Photogenerated carrier density dependence of ultrafast carrier dynamics in intrinsic 6H-SiC measured by optical-pump terahertz-probe spectroscopy

Li, Gaofang; Liao, Yu-Ao; Yin, Wen; Zhou, Wei; Gao, Yanqing; Xia, Nenghong; Cui, Haoyang

doi:10.1016/j.optcom.2022.127979

Cited by 5 publications

(2 citation statements)

References 31 publications

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“…The fast process can be attributed to the generation and recombination of photogenerated carriers, and the slow process can be ascribed to the nonradiative relaxation of excited electron–hole pairs. Initially, once the Ti 2 O 3 film is optically pumped, a pronounced and sharp decrease of THz transmission was observed within about 4 ps, which is ascribed to the generation of photogenerated carriers. , Subsequently, THz transmittance demonstrated a rapid recovery within the next 2 ps because the excited photogenerated carriers were recombined. In this stage, with the increase of the pump fluence, the recovery of Δ T / T 0 linearly decreases, which can be attributed to the partial overlap of the energy bands under higher fluences.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast Dynamic Terahertz Response of Ti₂O₃ Film during Photoinduced Metal–Insulator Transition

Cai

Zhu

et al. 2022

J. Phys. Chem. C

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Ti2O3 with an ultranarrow bandgap of 0.1 eV, exhibiting an intriguing thermally induced metal–insulator transition (MIT), has drawn significant attention in photothermal conversion, photocatalysts, and mid-infrared photodetection. However, the ultrafast photoexcitation dynamics of Ti2O3 film and whether the laser excitation can trigger the MIT of Ti2O3 were rarely discussed. Here, a typical time-resolved optical pump terahertz probe (OPTP) spectroscopy was used to investigate the ultrafast terahertz response of Ti2O3 film excited by a femtosecond laser. We found that a transient photoinduced carrier generation process occurred within 4 ps. A fast relaxation with a time constant of approximately 2 ps followed, which can be attributed to the recombination of the photogenerated carriers. Subsequently, a slow transition process was observed after the fast recovery process, and this phenomenon can be ascribed to the ultrafast photothermal conversion through nonradiative relaxation. Our work will provide new sights for investigating MIT characteristics of Ti2O3 and open a route toward achieving ultrafast dynamic modulation optoelectronics operating in the terahertz regime.

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Section: Resultsmentioning

confidence: 99%

Ultrafast Dynamic Terahertz Response of Ti₂O₃ Film during Photoinduced Metal–Insulator Transition

Cai

Zhu

et al. 2022

J. Phys. Chem. C

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“…In our previous study, this technique was used to investigate another material for ionizing radiation and high-energy particle detectors, namely HR GaAs:Cr [19]. Previously, the OPTP technique with above-band-gap photoexcitation was applied to study 6H-SiC [20].…”

Section: Introductionmentioning

confidence: 99%

Electrical Relaxation and Transport Properties of ZnGeP2 and 4H-SiC Crystals Measured with Terahertz Spectroscopy

et al. 2023

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Terahertz photoconductivity and charge carrier recombination dynamics at two-photon (ZnGeP2) and three-photon (4H-SiC) excitation were studied. Thermally annealed, high-energy electron-irradiated and Sc-doped ZnGeP2 crystals were tested. The terahertz charge carrier mobilities were extracted from both the differential terahertz transmission at a specified photoexcitation condition and the Drude–Smith fitting of the photoconductivity spectra. The determined terahertz charge carrier mobility values are ~453 cm2/V·s for 4H-SiC and ~37 cm2/V·s for ZnGeP2 crystals. The charge carrier lifetimes and the contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of bulk and surface Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that ZnGeP2 possesses short charge carrier lifetimes (a~0.01 ps−1, b~6 × 10−19 cm3·ps−1 and c~7 × 10−40 cm6·ps−1) compared with 4H-SiC (a~0.001 ps−1, b~3 × 10−18 cm3·ps−1 and c~2 × 10−36 cm6·ps−1), i.e., τ~100 ps and τ~1 ns at the limit of relatively low injection, when the contribution from Auger and interband radiative recombination is small. The thermal annealing of as-grown ZnGeP2 crystals and the electron irradiation reduced the charge carrier lifetime, while their doping with 0.01 mass % of Sc increased the charger carrier lifetime and reduced mobility. It was found that the dark terahertz complex conductivity of the measured crystals is not fitted by the Drude–Smith model with reasonable parameters, while their terahertz photoconductivity can be fitted with acceptable accuracy.

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Surface states of photoelectrodes by surface-specific steady-state and time-resolved sum frequency spectroscopies

Zhang,

Brown,

Fisher

et al. 2024

Chinese Journal of Chemical Physics

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The surface states of photoelectrodes as catalysts heavily influence their performance in photocatalysis and photoelectrocatalysis applications. These catalysts are necessary for developing robust solutions to the climate and global energy crises by promoting CO2 reduction, N2 reduction, contaminant degradation, and water splitting. The semiconductors that can fill this role are beholden as photoelectrodes to the processes of charge generation, separation, and utilization, which are in turn products of surface states, surface electric fields, and surface carrier dynamics. Methods which are typically used for studying these processes to improve semiconductors are indirect, invasive, not surface specific, not practical under ambient conditions, or a combination thereof. Recently, nonlinear optical processes such as electronic sum-frequency generation (ESFG) and second-harmonic generation (ESHG) have gained popularity in investigations of semiconductor catalysts systems. Such techniques possess many advantages of in-situ analysis, interfacial specificity, non-invasiveness, as well as the ability to be used under any conditions. In this review, we detail the importance of surface states and their intimate relationship with catalytic performance, outline methods to investigate semiconductor surface states, electric fields, and carrier dynamics and highlight recent contributions to the field through interface-specific spectroscopy. We will also discuss how the recent development of heterodyne-detected ESHG (HD-ESHG) was used to extract charged surface states through phase information, time-resolved ESFG (TR-ESFG) to obtain in-situ dynamic process monitoring, and two-dimensional ESFG (2D-ESFG) to explore surface state couplings, and how further advancements in spectroscopic technology can fill in knowledge gaps to accelerate photoelectrocatalyst utilization. We believe that this work will provide a valuable summary of the importance of semiconductor surface states and interfacial electronic properties, inform a broad audience of the capabilities of nonlinear optical techniques, and inspire future original approaches to improving photocatalytic and photoelectrocatalytic devices.

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Photogenerated carrier density dependence of ultrafast carrier dynamics in intrinsic 6H-SiC measured by optical-pump terahertz-probe spectroscopy

Cited by 5 publications

References 31 publications

Ultrafast Dynamic Terahertz Response of Ti₂O₃ Film during Photoinduced Metal–Insulator Transition

Ultrafast Dynamic Terahertz Response of Ti₂O₃ Film during Photoinduced Metal–Insulator Transition

Electrical Relaxation and Transport Properties of ZnGeP2 and 4H-SiC Crystals Measured with Terahertz Spectroscopy

Surface states of photoelectrodes by surface-specific steady-state and time-resolved sum frequency spectroscopies

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Photogenerated carrier density dependence of ultrafast carrier dynamics in intrinsic 6H-SiC measured by optical-pump terahertz-probe spectroscopy

Cited by 5 publications

References 31 publications

Ultrafast Dynamic Terahertz Response of Ti2O3 Film during Photoinduced Metal–Insulator Transition

Ultrafast Dynamic Terahertz Response of Ti2O3 Film during Photoinduced Metal–Insulator Transition

Electrical Relaxation and Transport Properties of ZnGeP2 and 4H-SiC Crystals Measured with Terahertz Spectroscopy

Surface states of photoelectrodes by surface-specific steady-state and time-resolved sum frequency spectroscopies

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Ultrafast Dynamic Terahertz Response of Ti₂O₃ Film during Photoinduced Metal–Insulator Transition

Ultrafast Dynamic Terahertz Response of Ti₂O₃ Film during Photoinduced Metal–Insulator Transition