Carrier Relaxation Time Research Articles

Improved Electron Transport Properties of Zn-Rich In–Ga–Zn–O Thin-Film Transistors

Amorphous transparent oxide semiconductor InGaZnO4 (IGZO)-based thin-film transistors (TFTs) have been practically used as the backplane of flat panel displays. For future higher-definition displays, alternative active materials with a higher field effect mobility (μFE) are necessary. Although there are a few reports on InGaO3(ZnO)m with Zn-rich composition (IGZOm)-based TFTs, their electron transport properties have not been clarified. Here, we show that a Zn-rich composition enhances the electron transport properties of IGZOm-TFTs. The best TFT performance was obtained for m = 7 (μFE ∼12 cm2 V–1 s–1, subthreshold swing ∼0.1 V decade–1, and a negligibly small bias stress shift). The carrier effective mass (m*) of IGZOm films was found to be 0.16 m0, independent of the m-value. We found that μFE of IGZOm-TFT increased with the m-value for m ≤ 7, whereas it decreased for m > 7 due to the crystallization. The thermopower modulation analyses revealed that the effective channel thickness increased with m (m ≤ 7), which resulted in a longer carrier relaxation time. The present results provide an improving strategy toward new material design for next-generation TFTs with higher μFE values.

Carrier density tuning in CuS nanoparticles and thin films by Zn doping via ion exchange.

Copper sulphide (covellite) nanoplatelets have recently emerged as a plasmonic platform in the near-infrared with ultrafast nonlinear optical properties. Here we demonstrate that the free-carrier density in CuS, which is an order of magnitude lower than in traditional plasmonic metals, can be further tuned by chemical doping. Using ion exchange to replace Cu with an increasing content of Zn in the nanoparticles, the free-hole density can be lowered, resulting in a long-wavelength shift of the localised plasmon resonances from 1250 nm to 1750 nm. The proposed approach provides new opportunities for tuning the plasmonic response of covellite nanocrystals as well as the carrier relaxation time which decreases for lower free-carrier densities.

Janus 2H-MXTe (M = Zr, Hf; X = S, Se) monolayers with outstanding thermoelectric properties and low lattice thermal conductivities.

Two-dimensional (2D) materials have been one of the most popular objects in the research field of thermoelectric (TE) materials and have attracted substantial attention in recent years. Inspired by the synthesized 2H-MoSSe and numerous theoretical studies, we systematically investigated the electronic, thermal, and TE properties of Janus 2H-MXTe (M = Zr and Hf; X = S and Se) monolayers by using first-principles calculations. The phonon dispersion curves and AIMD simulations confirm the thermodynamic stabilities. Moreover, Janus 2H-MXTe were evaluated as indirect band-gap semiconductors with band gaps ranging from 0.56 to 0.90 eV using the HSE06 + SOC method. To evaluate the TE performance, firstly, we calculated the temperature-dependent carrier relaxation time with acoustic phonon scattering τac, impurity scattering τimp, and polarized scattering τpol. Secondly, the calculation of lattice thermal conductivity (κl) shows that these monolayers possess relatively poor κl with values of 3.4-5.4 W mK-1 at 300 K, which is caused by the low phonon lifetime and group velocity. After computing the electronic transport properties, we found that the n-type doped Janus 2H-MXTe monolayers exhibit a high Seebeck coefficient exceeding 200 μV K-1 at 300 K, resulting in a high TE power factor. Eventually, combining the electrical and thermal conductivities, the optimal dimensionless figure of merit (zT) at 300 K (900 K) can be obtained, which is 0.94 (3.63), 0.51 (2.57), 0.64 (2.72), and 0.50 (1.98) for n-type doping of ZrSeTe, HfSeTe, ZeSTe, and HfSTe monolayers. Particularly, the ZrSeTe monolayer shows the best TE performance with the maximal zT value. These results indicate the excellent application potential of Janus 2H-MXTe (M = Zr and Hf; X = S and Se) monolayers in TE materials.

Study of the mechanisms of the phonon bottleneck effect in CdSe/CdS core/shell quantum dots and nanoplatelets and their application in hot carrier multi-junction solar cells.

The hot carrier multi-junction solar cell (HCMJSC) is one of the promising advanced conceptual solar cells with theoretical efficiency greater than 65%, consisting of a thin top junction with a wide bandgap and a thicker junction at the bottom with a medium bandgap for absorption of high and low energy photons. The wide bandgap CdSe/CdS low-dimensional systems (e.g. quantum dots, QDs and nanoplatelets, NPLs) widely used in optoelectrical devices are expected to be an appropriate candidate for the top junction. However, the mechanisms underlying the carrier relaxation rate reduction (or phonon bottleneck effect, PBE) for HCMJSC in these material systems are not well understood so far. In this work, the carrier relaxation mechanisms in CdSe/CdS core/shell QDs and NPLs are quantitatively analyzed by calculating the thermalization coefficient (Qth) through steady state photoluminescence (SSPL) and picosecond-time resolved photoluminescence (ps-TRPL). A significantly extended carrier relaxation time of more than 20 ns was observed in the TRPL of QDs. This could be attributed to both the Auger reheating (AR) at the initial fast decay stage and acoustic phonon folding at the slow decay stage. For SSPL, the Qth value of QDs is much lower due to a 1 order of magnitude higher AR rate. A strong coupling may exist between AR and Qth with a high probability of PBE, where a lower Qth gives a higher AR rate. The AR may dominate carrier thermalization if the PBE level is high. Meanwhile, other mechanisms like acoustic phonon folding will also affect the carrier relaxation if the PBE is at a much lower level.

Elucidating the photovoltaic effect of monoclinic K2SnBr6 by mixed-cation mixed-halide substitution from first-principles calculations

Vacancy-ordered double perovskites (A2BX6) have recently received impressive attention for photovoltaic applications, and the compound K2SnBr6 has desirable features for use in solar cells in such a way that it exhibits direct bandgap behaviour with dispersed band edges. However, the large bandgap value limits its use in higher-efficiency solar cells. Therefore, we have carried out exploratory research by analysing the photovoltaic effect of K2SnBr6 by tuning its bandgap with cation and anion substitutions. We studied the properties of K(2−y)RbySnBr(6−x)I x and K2Sn(1−z)Ti z Br(6−x)I x compounds to explore the photovoltaic effect by gradual substitution of Rb+, Ti4+ and I−1 for K+, Sn4+ and Br−1, respectively. Our density functional calculations in the monoclinic ground state crystal structure with the space group P121 /n revealed that the K(2−y)Rb y SnBr(6−x)I x compounds considered in this study exhibit direct bandgap behaviour with well-dispersed band edges. Moreover, the bandgap value decreases as a function of the Rb and I concentrations. In addition to the low charge carrier effective mass, low excitonic binding energy values and low recombination rate, these compounds exhibit comparatively greater absorption coefficients in the visible range. The charge carrier transport properties, such as carrier mobility, carrier relaxation time, carrier diffusion coefficient and carrier diffusion length, are also seen in higher ranges for these Rb- and I-substituted compounds when compared to the parent compound. In addition, we have calculated the open-circuit voltage, fill factor, short-circuit current and power conversion efficiency for each compound. From the calculations and analysis, we observed that Rb and I substitution in K2SnBr6 increases the photovoltaic effect, and thus K(2−y)Rb y SnBr(6−x)I x compounds may be employed as absorbing layers in higher-efficiency solar cells.

Ultrafast Carrier Dynamics in 2D NbTe2 Films: Implications for Photonic and Optoelectronic Devices

As one of the representatives of emerging metallic transition-metal dichalcogenides, niobium ditelluride (NbTe2) has attracted intensive interest recently due to its distorted lattice structure and unique physical properties. Here, we report on the ultrafast carrier dynamics in NbTe2 measured using time-resolved pump–probe transient reflection spectroscopy. A thickness-dependent carrier relaxation time is observed, exhibiting a clear increase in the fast and slow carrier decay rates for thin NbTe2 flakes. In addition, pump-power-dependent measurements indicate that the carrier relaxation rates are power-independent and the peak amplitude of the transient reflectivity increases linearly with the pump power. The isotropic relaxation dynamics in NbTe2 is also verified by performing polarization-resolved pump–probe measurements. These results provide insight into the light–matter interactions and charge-carrier dynamics in NbTe2 and will pave the way for its applications to photonic and optoelectronic devices.

Graphene saturable absorber mirror for passive mode-locking of mid-infrared QCLs

Passive mode-locking in quantum cascade lasers (QCLs) remains one of the huge challenges because of the fast relaxation time of the excited carriers which is typically in the range of sub-picoseconds. The use of conventional techniques such as the semiconductor saturable absorber mirror is inefficient because the spatial hole burning effect dominates the carrier dynamics. To overcome this effect, longitudinal transition structures with relaxation time around $$50~\mathrm {ps}$$ were proposed. However, mode-locking is assured with an external modulation at a cavity roundtrip frequency. In this paper, we demonstrate that a single-layer graphene used as a saturable absorber permits to generate stable pulses in such structures. The graphene is integrated with a highly reflective mirror to increase the internal electric field and achieve the saturation intensity. The dynamic of the QCL is modeled with Maxwell-Bloch equations while Maxwell-Ampere equation is used for the graphene layer by considering a nonlinear conductivity. This system of equations is solved using the one-dimensional Finite-Difference Time-Domain ( FDTD) method. To model the single-layer graphene of a $$0.33~\mathrm {nm}$$ thickness, a specific sub-cell is implemented based on Maloney method. Simulation results of a $${\mkern 1mu} 6.2~\mu {\text{m}}$$ QCL with a diagonal radiative transition show a generation of isolated pulses with a peak electric field of $$80~\mathrm {MV.m^{-1}}$$ and a duration of $$51~\mathrm {fs}$$ . The mode-locking remains stable for QCLs with a vertical transition having a relaxation time below $$5~\mathrm {ps}$$ .

Optical nonlinearity of Cu1.81S nanodisks decorated with silver nanoparticles

The nonlinear absorption (NLA) and ultrafast dynamics process of Cu1.81S nanodisks (NDs) and Ag-Cu1.81S nanocomposites are investigated by using femtosecond Z-scan measurements and femtosecond time-resolved transient absorption spectrum, respectively. After decoration with Ag particles, Ag-Cu1.81S nanocomposites exhibit stronger saturable absorption and smaller saturable intensity at 600 and 800 nm. The carrier relaxation time is measured using femtosecond time-resolved techniques, and the results showed that the prolongation of the carrier relaxation time of the composite material can lead to a stronger saturation absorption effect.

Tailoring linear and nonlinear surface plasmon responses in borophene nanostructures

The newly reported 2D material ‘borophene’ provides a novel building block for nanoscale materials and devices. In this work, the linear and nonlinear plasmonic response of the electric dipole (ED) moment in metallic borophene is theoretically investigated. In our proposed model, a borophene nanostructure is deposited on the top of a dielectric layer sandwich with a silver layer acting as a mirror. It was found that the scattering at the scattering peak originates mainly from the exciting total ED. Our calculations demonstrate that scattering in the proposed model can be tuned well with carrier relaxation time, effective electron mass and free carrier density. The strongly localized fundamental field induces the desired increase in the second harmonic wave, which is discussed in detail by introducing the second-order nonlinear source. In addition, the evolution of the lifetime of linear and nonlinear plasmonic modes is also investigated, which helps us to study the underlying mechanism of microprocessing in the borophene plasmonic–photonic interaction. The manipulation of plasmonic behaviour and lifetime evolution makes borophene an excellent platform for tunable plasmonic–photonic devices.

Theoretical Understanding of thermoelectric energy conversion efficiency in Lead-Free halide double perovskites showing intrinsic defect tolerance

Thermoelectric devices based on the Seebeck effect can directly convert waste heat to electricity, but the demand for better thermoelectric materials remains unfulfilled. The lead-free halide double perovskites have recently shown promises for their stability and environment-friendly nature, but impacts from intrinsic defects (vacancies and anti-sites) on their thermoelectric performance remains elusive. Combing first-principle calculations, the Boltzmann transport theory, and the defect formation theory, we investigate the thermoelectric properties of lead-free double perovskite Cs2NaInCl6, taking the intrinsic defects into consideration. Our results demonstrate that the pristine Cs2NaInCl6 presents thermodynamic, mechanical, and dynamic stability. The band edges are mainly comprised of the electrons from In and Cl atoms. Furthermore, the double perovskite has an ultra-low lattice thermal conductivity and a high Seebeck coefficient, while showing a small charge carrier relaxation time and electric conductivity. Promisingly, the maximum ZT values can reach as high as ∼ 1.36 and ∼ 1.44 at 800 K temperature, respectively, with optimal extrinsic carrier concentrations of ∼ 1.9 × 1019 and 5.8 × 1020 cm−3 for N- and P-type carriers (holes and electrons), and the maximum power generation efficiency can reach ∼ 14% (for P-type) when the hot-side temperature is 800 K. Among various intrinsic defect types, we determine the preferable defect types in Cs2NaInCl6 based on the minimal defect formation energy criteria. The free carriers can be switched from N- to P-type under these two preferable defects, respectively, with Cl and Na vacancies. Even under a very high defect concentration of 2.1 × 1019/cm3 considered here, the extra carrier concentrations induced by the defects are only ∼ 1017 cm−3 at 800 K, showing strong defect tolerance in carrier concentration. This work suggests that lead-free halide double perovskites are promising thermoelectric materials, and they show strong intrinsic defect tolerance that prevents a negative impact on the extrinsic doping-controlled carrier concentrations.

The ultrafast tunable saturable absorption of three azo-Schiff base ligands and related metal complexes

Three azo-Schiff base ligands with large conjugated systems and five related transition metal complexes were synthesized and investigated by femetosecond open-aperture Z-scan and pump-probe system. The ultrafast tunable saturable absorption of the ligands and their metal complexes were observed at 400 nm wavelength. The obtained third-order nonlinear optical (NLO) absorption coefficients of eight compounds are evaluated to be −8.49 ∼ −80.63 cm/GW. Meanwhile, the ultrafast carrier relaxation time (187–592 fs) of all compounds was observed in the pump-probe experiment. The modulated impacts of metal coordination on NLO responses are analyzed by a five-level energy system. We deem that the performance of metal complexes is determined by the number of shell electrons of central metal. All the results indicate that those compounds have potential applications for tunable saturable absorber in NLO field.

A simple formula for calculating the carrier relaxation time

An empirical formula to calculate the carrier relaxation time as a function of temperature (τT) has been presented. The method mainly depends on the Seebeck coefficient and the temperature. The formula was tested on metals and several types of semiconductors (Clathrate, Half Heusler Alloy, Zintl phases…). The obtained values are in good agreement with the available experimental results, especially in poor metals and heavily doped semiconductors at low temperatures especially room temperature. On the other hand, the calculated values of electrical conductivity σ(T) and electronic thermal conductivity ke(T) under the constant relaxation time approximation (CRTA) are given as fractions (σ/τorke/τ). Treating τ as an empirical parameter (τ=cte) by fitting to one value at a specific carrier concentration is a common method utilized by researchers. However, it cannot explain the behaviour of conductivity as temperature rises. Whereas, in this case, using our formula is useful to investigate σ(T) and the obtained curves show a similar behaviour to the experimental ones when the temperature increases.

First-principles calculations to investigate structural, elastic, electronic, and thermoelectric properties of monolayer and bulk beryllium chalcogenides

A detailed first-principles investigation on the structural, vibrational, elastic, electronic, and thermoelectric properties of the family of beryllium chalcogenides (BeX; X = O, S, Se, Te) in hexagonal monolayer (h-BeX) and bulk (zinc blende; zb-BeX) phases are studied in this work. The stabilities of the compounds are assessed by phonon dispersion analysis and elastic properties. The band structure and partial density of states predicts the nature and understanding of the electronic properties of the considered BeX compounds. The effective mass, mobility and relaxation time for carriers are also predicted for both the BeX phases. The thermoelectric properties are evaluated for a wide temperature range of 50–800 K in terms of thermal conductivity (κ), electrical conductivity (σ), Seebeck coefficient (S) and figure of merit (ZT). The considered BeX materials shows outstanding thermoelectrical promises. The present findings will undoubtedly aid experimentalists in prospective synthesis and future thermoelectric power applications of the recognized BeX compounds.

Carrier dynamics in (Ga,In)(Sb,Bi)/GaSb quantum wells for laser applications in the mid-infrared spectral range

We present experimental studies on low-temperature (T={4.2}hbox { K}) carrier dynamics in (Ga,In)(Sb,Bi)/GaSb quantum wells (QWs) with the nominal In content of 3.7% and the Bi ranging from 6 to 8%. The photoreflectance experiment revealed the QW bandgap evolution with -{33}pm {1}hbox { meV}/hbox {at} % Bi, which resulted in the bandgap tunability roughly between 629 and {578}hbox { meV}, setting up the photon emission wavelength between 1.97 and {2.2},upmu hbox {m}. The photoluminescence experiment showed a relatively small 3–10hbox { meV} Stokes shift regarding the fundamental QW absorption edge, indicating the exciton localisation beneath the QW mobility edge. The localised state’s distribution, being the origin of the PL, determined carrier dynamics in the QWs probed directly by the time-resolved photoluminescence and transient reflectivity. The intraband carrier relaxation time to the QW ground state, following the non-resonant excitation, occurred within 3–25hbox { ps} and was nearly independent of the Bi content. However, the interband relaxation showed a strong time dispersion across the PL emission band and ranging nearly between 150 and {950}hbox { ps}, indicating the carrier transfer among the localised state’s distribution. Furthermore, the estimated linear dispersion variation parameter significantly decreased from Delta tau approx {20} to {10}hbox { ps}/hbox {meV} with increasing the Bi content, manifested the increasing role of the non-radiative recombination processes with Bi in the QWs.

Horizontal and vertical stacked Ag/MoS2 nanostructure enabled excellent carrier mobility and optoelectronic properties

Amongst 2D materials, MoS2 with highly exposed atomic edges and large specific surface area are considered potentially strong candidates for optoelectronic devices such as photogenerated electron transport layer, saturated/reverse saturated light absorber. With these prospects in mind, doped nanohybrid system was employed as a “accelerator” for problems related to conductivity and field emission. Herein, the horizontal-vertical stacked Ag/MoS2 films including horizontal nanolayer and vertical nanosheets (NSs) was firstly presented, which exhibit excellent carrier mobility and luminescence characteristics. We have confirmed that the morphology of the Ag/MoS2 NSs (including microworm-like, worm-like, and sheet-like shape), Ag content, micro strain and crystallinity can be adjusted under the different substrate temperature. Base on anisotropy bonding and ultrafast chemical conversion effect of MoS2, the cross-layer diffusion of sputtered atoms is suppressed, thereby the subsequent deposited atoms preferring to diffuse along the van der Waals gap. The efficient light-matter interaction and surface plasmon resonance (SPR) effect is introduced by the abundant exposed S-edges of horizontal-vertical stacked Ag-MoS2 nanostructure, which lead to excellent Raman signal and linear absorption characteristic. The carrier mobility and concentration of Ag/MoS2 NSs with excellent electrical behavior has reached 4480 cm2 V-1S-1 and 3.272 × 1018 cm−2, which can be regarded as the unique ohmic contact and the electron injection effect. Further, the luminescence performance (visible light region) of horizontal-vertical stacked Ag/MoS2-350 °C NSs is 2.5 times higher than that of the original MoS2 NSs, which is dominated by the hot electron injection effect. Importantly, the carrier relaxation time guided by the nonradiative recombination behavior of Ag/MoS2-350 °C NSs was not significantly changed by the incorporation of Ag nanoparticles. The above phenomenon implies that the hot electron injection effect mainly promotes the photoluminescence behavior induced by radiative recombination. The homogeneous and controllable Ag/MoS2 NSs exhibits excellent multiple optoelectronic properties, which can provide a valuable reference strategy for the application of optoelectronic nano-film materials.

Controlled sputtering time growth, ultrafast nonlinear absorption and carrier dynamics properties of vertically WSe2 films under photoexcitation

In this work, the vertically-grown-WSe2-films were successfully prepared using the RF magnetron sputtering. Their structure, morphology, growth mechanism and nonlinear optical properties were investigated by adjusting the growth time. The special "worm-like" structure was characterized by scanning electron microscopy, attributing to the two growth orientations in C-axis type I (C//) and type II (C⊥). The X-ray diffraction results confirmed the preferential growing on (002) and (008). The nonlinear optical properties were studied by femtosecond Z-scan to reveal the nonlinear absorption mechanism. WSe2 films exhibited the nonlinear optical process from saturable absorption to reverse saturable absorption with the growing time. The NA coefficient for WSe2 films is ∼10−9 m/W. The carrier relaxation time was determined by femtosecond transient absorption spectroscopy. This proposed WSe2 films will be an excellent candidate for developing optoelectronic devices due to the excellent nonlinear optical properties.

Transport properties of binary phosphide AgP2 denoting high Hall mobility and low lattice thermal conductivity

This study found that polycrystalline AgP2 shows intrinsic semiconducting electrical conductivity with Hall mobility of 51 cm2 V−1 s−1, which is as high as that of Mg2Si, and lattice thermal conductivity of 1.2 W K−1 m−1, which is as low as that of Bi2Te3. First-principles calculations theoretically indicate AgP2 as an intrinsic semiconductor, and indicate the estimated carrier relaxation time τ as 3.3 fs, which is long for a polycrystalline material. Moreover, the effective mass of hole m* is approximately 0.11 times that of free electrons. These results indicate that long τ and light m* of the carrier are the origins of the high experimentally obtained Hall mobility. Phonon calculations indicate that the Ag atoms in AgP2 exhibit highly anharmonic phonon modes with mode Grüneisen parameters of more than 2 in the 50–100 cm−1 low-frequency range. The large anharmonic vibrations of the Ag atoms reduce the phonon mean free path. Moreover, the lattice thermal conductivity was found, experimentally and theoretically, to be as low as approx. 1.2 W K−1 m−1 at room temperature by phonon–phonon and grain-boundary scattering.

Surface hopping dynamics in periodic solid-state materials with a linear vibronic coupling model.

We report a surface hopping approach in which the implemented linear vibronic coupling Hamiltonian is constructed and the electronic wavefunction is propagated in the reciprocal space. The parameters of the linear vibronic coupling model, including onsite energies, phonon frequencies, and electron-phonon couplings, are calculated with density-functional theory and density-functional perturbation theory and interpolated in fine sampling points of the Brillouin zone with maximally localized Wannier functions. Using this approach, we studied the relaxation dynamics of the photo-excited hot carrier in a one-dimensional periodic carbon chain. The results show that the completeness of the number of Hilbert space k points and the number of phonon q points plays an important role in the hot carrier relaxation processes. By calculating the relaxation times of hot carriers under different reciprocal space sampling and extrapolating with the stretched-compressed exponential function, the relaxation times of hot electrons and holes in the quasi-continuous energy band are obtained. By considering the feedback effect in the hopping processes and analyzing the time-dependent phonon energy in different normal modes, we found that the long-wave longitudinal optical phonons play a major role in the relaxation dynamics of hot electrons and holes. We, therefore, provided herein an efficient and accurate approach for modeling the photophysical processes in periodic solid-state material systems.

Efficient hot-carrier dynamics in near-infrared photocatalytic metals

Photoexcited metals can produce highly-energetic hot carriers whose controlled generation and extraction is a promising avenue for technological applications. While hot carrier dynamics in Au-group metals have been widely investigated, a microscopic description of the dynamics of photoexcited carriers in the mid-infrared and near-infrared Pt-group metals range is still scarce. Since these materials are widely used in catalysis and, more recently, in plasmonic catalysis, their microscopic carrier dynamics characterization is crucial. We employ \emph{ab initio} many-body perturbation theory to investigate the hot carrier generation, relaxation times, and mean free path in bulk Pd and Pt. We show that the direct optical transitions of photoexcited carriers in this metals are mainly generated in the near-infrared range. We also find that the electron-phonon mass enhancement parameter for Pt is 16 $\%$ higher than Pd, a result that help explains several experimental results showing diverse trends. Moreover, we predict that Pd (Pt) hot electrons possess total relaxation times of up to 35 fs (24 fs), taking place at approximately 0.5 eV (1.0 eV) above the Fermi energy. Finally, an efficient hot electron generation and extraction can be achieved in nanofilms of Pd (110) and Pd (100) when subject to excitation energies ranging from 0.4 to 1.6 eV.

Macroscopic assembled graphene nanofilms based room temperature ultrafast mid‐infrared photodetectors

AbstractGraphene with linear energy dispersion and weak electron–phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range. However, the limited absorption and serious backscattering of hot‐electrons result in inadequate quantum yields, especially in the mid‐infrared range. Here, we report a macroscopic assembled graphene (nMAG) nanofilm/silicon heterojunction for ultrafast mid‐infrared photodetection. The assembled Schottky diode works in 1.5–4.0 μm at room temperature with fast response (20–30 ns, rising time, 4 mm2 window) and high detectivity (1.6 × 1011 to 1.9 × 109 Jones from 1.5 to 4.0 μm) under the pulsed laser, outperforming single‐layer‐graphene/silicon photodetectors by 2–8 orders. These performances are attributed to the greatly enhanced photo‐thermionic effect of electrons in nMAG due to its high light absorption (~40%), long carrier relaxation time (~20 ps), low work function (4.52 eV), and suppressed carrier number fluctuation. The nMAG provides a long‐range platform to understand the hot‐carrier dynamics in bulk 2D materials, leading to broadband and ultrafast MIR active imaging devices at room temperature.image