Understanding coherent ultrafast charge transfer in two-dimensional van der Waals heterostructures is essential for revealing nonequilibrium processes and advancing optoelectronic device engineering. Here, we employ terahertz emission spectroscopy to probe gate-tunable coherent charge transfer (CT) in graphene/MoS2 heterostructures. Our experimental and analytical results demonstrate that the gate voltage modulates coherent CT (i.e., direct CT) by tuning the heterostructure's built-in electric field; a higher gate voltage diminishes this field, thereby suppressing the coherent CT component. In contrast, the incoherent CT (photothermionic emission) component exhibits the opposite trend. We attribute this to a gate-induced increase in hot carriers that can overcome the interfacial barrier, an effect that dominates the concurrent reduction in the built-in field. Our findings reveal the fundamental mechanisms of gate-controlled charge dynamics, providing deeper insight into carrier transport in van der Waals heterostructures and a guideline for device development.

Topological three-dimensional (3D) Dirac semimetals are promising for advanced optoelectronics due to their nontrivial band topology and ultrahigh carrier mobility. Their intrinsic centrosymmetry, however, should forbid second-order nonlinear optical processes, severely limiting their nonlinear photonics potential. Contrary to this expectation, we observe pronounced coherent terahertz (THz) emission arising from second-order nonlinear effects in both pristine 3D Dirac semimetal Cd3As2 thin films and its noncentrosymmetric alloy counterpart. This highly efficient, broadband THz radiation can be controlled by varying the pump polarization and incident angle, with the resulting transient photocurrents aligning with symmetry analysis. Crucially, we demonstrate two effective strategies to activate these nonlinear photocurrents: (i) using oblique excitation to create an asymmetric carrier distribution in momentum space, and (ii) deliberately breaking inversion symmetry via alloy engineering. Both strategies are generalizable approaches for unlocking second-order transient photocurrents in centrosymmetric Dirac semimetals through symmetry breaking. These findings establish new approaches for controlling nonlinear responses in 3D topological materials, advancing their application in next-generation, on-chip THz photonic devices.

Low-power and high-speed terahertz (THz) photonic devices are of significant importance for advancing THz technologies, demanding exceptional functional materials to load. In this work, we systematically investigate the transient charge transport dynamics in semimetallic mercury telluride (HgTe) films utilizing optical pump-THz probe (OPTP) spectroscopy. Remarkably, photoexcited bare HgTe exhibits an ultrasensitive transmission response in THz frequencies at room temperature-reaching a modulation depth of 28% at a mere pump fluence of 1 mu J/cm2 and up to 73% at 21 mu J/cm2-surpassing all reported materials under comparable conditions. Moreover, the photocarrier relaxation remains ultrafast and nearly constant (similar to 14.3 ps) across a wide range of pump fluences. Through detailed analysis of THz photoconductivity spectra, Drude-Smith model fitting, and temperature-dependent transient dynamics, we reveal that HgTe's superior performance stems from its semimetallic character, featuring ultrahigh electron mobility enabled by long momentum scattering times and a small effective mass, as well as its gapless electronic structure. Our findings provide deep insights into the photocarrier relaxation mechanism in HgTe and highlight its immense potential for developing energy-efficient, broadband, all-optically controlled, ultrafast THz modulators and other high-performance THz optoelectronic devices.

The nonlinear injection photocurrent, a second-order photogalvanic effect absent in centrosymmetric structures, can be revived by the photon-drag effect (PDE), leading to efficient terahertz (THz) radiation. Previous studies on THz emission from centrosymmetric films under oblique incidence attributed the effects to PDE-induced nonlinear photocurrents, and pump polarization-dependent THz emission was analyzed usually with the material's point group. However, these studies overlooked two critical issues: (1) the distinction between the photon-drag shift and injection currents in transient THz radiation and (2) the irrelevance of pump polarization-dependent THz emission to the point group in centrosymmetric materials. Our theoretical analysis reveals that when the band velocity of conduction bands is a substantial difference from that of valence bands, the photon-drag injection current dominates in thin films with inverse symmetry following optical excitation, while the nonlinear photon-drag shift current is negligible. This theory is supported by ultrafast THz emission spectroscopy on a 1T '-MoTe2 film and aligns well with existing literatures. This study introduces a new efficient THz emitter and enhances the understanding of nonlinear photon-drag currents in centrosymmetric materials, potentially guiding the design of THz radiation devices.

This study demonstrates a highly efficient F & ouml;rster resonance energy transfer (FRET) system between cadmium sulfide quantum dots (CdS QDs) and surface-anchored 3-perylenecarboxylic acid (PCA) acceptors. Systematic characterization reveals that 3.2 nm CdS QDs functionalized with carboxyl-terminated PCA molecules exhibit a FRET efficiency of 74 % with an energy transfer rate constant of 3 x 10(9) s(-1). Time-resolved photoluminescence studies combined with density functional theory calculations demonstrate that the carboxyl anchor groups form hybrid chemical bonds with undercoordinated Cd2+ surface sites, enhancing their band-edge emission intensity by similar to 75 % via suppression of non-radiative decay. This PL improvement directly elevates FRET efficiency by increasing the F & ouml;rster radius (R-0). The results presented here provide new insights for evaluating the energy transfer process in QD-molecular composites.

Objective Since the discovery of graphene in 2004, two-dimensional (2D) materials, owing to their atomic-scale thickness, absence of surface dangling bonds, and quantum confinement effects, have provided a revolutionary platform for the design of optoelectronic and spintronic devices. Semiconducting transition metal dichalcogenides (TMDs) represented by MoS2 can achieve tunable bandgaps (1.2?1.9 eV) through layer-number modulation. However, their inherently low carrier mobility and environmental sensitivity limit their applications in high-frequency optoelectronics. Moreover, most 1T-phase TMDs are prone to oxidation and instability in air, and their high phase-transition energy barriers pose challenges to controllable preparation. As a member of TMDs, MoTe2 has a 1T ' phase (semi-metal) and a 2H phase (semiconductor) that stably exist at room temperature, as well as a T-d phase (semi-metal) that exists only at low temperatures (<240 K), endowing it with rich phase-transition conditions. We focus on the 1T '-MoTe2 semimetallic thin film at room temperature to deeply analyze its ultrafast carrier dynamics mechanism and obtain key material parameters, laying a solid theoretical foundation for the design of ultrafast optoelectronic devices based on MoTe2. Methods We utilize a self-built optical pump-terahertz probe (OPTP) spectroscopy system. An ultrafast pulsed laser output from a titanium-doped sapphire regenerative amplifier is employed as the light source. The laser has a central wavelength of 780 nm, a pulse width of 120 fs, a repetition rate of 1 kHz, and a single-pulse energy of 3 mJ. In this system, the laser is split into generation light, pump light, and probe light by beam splitters. The generation light is focused on a 1-mm-thick ZnTe crystal with a <110> orientation to generate terahertz waves. These waves are then collimated and focused onto the detection crystal ZnTe. By using the Pockels effect induced by the terahertz wave electric field, combined with a balanced photodetector and a lock-in amplifier, the synchronous detection of terahertz signals is achieved. By moving the delay line of the pump light path, the change in the terahertz instantaneous transmittance induced by light is accurately measured, thereby obtaining the kinetic information of non-equilibrium carriers. Simultaneously moving the delay lines of both the pump and probe light paths allows for the measurement of terahertz transmission spectra at different pump delay time. Combined with relevant formulas, the change in the transient conductivity of the photo-excited sample is calculated, providing data support for the study of carrier dynamics. Results and Discussions A series of innovative results are achieved in the experiment. Under 780-nm light excitation, the 1T '-MoTe2 thin film exhibits positive terahertz photoconductivity, and its decay process shows obvious biexponential characteristics: a sub-picosecond fast process and a hundred-picosecond slow process. Through in-depth analysis, it is determined that the fast process originates from electron-phonon coupling, during which hot electrons rapidly transfers energy to optical phonons. The slow process is dominated by phonon-phonon interactions, facilitating the diffusion of heat in the lattice until thermal equilibrium with the environment is reached. By fitting the pump-dependent fast process using the two-temperature model (TTM), the electron-phonon coupling coefficient g(infinity) of 1T '-MoTe2 is accurately obtained as 7.7x10(15) Wm(-3)K-1, and the electron specific heat coefficient gamma is 2.1 Jm(-3)K-2, indicating a relatively high electron-phonon coupling strength in this semimetallic phase. When we study the complex photoconductivity of 1T '-MoTe2, fitting with the Drude-Smith model reveals that the enhanced localization trend of the fitting parameter c with the increase in the delay time before 0.6 ps might imply the rapid formation and dissociation of certain quasiparticles (such as large polarons). Although this phenomenon still requires further experimental verification, it provides a new perspective for studying carrier behavior. Conclusions Based on the comprehensive research results, it can be concluded that the relaxation of non-equilibrium carriers in the 1T '-MoTe2 semimetallic thin film under photoexcitation is mainly dominated by the electron?phonon coupling and phonon-phonon interactions. It is the first to comprehensively explore the ultrafast carrier dynamics of 1T '-MoTe2 using the optical pump-terahertz probe ultrafast spectroscopy among the massive literature. We clarify the physical mechanism of non-equilibrium carrier relaxation, which is derived from electron-phonon coupling and phonon-phonon interactions. Moreover, the relationship between the time constant of the fast process of non-equilibrium carrier relaxation and the excitation power density can be effectively described by the two-temperature model. These results not only deepen the understanding of the carrier dynamics of 2D semimetallic materials but also provide a crucial theoretical basis and accurate experimental data for the design and development of ultrafast optoelectronic devices based on 1T '-MoTe2, strongly promoting the applied research of two-dimensional materials in the field of terahertz optoelectronics.

Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials, which enables the precise modulation of energy band structure and microscopic dynamical interaction. Herein, we have studied the ultrafast photocarrier dynamics in Zn-doped 3D topological Dirac semimetal Cd3As2 utilizing time-resolved optical pump-terahertz probe spectroscopy. Comparing to the pristine Cd3As2, we found that the relaxation time of the lightly doped alloy is slightly shorter, while that of the heavily doped alloy exhibits a significant prolongation. Pump-fluence-and temperature-dependent transient terahertz spectroscopy indicated that in pristine and lightly doped samples within nontrivial semimetal phase, the photocarrier dynamics are dominated by the cooling of Dirac fermions. In heavily doped alloy, however, the observed longer relaxation process can be attributed to interband electron-hole recombination, which is a result of doping-induced transition into a trivial semiconductor phase. Our investigation highlights that Zn-doping is an effective and flexible scheme for engineering the electronic structure and transient carrier relaxation dynamics in Cd3As2, and offers a control knob for functional switching between diverse optoelectronic devices within the realm of practical applications. (c) 2025 Chinese Laser Press

Van der Waals (vdW) heterostructures constructed from transition metal dichalcogenidess provide an ideal platform for exploring various quasiparticle behaviors, with trion—composed of neutral exciton and charged carrier—being a notable example. There are typically three methods to generate trion: electrical doping, chemical doping, and direct optical doping. The first two methods generate static trion, while the last gives rise to transient trion. Here, we present an indirect optical doping approach to generate transient trion via ultrafast charge transfer (CT) and achieve control over the trion-to-exciton ratio by adjusting CT in Gr/MoS2 heterostructure. Furthermore, we demonstrated that dynamics of the transient trion generated with this method, which shows slightly longer lifetime than that of exciton accounted for the Coulomb interactions between trion and charged defect. This study provides fresh perspectives on the construction of desired quasiparticles, dynamical characterization, and the control of the many-body interaction in two-dimensional structure.

Heterostructures composed of graphene (Gr) and transition metal dichalcogenides (TMDs) establish a new platform for optoelectronic applications. A substantial amount of research has concentrated on the interfacial charge transfer (CT) within heterostructures, yet investigations into the nonlinear effects occurring within these heterostructures have been relatively scarce. Utilizing terahertz (THz) emission spectroscopy, we demonstrate the synergistic interaction between interfacial CT and nonlinear photocurrent within the Gr/MoS2 heterostructure. Our study shows that despite the cancellation of photocurrents from CT in the MoS2/Gr/MoS2 sandwich heterostructure, THz emissions are still observable, indicating additional photocurrents from other effects. By conducting experiments that involved varying the pump fluence, sample azimuthal angle, incidence angle, and pump polarization states, we determined that the THz radiation in the MoS2/Gr/MoS2 heterostructure is dominated by the photon drag effect (PDE), particularly dominated by the photon drag injection current. For the case of the Gr/MoS2 heterostructure, both CT and PDE play a role in THz emission, and the contribution of CT to THz emission is dominant, with an estimated CT:PDE ratio of 5:2. The study provides a foundation for the application of these heterostructures in next-generation optoelectronic devices.

Mode coupling can not only effectively control the frequency, amplitude and linewidth of the transmission spectrum, but also improve the Q-factor of the spectrum. Herein, we propose a H-shaped metamaterial, in which the dipole mode, LC mode and lattice mode can be excited selectively, and each mode frequency can be independently tuned by changing the polarization of incident THz wave as well as the lattice constant of the metamaterial structure, thus allowing greater degrees of freedom to customize the polarization components of different properties in the system. Under different polarization directions, the strong coupling between the lattice mode and the inductance-capacitance (LC) mode as well as the lattice mode and the dipole mode is realized, which makes the transmission resonance Q-factor of the hybrid state increase to 8 times that of the single resonance state, and the obvious anti-crossing phenomenon is observed. In addition, the LC mode and the dipole mode can be excited simultaneously, and the coupling between these two modes successfully excites a bound states in the continuum with an infinite Q-factor.

When graphene forms heterostructures with transition metal dichalcogenides (TMDCs), the photons with energy below the TMDCs' bandgap can be harvested by graphene and injected into TMDCs through ultrafast charge transfer. Controlling and understanding this ultrafast charge transfer are crucial for developing advanced photonic and optoelectronic devices. Here, we use ultrafast terahertz and transient absorption spectroscopy to demonstrate the significant potential of a gate-controlled method in controlling the ultrafast charge transfer efficiency in graphene-MoS2 heterostructures and reveal the fundamental limitation of the method. Our results show that the number of hot electrons transferred from graphene to MoS2 can be modulated several fold by gate bias, achieved by altering the Fermi distribution of hot electrons in graphene. There is an upper limit to the gate-controlled method in the aforementioned modulation, and we reveal that the underlying mechanism of this limitation is that, at high gate bias, the chemical potential of graphene surpasses the band edge of MoS2, leading to an increased energy barrier for charge transfer. A photothermionic emission model incorporating the gate-controlled limit can well reproduce the experimental findings. Our study demonstrates the role and fundamental limitation of the gate-controlled method in regulating ultrafast charge transfer in graphene-MoS2 heterostructures, providing insights for the development of related photodetectors, solar cells, and optoelectronic devices.

Two-dimensional transition-metal dichalcogenides (TMDCs) offer low-dimensional and strongly confined systems, making them important materials for fabricating novel optoelectronic devices and exploring the interaction between light and matter. However, in practical application processes, there are a series of issues that need to be addressed, including how to separate the electrons and holes generated by strong light-material interactions and how to weaken or avoid the many-body interactions caused by low-dimensional systems. The heterostructures formed by stacking TMDCs and graphene have been extensively studied as a means to separate electron-hole pairs in TMDCs via photoinduced charge transfer. However, due to the complexity of many-body interactions, there is still limited research on the impact of incorporating graphene on the many-body interactions in TMDCs. In this study, we report the slowing down of carrier relaxation in WS2 after forming heterostructures with graphene under excitation conditions above the WS2 band gap. After assigning lifetimes obtained from fitting transient absorption spectra, we show the complete carrier relaxation process in the heterostructure of WS2 and graphene and attribute the slowing of carrier relaxation in WS2 to the reduction in carrier density caused by direct hole transfer from WS2 to graphene, weakening the many-body annihilation processes associated with carrier density. This study shows the impact of WS2 forming heterostructures with graphene on the many-body interactions within WS2, which provides valuable insights for the development of optoelectronic devices involving TMDCs.

Due to strong quantum confinement effects and novel physical properties, two-dimensional transition metal dichalcogenides (TMDCs) as well as their heterostructures provide an attractive platform for studying excitonic effects and many-body interactions. However, manipulation on the excitonic effect in TMDCs remains challenge owing to the complex interplay of various factors. In this Letter, we report large exciton peak redshift and enhanced exciton–exciton annihilation in WSe2/Gr/hBN heterostructures investigated with static and transient optical spectroscopy. The pronounced redshift of exciton energy in the triple layer heterostructure arises from the charge transfer effect between graphene and WSe2, which leads to the reduction of the WSe2 exciton binding energy significantly due to the Coulomb screening effect. As a result, the reduced exciton binding energy increases the exciton delocalization in the WSe2 layer, leading to an increased probability of exciton–exciton collisions, which results in fast exciton annihilation rate. This study demonstrates the impact of graphene layer on exciton energy as well as the relaxation dynamics in WSe2/Gr/hBN heterostructures, which provides insights into the understanding of quasiparticle physics and many-body interactions in 2D materials.

Tin diselenide (SnSe2), a layered transition metal dichalcogenide (TMDC), stands out among other TMDCs for its extraordinary photoactive ability and low thermal conductivity. Consequently, it has stimulated many influential researches on photodetectors, ultrafast pulse shaping, thermoelectric devices, etc. However, the carrier mobility in SnSe2, as determined experimentally, remains limited to tens of cm2V-1s-1. This limitation poses a challenge for achieving high-performance SnSe2-based devices. Theoretical calculations, on the other hand, predict that the carrier mobility in SnSe2 can reach hundreds of cm2V-1s-1, approximately one order of magnitude higher than experimental value. Interestingly, the carrier mobility could be underestimated significantly in long-range transportation measurements due to the presence of defects and boundary scattering effects. To address this discrepancy, we employ optic pump terahertz probe spectroscopy to access the photoinduced dynamical THz photoconductivity of SnSe2. Our findings reveal that the intrinsic carrier mobility in conventional SnSe2 single crystal is remarkably high, reaching 353.2 ± 37.7 cm2V-1s-1, consistent with the theoretical prediction. Additionally, dynamical THz photoconductivity measurements reveal that the SnSe2 crystal containing rich defects efficiently capture photoinduced conduction-band electrons and valence-band holes with time constants of ∼20 and ∼200 ps, respectively. Meanwhile, we observe an impulsively stimulated Raman scattering at 0.60 THz. Our study not only demonstrates ultrafast THz spectroscopy as a reliable method for determining intrinsic carrier mobility and detection of low frequency coherent Raman mode in materials but also provides valuable reference for the future application of high-performance SnSe2-based devices.

Layered ternary type-II Weyl semimetals demonstrate promising applications in high-performance and broadband optoelectronics, therefore it is crucial to gain insights into their photocarriers' dynamics. In this work, the probing polarization dependence of non-equilibrium dynamics in NbIrTe4 is investigated by using transient reflectivity spectroscopy. Following photoexcitation at 3.18 eV, the dynamical response of 1.59 eV probe pulse exhibits a strong dependence on probe polarization. The relaxation comprises two components: a rapid recovery of approximate to 0.6 ps attributed to the electron-phonon scattering, and an anomalous slow recovery spanning hundreds of picoseconds attributed to the photoinduced quasi-particle. The polarization dependence of rapid relaxation time tau is indicative of the in-plane anisotropy of electron-phonon coupling in NbIrTe4. The slow relaxation modulated by a latest reported 16 cm(-1) coherent phonon also shows strong probing polarization dependence, further revealing the anisotropic nature of electron-phonon coupling and the possibility of anisotropic lattice distortion, as well as photoinduced polaron, under ultrafast photoexcitation in NbIrTe4. The dynamical anisotropy in NbIrTe4 has provided valuable guidance for the application of NbIrTe4 in polarization-sensitive nonlinear optics or optoelectronic devices and offers insights into the unique carrier transport as well as phonon transport properties of this newly established topological material.

Magnon and electromagnon excitations in RFeO3 (where R is a rare-earth element) are associated with the orderings of Fe and R ions, respectively, both of which strongly depend on temperature and applied magnetic field. Herein, by employing the magnetic and electric components of terahertz radiation, we have investigated the temperature and magnetic field dependent magnon and electromagnon excitations in Dy0.9Nd0.1FeO3 single crystals. Our results demonstrate that a small fraction of Nd-substituted Dy ion in Dy1-xNdxFeO3 (with x = 0.1) single crystals shows negligible influence on quasi-ferromagnetic (q-FM) and quasi-antiferromagnetic (q-AFM) modes when the temperature is above T-N (R), the ordering temperature of rare-earth ions. By contrast, introduction of 10% doping concentration of Nd element leads to changes in exchange interaction of rare-earth ions, consequently altering the frequencies of the electromagnon. Applying magnetic field along different crystal axes can tune the frequency of both q-FM and q-AFM modes and even trigger Fe3+-based spin reorientation phase transition. Furthermore, application of magnetic field can suppress the ordering of rare-earth ions and electromagnon excitation. We anticipate that our findings can advance the understanding of magnetoelectric coupling mechanisms and pave the way for the development of advanced multiferroic materials with tailored properties.

In light of the clinical challenges posed by bacterial infection and vascular damage in chronic diabetic wounds, this study presents a novel bioactive copper vanadate-based hydrogel (CVH) with multiple functions including the sustained release of copper and vanadium ions, photocatalytic activity under visible (VIS) light, and photothermal ability under near-infrared (NIR) light. In vitro experiments demonstrated that CVH effectively repairs high glucose-impaired human umbilical vein endothelial cells (HUVECs) and exhibits potent antibacterial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Furthermore, the dual biological functions are augmented by the NIR-light-induced mild photothermal effect, demonstrating a synergistic effect. The infected diabetic wound model further substantiates the therapeutic efficacy of the CVH dressing in eliminating bacteria and promoting angiogenesis under VIS/NIR light irradiation. Collectively, the CVH dressing demonstrates significant potential as a therapeutic intervention for managing chronic diabetic wounds.

Amorphous indium gallium zinc oxide (IGZO) thin film transistors (TFT) are widely used in active-matrix displays because of their excellent stability, low off-current, high field-effect mobility, and good process compatibility. Among IGZO TFT device structures, back channel etching (BCE) is favorable due to low production cost, short channel length and small SD-to-gate capacitance. In this work, prepared are the BCE IGZO TFTs each with the passivation layer of silicon dioxide (SiO2), polyimide (PI) or SiO2-PI stacked structure to study their difference in back channel hydrogen impurity and diffusion behavior. Comparing with the conventional SiO2 passivation BCE TFT, the performance of PI passivation TFT is improved greatly, specifically, the saturation field effect mobility increases from 4.7 to 22.4 cm2/(V·s), subthreshold swing decreases from 1.6 to 0.28 V/decade, and the an on-off current ratio rises dramatically from 1.1×107 to 1.5×1010. After the SiO2 passivation layer is substituted with PI, the I off decreases from 10–11 A to 10–14 A, which indicates that there exist less shallow-level donor states of hydrogen impurities, which might be explained by the following three mechanisms: first, in the film formation process of PI, the direct incorporation of hydrogen-related radicals from SiH4 precursor into the back channel is avoided; second, the hydrogen content in the PI film is lower and harder to diffuse into the back channel; third, the hydrogen impurity of back channel that is introduced by the H2O2-based etchant in the SD etching process could diffuse more easily toward the PI layer. The TFTs with PI passivation layer also shows the less electrical degradation after the annealing treatment at 380 ℃ and better output performance, which confirms less defects and higher quality of the back channel. The bias stabilities of PI devices are improved comprehensively, especially negative bias illumination stability with the threshold voltage shifting from –4.8 V to –0.7 V, which might be attributed to the disappearance of hydrogen interstitial sites and hydrogen vacancies that are charged positively in the back channel. The PI passivation layer is effective to avoid back channel hydrogen impurities of BCE TFT and promises to have broad applications in the display industry.

Ultrafast photocarrier dynamics of the topological insulator Bi2Te3 nanocrystal film was investigated using time-resolved terahertz (THz) spectroscopy. Unlike reducing the film thickness to increase the proportion of surface states, the influence of surface states on the bulk photocarrier dynamics remains important in Bi2Te3 nanocrystal films of a few hundred nanometers. After photoexcitation at 780 nm, the transient THz transmission of the Bi2Te3 nanocrystal film shows a slow dropping process with a typical time of about 3 ps, and the maximum modulation depth of THz transmission shows a nonlinear pump fluence dependence. Coupling rate equations involving both surface and bulk states were used to simulate the photocarrier dynamics of the Bi2Te3 film, which can reproduce the experimental data nicely. We conclude that the delayed dropping process for THz transmission is caused by phonon-assisted scattering of bulk carriers to the surface states. The present study provides new insight into the photocarrier dynamics in topological insulators and directions for technological applications at the nanoscale.

The quasi-two-dimensional van der Waals intrinsic ferromagnetic semiconductor CrGeTe3 possesses both a narrow semiconductor band gap and ferromagnetic properties, which makes it have a broad application prospect in the fields of spintronics and optoelectronics. In recent years, CrGeTe3 has received extensive attention from researchers. To the best of our knowledge, so far, these studies have mainly focused on the optical response in near infrared and visible light range, but little has been done in THz frequency range. Therefore, it is upmost importance to obtain the complex dielectric constant as well as the photocarrier dynamics of the CrGeTe3 at the THz frequency. Herewith, we use time-domain THz spectroscopy and time-resolved THz spectroscopy to investigate the fundamental properties of the CrGeTe3 crystal in the THz range, including refractive index and absorption coefficient in THz frequency, as well as the THz photocarrier dynamics under 780-nm optical excitation. The fundamental characterizations are carried out on a 33-μm-thick CrGeTe3 wafer by Fourier infrared spectroscopy, X-ray diffraction and Raman scattering. It is concluded that the CrGeTe3 wafer shows an indirect band gap of 0.38 eV and good crystalline quality. The THz time domain spectroscopy presents that the CrGeTe3 wafer has a refractive index and an absorption coefficient of 3.2 and 380 cm–1, respectively, both of which show almost negligible dispersion in the investigated THz frequency. Under the optical excitation of 780 nm, the subsequent photocarrier relaxation can be well reproduced by a double exponential function: the fast relaxation shows a lifetime of 1–2 ps, depending on pump fluence, which is contributed by electron-phonon coupling; the slow relaxation has a typical lifetime of 7–8 ps, which is due to phonon-assisted electron-phonon recombination. The Pump fluence and delay time dependence of THz photoconductivity dispersion can be well fitted with Drude-Smith model, and the fitted results demonstrate that the plasma frequency increases with pump fluence in a fixed delay time, and then decreases with delay time increasing at a fixed pump fluence. The momentum scattering time shows that it decreases with pump fluence increasing, and increases with delay time increasing. These pump fluence and delay time dependent fitting microscopic parameters show similar tendencies to those of a conventional semiconductor. In a word, the experimental study here demonstrates that the narrow band-gap CrGeTe3 wafer is well transparent and disperionless in a THz frequency range. From the above bandgap photoexcitation it follows that the wafer shows fast response and high modulation depth in THz radiation, providing a useful reference for the application of CrGeTe3 in optoelectronics and related fields.