bulk diamond with tetrahedral structure, graphite is another allotrope of carbon with layered hexagonal lattice structure. In single-or few-layer graphite, which is also referred to as graphene, carbon atoms are strongly coupled by covalent bonds in plane and weakly coupled through van der Waals (vdW)-like interactions in layered direction; [2,3] such 2D-layered atomic crystals are commonly referred as "2D vdW materials." [3][4][5] Following the discovery of graphene, insulating 2D-layered hexagonal boron nitride (h-BN) was initially predicted in theory and then synthesized in experiments. [6,7] Soon after the discovery of semimetallic graphene and the insulating h-BN, semiconductinglayered 2D vdW materials, for example, transition-metal dichalcogenides (TMDs), monochalcogenides, black phosphorus (BP), 2D oxides, and transition meal carbides/carbon nitrides (MXenes) were synthesized by using different physical or chemical synthesis approaches such as mechanical exfoliations, wet-chemical synthesis, and chemical vapor-phase depositions. [4,5,[8][9][10][11][12][13][14] To date, more than 500 types of 2D vdW materials have been synthesized in laboratories.Owing to their high in-plane charge carrier mobility [15] and a wide range of energy bandgaps varies from tens of millielectron volts (meV) to few electron volts (eV), [16,17] semiconducting 2D materials have been viewed as a key component for the nextgeneration optoelectronic devices. [18][19][20][21][22] In addition to the high carrier mobility and wide spectral range, intriguing spin-valley physics, induced by the strong spin-orbit coupling and band structures, [23][24][25] strong Coulomb interactions, which originate from the strict out-of-plane quantum confinement and reduced dielectric screenings, [26,27] along with the large exciton-binding energies enrich the physical properties of photoexcited quasiparticles (e.g., exciton, trion, and biexciton) in 2D vdW semiconductors. In addition to these exciting physical properties, another attractive characteristic of 2D vdW materials is to stack them into structures that are constructed through vdW interactions, without introducing defects or lattice distortions at the interfaces. The unique physical properties along with the vdW interlayer interaction allow for the fabrication of highperformance devices with extremely fast responses, such as high-mobility GHz-frequency field-effect transistors, [28,29] fast response phototransistors, [30] and extremely sensitive chemical detectors. [31] Owing to the fascinating and technologically useful electronic and optical properties, 2D van der Waals (vdW) materials are viewed as the key component for the next-generation optoelectronic, photovoltaic, and nanoelectronic devices. Fully understanding the ultrafast carrier dynamics in 2D vdW materials is essential to study the fundamental physics and realize potential applications. Time-resolved terahertz (THz) spectroscopy is a powerful tool used to investigate the ultrafast carrier dynamics and transport properties in semiconduc...