Controllable Synthesis of Narrow-Gap van der Waals Semiconductor Nb₂GeTe₄ with Asymmetric Architecture for Ultrafast Photonics

Abstract

Ultrafast photonics has become an interdisciplinary topic of great consequence due to the spectacular progress of compact and efficient ultrafast pulse generation. Wide spectrum bandwidth is the key element for ultrafast pulse generation due to the Fourier transform limitation. Herein, monoclinic Nb 2 GeTe 4 , an emerging class of ternary narrow-gap semiconductors, was used as a real saturable absorber (SA), which manifests superior wide-range optical absorption. The crystallization form and growth mechanism of Nb 2 GeTe 4 were revealed by a thermodynamic phase diagram. Furthermore, the Nb 2 GeTe 4 −SA showed reliable saturation intensity and larger modulation depth, ascribed to a built-in electric field driven by the asymmetric crystal architecture confirmed via X-ray diffraction, polarized Raman spectra, and scanning transmission electron microscopy. Based on the Nb 2 GeTe 4 −SA, femtosecond mode-locked operation with good overall performance was achieved by a properly designed ring cavity. These results suggest that Nb 2 GeTe 4 shows great promise for ultrafast photonic applications and arouse interests in exploring the intriguing properties of the ternary van der Waals material family.

Ternary GePdS3: 1D van der Waals Nanowires for Integration of High-Performance Flexible Photodetectors

“…To further quantitatively explore the different periodicity of Raman intensities, the polarization Raman was studied . The Raman scattering intensity from the vibration modes are defined as I ∝ | e i · R · e s |, where R represents the Raman tensor, and e i and e s correspond to the polarization vector of the incident light and scattered light, respectively. − The polarization vectors are (0, cos θ, sin θ) for both the incident and scattering light, and the Raman tensors of active modes could be analyzed as follows normalA normalg = ( true a d 0 d b 0 0 0 c ) goodbreak0em1em⁣ normalB normalg = ( true 0 0 e 0 0 f e f 0 ) where a–f represent the Raman tensor elements. The Raman intensity of the A g and B g modes under parallel polarization configurations are indicated as I A g ∥ ∝ | b | 2 ⁡ cos 4 ⁡ θ + | c | 2 sin 4 …”

Interfacial Charge Transfer and Ultrafast Photonics Application of 2D Graphene/InSe Heterostructure

“…The saturable intensity and modulation depth obtained are 1.33 GW/cm 2 and 12%, respectively. It should be noted that the large modulation depth and low saturation intensity are attributed to the lower recombination rate caused by the large built-in electric potential [ 30 ].…”

InSb-based saturable absorbers for ultrafast photonic applications

“…[3][4][5] In the past decade, the enormous progress of 2D materials has motivated their application in pulsed lasers and in the field of ultrafast optics. [6][7][8][9] Most 2D materials inherently exhibit stronger nonlinear optical responses and light-matter interactions compared to their bulk counterparts, making them widely used in portable photonic applications. 10 Based on their outstanding attributes such as wide spectral bands, good mechanical flexibility, high damage thresholds, and fine compatibility with optical components, 2D materials have been widely used in nonlinear optical devices, such as photonic chips, all-optical modulators, optical sensors, saturable absorbers (SAs), and four-wave mixing generators.…”