Persistent hot carrier diffusion in boron arsenide single crystals imaged by ultrafast electron microscopy

Choudhry, Usama; Pan, Fengjiao; Kim, Tae-Yong; Gnabasik, Ryan; Gamage, Geethal Amila; Sun, Haoran; Alex, Ackerman,; Ren, Zhifeng; Liao, Bolin

doi:10.1016/j.matt.2022.09.029

Cited by 10 publications

(3 citation statements)

References 32 publications

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“…\left(\mu\right)_{\text{e}} + \left(\mu\right)_{\text{h}} \left.\right)$ of 1600 cm 2 V −1 s −1 , and

\left(\kappa\right)_{\text{RT}}

of 1200 Wm −1 K −1 . Recent works by Yue et al [ 7 ] and Choudhry et al [ 8 ] also establish these facts from transient reflectivity microscopy and ultrafast electron microscopy, respectively. These observations make cubic BAs an attractive candidate for next‐generation semiconductor‐based technologies.…”

Section: Introductionmentioning

confidence: 61%

“…With that they found μ h > 1000 cm 2 V À1 s À1 , ambipolar mobility 2μ e μ h =ðμ e þ μ h Þ of 1600 cm 2 V À1 s À1 , and κ RT of 1200 Wm À1 K À1 . Recent works by Yue et al [7] and Choudhry et al [8] also establish these facts from transient reflectivity microscopy and ultrafast electron microscopy, respectively. These observations make cubic BAs an attractive candidate for next-generation semiconductorbased technologies.…”

Section: Introductionmentioning

confidence: 65%

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One‐Particle and Excitonic Band Structure in Cubic Boron Arsenide

Acharya

Pashov

Katsnelson³

et al. 2023

Physica Rapid Research Ltrs

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Cubic BAs has received recent attention for its large electron and hole mobilities and large thermal conductivity. This is a rare and much desired combination in semiconductor industry: commercial semiconductors typically have high electron mobilities, or hole mobilities, or large thermal conductivities, but not all of them together. Herein, predictions from an advanced self‐consistent many‐body perturbative theory are reported and it is shown that with respect to one‐particle properties, BAs is strikingly similar to Si. There are some important differences, notably there is an unusually small variation in the valence band masses. With respect to two‐particle properties, significant differences with Si appear. The excitonic spectrum for both q = 0 and finite q is reported, and it is shown that while the direct gap in cubic BAs is about 4 eV, dark excitons can be observed down to about ≈1.5 eV, which may play a crucial role in application of BAs in optoelectronics.

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“…\left(\mu\right)_{\text{e}} + \left(\mu\right)_{\text{h}} \left.\right)$ of 1600 cm 2 V −1 s −1 , and

\left(\kappa\right)_{\text{RT}}

Section: Introductionmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 65%

One‐Particle and Excitonic Band Structure in Cubic Boron Arsenide

Acharya

Pashov

Katsnelson³

et al. 2023

Physica Rapid Research Ltrs

View full text Add to dashboard Cite

show abstract

“…Whereas for rightward diffusion, we obtained a constant of D = 2510 ± 165 cm 2 s −1 and D = 69 ± 6 cm 2 s −1 for hot and relaxed carriers, respectively. [40][41][42][43] Note that the difference between the right and left maximum diffused distances is approximately 5 µm (For more details see Figures S5-S8, Supporting Information). The occurrence of charge diffusion along a preferred direction rather than being uniform was likely due to its dependence on the morphology and roughness of the surface near the excited area and defect centers around the laser footprint.…”

Section: Resultsmentioning

confidence: 99%

Visualization of Surface Charge Carrier Diffusion Lengths in Different Perovskite Crystal Orientations Using 4D Electron Imaging

Nughays

Yang

Nematulloev

et al. 2023

Advanced Optical Materials

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to their outstanding optical and transport properties, including a low concentration of defect states, tunable bandgap, and ultralong charge carrier diffusion lengths. [1][2][3][4][5][6][7] Therefore, perovskite single crystals are considered to be an excellent candidate for competing with, if not replacing, polycrystalline perovskite absorber layers, which exhibit impressive solar cell device performance with a world-record photoconversion efficiency of 25.7%. [8] However, the performance of such devices has plateaued due to the large density of trap states at grain boundaries. [9,10] This obstacle can be overcome in perovskite single crystals that are free of grains, and enormous studies have been done to improve surface quality by different passivation methods for better device performance. [11,12] Hence, the correlation between the charge carrier dynamics and the surface orientation of these crystals at the femtosecond and nanometer scales needs to be fully established. Note that the charge carrier dynamics at the interface with electron and hole transporting layers is extremely difficult, if not impossible, to obtain using conventional time-resolved pump-probe techniques due to the large penetration depth Understanding charge carrier dynamics on the surface of materials at the nanometer and femtosecond scales is one of the key elements to optimizing the performance of light-conversion devices, including solar cells. Unfortunately, most of the pump-probe characterization techniques are surfaceinsensitive and obtain information from the bulk due to the large penetration depth of the pulses. However, ultrafast scanning electron microscopy (USEM) is superior in visualizing carrier dynamics at the surface with high spatialtemporal resolution. Here, the authors successfully used USEM to uncover the tremendous effect of surface orientations and termination on the charge carrier of MAPbI 3 perovskite single crystals. Time-resolved secondary electrons snapshots and density functional theory calculations clearly demonstrate that charge carrier diffusion, surface trap density, surface work function, and carrier concentration are strongly facet-dependent. The results display a diffusion length of 22 micrometers within 6.0 nanoseconds along (001) orientation. While (100) facet forms defect states that prevent carrier diffusion and shows an increase in the surface work function leading to dark contrast and fast charge carrier recombination. These findings provide a new key component to optimizing the surface of perovskites, thus paving the way for even more efficient and stable solar-cell devices based on perovskite single crystals.

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A Femtosecond Electron‐Based Versatile Microscopy for Visualizing Carrier Dynamics in Semiconductors Across Spatiotemporal and Energetic Domains

Zhang,

Chen,

et al. 2024

Advanced Science

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Carrier dynamics detection in different dimensions (space, time, and energy) with high resolutions plays a pivotal role in the development of modern semiconductor devices, especially in low‐dimensional, high‐speed, and ultrasensitive devices. Here, a femtosecond electron‐based versatile microscopy is reported that combines scanning ultrafast electron microscopy (SUEM) imaging and time‐resolved cathodoluminescence (TRCL) detection, which allows for visualizing and decoupling different dynamic processes of carriers involved in surface and bulk in semiconductors with unprecedented spatiotemporal and energetic resolutions. The achieved spatial resolution is better than 10 nm, and the temporal resolutions for SUEM imaging and TRCL detection are ≈500 fs and ≈4.5 ps, respectively, representing state‐of‐the‐art performance. To demonstrate its unique capability, the surface and bulk carrier dynamics involved in n‐type gallium arsenide (GaAs) are directly tracked and distinguished. It is revealed, in real time and space, that hot carrier cooling, defect trapping, and interband‐/defect‐assisted radiative recombination in the energy domain result in ordinal super‐diffusion, localization, and sub‐diffusion of carriers at the surface, elucidating the crucial role of surface states on carrier dynamics. The study not only gives a comprehensive physical picture of carrier dynamics in GaAs, but also provides a powerful platform for exploring complex carrier dynamics in semiconductors for promoting their device performance.

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Persistent hot carrier diffusion in boron arsenide single crystals imaged by ultrafast electron microscopy

Cited by 10 publications

References 32 publications

One‐Particle and Excitonic Band Structure in Cubic Boron Arsenide

One‐Particle and Excitonic Band Structure in Cubic Boron Arsenide

Visualization of Surface Charge Carrier Diffusion Lengths in Different Perovskite Crystal Orientations Using 4D Electron Imaging

A Femtosecond Electron‐Based Versatile Microscopy for Visualizing Carrier Dynamics in Semiconductors Across Spatiotemporal and Energetic Domains

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