Broadband Nonlinear Photoresponse and Ultrafast Carrier Dynamics of 2D PdSe₂

Abstract

Palladium diselenide (PdSe2) exhibits considerable potential for application in broadband optoelectronic devices. In this work, the broadband nonlinear optical performance and ultrafast carrier dynamics from ultraviolet to near‐infrared of a trilayer PdSe2 are systematically studied. PdSe2 is found to achieve a giant saturable absorption performance. The modulation depth is 22.47% at 520 nm, whereas the nonsaturable loss and saturation intensity are only 3.83% and 15.47 GW cm−2, respectively, which are better than those of many 2D semiconductors. Based on these findings, a PdSe2‐based visible light thresholder is proposed, its function is to extract an undetectable pulse signal drowned in strong stochastic noise and thereby improve the signal‐to‐noise ratio. Pump–probe technique, along with first‐principles calculation and transient absorption spectra, reveals the intrinsic recombination mechanism, including Auger scattering and trap saturation. This work is expected to establish the foundation for the development of next‐generation PdSe2‐based devices in optoelectronics and visible light communication.

Ultrafast Dynamics of Defect-Assisted Auger Process in PdSe2 Films: Synergistic Interaction between Defect Trapping and Auger Effect

“…The intrinsic carrier density of PdSe 2 films with different thicknesses is obtained by THz-TDS, which is given in Figure S1. The initial surface carrier density of 15L PdSe 2 films is ∼2 × 10 13 cm –2 , and the pump fluences varying from 72 to 192 μJ/cm 2 correspond to carrier density change from 4.3 × 10 13 to 11.3 × 10 13 cm –2 , showing values similar to those reported in ref . The simulated fast and slow defect electron occupancy F f (left) and F s (right) as a function of delay time are given in Figure d.…”

“…Moreover, through the use of ultrafast optical pump–probe spectroscopy, the layer-dependent interlayer breathing mode, and the longitudinal coherent acoustic phonon mode in PdSe 2 films have been studied, and the interlayer force constant and sound velocity were obtained in our previous study . In general, the carrier dynamics in PdSe 2 and other TMD films is conventionally described as defect capture. − The detailed mechanisms, such as the roles of phonon, defect, and Auger process on the photocarriers, remain under debate and to be elucidated.…”

Topological bands in the PdSe2 pentagonal monolayer

“…Different forms of pentagonal PdSe 2 with a variable number of layers have been reported, possessing high stability in air, [18][19][20][21][22] which is an essential characteristic for their extended (long-term) use. Also, electrical transport characteristics, 23 remarkable optical, [24][25][26][27] and good thermoelectric properties 28 have been experimentally reported. On the theoretical side, several works have analyzed the physical properties of the material in its monolayer and multilayer forms.…”

Anomalous Oscillating Behavior of Ultrafast Spatiotemporal Hot Carrier Diffusion in Two-Dimensional PtSe2

“…Platinum diselenide (PtSe 2 ) is a recently emerging layered two-dimensional transition metal dichalcogenide (2D TMD), , exhibiting excellent physical properties such as high carrier mobility, , strong air stability, and intriguing spintronic and magnetic properties. , Also, bulk PtSe 2 is known as a type-II Dirac semimetal; thus, this material provides a platform for exploring novel quantum phenomena. The bandgap of PtSe 2 is zero in bulk, but it opens as the thickness decreases, becoming a semiconductor with a bandgap larger than 1 eV in the monolayer. − Owing to this significant thickness dependence of bandgap and the above-mentioned outstanding physical properties, PtSe 2 has been demonstrated as a great material for thickness-engineered broadband photosensors, − modulators, and saturable absorbers. − The remarkable thickness dependence in PtSe 2 originates from strong coupling between layers resulting from covalent-like interlayer interactions. , Another consequence of the strong interlayer coupling is the pronounced interlayer phonon modes. Recent studies found that ultrafast laser excitation of PtSe 2 induces coherent phonons (CP) with large interlayer breathing force constants compared with other layered materials.…”