Ultrafast Interlayer Charge Transfer between Bilayer PtSe₂ and Monolayer WS₂

Abstract

Interlayer charge transfer (CT) between PtSe2 and WS2 is studied experimentally. Layer-selective pump–probe and photoluminescence quenching measurements reveal ultrafast interlayer CT in the heterostructure formed by bilayer PtSe2 and monolayer WS2, confirming its type-II band alignment. The CT facilitates the formation of the interlayer excitons with a lifetime of several hundred ps to 1 ns, a diffusion coefficient of 0.9 cm2 s–1, and a diffusion length reaching 200 nm. These results demonstrate the integration of PtSe2 with other materials in van der Waals heterostructures with novel charge-transfer properties and help develop fundamental understanding on the performance of various optoelectronic devices based on heterostructures involving PtSe2.

Improved Ultrafast Carrier Relaxation and Charge Transfer Dynamics in CuI Films and Their Heterojunctions via Sn Doping

“…This observation further supports the finding that in-gap trap states in CuSnI are significantly reduced relative to CuI. Because the photoexcited density of charge carriers was low, processes such as radiative recombination and Auger recombination were insignificant. − Therefore, the ultrafast, medium, and long-lived time constants of CuSnI are attributed to the intraband cooling, trapping into shallow trap states, and Shockley–Read–Hall recombination (Figure b), respectively …”

“…These two results coincide with previous observations of other type-II heterostructures. These dynamic changes upon formation of the heterostructure are typical of interlayer charge separation across the heterojunction. ,,,− The rise of the TA signal in CuSnI/ZnO is rapid (within the instrument response function), indicating that the interlayer charge transfer in CuSnI/ZnO is an ultrafast process. Similar results were reported in other type-II heterostructures. , …”

Ultrafast Photocarrier Dynamics and Nonlinear Optical Absorption of a Layered Quaternary AgInP2S6 Crystal

“…Clearly, it contradicts the PL excitation efficiency, so there is another dominant relaxation pathway for nonequilibrium carriers at the CBM besides charge transfer. 35,36 Since there is no PL emission around the band gap, this relaxation pathway is nonradiative recombination via carrier− phonon scattering (Figure 3). Under interband excitation, after the initial intraband relaxation, most of the nonequilibrium carriers relax directly back to thermal equilibrium via nonradiative recombination, while only a small number of nonequilibrium carriers will be transferred to the defect bands.…”

“…As shown in Figure c, the interband absorption is much stronger than the defect-state absorption, thus the number of photogenerated carriers should be larger for interband absorption as compared with the defect-state absorption, provided the number of incident photons is same. Clearly, it contradicts the PL excitation efficiency, so there is another dominant relaxation pathway for nonequilibrium carriers at the CBM besides charge transfer. , Since there is no PL emission around the band gap, this relaxation pathway is nonradiative recombination via carrier–phonon scattering (Figure ). Under interband excitation, after the initial intraband relaxation, most of the nonequilibrium carriers relax directly back to thermal equilibrium via nonradiative recombination, while only a small number of nonequilibrium carriers will be transferred to the defect bands.…”

Phase modulated scanning near field optical luminescence imaging as a probe of exciton dark lifetime and diffusivity in persistently luminescent micro- and nanocrystals

“…Table 1 assesses the resolution, both spatial (lateral) and in the time domain of different techniques normally used to determine the exciton diffusion length in optical materials and nanomaterials. A significant advantage of PM-SNOL is that it possesses both significant lateral and time-domain resolution differently from state-of-the-art ultrafast [51][52][53][54][55][56][57][58][59] (Table 1, first row) imaging [60][61][62][63][64][65] (second row) techniques for exciton diffusion length measurements, which only possess either of them. As far as ultimate lateral resolution is concerned, PM-SNOL measurements are only limited by the ultimate resolution of the scanning-near field optical microscope used to perform them, which in our case is of the order of the tip aperture, 28,66 and therefore of the order of hundreds of nanometers.…”