Optically controlled ultrafast terahertz switching in a CdTe nanostructure thin film

Zhang, Wenjie; Guo, Jiajia; Suo, Peng; Lv, Liping; Liu, Junxing; Lin, Xian; Jin, Zuanming; Liu, Weimin; Ma, Guohong

doi:10.1364/ao.58.008200

Cited by 12 publications

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“…45,46 The ultrafast relaxation of Δσ(t) as well as the absence of long relaxation process for all PtSe 2 films strongly indicates that photocarrier trapping by defect states play the dominated role for the recovery of photoconductivity. 25,47 It is also noted that the recovery time increases monotonously with pump fluences for all four films, which was also reported in other materials with high density of defects. 25,48 The longer recovery time with higher pump fluence reveals saturation effect of the defect trapping process under higher pump fluence.…”

Section: ■ Results and Discussionsupporting

confidence: 82%

“…25,47 It is also noted that the recovery time increases monotonously with pump fluences for all four films, which was also reported in other materials with high density of defects. 25,48 The longer recovery time with higher pump fluence reveals saturation effect of the defect trapping process under higher pump fluence. Additionally, it is seen that the thicker film shows the faster recovery times and greater PA signal, indicating the thicker film has more edge sites, this result is consistent with the conclusion of thickness dependent Raman spectra, in which the ratio of A 1g / E g increases with the film thickness.…”

Section: ■ Results and Discussionsupporting

confidence: 82%

“…The transient THz photoconductivity, Δσ( t ), is proportional to population of photocarrier Δ n ( t ), and photocarrier mobility μ. , The ultrafast relaxation of Δσ(t) as well as the absence of long relaxation process for all PtSe 2 films strongly indicates that photocarrier trapping by defect states play the dominated role for the recovery of photoconductivity. , It is also noted that the recovery time increases monotonously with pump fluences for all four films, which was also reported in other materials with high density of defects. , The longer recovery time with higher pump fluence reveals saturation effect of the defect trapping process under higher pump fluence. Additionally, it is seen that the thicker film shows the faster recovery times and greater PA signal, indicating the thicker film has more edge sites, this result is consistent with the conclusion of thickness dependent Raman spectra, in which the ratio of A 1g /E g increases with the film thickness.…”

Section: Resultssupporting

confidence: 66%

“…The recovery process can be well fitted with a single exponent decay function. 25,32 Figure 4b displays the normalized transient transmission of F4 and the inset plots the fitting time constants as a function of pump fluence for all four thin films, from which two main features are seen clearly: (i) the recovery time increases monotonously with pump fluences for all four films, and (ii) a thicker film shows faster recovery time at fixed pump fluence. We would like to mention that an additional long relaxation process with typical time constant of longer than 100 ps and weight of ∼5% is observed under the highest pump fluence, which could come from the recombination process between the conduction band electrons and valence band holes.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Lin et al reported that PtSe 2 films, synthesized by selenization of Pt films, have the positive correlation with the thickness as well as the density of edge states, which is a common 1D defect in many other 2D materials, and the existence of this kind of defect can increase the cathodic current density and further improve the activity of the HER significantly . As far as we have learned, few researchers were concerned with the roles of defect states on the photocarrier dynamics in PtSe 2 films. − As a matter of fact, the photocarrier dynamics is fundamentally important in evaluating the response of photonic devices, such as modulator, switch, and fast detector etc ., and it is also important for assessing the performance of photocatalysis effect for a catalyst. Here, we employ the transient absorption (TA) and optical pump and THz probe spectroscopy (OPTP) to investigate the photocarrier dynamics of 1T-PtSe 2 films with various thicknesses, which were synthesized by selenization of metallic Pt films with thickness of 1, 3, 10, and 15 nm.…”

Section: Introductionmentioning

confidence: 99%

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Thickness-Dependent Ultrafast Photocarrier Dynamics in Selenizing Platinum Thin Films

Chen

et al. 2020

J. Phys. Chem. C

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The atomically thin layered transition metal dichalcogenide (TMDCs) PtSe2 is a new emerging two-dimension (2D) material, which has a transition from indirect-gap semiconductor to semimetal with increasing thickness. Defects in 2D TMDCs are very ubiquitous and play a crucial role in understanding many electronics and optoelectronics in TMDCs. In this article, PtSe2 films with different thickness are obtained by selenizing the variously thick Pt films. Extrapolation of the onset absorption from the visible-infrared spectrum demonstrates that the selenization of 1 and 3 nm Pt films shows semiconductor-like character, while those of thick Pt films (with thickness of 10 and 15 nm) show metallic behavior. The transient absorption (TA) spectroscopy reveals that all films show immediately photobleaching signals after photoexcitation at 800 nm, and the subsequent relaxation process shows strongly thickness dependence. The thinnest film shows biexponential relaxation with typical time constants of 1.28 and 101.2 ps. In contrast, the photobleaching signals are developed into photoinduced absorption signals in thicker films, and the absorption magnitude increases with the thickness of the films. The optical pump and terahertz (THz) probe spectroscopy reveals that all samples show positive photoconductivity after photoexcitation of 800 nm, the subsequent recovery is completed within 2.0 ps, and the recovery time constant decreases with the increase of the films’ thickness. Our TA and THz spectroscopy results reveal that the defect states of the films play dominated role in the relaxation of photocarrier after photoexcitation, and edge-site states are inferred to make dominated contributions to the defect states in the selenization of platinum films.

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