the interface. [34,35,67,68] Generally, certain changes in the electronic states of the semiconductor in MSJs can be explained by metal/defect-induced gap states (MIGS, DIGS), or interfacial dipoles that cause the FLP observed in different MSJs. [21,22,68,69] Since the MIGS store the electrons and holes and then pin the Fermi level, they can modulate the carrier dynamics of Bi2Se3.…”

“…[34,35,67,68] Generally, certain changes in the electronic states of the semiconductor in MSJs can be explained by metal/defect-induced gap states (MIGS, DIGS), or interfacial dipoles that cause the FLP observed in different MSJs. [21,22,68,69] Since the MIGS store the electrons and holes and then pin the Fermi level, they can modulate the carrier dynamics of Bi2Se3. However, this can be sufficiently suppressed in the case of vdW MSJs owing to the vdW interaction.…”